TDA7512 Datasheet, PDF (15/42 Pages) STMicroelectronics – AM/FM CAR RADIO TUNER IC WITH INTELLIGENT SELECTIVITY SYSTEM ISS

TDA7512
1. Functional Description
1.1 FM Section
1.2 Mixer1, AGC and 1.IF
FM quadrature I/Q-mixer converts FM RF to IF1 of 10.7MHz. The mixer provides inherent image rejection and
wide dynamic range with low noise and large input signal performance. The mixer1 tank can be adjusted by
software (IF1T). For accurate image rejection the gain- and phase-error generated as well in mixer as VCO
stage can be compensated by software (G,PH)
It is capable of tuning the US FM, US weather, Europe FM, Japan FM and East Europe FM bands
– US FM = 87.9 to 107.9 MHz
– US weather = 162.4 to 162.55 MHz
– Europe FM = 87.5 to 108 MHz
– Japan FM = 76 to 91 MHz
– East Europe FM = 65.8 to 74 MHz
The AGC operates on different sensitivities and bandwidths in order to improve the input sensitivity and dynamic
range. AGC thresholds are programmable by software (RFAGC,IFAGC,KAGC). The output signal is a con-
trolled current for double pin diode attenuator.
Two 10.7MHz programmable amplifiers (IFG1, IFG2) correct the IF ceramic insertion loss and the costumer lev-
el plan application.
1.3 Mixer2, Limiter and Demodulator
In this 2. mixer stage the first 10.7MHz IF is converted into the second 450kHz IF. A multi-stage limiter generates
signals for the complete integrated demodulator without external tank. MPX output DC offset versus noise DC
level is correctable by software (DEM).
1.4 Quality Detection and ISS
1.4.1 Fieldstrength
Parallel to mixer2 input a 10.7MHz limiter generates a signal for digital IF counter and a fieldstrength output sig-
nal. This internal unweighted fieldstrength is used for keying AGC, adjacent channel and multipath detection
and is available at PIN14 (FSU) after +6dB buffer stage. The behaviour of this output signal can be corrected
for DC offset (SL) and slope (SMSL). The internal generated unweighted fieldstrength is filtered at PIN35 and
used for softmute function and generation of ISS filter switching signal for weak input level (sm).
1.4.2 Adjacent Channel Detector
The input of the adjacent channel detector is AC coupled from internal unweighted fieldstrength. A programma-
ble highpass or bandpass (ACF) and amplifier (ACG) as well as rectifier determines the influences. This voltage
is compared with adjustable comparator1 thresholds (ACWTH, ACNTH). The output signal of this comparator
generates a DC level at PIN15 by programmable time constant. Time control (TISS) for a present adjacent chan-
nel is made by charge and discharge current after comparator1 in an external capacitance. The charge current
is fixed and the discharge current is controlled by I²C Bus. This level produces digital signals (ac, ac+) in an
additional comparator4. The adjacent channel information is available as analog output signal after rectifier and
+8dB output buffer.
1.4.3 Multipath Detector
The input of the multipath detector is AC coupled from internal unweighted fieldstrength. A programmable band-
pass (MPF) and amplifier (MPG) as well as rectifier determines the influences. This voltage is compared with
an adjustable comparator2 thresholds (MPTH). The output signal of this comparator2 is used for the "Milano"
effect. In this case the adjacent channel detection is switched off. The "Milano" effect is selectable by I²C Bus
(MPOFF). The multipath information is available as analog output signal after rectifier and +8dB output buffer.
15/42