Philips CEM5000/00, Service Manual

Page: 66 / 83

TDA7703/TDA7703R
5.0 FUNCTION DESCRIPTION
5.1 FM-Mixer
The IMR mixer is optimized for optimum performance in case of a passive tuned prestage and for a
passive fixed bandpass without tuning for low-cost application.
The input frequency is downconverted to low IF with high image rejection.
5.2 FM - AGC
The programmable RFAGC senses the mixer input, the IFAGC senses the IFADC input to avoid
overload.
The PIN diode driver is able to drive external PIN diodes with up to 15mA current.
The time constant of the FM-AGC is defined with an external capacitor.
5.3 AM – LNA
The AM-LNA is integrated with low noise and high IIP
2
and IIP
3
. The gain of the LNA is controlled
by the AGC. The maximum gain is set with an external resistor, typ. 26 dB with 1 Kohm.
5.4 AM-AGC
The programmable AM-RF-AGC senses the mixer input and controls the internal PIN diode and
LNA-gain.
First the LNA gain is reduced by about 10dB, then the PIN diodes are used to attenuate the signal.
The time constant of the AM-AGC is defined by an external capacitor and programmable internal
currents.
5.5 AM - Mixer
The IMR mixer supports LW and MW.
The input frequency is converted to low IF with high image rejection.
5.6 IF A/D CONVERTERS
A high performance IQ-IFADC converts the IF-signal to digital IF for the digital signal processing.
5.7 AUDIO D/A CONVERTERS
A stereo DAC provides the left / right audio signal after IF-processing and stereodecoding of the
DSP.
5.8 VCO
The VCO is fully integrated without any external tuning component. It covers all FM frequency
bands including EU, US, Japan, EastEU and the LW and MW AM-bands.
5.9 PLL
The high speed PLL is able to tune within about 300us for fast RDS applications (for TDA7703R).
The frequency step can go down to 5 kHz in FM and 500 Hz in AM.
5.10 Crystal oscillator
The device works with a standard 37.05 MHz fundamental tone crystal, and can be used also with
a 3
rd
overtone 37.05 MHz crystal.
5.11 DSP
The DSP and its hardware accelerators are performing all the digital signal processing. The main
program is fixed in ROM. Additional control parameters are accessible and can be set in the RAM.
It performs:
•
digital downconversion of the IF
•
bandwidth selection with variable controlled bandwidth
•
FM/AM demodulation with softmute, weak signal processing and quality detection
•
FM stereo decoding including highcut, stereoblend
•
RDS demodulation including block and group synchronization with generation of an RDS
interrupt for the main uP (TDA7703R only)
•
Autonomous control of RDS-AF tests (TDA7703R only)
Rev. 1.0 5/22