ATR4258 Datasheet, PDF (5/38 Pages) ATMEL Corporation – AM/FM RECEIVER IC

Functional
Description
Reception Mode
ATR4258
The ATR4258 implements an AM up/down-conversion reception path from the RF input
signal to the AM-demodulated audio frequency output signal, and for FM/WB reception
a double-conversion reception path from the RF input signal to the FM-demodulated
multiplex 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 imple-
mented 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 20. The meaning of the control bits is mentioned in the following
sections.
The integrated VCO has a high frequency range. Additionally the VCO has a special
VCO divider which allows (in connection with the VCO) the reception of all analog world
bands.
The IC can be operated in four different modes. Mode AM, FM, WB, and Standby are
selected by means of bit 92 and bit 93 according to Table 1 on page 6.
Additionally to the operating modes, the signal paths can be set separately. Bit 62
selects the first mixer and AGC, bit 63 selects the 1^st amplifier stage. The recommended
settings of bit 62 and bit 63 are included in Table 1 on page 6.
In AM mode the AM mixer, the AM RF-AGC and the 1^st IF AM amplifier at pin 33 are
activated. The input of the 2^nd IF amplifier is connected to pin 28 and the output of the
2^nd 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 1^st 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 and pin 24 and pin 28. The output of
the 2^nd IF amplifier is fed to the integrated band filter and FM demodulator. The output of
the FM demodulator is available at MPX output pin 11.
The WB mode is similar to the FM mode, but to reduce the bandwidth the AM IF ampli-
fier with the AM filter (bit 63 = 1) can be used. In WB mode the range of the integrated
filter bandwidth control 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.
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