TDA7705_10 Datasheet, PDF (10/42 Pages) STMicroelectronics – Highly integrated tuner for AM/FM car radio

Function description
2
Function description
TDA7705
2.1
FM - mixers
The image-rejection mixer has two FM inputs, selectable through software. These inputs
feed stages with different gains, noise figures, and IIP3. They are optimized for best
performance in case of a passive tuned prestage and for a passive fixed bandpass without
tuning for low-cost application respectively.
The second input offers also the possibility of an easy addition of a weather-band
preselection filter.
The input frequency is downconverted to low IF with high image rejection.
The tuned application is supported by an 8-bit tuning DAC. The alignment of the DAC is
performed automatically.
2.2
FM - AGC
The programmable RFAGC senses the mixer input whereas the IFAGC senses the IFADC
input to avoid overload.
The PIN diode driver is able to drive external PIN diodes with a current value as high as
15mA.
The time constant of the FM-AGC is defined by an external capacitor.
2.3
AM - LNA
The AM-LNA is integrated with low noise and high IIP2 and IIP3. The gain of the LNA is
controlled by the AGC. The maximum gain is set with an external resistor, typically 26 dB
with 1 kΩ.
2.4
AM - AGC
The programmable AM-RF-AGC senses the mixer inputs and controls the internal PIN diode
and LNA gain.
First the LNA gain is reduced by about 10dB, then the PIN diodes are activated to attenuate
the signal.
The time constant of the AM-AGC is defined with an external capacitor and programmable
internal currents.
2.5
AM - mixers
The image-rejection mixer has two AM inputs selectable via software. It easily supports low-
cost applications for extended frequency bands like SW, DRM.
The input frequency is converted to low IF with high image rejection.
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Doc ID 15938 Rev 8