Benefon EXION TDP80DN, Service Manual

Page: 40 / 63

9.2.2001
4Z2700GB.fm 13
Product: TDP80DN / OC2720 Processor/Audio/RF
5.4.3 Control- and Output-Signals
5.5 RECEIVER
5.5.1 General
The module contains all FM-receiver functional blocks.
When the RF signal is received it is brought through the RX-filter(X500) to the ampli-
fier stage Q500. The amplified signal is passed through the attenuator to the bal-
anced mixer.The balanced mixer is made by using discrete components, diode D510
and RF-transformer M510.
The upper side injection frequency is brought from the synthesizer through a small
resistive attenuator to the mixer. The 78.45 MHz intermediate frequency from the
mixer output is fed through the IF- filter X520 to the FM IF-circuit I550.
RX injection frequency 540.950...545.925MHz
Injection-level/imp1 dBm / 50 ohm
The second intermediate-frequency local-oscillator-frequency required by the FM IF-
circuit is generated by multiplying the 13.00 MHz reference-oscillator frequency by
six. The multiplier circuit is made with transistor Q530.
The second intermediate frequency is 450 kHz. The phase-shift required by the
quadrature detector is made with the L550. The detected AF-signal temperature cor-
rection is done in the buffer amplifier stage.
VTXS TX synthesizer operating voltage (3.0 V)
TXAUDIO Transmitter audio signal
13MHz 13.00 MHz signal to the receiver circuit.
SCLK Clock signal for synthesizer control data
SDATA Synthesizer control data
SLE ENABLE pulse to the synthesizer
TXINJ TX synthesizer output to the transmitter (+6 dBm)
AFC AFC control voltage from processor
TXS_REG Control line for VTXS-regulator
RF-amplifier 3SK320
1. mixer balanced mixer
1. IF-amplifier 3SK320
FM IF system SA 607 includes the following blocks:
2. mixer
IF limiter
quadrature detector
RSSI (received signal strength indicator)