(No.RA070)1-132.3.4 Transmitter System2.3.4.1 Audio Band CircuitThe signal from microphone is amplified and converted to digital signal by IC601, IC601 includes AGC function. Digital signal istransferred to MPU/DSP (IC401).2.3.4.2 Baseband CircuitThe audio signal transferred from CODEC (IC601) is processed at MPU/DSP (IC401). Voice signals of 300Hz or lower and frequenciesof 3kHz or higher are cut off and an audio range 300Hz to 3kHz is extracted. The audio signal is then pre-emphasized in FM modeand synthesized with the signals, such as QT and DQT, as required, and is transferred to PLL Frequency Synthesizer block inTransceiver IC (IC303). The DTMF and MSK baseband signals are also generated by MPU/DSP (IC401).In Digital mode, the audio signal is converted to the 4-Level FSK baseband signal and is transferred to PLL Frequency Synthesizerblock in Transceiver IC (IC303).Fig.4 Audio and Baseband circuit2.3.4.3 Drive and Final AmplifierThe signal from the Transceiver IC (IC303) is amplified by pre-drive amplifier (IC202). The output of the pre-drive amplifier is amplifiedby the drive amplifier (Q201) and final amplifier (Q202) to 3W (1W when the power is low). IC202 is MMIC. Q201 and Q202 are MOSFET. The output of the final amplifier is then passed through the harmonic filter (LPF) and antenna switch (D201 and D207, D202 andD203) and applied to the antenna terminal.2.3.4.4 APC CircuitThe APC circuit always monitors the current flowing through the drive amplifier (Q201) and final amplifier (Q202). And APC keepscurrent constant.The voltage drop at R248 and R250 is caused by the current flowing through the RF power amplifier and this voltage is applied to APCcircuit. Output voltage from APC controls the VGG of Q201 and Q202 to keep the current constant. The change of power high/low iscarried out by the change of the reference voltage.Fig.5 Drive and Final amplifier and APC circuit2.3.5 PLL Frequency Synthesizer2.3.5.1 TCXO (X401)TCXO (X401) generates a reference frequency of 19.2MHz for the PLL frequency synthesizer. This reference signal is buffered byQ401. And it is distributed to PLL (incorporated in Transceiver IC (IC303)), MPU/DSP (IC401) and IC351.The oscillation frequency is adjusted TCXO directly by controlled the D/A converter of FCNT.ADI/FTransceiver ICIC303SerialDSPMPU/DSPIC401 IC601CODECI2CI2SExternal MICInternal MIC+BTXAPC reference voltageIC203APCR250R248ANT SWFinalD201, D202,D203, D207Q202Q201DrivePre-DriveIC202
