TDA 6812-5 is a complete system for stereo TV-sound, controlled on an

C Bus. The device is

made up of three functional blocks.

1. Stereo Processing with High Quality (better than DIN 45500; suitable for NICAM and CD for

G-standard with

C-controlled crosstalk compensation; selectable gain 0/6 dB

a) Three stereo AF-inputs
b) Random switching of all inputs to all outputs
c) Stereo SCART-interface
d) Stereo loudspeaker signal section with volume precontrol, treble/bass control, enlargement of

quasi-stereo/stereo sound base, separate L/R-volume control, equalizer interface after tone
control

e) Stereo headphones signal section with Ch1/Ch2 and volume control

2. TV-Identification-Signal Decoder

a) Active pilot-tone filter
b) Phase-independent rectifier with very narrow bandwidth for identification-signal decoding
c) Digital integrator for noise rejection
d) Multiplexer for cyclic scanning for stereo or dual-sound identification
e) Externally synchronized PLL for reference-signal generation: synchronization with line sync

pulse or 62.5-kHz clock, integrated crystal oscillator and 4-MHz crystal, or with external
4-MHz timing signal

Type

Ordering Code

Package

TDA 6812-5

Q67000-A5127

P-DIP-40-2

TV-Stereo Processor

Preliminary Data

Bipolar IC

TDA 6812-5

P-DIP-40-2

Features

High quality stereo signal processing

High S/N ratio

C Bus

Clipping detector and clock generator

NICAM or AM sound inputs

Volume control

Universal audio interface for DOLBY, EQUALIZER,
SURROUND SOUND features

Multiplex 3-SCART connections

Independent headphones

113

06.94

TDA 6812-5

Semiconductor Group

114

3. Control

C Bus interface with listen/talk function

b) Control of entire audio processing
c) Reading of clipping detector
d) Control of identification-signal decoder
e) Reading of identification-signal decoder
f) Test modes

Pin Functions

Pin No.

Function

AF-input mono, left, sound 1 (adjustable)

Bias AF-operating point

AF-input, right, sound 2

N.C.

54-kHz input

54-kHz filter

SCART-input 1, left

SCART-input 1, right

SCART-input 2, left

SCART-input 2, right

SCART-input 3, left

SCART-input 3, right

AF-output SCART (mono, sound 1, left)

AF-output SCART (mono, sound 2, right)

Output port 1 (open collector)

Output port 2 (open collector)

Phase shifter quasi-stereo

Cut-off frequency bass (sound base), left

Cut-off frequency bass (sound base), right

AF-output, loudspeaker, right

AF-output, loudspeaker, left

N.C.

AF-input, volume control, right

Semiconductor Group

117

TDA 6812-5

Circuit Description

Signal Section

The dematrixing and switching of multichannel TV-sound signals are performed in the matrix and
switch section by the dual-carrier method. Crosstalk compensation is on the sound 1 input. The
compensation stage has a range of

�

3 dB with a smallest increment of 0.2 dB, and gain can also

be switched between 0 and 6 dB. In addition to the two inputs for the demodulated sound carriers,
there are three dual-channel SCART-inputs. The two matrix AF-inputs can be bypassed internally
so that decoded stereo signals of other systems (NICAM) can also be processed. The switch
section terminates in the SCART-output and signal paths for the loudspeaker and headphones
outputs. AF-inputs can be randomly switched to AF-outputs (8-6 matrix).

In the loudpeaker signal path there is an inital volume control with a range of 0/� 15 dB and an
increment of 1.25 dB. In conjunction with the main volume control that follows the tone control, very
high overdriving immunity is ensured. The switchable quasi-stereo section that follows produces a
stereo listening effect for mono signals through a 180

C phase shift at mid-range frequencies

(approx. 1 kHz) in one channel. The following bass control has an increment of 3 dB in its setting
range of + 15/� 12 dB. The cut-off frequency for each channel is set by an external capacitor. The
circuit for enlarging the stereo sound base can be cut in for stereo signals to make the aural
impression even more stereo-like by frequency-dependent antiphase crosstalk of 55 %. This works
with the same cut-off frequency as the bass control, but the function is largely independent. The
treble control, whose cut-off frequency is also set by an external capacitor, likewise has an
increment of 3 dB in a setting range of

�

12 dB. The main value control with maximum gain of 10

dB, which can be adjusted separately for L and R, terminates the loudspeaker signal path. 57 steps
with an increment of 1.25 dB mean a setting range of 71.25 dB. Functions like balance or loudness
are implemented by software setting of the appropriate tone and volume controls. In the tone-
control section there is a clipping detector that can be read on the

C Bus and enables automatic

volume correction by the controller. After each reading the clipping bit is reset, which enables a
renewed check for clipping with each

C Bus read operation.

The headphones signal path includes a volume control with joint L/R-setting. 32 increments of 2 dB
produce a range of 62 dB (31 x 2 dB = 62 dB).

Identification-Signal Decoder

The input of the identification-signal decoder consists of an operational amplifier for selectivity of
the pilot tone and its sidebands with an external LC-circuit. The signal is fed to a phase-independent
active bandpass filter of very narrow bandwidth (externally adjustable) that detects the presence of
the lower sideband of the pilot carrier modulated with the identification signal. The center frequency
of the filter is switched back and forth between dual and stereo by a multiplexer (software-controlled
timing). The multiplexer halts when a sideband is detected. This first "detected" criterion is freed
from noise by a digital integrator followed by a comparator and can then be read on the

C Bus

(talker) as stereo or dual mode. The

�

C controls the signal paths. All necesssary timing signals are

derived from a fast settling PLL synchronized by a reference frequency. This reference must be
sufficiently identical to the horizontal frequency, but no phase locking is necessary. This means
that it is possible to use the crystal-controlled frequency of 62.5 kHz that is often found in PLL-tuning
systems. As further alternatives there is an integrated crystal oscillator that requires a 4-MHz
crystal, or it is possible to use a clock frequency of 1 or 4 MHz.

Электронный компонент: TDA6812-5