TDA7513T datasheet(17/59 Pages) STMICROELECTRONICS

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TDA7513T

FUNCTIONAL DESCRIPTION

5.1 FM Section

5.1.1 Mixer1, AGC and 1st IF

Mixer1 is a wide dynamic range stage with low noise and large input signal performance. The mixer1 tank

center frequency can be adjusted by software (IF1T). The AGC operates on different sensitivities and

bandwidths (FMAGC) in order to improve the input sensitivity and dynamic range (keyed AGC). The output

signals of AGC are controlled voltage and current for preamplifier and prestage P-I-N diode attenuator

(see Figure 5). Two 10.7MHz amplifiers (IFG1 - fixed gain - and IFG2 - programmable) correct the IF ce-

ramic insertion loss.

5.1.2 Mixer2, Limiter and Demodulator

In this 2nd 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

compensation is possible via software.

5.1.3 Quality Detection and ISS (see Figure 3) Fieldstrength

Parallel to the mixer2 input a 10.7MHz limiter generates a signal for the digital IF counter and a field-

strength output signal. This internal unfiltered fieldstrength is used for adjacent channel and multipath de-

tection. The behaviour of this output signal can be corrected for DC offset (SL). The internally generated

unfiltered fieldstrength is filtered at pin #SMETERTC and used for softmute function, FM AGC keying and

generation of ISS filter switching signal for weak input level (sm).

5.1.4 Adjacent Channel Detector

The input of the adjacent channel detector is AC coupled to the internal unfiltered fieldstrength. A pro-

grammable and configurable highpass or bandpass filter (ACF) and amplifier (ACG) followed by a rectifier

measure the adjacent channel content. This voltage is compared with an adjustable threshold (ACWTH,

ACNTH) comparator (comparator1). The output signal of this comparator generates a DC level at PIN15

with a programmable time constant. Time constant control (TISS) for the adjacent channel is made by lin-

early charging and discharging an external capacitor following. The charge current is fixed and the dis-

charge current is controlled by I2C bus. This level produces digital signals (ac, ac+) after comparing by the

following comparator4. The adjacent channel information after filtering and rectification is available as an-

alog output on pin #TUNQUALITY (the gain can be selected via I2C bus) in combination with multipath

content information. It is possible to enable adjacent channel content information output only via I2C bus

control.

Symbol

Parameter

Test Condition

Min.

Typ.

Max.

Unit

Multipath Influence Factor

Addr. 12 / Bit 5+6

0.7

0.85

1.15

Noise Influence Factor

Addr. 16 / Bit 1+2

Table 27. Multipath And Quality Detectors

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