TDA7541TR datasheet(31/76 Pages) STMICROELECTRONICS

31 / 76 page

TDA7541

Functional description

31/76

4.1.5

Weak signal mute

The filtered field strength signal (FSWO) is the reference for soft slope mute control in weak

signal condition to eliminate audible effects. The start point and mute depth are

programmable (WMTH, WMD) in a wide range. These settings together with FSWO bits are

influencing the weak signal mute behaviour. The time constant is defined by external

capacitance at PIN 42. Additional adjacent channel mute function is supported. A high pass

filter with -3dB threshold frequency of 100 kHz, amplifier and peak rectifier generates an

adjacent noise signal from Demodulator output. This value is compared with adjustable

threshold (ACMTH). For present strong adjacent channel the MPX signal is additional

attenuated (ACMD) and has the same time constant as weak signal mute.

4.1.6

Weather band input

If the weather band input is used the chip must be set in FM mode (FMON). In addition to

that the ISS filter must be switched ON (ISSENA), mixer2 quality must set to IF2Q=”00” and

the ISS filter must be set in manual control mode. The bit WBON is activating the WB input

and is switching the ISS filter in WB mode (24 kHz band width).

4.2

AM section

The up/down conversion in AM signal path is combined with gain control circuit sensing

three input signals, narrow band information (DAGC) referred to PIN 56, up conversion

signal (IFAGC) at PIN 61 and wide band information (RFAGC) at PIN 3.This gain control

gives two output signals. The first one is a current for pin diode attenuator and the second

one is a voltage for preamplifier. Time constant of RF- and IF-AGC is defined by internal

100k resistor and external capacitor at PIN 54. The intervention points for AGC (DAGC,

IFAGC and RFAGC) are programmable by software. The oscillator frequency for

upconversion mixer1 is generated by dividing the VCO frequency after VCO divider (VCOD)

and AM predivider (AMD).

Two 10,7MHz ceramic filters before mixer2 input increase 900KHz attenuation.

Table 12.

ISS control modes

Input signals

Mode1

Mode2

ac+

dev

dev+

inton

int80

Function

inton

int80

Function

wide

narrow

wide

mid

wide

narrow

Mid

narrow

Narrow

mid

Mid

mid

Narrow

TDA7541TR bảng dữ liệu(PDF) 31 Page - STMicroelectronics

TDA7541TR bảng dữ liệu(HTML) 31 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 76

bảng dữ liệu tải về

Link URL