Audio Amplifier Circuit; Squelch Circuit; Microphone Amplifier Circuit; Driver And Final Amplifier Circuit - Kenwood TK-2317 Service Manual

CIRCUIT DESCRIPTION / 电路说明
2-5. Audio Amplifi er Circuit
The demodulated signal from IC401 is sent to an audio
power amplifi er (IC815) through baseband IC (IC812), where
it is amplifi ed and output to the speaker.

2-6. Squelch Circuit

Part of the AF signal from the IC401 enters the FM sys-
tem IC (IC401) again, and the noise component is amplifi ed
and rectified by a filter and an amplifier to produce a DC
voltage corresponding to the noise level.
The DC signal from the FM IC goes to the analog port of
the MCU (IC820). IC820 determines whether or not to output
sounds from the speaker by checking if the input voltage is
higher or lower than the preset value.
To output sounds from the speaker, IC820 sends a high
signal to the AF_CONT line and turns IC815 on through
Q813, Q814, Q818 and Q819.
3. Transmitter System
3-1. Microphone Amplifi er Circuit
The signal from the microphone is limited by the AGC
circuit, which is composed of D807, D808, Q810, Q811 and
the mute switch (Q809). IC812 is composed of a high-pass
fi lter, low-pass fi lter and pre-emphasis/IDC circuit.
The signal from the microphone and the low speed data
from the MCU (IC820) enter the baseband IC (IC812) and
pass through each path and are mixed inside the IC.
The output signal from the baseband IC goes to the VCO
modulation input. The other output signal passes through the
amplifi er (IC3) and goes to the TCXO modulation input.
Fig. 4 Microphone amplifi er circuit / 图 4 麦克风放大器电路
3-2. Driver and Final Amplifi er Circuit
The signal from the T/R switch (D18 is on) is amplifi ed by
the RF AMP (Q201) and pre-drive amplifi er (Q203) to 50mW.
The output of the pre-drive amplifi er is amplifi ed by the
drive amplifi er (Q204) and the RF fi nal amplifi er (Q205) to
5.0W (1W when the power is low).
The drive amplifi er and the RF fi nal amplifi er consist of
two MOS FET stages.
The output of the RF final amplifier is then passed
through the antenna switch (D201 and D202) and the har-
monic fi lter (LPF), and is applied to the antenna terminal.
MIC IC812
Baseband
IC
D807,808
AGC
Q810,811
LSD
MIC_MT SW
OUT
Q809
2-5. 音频放大器电路
来自于 I C401 的解调信号，并通过 I C815 送到 A F 放大器，
在音频功率放大器 (IC815) 进行放大后输出到扬声器。
2-6. 静噪电路
FM IC(IC401) 输出的 AF 信号的一部分再进入 IC，噪声成
份通过滤波器和放大器进行放大和修正，生成与噪声电平相
应的 DC 电压。
DC 信号通过 FM IC 被送到微处理器的模拟端口微处理器
(I C820)。I C820 通过检测输入的电压是高于还是低于预设值
来决定是否从扬声器输出声音。
由扬声器输出声音时，IC820 发送高电平信号给 AF_CONT，
通过 Q813、Q814、Q818 和 Q819 打开 IC815。
3. 发射机系统
3-1. 麦克风放大器电路
麦克风的信号被并受由 D807, D808,Q810 和 Q811 组成的
AGC 电路的限幅，然后通过静音开关 (Q809)。IC812 由高通滤
波器、低通滤波器和预加重 /IDC 电路组成。
麦克风的信号和从微处理器来的低速数据进入基带 I C 后
这些信号在 IC 内部被混合。
基带 IC 的输出信号送入 VCO 调制输入。基带 IC 的其他输
出信号送入 TCXO 调制输入。
VCO
IC3 X1
AMP TCXO
3-2. 驱动器和终端放大器电路
来自于 T/R 开关 (D18 ON) 的信号被预驱动放大器 (Q203)
和驱动放大器 (Q204) 放大到 50mW。
驱动放大器的输出被 RF 功率放大器 (Q205) 放大到 5.0W( 当
低功率时为 1W)。RF 功率放大器由 2 个 MOS FET 构成。
R F 功率放大器的输出通过谐波滤波器 ( LP F ) 和天线开关
(D201 和 D202) 并且送到天线终端。
TK-2317
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