Benefon EXION TDP80DN, Service Manual

Page: 38 / 63

9.2.2001
4Z2700GB.fm 11
Product: TDP80DN / OC2720 Processor/Audio/RF
RF
5.3 RX SYNTHESIZER
5.3.1 General
The RX synthesizer generates an upper side injection frequency for the receiver.
The injection frequency is fed to the receiver's first mixer.
5.3.2 Functional Description
The RX injection frequency is generated with a phase locked loop. The Voltage Con-
trolled Oscillator (VCO) produces the injection frequency determined by the control
voltage. After the VCO stage comes the amplifier stage Q430. After the amplifier
stage, part of the signal is fed to the synthesizer circuits I400 pre-scaller Fin1. The
synthesizer circuit contains a pre-scaler, programmable divider, reference frequency
divider, and a phase detector.
The synthesizer circuit produces current pulses at output DO1 as controlled by the
phase detector. The current pulses either charge or discharge the loop filter. The
VCO control voltage is derived from the loop filter output.
The synthesizer 12.5kHz reference frequency is made by dividing the 13.00 MHz
signal from the temperature compensated oscillator (TCXO). The series-form signal
which controls the channel frequency comes from the processor. SDATA, SCLK and
SLE signals are common to both TX- and RX-synthesizers. A positive pulse in the
SLE line loads the division ratio (corresponding to the frequency of the channel) fed
to the SDATA line, to the synthesizer circuit I400.
5.3.3 Control- and Output-Signals
Operating voltage 3.0 VDC
Current consumption 14 mA
Output level to the receiver +1 dBm
Frequency range 540.950...545.925 MHz
VRX RX synthesizer operating voltage 3.0 V
SCLK Clock signal for the synthesizer control data
SDATA Synthesizer control data
SLE ENABLE pulse to the synthesizer
RXINJ RX synthesizer output to the receiver +1 dBm
RX_REG Control line for VRX-regulator