TDA7512F datasheet(18/45 Pages) STMICROELECTRONICS

18 / 45 page

Functional description

TDA7512F

18/45

Doc ID 12668 Rev 2

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 +8 dB output buffer.

4.3.3

Multipath detector

The input of the multipath detector is AC coupled from internal unweighted fieldstrength. A

programmable bandpass (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 comparator 2 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

+8 dB output buffer.

4.3.4

450 kHz IF narrow bandpass filter (ISS filter)

The device gets an additional second IF narrow bandpass filter for suppression of noise and

adjacent channel signal influences. This narrow filter has three switchable bandwidthes,

narrow range of 80 kHz, mid range of 120 kHz and 30 kHz 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 mixer 2 before 450 kHz limiter stage. The centre frequency is

matching to the demodulator center frequency.

4.3.5

Deviation detector

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

present overdeviation. Hence the demodulator output signal is detected.

A lowpass filtering and peak rectifier generates a signal that is defined by software

controlled current (TDEV) in an external capacitance. This value is compared with a

programmable comparator3 thresholds (DWTH, DTH) and generates two digital signals

(dev, dev+). For weak signal condition deviation threshold is proportinal to FSU.

4.3.6

ISS switch logic

All digital signals coming from adjacent channel detector, deviation detector and softmute

are acting via switching matrix on ISS filter switch. The IF bandpass switch mode is

controlled by software (ISSON, ISS30, ISS80, CTLOFF).

The switch ON of the IF bandpass is also available by external manipulation of the voltage at

PIN15.

Two application modes are available (APPM). The conditions are described in table 34.

4.4

Soft Mute control

The external fieldstrength signal at PIN 35 is the reference for mute control. The startpoint

and mute depth are programmable (SMTH, SMD) in a wide range. The time constant is

defined by external capacitance. Additional adjacent channel mute function is supported.

A highpass filter with -3 dB threshold frequency of 100 kHz, amplifier and peak rectifier

generates an adjacent noise signal from MPX output with the same time constant for

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