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.

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.