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TDMA M3090/M3097:
IF
2nd LO
U1000
DATA
CLK
SPI BUS
CEX
Ref Osc
Description
U401(ZIF_SYNTH) can be divided into two functional subsystems: The ZIF (Zero-Intermediate-Frequency) which provides all of the functions of the back-end of a
receiver, and the SYN (SYNthesizer) which contains phase-locked loops and modulators to produce t he Local Oscillator (LO) and modulated transmit carrier.
The ZIF implements the back end of the receiver. The incoming signal is attenuated, amplified and mixed down to an extremely low frequency(Baseband)-not quite DC.
The first amplifier and an Automatic Gain Control(AGC) circuit adjusts the amplifier gain to maintain a constant level in the baseband filter. C401 is used to add stability
to the AGC circuit.
The first mixing that occurs in th e ZIF requires a 2nd Local Oscill ator that is running at 221.184MH z. The 2nd LO is divided down the n phased shifted before being
mixed with the IF signal., producing the baseband signal
The baseband signal is low-pass filtered using a programmable low-pass filter. In TDMA mode, the baseband signal is routed to U201(DCI) via the RX_I and RX_Q
lines. In analog mode, the baseband signal is up-converted and then FM-demodulated, producing the DEMOD signal which is routed to U201(D CI) for filtering and de-
emphasis.
The RSSI(Receive Signal Strength Indicator) is a voltage that increases with respect to the rec eived signal strength.
The SPI Bus is a serial interface used to program the internal filters and frequency di viders for U401, allowing selectivity of cellular channels.
RF 19.44Mhz input is used to p rovide a frequency reference for U401.
ZIF_SYNTH (U401)
C401
Step
Atten.
Shifter
SPI BUS
8/16/96 BIT
MODES
19.44MHz
RSSI
LP_SWITCH
U401
MAIN
LOOP
Offset
LOOP
UP
Demod
Converter
Cap
Filters
AGC_RSSI
VCO
Offset VCO
DEMOD
RX_I
RX_Q
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