Transmitter System; Pll Frequency Synthesizer; Drive And Final Amplifier; Apc Circuit - Kenwood NX-3220 K Service Manual

2.3.4 Transmitter System

2.3.4.1 Audio Band Circuit
The signal from microphone is amplified and converted to digital signal by IC601, IC601 includes AGC function. Digital signal is
transferred to IC401.
2.3.4.2 Baseband Circuit
The audio signal transferred from IC601 is processed at IC401.
Voice signals of 300Hz or lower and frequencies of 3kHz or higher are cut off and an audio range 300Hz to 3kHz is extracted. The
audio signal is then pre-emphasized in FM mode and synthesized with the signals, such as QT and DQT, as required, and is
transferred to PLL Frequency Synthesizer block in IC303. The DTMF and MSK baseband signals are also generated by IC401.
In Digital mode, the audio signal is converted to the 4-Level FSK baseband signal and is transferred to PLL Frequency Synthesizer
block in IC303.
Transceiver IC
IC303
2.3.4.3

Drive and Final amplifier

The signal from the IC303 is amplified by pre-drive amplifier (IC202). The output of the pre-drive amplifier is amplified by the drive
amplifier (Q201) and final amplifier (Q202) to 5W (1W when the power is low). IC202 is MMIC. Q201 and Q202 are MOS FET. The
output of the final amplifier is then passed through the harmonic filter (LPF) and antenna switch (D201, D202 and D203) and applied
to the antenna terminal.
2.3.4.4

APC circuit

The APC circuit always monitors the current flowing through the drive amplifier (Q201) and final amplifier (Q202). And APC keeps
current 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 APC
circuit. Output voltage from APC controls the VGG of Q201 and Q202 to keep the current constant. The change of power high/low is
carried out by the change of the reference voltage.
IC202
IC303
Pre-Drive

2.3.5 PLL Frequency Synthesizer

2.3.5.1 TCXO (X401)
TCXO (X401) generates a reference frequency of 19.2MHz for the PLL frequency synthesizer. This reference signal is buffered by
Q401. And it is distributed to PLL (IC303), IC401 and IC351.
The oscillation frequency is adjusted TCXO directly by controlled the D/A converter of FCNT.
1-16 (No.RA053<Rev.001>)
Serial
I/F
DSP
MPU/DSP
IC401
Fig.4 Audio and Baseband circuit
Q201
Drive
Fig.5 Drive and Final amplifier and APC circuit
I2S
AD
I2C
CODEC
IC601
Q202
Final
R248
+B
Internal MIC
External MIC
ANT SW
R250
APC
IC203
APC reference voltage