REV. B

Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.

AD9884A

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700

World Wide Web Site: http://www.analog.com

Fax: 781/326-8703

© Analog Devices, Inc., 2000

100 MSPS/140 MSPS

Analog Flat Panel Interface

GENERAL DESCRIPTION

The AD9884A is a complete 8-bit 140 MSPS monolithic analog
interface optimized for capturing RGB graphics signals from
personal computers and workstations. Its 140 MSPS encode
rate capability and full-power analog bandwidth of 500 MHz
supports display resolutions of up to 1280

1024 (SXGA) at

75 Hz with sufficient input bandwidth to accurately acquire and
digitize each pixel.

To minimize system cost and power dissipation, the AD9884A
includes an internal +1.25 V reference, PLL to generate a pixel
clock from HSYNC, and programmable gain, offset and clamp
circuits. The user provides only a +3.3 V power supply, analog
input, and HSYNC signals. Three-state CMOS outputs may be
powered by a supply between 2.5 V and 3.3 V.

The AD9884A's on-chip PLL generates a pixel clock from the
HSYNC input. Pixel clock output frequencies range from

FEATURES
140 MSPS Maximum Conversion Rate
500 MHz Analog Bandwidth
0.5 V to 1.0 V Analog Input Range
400 ps p-p PLL Clock Jitter
Power-Down Mode
3.3 V Power Supply
2.5 V to 3.3 V Three-State CMOS Outputs
Demultiplexed Output Ports
Data Clock Output Provided
Low Power: 570 mW Typical
Internal PLL Generates CLOCK from HSYNC
Serial Port Interface
Fully Programmable
Supports Alternate Pixel Sampling for Higher-
Resolution Applications

APPLICATIONS
RGB Graphics Processing
LCD Monitors and Projectors
Plasma Display Panels
Scan Converters

FUNCTIONAL BLOCK DIAGRAM

SDA SCL A

PWRDN

HSYNC

COAST

CLAMP

FILT

CKEXT

REFIN

CKINV

REFOUT

A/D

CLAMP

A/D

CLAMP

A/D

CLAMP

REF

SOGIN

0.15V

AD9884A

CLOCK

GENERATOR

SOGOUT

DATACK

OUTA

OUTB

OUTA

OUTB

OUTA

OUTB

HSOUT

CONTROL

20 MHz to 140 MHz. PLL clock jitter is typically 400 ps p-p
relative to the input reference. When the COAST signal is pre-
sented, the PLL maintains its output frequency in the absence
of HSYNC. A 32-step sampling phase adjustment is provided.
Data, HSYNC and Data Clock output phase relationships are
always maintained. The PLL can be disabled and an external
clock input provided as the pixel clock.

A clamp signal is generated internally or may be provided by the
user through the CLAMP input pin. This device is fully program-
mable via a two-wire serial port.

Fabricated in an advanced CMOS process, the AD9884A is
provided in a space-saving 128-lead MQFP surface mount plas-
tic package and is specified over a 0

C to +70

C temperature

range.

REV. B

AD9884ASPECIFICATIONS

= +3.3 V, V

= +3.3 V, PV

= +3.3 V, ADC Clock Frequency = Maximum, PLL

Clock Frequency = Maximum, Control Registers Programmed to Default State)

Test

AD9884AKS-100

AD9884AKS-140

Parameter

Temp

Level

Min

Typ

Max

Min

Typ

Max

Unit

RESOLUTION

Bits

DC ACCURACY

Differential Nonlinearity

+25

0.5

1.0

0.5

+1.15/1.0

LSB

Full

1.0

+1.25/1.0

LSB

Integral Nonlinearity

+25

0.5

1.25

0.8

1.4

LSB

Full

1.75

2.5

LSB

No Missing Codes

Full

Guaranteed

ANALOG INPUT

Input Voltage Range

Minimum

Full

0.5

V p-p

Maximum

Full

1.0

V p-p

Gain Tempco

+25

100

280

ppm/

Input Bias Current

+25

Full

Input Offset Voltage

Full

Input Full-Scale Matching

Full

1.5

5.0

1.5

5.0

%FS

Offset Adjustment Range

Full

23.5

%FS

REFERENCE OUTPUT

Output Voltage

Full

+1.20

+1.25

+1.30

+1.20

+1.25

+1.30

Temperature Coefficient

Full

ppm/

SWITCHING PERFORMANCE

Maximum Conversion Rate

Full

100

140

MSPS

Minimum Conversion Rate

Full

MSPS

Data to Clock Skew, t

SKEW

Full

0.5

+2.0

0.5

+2.0

BUFF

Full

4.7

STAH

Full

4.0

DHO

Full

DAL

Full

4.7

DAH

Full

4.0

DSU

Full

250

STASU

Full

4.7

STOSU

Full

4.0

HSYNC Input Frequency

Full

110

kHz

Maximum PLL Clock Rate

Full

100

140

MHz

Minimum PLL Clock Rate

Full

MHz

PLL Jitter

+25

400

700

475

750

ps p-p

Full

1000

ps p-p

Sampling Phase Tempco

Full

ps/

DIGITAL INPUTS

Input Voltage, High (V

)

Full

2.5

Input Voltage, Low (V

)

Full

0.8

Input Current, High (I

)

Full

1.0

Input Current, Low (I

)

Full

1.0

Input Capacitance

+25

DIGITAL OUTPUTS

Output Voltage, High (V

)

Full

0.1

Output Voltage, Low (V

)

Full

0.1

Duty Cycle

DATACK,

DATACK

Full

Output Coding

Binary

REV. B

AD9884A

Test

AD9884AKS-100

AD9884AKS-140

Parameter

Temp

Level

Min

Typ

Max

Min

Typ

Max

Unit

POWER SUPPLY

Supply Voltage

Full

3.0

3.3

3.6

3.0

3.3

3.6

Supply Voltage

Full

2.2

3.3

3.6

2.2

3.3

3.6

Supply Voltage

Full

3.0

3.3

3.6

3.0

3.3

3.6

Supply Current (V

)

+25

125

135

Supply Current (V

)

+25

IPV

Supply Current (PV

)

+25

Total Power Dissipation

Full

570

675

650

775

Power-Down Supply Current

Full

2.0

Power-Down Dissipation

Full

6.6

82.5

6.6

82.5

DYNAMIC PERFORMANCE

Analog Bandwidth, Full Power

+25

500

MHz

Transient Response

+25

Overvoltage Recovery Time

+25

1.5

Signal-to-Noise Ratio (SNR)

+25

44.0

46.5

43.5

46.2

(Without Harmonics)

Full

46.0

45.0

= 40.7 MHz

Crosstalk

Full

dBc

THERMAL CHARACTERISTICS

Junction-to-Case

Thermal Resistance

8.4

C/W

Junction-to-Ambient

Thermal Resistance

C/W

NOTES

VCORNGE = 01, CURRENT = 001, PLLDIV = 1693

VCORNGE = 10, CURRENT = 110, PLLDIV = 1600

DEMUX = 1; DATACK and

DATACK load = 15 pF; Data load = 5 pF.

Using external pixel clock.

Specifications subject to change without notice.

ORDERING GUIDE

Temperature Package

Package

Model

Range

Description

Option

AD9884AKS-140 0

C to +70

MQFP

S-128

AD9884AKS-100 0

C to +70

MQFP

S-128

AD9884A/PCB

+25

Evaluation Board

EXPLANATION OF TEST LEVELS
Test Level
I.

100% production tested.

II.

100% production tested at +25

C and sample tested at specified

temperatures.

III. Sample tested only.
IV. Parameter is guaranteed by design and characterization testing.
V.

Parameter is a typical value only.

VI. 100% production tested at +25

C; guaranteed by design and

characterization testing.

ABSOLUTE MAXIMUM RATINGS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.5 V to +4 V

to V

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

0.5 V

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.5 V to +4 V

Analog Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . V

to 0.5 V

REFIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V

to 0.0 V

Digital Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . V

to 0.0 V

Digital Output Current . . . . . . . . . . . . . . . . . . . . . . . . 20 mA
Operating Temperature . . . . . . . . . . . . . . . . . 20

C to +85

Storage Temperature . . . . . . . . . . . . . . . . . . 65

C to +150

Maximum Junction Temperature . . . . . . . . . . . . . . . +175

Maximum Case Temperature . . . . . . . . . . . . . . . . . . +150

*Stresses above those listed under Absolute Maximum Ratings may cause perma-

nent damage to the device. This is a stress rating only; functional operation of the
device at these or any other conditions outside of those indicated in the operation
sections of this specification is not implied. Exposure to absolute maximum ratings
for extended periods may affect device reliability.

CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection.
Although the AD9884A features proprietary ESD protection circuitry, permanent damage may
occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD
precautions are recommended to avoid performance degradation or loss of functionality.

WARNING!

ESD SENSITIVE DEVICE

REV. B

AD9884A

Table I. Package Interconnections

Signal Type

Name

Function

Value

Package Pin

Inputs

AIN

Analog Input for RED Channel

0.5 V to 1.0 V FS

AIN

Analog Input for GREEN Channel

0.5 V to 1.0 V FS

AIN

Analog Input for BLUE Channel

0.5 V to 1.0 V FS

HSYNC

Horizontal Sync Input

3.3 V CMOS

COAST

Clock Generator Coast Input (Optional) 3.3 V CMOS

CLAMP

External Clamp Input (Optional)

3.3 V CMOS

SOGIN

Sync On Green Slicer Input (Optional)

0.5 V to 1.0 V FS

CKEXT

External Clock Input (Optional)

3.3 V CMOS

CKINV

Sampling Clock Inversion (Optional)

3.3 V CMOS

Outputs

7-0

Data Output, Red Channel, Port A

3.3 V CMOS

105112

7-0

Data Output, Red Channel, Port B

3.3 V CMOS

95102

7-0

Data Output, Green Channel, Port A

3.3 V CMOS

8592

7-0

Data Output, Green Channel, Port B

3.3 V CMOS

7582

7-0

Data Output, Blue Channel, Port A

3.3 V CMOS

6572

7-0

Data Output, Blue Channel, Port B

3.3 V CMOS

5562

DATACK

Data Output Clock

3.3 V CMOS

115

DATACK

Data Output Clock Complement

3.3 V CMOS

116

HSOUT

Horizontal Sync Output

3.3 V CMOS

117

SOGOUT

Sync On Green Slicer Output

3.3 V CMOS

118

Control

SDA

Serial Data I/O

3.3 V CMOS

SCL

Serial Interface Clock

3.3 V CMOS

, A

Serial Port Address LSBs

3.3 V CMOS

31, 32

PWRDN

Power-Down Control Input

3.3 V CMOS

125

Analog Interface

REFOUT

Internal Reference Output

+1.25 V

126

REFIN

Reference Input

+1.25 V

10%

127

FILT

External Filter Connection

Power Supply

Main Power Supply

3.3 V

10%

4, 8, 10, 11, 16, 18, 19, 23, 25,
124, 128

Digital Output Power Supply

2.5 V to 3.3 V

10% 54, 64, 74, 84, 94, 104, 114, 120

Clock Generator Power Supply

3.3 V

10%

33, 34, 43, 48, 50

GND

Ground

0 V

5, 6, 9, 12, 13, 17, 20, 21, 24, 26,
35, 39, 42, 47, 49, 51, 52, 53, 63,
73, 83, 93, 103, 113, 119, 121,
122, 123

No Connect

13, 3638, 46

REV. B

AD9884A

PIN CONFIGURATION

101

102

100

123

124

125

126

127

119

PIN 1
IDENTIFIER

TOP VIEW

PINS DOWN

(Not to Scale)

REFIN

REFOUT

PWRDN

GND

SOGOUT

HSOUT

DATACK

GND

HSYNC

COAST

GND

CKEXT

FILT

GND

AIN

GND

SOGIN

AIN

GND

AIN

GND

CKINV

CLAMP

SDA

SCL

GND

AD9884A

GND

NC = NO CONNECT

REV. B

AD9884A

PIN FUNCTION DESCRIPTIONS

Pin Name

Function

INPUTS

AIN

Analog Input for RED Channel

AIN

Analog Input for GREEN Channel

AIN

Analog Input for BLUE Channel
High impedance inputs that accepts the RED, GREEN, and BLUE channel graphics signals, respectively. The
three channels are identical, and can be used for any colors, but colors are assigned for convenient reference. They
accommodate input signals ranging from 0.5 V to 1.0 V full scale. Signals should be ac-coupled to these pins to
support clamp operation.

HSYNC

Horizontal Sync Input
This input receives a logic signal that establishes the horizontal timing reference and provides the frequency refer-
ence for pixel clock generation. The logic sense of this pin is controlled by HSPOL. Only the leading edge of
HSYNC is active. When HSPOL = 0, the falling edge of HSYNC is used. When HSPOL = 1, the rising edge is
active. The input includes a Schmitt trigger for noise immunity, with a nominal input threshold of 1.5 V.
Electrostatic Discharge (ESD) protection diodes will conduct heavily if this pin is driven more than 0.5 V above
the 3.3 V power supply (or more than 0.5 V below ground). If a 5 V signal source is driving this pin, the signal
should be clamped or current limited.

COAST

Clock Generator Coast Input (optional)
This input may be used to cause the pixel clock generator to stop synchronizing with HSYNC and continue pro-
ducing a clock at its present frequency and phase. This is useful when processing sources that fail to produce hori-
zontal sync pulses when in the vertical interval. The COAST signal is generally NOT required for PC-generated
signals. The logic sense of this pin is controlled by CSTPOL. COAST may be asserted at any time. When not
used, this pin must be grounded and CSTPOL programmed to 1. CSTPOL defaults to 1 at power-up.

CLAMP

External Clamp Input (optional)
This logic input may be used to define the time during which the input signal is clamped to ground, establishing a
black reference. It should be exercised when a black signal is known to be present on the analog input channels,
typically during the back porch period of the graphics signal. The CLAMP pin is enabled by setting control bit
EXTCLMP to 1 (default power-up is 0). When disabled, this pin is ignored and the clamp timing is determined
internally by counting a delay and duration from the trailing edge of the HSYNC input. The logic sense of this pin
is controlled by CLAMPOL. When not used, this pin must be grounded and EXTCLMP programmed to 0.

SOGIN

Sync On Green Slicer Input (optional)
This input is provided to assist in processing signals with embedded sync, typically on the GREEN channel. The
pin is connected to a high speed comparator with an internally-generated threshold of 0.15 V. When connected to
a dc-coupled graphics signal with embedded sync, it will produce a noninverting digital output on SOGOUT that
changes state whenever the input signal crosses 0.15 V. This is usually a composite sync signal, containing both
vertical and horizontal sync information that must be separated before passing the horizontal sync signal to HSYNC.
The SOG slicer comparator continues to operate when the AD9884A is put into a power-down state. When not
used, this input should be grounded.

CKEXT

External Clock Input (optional)
This pin may be used to provide an external clock to the AD9884A, in place of the clock internally-generated from
HSYNC. This input is enabled by programming EXTCLK to 1. When an external clock is used, all other internal
functions operate normally. When unused, this pin should be tied through a 10 k

resistor to GROUND, and

EXTCLK programmed to 0. The clock phase adjustment still operates when an external clock source is used.

CKINV

Sampling Clock Inversion (optional)
This pin may be used to invert the pixel sampling clock, which has the effect of shifting the sampling phase
180 degrees. This is in support of Alternate Pixel Sampling mode, wherein higher frequency input signals (up to
280 Mpps) may be captured by first sampling the odd pixels, then capturing the even pixels on the subsequent
frame. This pin should be exercised only during blanking intervals (typically vertical blanking) as it may produce
several samples of corrupted data during the phase shift. CKINV should be grounded when not used.

REV. B

AD9884A

PIN FUNCTION DESCRIPTIONS (Continued)

Pin Name

Function

OUTPUTS

Data Output, Red Channel, Port A

Data Output, Red Channel, Port B

Data Output, Green Channel, Port A

Data Output, Green Channel, Port B

Data Output, Blue Channel, Port A

Data Output, Blue Channel, Port B
The main data outputs. Bit 7 is the MSB. Each channel has two ports. When the part is operated in Single Chan-
nel mode (DEMUX = 0), all data are presented to Port A, and Port B is placed in a high impedance state. Pro-
gramming DEMUX to 1 establishes Dual Channel mode, wherein alternate pixels are presented to Port A and
Port B of each channel. These will appear simultaneously, two pixels presented at the time of every second input
pixel, when PAR is set to 1 (parallel mode). When PAR = 0, pixel data appear alternately on the two ports, one
new sample with each incoming pixel (interleaved mode). In Dual Channel mode, the first pixel sampled after
HSYNC is routed to Port A. The second pixel goes to Port B, the third to A, etc. The delay from pixel sampling
time to output is fixed. When the sampling time is changed by adjusting the PHASE register, the output timing is
shifted as well. The DATACK,

DATACK and HSOUT outputs are also moved, so the timing relationship among

the signals is maintained.

DATACK

Data Output Clock

DATACK

Data Output Clock Complement
Differential data clock output signals to be used to strobe the output data and HSOUT into external logic. They
are produced by the internal clock generator and are synchronous with the internal pixel sampling clock. When the
AD9884A is operated in Single Channel mode, the output frequency is equal to the pixel sampling frequency.
When operating in Dual Channel mode, the Data Output Clock and the Output Data are presented at one-half the
pixel rate. When the sampling time is changed by adjusting the PHASE register, the output timing is shifted as
well. The Data, DATACK,

DATACK and HSOUT outputs are all moved, so the timing relationship among the

signals is maintained. Either or both signals may be used, depending on the timing mode and interface design
employed.

HSOUT

Horizontal Sync Output
A reconstructed and phase-aligned version of the HSYNC input. This signal is always active HIGH. By maintain-
ing alignment with DATACK,

DATACK, and Data, data timing with respect to horizontal sync can always be

clearly determined.

SOGOUT

Sync On Green Slicer Output
The output of the Sync On Green slicer comparator. When SOGIN is presented with a dc-coupled ground-referenced
analog graphics signal containing composite sync, SOGOUT will produce a digital composite sync signal. This
signal gets no other processing on the AD9884A. The SOG slicer comparator continues to operate when the
AD9884A is put into a power-down state.

CONTROL

SDA

Serial Data I/O
Bidirectional data port for the serial interface port.

SCL

Serial Interface Clock
Clock input for the serial interface port.

Serial Port Address LSBs
The two least significant bits of the serial port address are set by the logic levels on these pins. Connect a pin to
ground to set the address bit to 0. Tie it HIGH (to V

through 10 k

) to set the address bit to 1. Using these pins,

the serial address may be set to any value from 98h to 9Fh. Up to four AD9884As may be used on the same serial
bus by appropriately setting these bits. They can also be used to change the AD9884A address if a conflict is found
with another device on the bus.

PWRDN

Power-Down Control Input
Bringing this pin LOW puts the AD9884A into a very low power dissipation mode. The output buffers are placed
in a high impedance state. The clock generator is stopped. The control register contents are maintained. The Sync
On Green Slicer (SOGOUT) and internal reference continue to function.

REV. B

AD9884A

PIN FUNCTION DESCRIPTIONS (Continued)

Pin Name

Function

ANALOG INTERFACE

REFOUT

Internal Reference Output
Output from the internal 1.25 V bandgap reference. This output is intended to drive relatively light loads. It can
drive the AD9884A Reference input directly, but should be externally buffered if it is used to drive other loads as
well. The absolute accuracy of this output is

4%, and the temperature coefficient is

50 ppm, which is adequate

for most AD9884A applications. If higher accuracy is required, an external reference may be employed. If an exter-
nal reference is used, tie this pin to ground through a 0.1

F capacitor.

REFIN

Reference Input
The reference input accepts the master reference voltage for all AD9884A internal circuitry (+1.25 V

10%). It

may be driven directly by the REFOUT pin. Its high impedance presents a very light load to the reference source.
This pin should be bypassed to Ground with a 0.1

F capacitor.

FILT

External Filter Connection
For proper operation, the pixel clock generator PLL requires an external filter. Connect the filter shown in Figure
10 to this pin. For optimal performance, minimize noise and parasitics on this node.

POWER SUPPLY

Main Power Supply
These pins supply power to the main elements of the circuit. It should be as quiet and filtered as possible.

Digital Output Power Supply
A large number of output pins (up to 52) switching at high speed (up to 140 MHz) generates a lot of power supply
transients (noise). These supply pins are identified separately from the V

pins so special care can be taken to

minimize output noise transferred into the sensitive analog circuitry. If the AD9884A is interfacing with lower-
voltage logic, V

may be connected to a lower supply voltage (as low as 2.5 V) for compatibility.

Clock Generator Power Supply
The most sensitive portion of the AD9884A is the clock generation circuitry. These pins provide power to the
clock PLL and help the user design for optimal performance. The designer should provide "quiet," noise-free
power to these pins.

GND

Ground
The ground return for all circuitry on chip. It is recommended that the AD9884A be assembled on a single solid
ground plane, with careful attention to ground current paths. See the Design Guide for details.

REV. B

AD9884A

CONTROL REGISTER MAP

The AD9884A is initialized and controlled by a set of registers
that determine the operating modes. An external controller is
employed to write and read the control registers through the
2-line serial interface port.

Table II. Control Register Map

Reg Bit Default

Mnemonic

Function

PLL Divider Control
00

70 01101001 PLLDIVM

PLL Divide Ratio MSBs

74 1101

····

PLLDIVL

PLL Divide Ratio LSBs

····

0000

Reserved, Set to Zero

Input Gain
02

70 10000000 REDGAIN

Red Channel Gain Adjust

70 10000000 GRNGAIN

Green Channel Gain Adjust

70 10000000 BLUGAIN

Blue Channel Gain Adjust

Input Offset
05

72 100000

··

REDOFST

Red Channel Offset Adjust

······

Reserved, Set to Zero

72 100000

··

GRNOFST

Green Channel Offset Adjust

······

Reserved, Set to Zero

72 100000

··

BLUOFST

Blue Channel Offset Adjust

······

Reserved, Set to Zero

Clamp Timing
08

70 10000000 CLPLACE

Clamp Placement

70 10000000 CLDUR

Clamp Duration

General Control 1
0A

·······

DEMUX

Output Port Select

······

PAR

Output Timing Select

··

·····

HSPOL

HSYNC Polarity

···

····

CSTPOL

COAST Polarity

····

···

EXTCLMP

Clamp Signal Source

·····

··

CLAMPOL

Clamp Signal Polarity

······

EXTCLK

External Clock Select

·······

Reserved, Set to Zero

Clock Generator Control
0B

73 10000

···

PHASE

Clock Phase Adjust

·····

000

Reserved, Set to Zero

·······

Reserved, Set to Zero

·····

VCORNGE VCO Range Select

···

001

··

CURRENT Charge Pump Current

······

Reserved, Set to Zero

General Control 2
0D

75 000

·····

Reserved, Set to Zero

···

····

OUTPHASE Output Port Phase

····

000

REVID

Die Revision ID

·······

Reserved, Set to Zero

70 00000000

Reserved, Set to Zero

Table III. Default Register Values

Reg

Value

Reg

Value

01101001

69h

10000000

80h

1101 0000

D0h

10000000

80h

10000000

80h

11110100

F4h

10000000

80h

10000 000

80h

10000000

80h

0 01 001 00

24h

100000 00

80h

00000000

00h

100000 00

80h

0000xxx0

0xh

100000 00

80h

00000000

00h

CONTROL REGISTER DETAIL

PLL DIVIDER CONTROL

70

PLLDIVM

PLL Divide Ratio MSBs

The eight most significant bits of the 12-bit PLL divide ratio
PLLDIV. The operational divide ratio is PLLDIV + 1.

The PLL derives a master clock from an incoming HSYNC
signal. The master clock frequency is then divided by an integer
value, and the divider's output is phase-locked to HSYNC. This
PLLDIV value determines the number of pixel times (pixels
plus horizontal blanking overhead) per line. This is typically
20% to 30% more than the number of active pixels in the display.

The 12-bit value of PLLDIV supports divide ratios from 2 to
4095. The higher the value loaded in this register, the higher
the resulting clock frequency with respect to a fixed HSYNC
frequency.

VESA has established some standard timing specifications,
which will assist in determining the value for PLLDIV as a
function of horizontal and vertical display resolution and frame
rate (Table VII). However, many computer systems do not
conform precisely to the recommendations, and these numbers
should be used only as a guide. The display system manufac-
turer should provide automatic or manual means for optimizing
PLLDIV. An incorrectly set PLLDIV will usually produce one
or more vertical noise bars on the display. The greater the error,
the greater the number of bars produced.

The power-up default value of PLLDIV is 1693 (PLLDIVM =
69h, PLLDIVL = Dxh).

74

PLLDIVL

PLL Divide Ratio LSBs

The four least significant bits of the 12-bit PLL divide ratio
PLLDIV. The operational divide ratio is PLLDIV + 1.

The power-up default value of PLLDIV is 1693 (PLLDIVM =
69h, PLLDIVL = Dxh).

REV. B

AD9884A

INPUT GAIN

70

REDGAIN

Red Channel Gain Adjust

An 8-bit word that sets the gain of the RED channel. The
AD9884A can accommodate input signals with a full-scale
range of between 0.5 V and 1.0 V p-p. Setting REDGAIN to
255 corresponds to an input range of 1.0 V. A REDGAIN of
0 establishes an input range of 0.5 V. Note that increasing
REDGAIN results in the picture having less contrast (the
input signal uses fewer of the available converter codes). See
Figure 8.

The power-up default value is REDGAIN = 80h.

70

GRNGAIN

Green Channel Gain Adjust

An 8-bit word that sets the gain of the GREEN channel. See
REDGAIN (02).

The power-up default value is GRNGAIN = 80h.

70

BLUGAIN

Blue Channel Gain Adjust

An 8-bit word that sets the gain of the BLUE channel. See
REDGAIN (02).

The power-up default value is BLUGAIN = 80h.

INPUT OFFSET

72

REDOFST

Red Channel Offset Adjust

A six-bit offset binary word that sets the dc offset of the RED
channel.

One LSB of offset adjustment equals approximately one LSB
change in the ADC offset. Therefore, the absolute magnitude of
the offset adjustment scales as the gain of the channel is changed
(Figure 9). A nominal setting of 31 results in the channel nomi-
nally clamping the back porch (during the clamping interval) to
code 00. An offset setting of 63 results in the channel clamping
to code 31 of the ADC. An offset setting of 0 clamps to code
31 (off the bottom of the range). Increasing the value of
REDOFST decreases the brightness of the channel.

The power-up default value is REDOFST = 80h.

72

GRNOFST

Green Channel Offset Adjust

A six-bit offset binary word that sets the dc offset of the GREEN
channel. See REDOFST (05).

The power-up default value is GRNOFST = 80h.

72

BLUOFST

Blue Channel Offset Adjust

A six-bit offset binary word that sets the DC offset of the GREEN
channel. See REDOFST (05).

The power-up default value is BLUOFST = 80h.

CLAMP TIMING

70

CLPLACE

Clamp Placement

An 8-bit register that sets the position of the internally generated
clamp.

When EXTCLMP = 0, a clamp signal is generated internally, at
a position established by CLPLACE and for a duration set by
CLDUR. Clamping is started CLPLACE pixel periods after the
trailing edge of HSYNC. CLPLACE may be programmed to
any value between 1 and 255. CLPLACE = 0 is not supported.

The clamp should be placed during a time that the input signal
presents a stable black-level reference, usually the back porch
period between HSYNC and the image. A value of 08h will
usually work.

When EXTCLMP = 1, this register is ignored.

The power-up default value is CLPLACE = 80h.

70

CLDUR

Clamp Duration

An 8-bit register that sets the duration of the internally gener-
ated clamp.

When EXTCLMP = 0, a clamp signal is generated internally, at
a position established by CLPLACE and for a duration set by
CLDUR. Clamping is started CLPLACE pixel periods after the
trailing edge of HSYNC, and continues for CLDUR pixel peri-
ods. CLDUR may be programmed to any value between 1 and
255. CLDUR = 0 is not supported.

For the best results, the clamp duration should be set to include
the majority of the black reference signal time found following
the HSYNC signal trailing edge. Insufficient clamping time can
produce brightness changes at the top of the screen, and a slow
recovery from large changes in the Average Picture Level (APL),
or brightness. A value of 10h to 20h works with most standard
signals.

When EXTCLMP = 1, this register is ignored.

The power-up default value is CLDUR = 80h.

REV. B

AD9884A

GENERAL CONTROL

DEMUX

Output Port Select

A bit that determines whether all pixels are presented to a single
port (A), or alternating pixels are demultiplexed to Ports A and B.

DEMUX

Function

All Data Goes to Port A

Alternate Pixels Go to Port A and Port B

When DEMUX = 0, Port B outputs are in a high impedance
state.

The power-up default value is DEMUX = 1.

PARALLEL

Output Timing Select

Setting this bit to a Logic 1 delays data on Port A and the
DATACK output by one-half DATACK period so that the
rising edge of DATACK may be used to externally latch data
from both Port A and Port B. When this bit is set to a Logic 0,
the rising edge of DATACK may be used to externally latch
data from Port A only, and the

DATACK rising edge may be

used to externally latch data from Port B.

PARALLEL

Function

Data Alternates Between Ports

Simultaneous Data on Alternate DATACKs

When in single port mode (DEMUX = 0), this bit is ignored.

The power-up default value is PARALLEL = 1.

HSPOL

HSYNC Polarity

A bit that must be set to indicate the polarity of the HSYNC
signal that is applied to the HSYNC input.

HSPOL

Function

Active LOW

Active HIGH

Active LOW is the traditional negative-going HSYNC pulse.
Sampling timing is based on the leading edge of HSYNC, which
is the FALLING edge. The Clamp Position, as determined by
CLPLACE, is measured from the trailing edge.

Active HIGH is inverted from the traditional HSYNC, with a
positive-going pulse. This means that sampling timing will be
based on the leading edge of HSYNC, which is now the RIS-
ING edge, and clamp placement will count from the FALLING
edge.

The device will operate more-or-less properly if this bit is set
incorrectly, but the internally generated clamp position, as es-
tablished by CLPOS, will not be placed as expected, which may
generate clamping errors.

The power-up default value is HSPOL = 1.

CSTPOL

COAST Polarity

A bit that must be set to indicate the polarity of the COAST
signal that is applied to the COAST input.

CSTPOL

Function

Active LOW

Active HIGH

Active LOW means that the clock generator will ignore HSYNC
inputs when COAST is LOW, and continue operating at the
same nominal frequency until COAST goes HIGH.

Active HIGH means that the clock generator will ignore HSYNC
inputs when COAST is HIGH, and continue operating at the
same nominal frequency until COAST goes LOW.

The power-up default value is CSTPOL = 1.

EXTCLMP

Clamp Signal Source

A bit that determines the source of clamp timing.

EXTCLMP

Function

Internally-generated clamp

Externally-provided clamp signal

A 0 enables the clamp timing circuitry controlled by CLPLACE
and CLDUR. The clamp position and duration is counted from
the trailing edge of HSYNC.

A 1 enables the external CLAMP input pin. The three channels
are clamped when the CLAMP signal is active. The polarity of
CLAMP is determined by the CLAMPOL bit.

The power-up default value is EXTCLMP = 0.

CLAMPOL

Clamp Signal Polarity

A bit that determines the polarity of the externally provided
CLAMP signal.

CLAMPOL

Function

Active LOW

Active HIGH

A 0 means that the circuit will clamp when CLAMP is LOW,
and it will pass the signal to the ADC when CLAMP is HIGH.

A 1 means that the circuit will clamp when CLAMP is HIGH,
and it will pass the signal to the ADC when CLAMP is LOW.

The power-up default value is CLAMPOL = 1.

EXTCLK

External Clock Select

A bit that determines the source of the pixel clock.

EXTCLK

Function

Internally generated clock

Externally provided clock signal

A 0 enables the internal PLL that generates the pixel clock from
an externally-provided HSYNC.

A 1 enables the external CKEXT input pin. In this mode, the
PLL Divide Ratio (PLLDIV) is ignored. The clock phase adjust
(PHASE) is still functional.

The power-up default value is EXTCLK = 0.

REV. B

AD9884A

CLOCK GENERATOR CONTROL

73

PHASE

Clock Phase Adjust

A five-bit value that adjusts the sampling phase in 32 steps across
one pixel time. Each step represents an 11.25 degree shift in
sampling phase.

The power-up default value is PHASE = 16.

65

VCORNGE

VCO Range Select

Two bits that establish the operating range of the clock generator.

VCORNGE

Range (MHz)

20-60

50-90

80-120

110-140

VCORNGE must be set to correspond with the desired operat-
ing frequency (incoming pixel rate).

The power-up default value is VCORNGE = 01.

42

CURRENT

Charge Pump Current

Three bits that establish the current driving the loop filter in the
clock generator.

CURRENT

Current ( A)

000

001

100

010

150

011

250

100

350

101

500

110

750

111

1500

CURRENT must be set to correspond with the desired operat-
ing frequency (incoming pixel rate).

The power-up default value is CURRENT = 001.

OUTPHASE

Output Port Phase

One bit that determines whether even pixels or odd pixels go to
Port A.

OUTPHASE

First Pixel After HSYNC

Port A

Port B

In normal operation (OUTPHASE = 0), when operating in
Dual Channel output mode (DEMUX = 1), the first sample
after the HSYNC leading edge is presented at Port A. Every
subsequent ODD sample appears at Port A. All EVEN samples
go to Port B.

When OUTPHASE = 1, these ports are reversed and the first
sample goes to Port B.

When DEMUX = 0, this bit is ignored.

When reading back the value of OUTPHASE, the bit appears at
register 0D, Bit 7.

31

REVID

Silicon Revision ID

The die revision of the AD9884A can be determined by reading
these three bits.

Serial Control Port

A 2-wire serial control interface is provided. Up to four AD9884A
devices may be connected to the 2-wire serial interface, with
each device having a unique address.

The 2-wire interface comprises a clock (SCL) and a bidirec-
tional data (SDA) pin. The Analog Flat Panel Interface acts as a
slave for receiving and transmitting data over the serial interface.
When the serial interface is not active, the logic levels on SCL
and SDA are pulled HIGH by external pull-up resistors.

Data received or transmitted on the SDA line must be stable for
the duration of the positive-going SCL pulse. Data on SDA
must change only when SCL is LOW. If SDA changes state
while SCL is HIGH, the serial interface interprets that action as
a start or stop sequence.

There are six components to serial bus operation:
· Start Signal
· Slave Address Byte
· Base Register Address Byte
· Data Byte to Read or Write
· Stop Signal

When the serial interface is inactive (SCL and SDA are HIGH)
communications are initiated by sending a start signal. The start
signal is a HIGH-to-LOW transition on SDA while SCL is
HIGH. This signal alerts all slaved devices that a data transfer
sequence is coming.

The first eight bits of data transferred after a start signal com-
prising a seven bit slave address (the first seven bits) and a
single R/

W bit (the eighth bit). The R/W bit indicates the direc-

tion of data transfer, read from (1) or write to (0) the slave
device. If the transmitted slave address matches the address of
the device (set by the state of the SA

1-0

input pins in Table IV),

the AD9884A acknowledges by bringing SDA LOW on the
ninth SCL pulse. If the addresses do not match, the AD9884A
does not acknowledge.

Table IV. Serial Port Addresses

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

(MSB)

(LSB)

Data Transfer via Serial Interface

For each byte of data read or written, the MSB is the first bit of
the sequence.

If the AD9884A does not acknowledge the master device during
a write sequence, the SDA remains HIGH so the master can
generate a stop signal. If the master device does not acknowl-
edge the AD9884A during a read sequence, the AD9884A inter-
prets this as "end of data." The SDA remains HIGH so the
master can generate a stop signal.

REV. B

AD9884A

Writing data to specific control registers of the AD9884A requires
that the 8-bit address of the control register of interest be written
after the slave address has been established. This control register
address is the base address for subsequent write operations. The
base address autoincrements by one for each byte of data written
after the data byte intended for the base address. If more bytes
are transferred than there are available addresses, the address
will not increment and remain at its maximum value of 0Eh. Any
base address higher than 0Eh will not produce an ACKnowledge
signal.

Data are read from the control registers of the AD9884A in a
similar manner. Reading requires two data transfer operations:

The base address must be written with the R/

W bit of the slave

address byte LOW to set up a sequential read operation.

Reading (the R/

W bit of the slave address byte HIGH) begins at

the previously established base address. The address of the read
register autoincrements after each byte is transferred.

To terminate a read/write sequence to the AD9884A, a stop
signal must be sent. A stop signal comprises a LOW-to-HIGH
transition of SDA while SCL is HIGH.

A repeated start signal occurs when the master device driving
the serial interface generates a start signal without first generat-
ing a stop signal to terminate the current communication. This is
used to change the mode of communication (read, write) between
the slave and master without releasing the serial interface lines.

Serial Interface Read/Write Examples
Write to One Control Register

· Start Signal
· Slave Address Byte (R/

W Bit = LOW)

· Base Address Byte
· Data Byte to Base Address
· Stop Signal

STOSU

DAH

SDA

SCL

BUFF

STAH

DHO

DSU

DAL

STASU

Figure 1. Serial Port Read/Write Timing

SDA

SCL

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

ACK

Figure 2. Serial Interface--Typical Byte Transfer

Write to Four Consecutive Control Registers

· Start Signal
· Slave Address Byte (R/

W Bit = LOW)

· Base Address Byte
· Data Byte to Base Address
· Data Byte to (Base Address + 1)
· Data Byte to (Base Address + 2)
· Data Byte to (Base Address + 3)
· Stop Signal

Read from One Control Register

· Start Signal
· Slave Address Byte (R/

W Bit = LOW)

· Base Address Byte
· Start Signal
· Slave Address Byte (R/

W Bit = HIGH)

· Data Byte from Base Address
· Stop Signal

Read from Four Consecutive Control Registers

· Start Signal
· Slave Address Byte (R/

W Bit = LOW)

· Base Address Byte
· Start Signal
· Slave Address Byte (R/

W Bit = HIGH)

· Data Byte from Base Address
· Data Byte from (Base Address + 1)
· Data Byte from (Base Address + 2)
· Data Byte from (Base Address + 3)
· Stop Signal

REV. B

AD9884A

FREQUENCY Mpps

400

100

700

600

500

800

120

140

160

Figure 3. Power Dissipation vs. Frequency

DESIGN GUIDE

GENERAL DESCRIPTION

The AD9884A is a fully-integrated solution for capturing analog
RGB signals and digitizing them for display on flat panel moni-
tors or projectors. The circuit is also ideal for providing a com-
puter interface for HDTV monitors or as the front-end to high
performance video scan converters.

Implemented in a high performance CMOS process, the inter-
face can capture signals with pixel rates of up to 140 MegaPixels
Per Second (Mpps), and with an Alternate Pixel Sampling mode,
up to 280 Mpps.

355

Figure 4. Equivalent Analog Input Circuit

DIGITAL

INPUT

360

Figure 5. Equivalent Digital Input Circuit

DIGITAL

OUTPUT

Figure 6. Equivalent Digital Output Circuit

The AD9884A includes all necessary input buffering, signal dc
restoration (clamping), offset and gain (brightness and contrast)
adjustment, pixel clock generation, sampling phase control, and
output data formatting. All controls are programmable via a
2-wire serial interface. Full integration of these sensitive analog
functions makes system design straightforward and less sensitive
to the physical and electrical environment.

With a typical power dissipation of only 570 mW and an operat-
ing temperature range of 0

C to 70

C, the device requires no

special environmental considerations.

INPUT SIGNAL HANDLING
Analog Inputs

The AD9884A has three high impedance analog input pins for
the red, green, and blue channels. They will accommodate
signals ranging from 0.5 V to 1.0 V p-p.

Signals are typically brought onto the interface board via a 15-
pin D connector, a VESA P&D connector, a DDWG DVI
connector, or via BNC connectors. The AD9884A should be
located as close as practical to the input connector. Signals
should be routed via matched- impedance traces (normally
75

) to the IC input pins.

At that point the signal should be resistively terminated (75

to the signal ground return) and capacitively coupled to the
AD9884A inputs through 47 nF capacitors. These capacitors
form part of the dc restoration circuit.

In an ideal world of perfectly matched impedances, the best
performance can be obtained with the widest possible signal
bandwidth. The ultrawide bandwidth inputs of the AD9884A
(500 MHz) can track the input signal continuously as it moves
from one pixel level to the next, and digitize the pixel during a
long, flat pixel time. In many systems, however, there are mis-
matches, reflections, and noise, which can result in excessive
ringing and distortion of the input waveform. This makes it
more difficult to establish a sampling phase that provides good
image quality. It has been shown that a small inductor in series
with the input is effective in rolling off the input bandwidth
slightly, and providing a high quality signal over a wider range of
conditions. Using a Fair-Rite #2508051217Z0 High-Speed
Signal Chip Bead inductor in the circuit of Figure 7 gives good
results in most applications.

AIN

RGB

INPUT

47nF

Figure 7. Analog Input Interface Circuit

HSYNC, VSYNC Inputs

The interface also takes a horizontal sync signal, which is used
to generate the pixel clock and clamp timing. It is possible to
operate the AD9884A without applying HSYNC (using an
external clock, external clamp, and single port output mode) but
a number of features of the chip will be unavailable, so it is
recommended that HSYNC be provided. This can be either a
sync signal directly from the graphics source, or a preprocessed
TTL or CMOS level signal. The HSYNC input includes a
Schmitt trigger buffer for immunity to noise and signals with
long rise times.

REV. B

AD9884A

In typical PC-based graphic systems, the sync signals are simply
TTL-level drivers feeding unshielded wires in the monitor
cable. Since the AD9884A operates from a 3.3 V power supply,
and TTL sources may drive a high level to 5 V or more, it is
recommended that a 1 k

series current-limiting resistor be placed

in series with HSYNC and COAST. If these pins are driven
more than 0.5 V outside the power supply voltages, internal
ESD protection diodes will conduct, and may dissipate consid-
erable power if the sync source is of particularly low impedance.
If a signal is applied to the AD9884A when the IC's power is
off, then even a 1 V signal can turn on the ESD protection
diodes. The 1 k

series resistor will protect the device from

overstress in this situation as well.

Serial Control Port

The serial control port (SDA, SCL) is designed for 3.3 V logic.
If there are 5 V drivers on the bus, these pins should be pro-
tected with 150

series resistors.

OUTPUT SIGNAL HANDLING

The digital outputs are designed and specified to operate from a
3.3 V power supply (V

). They can also work with a V

low as 2.5 V for compatibility with other 2.5 V logic.

CLAMPING

To properly digitize the incoming signal, the dc offset of the
input signal must be adjusted to fit the range of the on-board
A/D converters.

Most graphic systems produce RGB signals with black at ground
and white at approximately +0.75 V. However, if sync signals
are embedded in the graphics, then the sync tip is often at ground
potential, and black is at +300 mV. Then white is at approxi-
mately +1.0 V. Some common RGB line amplifier boxes use
emitter-follower buffers to split signals and increase drive capa-
bility. This introduces a 700 mV dc offset to the signal which
must be removed for proper capture by the AD9884A.

The key to clamping is to identify a portion (time) of the signal
when the graphic system is known to be producing black. An
offset is then introduced which results in the A/D converters
producing a black output (code 00h) when the known black
input is present. That offset then remains in place when other
signal levels are processed, and the entire signal is shifted to
eliminate offset errors.

In most graphic systems, black is transmitted between active
video lines. Going back to CRT displays, when the electron
beam has completed writing a horizontal line on the screen (at
the right side), the beam is deflected quickly to the left side of
the screen (called horizontal retrace) and a black signal is pro-
vided to prevent the beam from disturbing the image.

In systems with embedded sync, a blacker-than-black signal
(HSYNC) is produced briefly to signal the CRT that it is time
to begin a retrace. For obvious reasons, it is important to avoid
clamping on the tip of HSYNC. Fortunately, there is virtually
always a period following HSYNC called the back porch where
a good black reference is provided. This is the time when clamp-
ing should be done.

The clamp timing can be established by simply exercising the
CLAMP pin at the appropriate time (with EXTCLMP = 1).
The polarity of this signal is set by the CLAMPOL bit.

A simpler method of clamp timing employs the AD9884A inter-
nal clamp timing generator. Register CLPLACE is programmed
with the number of pixel times that should pass after the trailing
edge of HSYNC before clamping starts. A second register
(CLDUR) sets the duration of the clamp. These are both 8-bit
values, providing considerable flexibility in clamp generation.
The clamp timing is referenced to the trailing edge of HSYNC
because, though HSYNC duration can vary widely, the back
porch (black reference) always follows HSYNC. A good start-
ing point for establishing clamping is to set CLPLACE to 08h
(providing 8 pixel periods for the graphics signal to stabilize
after sync) and set CLDUR to 14h (giving the clamp 20 pixel
periods to reestablish the black reference).

Clamping is accomplished by placing an appropriate charge on
the external input coupling capacitor. The value of this capaci-
tor affects the performance of the clamp. If it is too small, there
will be a significant amplitude change during a horizontal line
time (between clamping intervals). If the capacitor is too large,
then it will take excessively long for the clamp circuit to recover
from a large change in incoming signal offset. The recommended
value results in recovering from a step error of 100 mV to within
1/2 LSB in 10 lines with a clamp duration of 20 pixels on a
60 Hz SXGA signal.

GAIN AND OFFSET CONTROL

The AD9884A can accommodate input signals with inputs
ranging from 0.5 V to 1.0 V full scale. The full-scale range is set
in three 8-bit registers (REDGAIN, GRNGAIN, BLUGAIN).

A code of 0 in a gain register establishes a minimum input range
of 0.5 V; 255 corresponds with the maximum range of 1.0 V.
Note that INCREASING the gain setting results in an image
with LESS contrast.

The offset control shifts the entire input range, resulting in a
change in image brightness. Three 6-bit registers (REDOFST,
GRNOFST, BLUOFST) provide independent settings for each
channel.

The offset controls provide a

31 LSB adjustment range. This

range is connected with the full-scale range, so if the input range
is doubled (from 0.5 V to 1.0 V) then the offset step size is also
doubled (from 2 mV per step to 4 mV per step).

Figure 8 illustrates the interaction of gain and offset controls.
The magnitude of an LSB in offset adjustment is proportional
to the full-scale range, so changing the full-scale range also
changes the offset. The change is minimal if the offset setting is
near midscale. When changing the offset, the full-scale range is
not affected, but the full-scale level is shifted by the same amount
as the zero scale level.

REV. B

AD9884A

INPUT RANGE

1.0V

0.0V

0.5V

OFFSET = 1FH

OFFSET = 3FH

OFFSET = 0FH

OFFSET = 1FH

OFFSET = 3FH

OFFSET = 0FH

GAIN

00h

FFh

Figure 8. Gain and Offset Control

CLOCK GENERATION

A Phase Locked Loop (PLL) is employed to generate the pixel
clock. In this PLL, the HSYNC input provides a reference
frequency. A Voltage Controlled Oscillator (VCO) generates a
much higher pixel clock frequency. This pixel clock is divided
by the value PLLDIV programmed into the AD9884A, and
phase compared with the HSYNC input. Any error is used to
shift the VCO frequency and maintain lock between the two
signals.

The stability of this clock is a very important element in provid-
ing the clearest and most stable image. During each pixel time,
there is a period during which the signal is slewing from the old
pixel amplitude and settling at its new value. Then there is a
time when the input voltage is stable, before the signal must
slew to a new value (Figure 9). The ratio of the slewing time to
the stable time is a function of the bandwidth of the graphics
DAC and the bandwidth of the transmission system (cable and
termination). It is also a function of the overall pixel rate.
Clearly, if the dynamic characteristics of the system remain
fixed, then the slewing and settling time is likewise fixed. This
time must be subtracted from the total pixel period, leaving the
stable period. At higher pixel frequencies, the total cycle time is
shorter, and the stable pixel time becomes shorter as well.

Any jitter in the pixel clock reduces the precision with which the
sampling time can be determined, and must also be subtracted
from the stable pixel time.

PIXEL CLOCK

INVALID SAMPLE TIMES

Figure 9. Pixel Sampling Times

Considerable care has been taken in the design of the AD9884A's
clock generation circuit to minimize jitter. As indicated in Fig-
ure 11 and Table VI, the clock jitter of the AD9884A is less
than 5% of the total pixel time in all operating modes, making
the reduction in the valid sampling time due to jitter negligible.

The PLL characteristics are determined by the loop filter de-
sign, by the PLL Charge Pump Current (CURRENT), and by
the VCO Range setting (VCORNGE). The loop filter design is
illustrated in Figure 10. Recommended settings of VCORNGE
and CURRENT for VESA standard display modes are listed in
Table VII.

Table V. Typical K

VCO

Derived From VCORNGE

Pixel Rate (MHz)

VCORNGE

VCO

(MHz/V)

2060

100

5090

100

80120

150

110140

180

0.039 F

3.3k

0.0039 F

FILT

Figure 10. PLL Loop Filter Detail

Table VI. Pixel Clock Jitter vs Frequency

Pixel Rate

Jitter p-p

(MSPS)

(ps)

(% of Pixel Time)

135

350

4.7%

108

400

4.3%

400

3.4%

450

3.4%

600

3.9%

500*

2.4%

500*

2.0%

550*

1.8%

1000*

2.5%

*AD9884A in oversampled mode.

REV. B

AD9884A

Table VII. Recommended VCORNGE and CURRENT Settings for Standard Display Formats

Refresh

Horizontal

Standard

Resolution

Rate

Frequency

Pixel Rate

VCORNGE

CURRENT

VGA

640

480

60 Hz

31.5 kHz

25.175 MHz

000

72 Hz

37.7 kHz

31.500 MHz

000

75 Hz

37.5 kHz

31.500 MHz

000

85 Hz

43.3 kHz

36.000 MHz

001

SVGA

800

600

56 Hz

35.1 kHz

36.000 MHz

001

60 Hz

37.9 kHz

40.000 MHz

001

72 Hz

48.1 kHz

50.000 MHz

010

75 Hz

46.9 kHz

49.500 MHz

001

85 Hz

53.7 kHz

56.250 MHz

010

XGA

1024

768

60 Hz

48.4 kHz

65.000 MHz

010

70 Hz

56.5 kHz

75.000 MHz

011

75 Hz

60.0 kHz

78.750 MHz

011

80 Hz

64.0 kHz

85.500 MHz

011

85 Hz

68.3 kHz

94.500 MHz

011

SXGA

1280

1024

60 Hz

64.0 kHz

108.000 MHz

011

75 Hz

80.0 kHz

135.000 MHz

100

85 Hz

91.1 kHz

157.500 MHz*

100

UXGA

1600

1200

60 Hz

75.0 kHz

162.000 MHz*

100

65 Hz

81.3 kHz

175.500 MHz*

100

70 Hz

87.5 kHz

189.000 MHz*

101

75 Hz

93.8 kHz

202.500 MHz*

101

85 Hz

106.3 kHz

229.500 MHz*

110

VESA Monitor Timing Standards and Guidelines, September 17, 1998
*Graphics sampled at 1/2 incoming pixel rate using Alternate Pixel Sampling mode.

Figure 11 illustrates the AD9884A's jitter as a percentage of the
total clock period over the range of operating frequencies.
Though the jitter is very low over most of the range (less than
5% of the pixel period), the jitter increases at clock rates below
40 MHz. At lower frequencies, the jitter can be reduced by
operating the AD9884A at twice the desired frequency, and
using only every other data sample produced. This can be easily
implemented by placing the part in Dual Channel mode (for
example, as in Figure 21), and reading the data from only one of
the output ports. The DATACK and

DATACK outputs will

run at the desired, lower, sample rate.

PIXEL CLOCK MHz

100

JITTER %

120

140

160

JITTER p-p (%)

OVERSAMPLED RATE

JITTER p-p (%)

Figure 11. Pixel Clock Jitter vs. Frequency

REV. B

AD9884A

Two things happen to Horizontal Sync in the AD9884A. First,
HSOUT is always produced in an active HIGH state: that is,
the leading edge of HSOUT is always a RISING edge. Then,
HSOUT is aligned with DATACK and the data outputs. This is
the sync signal that should be used to drive the rest of the dis-
play system.

The trailing edge of HSOUT is NOT time-aligned: it remains
linked to the incoming HSYNC. Refer to the timing diagrams
for HSOUT leading edge placement. HSOUT trailing edge is
coincident with HSYNC input trailing edge. There can be no
guarantee of the timing relationship between the HSOUT trail-
ing edge and DATACK. Therefore, the leading edge of HSOUT
should be used for all display system timing.

HSOUT is forced LOW at midline, whether or not the incom-
ing HSYNC trailing edge has arrived. If HSOUT exhibits a
50% duty cycle (while HSYNC input does not) it is an indica-
tion that the HSPOL bit is incorrectly set. This characteristic
can be used to produce an HSOUT with synchronous leading
and trailing edges by programming HSPOL to use the trailing
edge of HSYNC instead of the leading edge. In this case, if the
internal clamp function is used, be aware that the clamp posi-
tion is now measured from the LEADING edge of HSYNC,
and program it accordingly.

COAST Timing

In most computer systems, the HSYNC signal is provided con-
tinuously on a dedicated wire. In these systems, the COAST
input and function are unnecessary, and should not be used.

In some systems, however, HSYNC is disturbed during the
Vertical Sync period (VSYNC). In some cases, HSYNC pulses
disappear. In other systems, such as those that employ Compos-
ite Sync (CSYNC) signals or embed Sync On Green (SOG),
HSYNC includes equalization pulses or other distortions during
VSYNC. To avoid upsetting the clock generator during VSYNC,
it is important to ignore these distortions. If the pixel clock PLL
sees extraneous pulses, it will attempt to lock to this new fre-
quency, and will have changed frequency by the end of the
VSYNC period. It then will take a few lines of correct HSYNC
timing to recover at the beginning of a new frame, resulting in a
"tearing" of the image at the top of the display.

The COAST input is provided to eliminate this problem. It is
an asynchronous input that disables the PLL input and allows
the clock to free-run at its then-current frequency. The PLL can
free-run for several lines without significant frequency drift.

COAST can be driven directly from a VSYNC input, or it can
be provided by the graphics controller.

TIMING

The following timing diagrams show the operation of the
AD9884A in all clock modes. The part establishes timing by
having the sample that corresponds to the pixel digitized when
the leading edge of HSYNC occurs sent to the "A" data port (to
the B data port if 0Dh, Bit 4 = 1). In Dual Channel mode, the
next sample is sent to the "B" port (to the A data port if 0Dh,
Bit 4 = 1). Subsequent samples are alternated between the "A"
and "B" data ports. In Single Channel mode, data is only sent
to the "A" data port, and the "B" port is placed in a high im-
pedance state.

When operating in Dual Channel mode, since the first pixel
after HSYNC is always sent to the A port, there are situations
where the first DESIRED pixel (the first active pixel of a line)
may appear on the B port. If the graphics controller or memory
buffer requires that the first pixel appear on the A port, the
OUTPHASE control bit will swap the data to the A and B
ports.

The Output Data Clock signal is created so that its rising edge
always occurs between "A" data transitions, and can be used to
latch the output data externally. The HSYNC output is pipelined
with the data in a fixed timing relationship between the two in
all Single Channel modes.

There is a pipeline in the AD9884A, which must be flushed
before valid data becomes available. In all single channel
modes, four data sets are presented before valid data is avail-
able. In all dual channel modes, two data sets are presented
before valid "A" port data is available.

PER

DCYCLE

SKEW

DATACK

DATA

HSOUT

Figure 12. Output Timing

Horizontal Sync Timing

Horizontal Sync is processed in the AD9884A to eliminate
ambiguity in the timing of the leading edge with respect to the
phase-delayed pixel clock and data.

The HSYNC input is used as a reference to generate the pixel
sampling clock. The sampling phase can be adjusted, with re-
spect to HSYNC, through a full 360

in 32 steps via the PHASE

register (to optimize the pixel sampling time). Display systems
use HSYNC to align memory and display write cycles, so it is
important to have a stable timing relationship between HSOUT
and DATACK.

REV. B

AD9884A

Figure 14. Odd Pixels from Frame 1

Figure 15. Even Pixels from Frame 2

ALTERNATE PIXEL SAMPLING MODE

A Logic 1 input on CKINV (Pin 27) shifts the sampling phase
180 degrees. CKINV can be switched between frames to imple-
ment the alternate pixel sampling mode. This allows higher
effective image resolution to be achieved at lower pixel rates,
but with lower frame rates.

Figure 13. Odd and Even Pixels in a Frame

On one frame, only even pixels are digitized. On the subsequent
frame, odd pixels are sampled. By reconstructing the entire frame
in the graphics controller, a complete image can be reconstructed.
This is very similar to the interlacing process that is employed in
broadcast television systems, but the interlacing is vertical instead
of horizontal. The frame data is still presented to the display at
the full desired refresh rate (usually 60 Hz) so there are no flicker
artifacts added.

O1 E2 O1 E2 O1 E2 O1 E2 O1 E2 O1 E2

Figure 16. Combined Frame Output from Graphics
Controller

O3 E2 O3 E2 O3 E2 O3 E2 O3 E2 O3 E2

Figure 17. Subsequent Frame from Controller

REV. B

AD9884A

PCB LAYOUT RECOMMENDATIONS

The AD9884A is a high precision, high speed analog device. As
such, to get the maximum performance out of the part it is
important to have a well laid-out board.

Inputs

Using the following layout techniques on the graphics inputs is
extremely important:

Minimize the trace length running into the graphics inputs. This
is accomplished by placing the AD9884A as close as possible to
the input connector. Long input trace lengths are undesirable
because they will pick up more noise from the board and other
external sources.

Place the 75

termination resistors as close to the AD9884A as

possible. Any additional trace length between the termination
resistors and the input of the AD9884A increases the magnitude
of reflections, which will corrupt the graphics signal.

Use 75

matched impedance traces. Trace impedances other

than 75

will also increase the magnitude of reflections.

The AD9884A has very high input bandwidth (500 MHz). While
this is desirable for acquiring a high resolution PC graphics
signal with fast edges, it means that it will also capture any high
frequency noise present. Therefore, it is important to reduce the
amount of noise that gets coupled to the inputs. Avoid running
any digital traces near the analog inputs.

Due to the high bandwidth of the AD9884A, sometimes low-
pass filtering the analog inputs can help to reduce noise. (For
many applications, filtering is unnecessary.) Our experiments
have shown that placing a series ferrite bead prior to the 75

termination resistor is helpful in filtering out excess noise. Spe-
cifically, we used the Part #2508051217Z0 from Fair-Rite, but
each application may work best with a different bead value.

Power Supply Bypassing

We recommend you bypass each power supply pin with a 0.1

capacitor. The exception is in the case where two or more sup-
ply pins are adjacent. For these groupings of powers/grounds, it

is only necessary to have one bypass capacitor. The fundamental
idea is to have a bypass capacitor within about 0.5 cm of each
power pin. Also, avoid placing the capacitor on the opposite side
of the PC board from the AD9884A, as that interposes resistive
vias in the path.

The bypass capacitors should be connected between the power
plane and the power pin. Current should flow from the power
plane ¡ capacitor ¡ power pin. Do not make the power connec-
tion between the capacitor and the power pin. Placing a via
underneath the capacitor pads, down to the power plane, is
generally the best approach.

It is particularly important to maintain low noise and good
stability of PV

(the clock generator supply). Abrupt changes in

can result in similarly abrupt changes in sampling clock

phase and frequency. This can be avoided by careful attention
to regulation, filtering, and bypassing. It is highly desirable to
provide a separately regulated supply for the analog circuitry
(V

and P

Some graphic controllers use substantially different levels of
power when active (during active picture time) and when idle
(during Horizontal and Vertical sync periods). This can result in
a measurable change in the voltage supplied to the analog supply
regulator, which can in turn produce changes in the regulated
analog voltage. This can be mitigated by regulating the analog
supply, or at least P

, from a different, cleaner, power source

(for example, from a +12 V supply).

We also recommend that you use a single ground plane for the
entire board. Experience has repeatedly shown that the noise
performance is better, or at least the same, with a single ground
plane. Using multiple ground planes can be detrimental because
each separate ground plane is smaller, and long ground loops
can result.

RGBIN

P0 P1 P2 P3 P4 P5

HSYNC

PXCK

ADCCK

DATACK

DOUTA

HSOUT

DOUTB

6.5 PIPE DELAY

Figure 26. Dual Channel Mode, Parallel Outputs, Alternate Pixel Sampling (Odd Pixels)

REV. B

AD9884A

In some cases, using separate ground planes is unavoidable. For
those cases, we recommend to at least place a single ground
plane under the AD9884A. The location of the split should be
at the receiver of the digital outputs. For this case it is even
more important to place components wisely because the current
loops will be much longer, (current takes the path of least resis-
tance). An example of a current loop:

POWER PLANE

AD9884A

DIG

ITA

D P

LAN

DIG

ITAL

GROU

ND PLANE

DIGITAL DAT

A RE

CEIV

Figure 27.

PLL

Place the PLL loop filter components as close to the AD9884A
pins as possible.

Do not place any digital or other high frequency traces near
these components.

Use the values suggested in the data sheet with 5% tolerance or
less.

Outputs (Both Data and Clocks)

Try to minimize the trace length that the digital outputs have to
drive. Longer traces have higher capacitance, which requires
more current, which causes more internal digital noise.

Shorter traces reduce the possibility of reflections.

Adding a series resistor of value 50

200

can suppress

reflections, reduce EMI, and reduce the current spikes inside of
the AD9884A. If series resistors are used, place them as close to
the AD9884A pins as possible, (although try not to add vias or
extra length to the output trace in order to get the resistors closer).

If possible, limit the capacitance that each of the digital outputs
drives to less than 10 pF. This can easily be accomplished by
keeping traces short and by connecting the outputs to only one
device. Loading the outputs with excessive capacitance will
increase the current transients inside of the AD9884A, and
create more digital noise on its power supplies.

Digital Inputs

The digital inputs on the AD9884A were designed to work with
3.3 V signals. Connecting 5 V digital signals to the part may
cause damage. To accommodate 5 V digital signals, we recom-
mend adding a series resistor at the AD9884A pin of 1 k

. The

only exception is the two serial interface pins, SDA and SCL.
On these two pins, a resistor value of 150

should be used and

it should be placed between the AD9884A pin and the pull-up
resistors.

Any noise that gets onto the HSYNC input trace will add jitter
to the system, so, try to minimize the trace length and try not to
run any digital or other high frequency traces near it.

Voltage Reference

Bypass with a 0.1

F capacitor. Place it as close to the AD9884A

pin as possible. Make the ground connection as short as possible.

REFOUT is easily connected to REFIN with a short trace.
Avoid making this trace any longer than it needs to be.

When using an external reference, the REFOUT output,
while unused, still needs to be bypassed to ground with a
0.1

F capacitor to avoid ringing.

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