Benefon EXION TDP80DN, Service Manual

Page: 42 / 63

9.2.2001
4Z2700GB.fm 15
Product: TDP80DN / OC2720 Processor/Audio/RF
5.6 TRANSMITTER
5.6.1 General
5.6.2 Function Description
The transmitter unit is comprised of three amplifier stages and two filters. The ampli-
fier chain consists of pre-amplifier Q620/Q621 and power module I650.
The attenuator R620/R621 is included to enhance the electric separation between
the TX synthesizer and the transmitter.
The filter X620 and duplexfilter X660 ensure that unwanted signals will not reach the
antenna.
The operational amplifier I640 and transistors Q641 and Q642 serve as a power reg-
ulator circuit, which adjusts the power level so that the voltage from the transmitter
power detector X650/D660 and the control voltage TXPWR from the processor unit
are equal at inputs of I640.
The negative voltage is generated with the Switched Capacitor Voltage Inverter
I610.
The switching frequency is typically 100 kHz and resistors R611/R612 sets the out-
put voltage to -2.5 V.
I600 serves as voltage regulator for pre-amplifier and for the negative voltage
generetor.
Q631 is ON/OFF switch for the power amplifier.
5.6.3 Control- and Output-Signals
Operating voltage 3.5 ... 4.5 v
Current consumption mid power max. 1.1 A
low power max. 0.45 A
Input level from the synthesizer +6 dBm
Output level to the duplex filter mid power 33 dBm (2.0W)
low power 24.7 dBm (0.3W)
Frequency range 452.500...457.475 MHz
VBAT
Transmitter operating voltage from the
battery-pack (fused)
TXBIAS Power ON/OFF control
TXPWR
Power level control signal from the D/A
converter
0...3V
TXINJ RF signal from the TX synthesizer +6dBm
RXDUPLEX To RX duplex filter