Kenwood TK-3230 Service Manual page 13

The VCO output is divided by the divide ratio set by the
divider in the PLL IC to generate 6.25kHz/5kHz. It is com-
pared with the reference comparison frequency by the
phase comparator to detect a phase difference.
The charge pump circuit in the PLL IC converts it to a
control voltage that can drive the VCO directly.
The control voltage passes through a loop filter which
passes low frequency and is applied to the VCO control pin
to control the oscillator frequency. The loop fi lter removes
unwanted harmonics and noise contained in the output from
the phase comparator and determines PLL response and
synchronizing characteristics by the amplitude and phase
characteristics (Fig. 8).
■ Unlock Detection Circuit
If the PLL cannot be synchronized for some reason or
other when switching the channel or changing between
transmission and reception, the PLL IC outputs a low un-
lock detection signal. This signal goes to the MCU to inhibit
transmission when the PLL is unlocked.
+
Loop filter
LV
VCO
3C,T/R,MOD
Control System
■ Reset Circuit
When a battery voltage is dropped, IC401 is detected low
voltage, and this detected signal input to IC403 for stop the
MCU function. IC400 is detected the reset voltage.
■ Battery Voltage Detection Circuit
The unit detects a low battery voltage and display the
BATT indicator on the LCD. The battery voltage is divided
and applied to the analog value input pin (BATT) of the MCU,
and converted to a digital signal.
■ Power Supply Circuit
The power supply voltage is maintained to 3.0V by the
series regulator (IC404). It is used as MCU power 3M, 3C,
3R and 3T.
The B (battery voltage) is supplied to the RF fi nal transis-
tor Q104.
CIRCUIT DESCRIPTION /
CP1 XIN
+
+
PLL IC
IC1
LD
F OUT
FIN1
STB
DATA
CK
VCO OUT
Fig. 8 PLL circuit / 图 8 PLL 电路
电路说明
VCO 输出信号由 PLL IC 中分频器设置的分频倍率进行分频，
进而产生 6.25kHz/5kHz 的频率，随后由相位比较器与基准比
较频率进行比较来检测相位差。
PLL IC 中的电荷泵电路将其转换为可以直接驱动 VCO 的控
制电压。
控制电压通过环路滤波器，经过低频并应用到 V C O 控制针
脚来控制振荡频率。环路滤波器消除相位比较器输出信号中
所带的不需要的谐波和噪音，并由振幅及相位特性确定 P L L
响应及同步特性 ( 图 8)。
■失锁检测电路
切换信道或在发射与接收之间进行切换时，如果由于某些
其他原因造成 PLL 无法同步，则 PLL IC 会输出低失锁检测信
号。PLL 失锁时，该信号进入 MCU 禁止发射。
X1 12.8MHz
TCXO
3C
3M
MCU (IC403)
UL
PLL data
(MCU)
控制系统
■复位电路
电池电压下降时，I C401 检测到低电压并且该检测信号输
入到 IC403 用于停止 MCU 功能。IC400 检测复位电压。
■电池电压检测电路
本单元检测低电压并在 LCD 上显示 BATT 指示。电池电压随
后进行划分并应用到 MCU 的模拟数值输入针脚 (BATT)，然后
转换为数字信号。
■电源电路
电源电压由串联稳压器 ( I C404) 稳压至 3.0V，用作 M C U 电
源 3M、3C、3R 和 3T。
B( 电池电压 ) 为 RF 末级晶体管 Q104 供电。
TK-3230
TO
IC100
DAC
13