TDA7529_11 Datasheet, PDF (13/61 Pages) STMicroelectronics – RF front-end for AM/FM DSP car-radio with IF sampling

TDA7529
Figure 4.
Positive/negative current diagram
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M!
FE CURRENT
6
Function description
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3. Constant current mode: the output current can be set to 2 mA source current. The AGC
detector is in power -down mode and only the PIN diode driver is active.
4. Voltage and current mode with hand-over: the Vthr level is programmable with 6 bit in
the range of 0.2V to 2.56V. The voltage Vthr is the internal reference voltage of an
external cascode transistor emitter feedback loop.
Figure 5.
Voltage and current mode with hand-over
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6THR
6THR
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The voltage output swing is comprised between 0V and 3.3V (VDD).
The microcontroller can read the voltage at the AGC capacitor via the serial control
interface.
3.3
AM RF-AGC
The AM AGC system is controlled by an average detector. The time constant of the AM RF-
AGC is defined by an external capacitor connected to TCAM and programmable internal
currents with symmetrical attack/decay behavior.
The AM RF-AGC has two output pins to drive one PIN diode attenuator and the external
preamplifier gain control.
The AGC outputs can be programmed to the same modes as the FM RF-AGC with the
exception of pos/neg current.
The microcontroller can read the voltage at the AGC capacitor via the serial control
interface.
Doc ID 13311 Rev 4
13/61