TDA7529 datasheet(14/60 Pages) STMICROELECTRONICS

14 / 60 page

Function description

TDA7529

14/60

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:

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.

Table 3.

IF AGC and IF amplifier

IFAGC2

IFAGC1

Gain

G - 6dB

G - 12dB

G - 18dB

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