TDA6170 Datasheet, PDF (11/27 Pages) Infineon Technologies AG – Components for Entertainment Electronics, Satellite Sound IF

Data Sheet
TDA6170X
7.6 Expander Description
The demodulated and level controlled audio signals are fed via low-pass filters to the inputs of two identical
expander circuits. The IF3 audio signal is also applied in parallel via different de-emphasis networks to the
input of the audio switch for broadband mono reception. The expander circuits have the reverse characteris-
tics of the audio compressor of the TV station. A 3 bit pre volume control (control byte 3: PVL2...PVL0 and
PVR2...PVR0) for each audio channel enables a correct adjustment of the expander characteristics and
allows the possibility to align to the right level for both broadband and smallband sound IF reception.
7.7 AF Switch and Volume Control
The input signals of the AF switch can be derived from the external audio input pair. However, these signals
can also be derived from either the different de-emphasis networks or from both expanders. The selection of
the output signals from IF1, IF2 or IF3 is done by using the I²C-bus interface. The switches are followed by a
volume control section with buffered outputs Ch1 and Ch2.
In case of small-band reception the demodulated signals of IF1 and IF2 are processed in both expanders and
fed to the switches. So it is possible to select one of each or both in the audio switches for both AF outputs
Ch1 and Ch2.
In the case of broad-band audio transmission with 50µs, 75µs or J17 pre-emphasis the IF3 input is active and
with the audio switch the demodulated audio signals are selected after the three de-emphasis networks and
fed to both AF outputs in mono mode.
The 3 bit volume control (control byte 2: VL2...VL0 and VR2...VR0) in front of each AF output enables the
same audio level for different FM deviations of several satellite transponders.
Semiconductor Group
7
21.7.99