TDA7706 Function description
Doc ID 022898 Rev 3 9/16
2 Function description
2.1 FM - mixers
The FM Image Rejection mixer has two single ended inputs, selectable through software.
They are designed for achieving best performance both in case of a passive tuned
preselection and for a passive fixed band-pass preselection without tuning for lower cost
applications.
The input frequency is down-converted to very 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 on-chip.
2.2 FM - AGC
The programmable RFAGC senses the mixer input to avoid overload.
When the RFAGC threshold is reached, the PIN diode output is activated in order to
attenuate the incoming RF signal
The PIN diode driver is able to drive external PIN diodes with up to 15 mA current.
The time constant of the FM AGC is defined by the combination of an external capacitor and
internal currents. There are two programmable attack and decay time constants.
2.3 AM - LNA
The integrated AM LNA feature 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 470 ohm.
2.4 AM - AGC
The programmable AM RFAGC senses the mixer inputs and controls the internal PIN diodes
and LNA gains.
Firstly the LNA gain is reduced by about 10d B, and then the PIN diodes are activated to
further attenuate the signal.
The time constant of the 2
nd
order AM AGC LPF is defined by both external components
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 short-waves.
The input frequency is converted to low IF with high image rejection.
