TDA7529_11 Datasheet, PDF (14/61 Pages) STMicroelectronics – RF front-end for AM/FM DSP car-radio with IF sampling

Function description
TDA7529
3.4
IF AGC and IF amplifier
The IF AGC system is controlled in AM with an average detector and in FM with a peak
detector, and reduces the mixer gain. The time constant is defined by two external
capacitors connected to TCIF1 and TCIF2 respectively, and programmable internal
currents.
The microcontroller can read the voltage at the AGC capacitors via the serial control
interface.
The IF amplifier gain is not affected by the on-chip IF-AGC but is meant to be controlled by
the back-end part of the system through pins IFAGC1 and IFAGC2. The gain is reduced in 6
dB steps starting from the programmed value "G" according to the following table:
Table 3.
IF AGC and IF amplifier
IFAGC2
0
0
1
1
IFAGC1
0
1
1
0
Gain
G
G - 6 dB
G - 12 dB
G - 18 dB
3.5
Dividers
The mixer divider V is followed by a divide-by-4-stage that generates 0°/90°/-90° LO signals
for the IMR mixer (90°/-90° mode to switch between upper or lower side-band suppression
in the IMR mixer).
The main divider N can be operated in integer mode.
3.6
D/A converters
The front-end contains two D/A-converters for tuning the filters of the FM pre-stage. The
converters have a resolution of 9 bit.
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Doc ID 13311 Rev 4