ATR4255 datasheet(4/32 Pages) ATMEL

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ATR4255

4837A–AUDR–10/04

Functional Description

The ATR4255 implements an AM up/down-conversion reception path from the RF input

signal to the AM-demodulated audio frequency output signal, and for FM reception a

double-conversion reception path from the RF input signal to the FM-demodulated mul-

tiplex signal (MPX). A VCO and an LO prescaler for AM are integrated to generate the

LO frequency for the 1

st mixer. Automatic gain control (AGC) circuits are implemented to

control the preamplifier and IF stages in the AM and FM reception path.

For improved FM performance, an integrated IF filter with adjustable bandwidth, a soft-

mute feature and an automatic multipath noise cancellation (MNC) circuit are fully

integrated. A powerful set of sensors is provided for receiving condition analysis and

stop signal generation.

Several register bits (bit 0 to bit 93) are used to control circuit operation and to adapt

certain circuit parameters to the specific application. The control bits are organized in

two 8-bit and three 24-bit registers that can be programmed by the 3-wire bus protocol.

The bus protocol and the bit-to-register mapping is described in the section “3-wire Bus

Description” on page 17. The meaning of the control bits is mentioned in the following

sections.

Reception Mode

The IC can be operated in four different modes. Mode AM, FM, WB, Standby are

selected by means of bit 92 and bit 93 according to Table 1.

In AM mode the AM mixer, the AM RF-AGC and the 1st IF AM amplifier at pin 33 are

activated. The input of the 2nd IF amplifier is connected to pin 28 and the output of the

2nd IF amplifier is fed to the AM demodulator. The output of the AM demodulator is

available at MPX output pin 11.

In FM mode the FM mixer, the FM RF-AGC and the 1st IF FM amplifier at pin 38 are acti-

vated. The bandwidth of the output tank at pin 23, pin 24 is increased and the input of

the 2

nd IF amplifier can be switched between pin 23, pin 24 and pin 28. The output of the

nd IF amplifier is fed to the integrated bandfilter and FM demodulator. The output of the

FM demodulator is available at MPX output pin 11.

WB mode is similar to FM mode but the input of the 2

nd IF amplifier is fixed to pin 28, the

range of the bandwidth control of the integrated band filter is shifted to lower bandwidth

and the gain of the FM demodulator is increased.

In standby mode the mixers, IF amplifiers and AGC circuits are deactivated to reduce

current consumption.

Table 1. Operating Mode

AM/FM/Weather Channel

Bit 93

Bit 92

Standby

Weather band

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