Hytera PT580, Service Manual, Page: 7 / 104

Service Manual
Cartesian IC
DCMEAS
RF_SCLK
RF_DIN
RF_DOUT
TxI+
TxI-
TxQ+
TxQ-
Tx_LO
3V_Tx
RF_SW
7V5
Antenna
PA
3V6_RF
3V_A
Temperature
Sensor
RF_FB
TMP_ALERT
SDA
SCL
RX
PA_BIAS1
PA_BIAS2
3V_TxA 3V_TxD
attenuator
CSN
DOI
DOQ
RF_FB
Figure 2 Diagram of TX Circuit
The TX circuit consists of PA, harmonic filter, pre-amplifier, duplexer, coupler, temperature sensor,
TX/RX switch, antenna and etc. The working principle of the TX circuit is described below:
The TX circuit sends the I/Q signal from the baseband section to the Cartesian IC, which outputs
800MHz TX signal after appropriate processing. The TX signal goes to the filter and then to the PA circuit
for amplification after it is converted by BALUN.
The PA circuit is to amplify the RF signal output by the Cartesian IC to obtain an appropriate power level.
Then the signal passes through the TX/RX switch and is sent out from the antenna.
The feedback channel is to couple the power output by the main PA to the Cartesian IC, to form a
complete Cartesian loop. In this way, the output power can be controlled via the attenuation of the
feedback loop.
The temperature sensor will give protection signal if the PA temperature is too high. In such case, the
output power of the PA will be decreased appropriately to prevent damage to the parts.
The signal output by the main PA passes through the TX/RX switch and then goes to the antenna. The
TX/RX switch controls the TX/RX status according to the control signal output by the baseband.
The interfaces between the TX circuit and the baseband or other circuits are described below.
(1) TMP_ALERT
This is the alarm output interface of the temperature sensor, and is connected with the baseband. It
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