TDA7540B datasheet(25/75 Pages) STMICROELECTRONICS

25 / 75 page

TDA7540B

Functional description

25/75

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.

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 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.

450kHz IF narrow bandpass filter (ISS filter)

The device gets an additional 450KHz IF narrow bandpass filter for suppression of noise

and adjacent channel signal 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 located between mixer2 and 450kHz limiter stage. The centre frequency is matched

to the demodulator center frequency.

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

dependent on FSWO.

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 voltage at PIN27. Two application modes are

available (APPM).

The conditions are described in table 51.

4.1.4

Soft mute control

The filtered fieldstrength (FSWO) signal 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 -3dB threshold frequency of 100kHz, amplifier and peak rectifier

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

softmute. This value is compared with comparator5 thresholds (ACM). For present strong

adjacent channel the MPX signal is additional attenuated (ACMD).

TDA7540B датащи(PDF) 25 Page - STMicroelectronics

TDA7540B датащи(HTML) 25 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75

датащи скачать

ссылки URL