TDA7511

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1

FUNCTIONAL DESCRIPTION

1.1

FM Section

1.2

Mixer1, AGC and 1.IF

Mixer1 is a wide dynamic range stage with low noise and large input signal performance. The mixer1 tank 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 (keying AGC). The output signals of AGC are controlled volt-

age and current for preamplifier and prestage pin diode attenuator. (look at Figure 4)

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 compensation is

possible by software (DEM).

1.4

Quality Detection and ISS (look at Figure 2)

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).

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

additional comparator4. The adjacent channel information is available as analog output signal after rectifier and

+8dB output buffer.

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"

(MPOFF). The multipath information is available as analog output signal after rectifier and +8dB output buffer.

450kHz IF Narrow Bandpass Filter (ISS filter)

The device gets an additional second IF narrow bandpass filter for suppression noise and adjacent channel sig-

nal influences. This narrow filter has three switchable bandwidthes, narrow range of 80kHz, mid range of

120kHz and 30KHz for weather band information. Without ISS filter the IF bandwidth (wide range) is defined

only by ceramic filter chain. The filter is switched in after mixer2 before 450kHz limiter stage. The centre fre-

quency and matching to the demodulator center frequency can be fine adjusted (AISS) by software..

Deviation Detector

In order to avoid distortion in audio output signal the narrow ISS filter is switched OFF for present overdeviation.