TDA7512F Datasheet, PDF (17/45 Pages) STMicroelectronics – FM car-radio tuner IC with intelligent selectivity system (ISS)

TDA7512F
4
Functional description
Functional description
4.1
Mixer 1, AGC and 1.IF
FM quadrature I/Q-mixer converts 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 controlled current for double pin diode
attenuator. Two 10.7 MHz programmable amplifiers (IFG1, IFG2) correct the IF ceramic
insertion loss and the costumer level plan application.
4.2
Mixer 2, limiter and demodulator
In this 2. mixer stage the first 10.7 MHz IF is converted into the second 450 kHz 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).
4.3
4.3.1
4.3.2
Quality detection and ISS
Fieldstrength
Parallel to mixer 2 input a 10.7 MHz limiter generates a signal for digital IF counter and a
fieldstrength output signal. 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).
Adjacent channel detector
The input of the adjacent channel detector is AC coupled from internal unweighted
fieldstrength. A programmable 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 channel
is made by charge and discharge current after comparator1 in an external capacitance. The
Doc ID 12668 Rev 2
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