tda6612-2 Infineon Technologies Corporation, tda6612-2 Datasheet - Page 3

• Manufacturer Part Number: tda6612-2
• Description: Tv-stereo-sound
• Manufacturer: Infineon Technologies Corporation

TDA 6612-2
Circuit Description
Signal Section
The audio signal processing in the matrix and the switch-over for multi channel TV-sound signals
according to the two carrier system used in Germany takes place in the matrix and switching sec-
tions. Crosstalk compensation is carried out in the sound 1 input stage. The crosstalk compensation
range has an adjustment range of
3 dB with a step width of 0.2 dB. In addition to the two inputs
for the demodulated sound carrier a two channel SCART-input and an additional mono input (e.g.
for demodulated L-standard sound) are provided. The two AF (pin 1 and pin 2) inputs can be by-
passed internally in such a way that decoded stereo sound of other audio systems (NICAM) can be
processed. The switching section includes also the SCART-output with the possibility to select the
sound 1 or 2 during the "dual" mode. The Ch1/Ch2-switches for the loudspeaker and headphone
outputs are independently switchable.
In the signal path for the volume control unit output there is the Ch1/Ch2-switch followed by two dif-
ferent volume control units. The first has a control range from 0 to – 15 dB with a step width of 1.25
dB. In conjunction with the main volume control after bass and treble control a high immunity against
overdriving the output stage is reached. The first volume control is used as a "pre-stage" of the main
volume control in conjuntion with the clipping detector. This section is followed by a switchable quasi
stereo stage which provides a stereophonic audio effect with mono signals due to a 180˚ phase shift
at medium frequencies (about 1 kHz) in one channel. The following bass control has a control range
of +15/–12 dB with a step width of 3 dB. The cut-off frequency for each channel is set with an ex-
ternal capacitor. The implemented switchable circuit for stereo base width expansion provides a
three dimensional aural reception. This is realized with a 50% frequency dependent crosstalk with
opposite phase of the signal between both channels. The circuit operates with the same cut-off fre-
quency as the bass control, but the function is widely independent. The treble control has a step
width of 3 dB with an control range of +/–12 dB. The cut-off frequency of the treble control is derived
from one capacitor for each channel. The loudspeaker signal path is terminated with the loudspea-
ker control, independently adjustable for left and right. With 57 steps of 1.25 dB the adjustment ran-
ge is 70 dB, where step 57 activates the "MUTE" function. Functions such as "balance" or "loud-
ness" are realized by software and adjustment of the appropriate tone and volume controls. In the
volume control unit there is a clipping detector. The status of the clipping detector can be evaluated
via the I
2
C Bus. Therefore it is possible to implement an automatic volume control using the clipping
detector and software implemented into the controller.
After every evaluation the clipping bit is reset. Therefore after a read access to the clipping bit a new
evaluation of the clipping detector status is possible.
The signal path for the headphones contains a volume control after the Ch1/Ch2-switch with a com-
mon adjustment for left and right. Thirty two steps of 2 dB give an adjustment range of 62 dB (31 x
2 dB = 62 dB, the 32nd step is MUTE).
Identification Signal Decoder
The input of the identification signal decoder consists of an op-amp for the pilot signal with its side
bands. An external LC-circuit is used. The signal is then passed to a phase independent active
band-pass filter with a very narrow bandwidth (adjustable externally). This filter detects whether the
lower side band of the pilot carrier, which is modulated with the identification signal, is present. The
Semiconductor Group
3