Kenwood TK-3160 Service Manual page 14

(4) DTMF
The DTMF input signal from the IF IC (IC401) is amplified
by IC602 and goes to IC601. The decoded information is
then processed by the CPU.
3. PLL Frequency Synthesizer
The PLL circuit generates the first local oscillator signal for
reception and the RF signal for transmission.
1) PLL
The frequency step of the PLL circuit is 5 or 6.25kHz.
A 16.8MHz reference oscillator signal is divided at IC1 by a
fixed counter to produce an oscillator (VCO) output signal
which is buffer amplified by Q9 then divided in IC1 by a
dual-module programmable counter. The divided signal is
compared in phase with the 5 or 6.25kHz reference signal
from the phase comparator in IC1. The output signal from
the phase comparator is filtered through a low-pass filter
and passed to the VCO to control the oscillator frequency.
(See Fig. 6)
2) VCO
The operating frequency is generated by Q6 in transmit
mode and Q5 in receive mode. The oscillator frequency is
controlled by applying the VCO control voltage, obtained
from the phase comparator, to the varactor diodes (D4 and
D7 in transmit mode and D3 and D9 in receive mode). The
RX pin is set high in receive mode causing Q8 and Q12 to
turn Q6 off and Q5 on.
The TX pin is set high in transmit mode. The outputs from
Q5 and Q6 are amplified by Q9 and sent to the RF amplifiers.
CIRCUIT DESCRIPTION /
LPF
LPF
PLL IC IC1
PLL DATA
REF OSC
X1
16.8MHz
Fig. 6 PLL circuit / 图 6 PLL 电路
电路说明
(4) DTMF
I F I C ( I C 4 0 1 ) 的 D T M F 输出信号被 I C 6 0 2 放大并且送到
IC601。解码数据由 CPU 处理。
3. PLL 频率合成
PLL 电路产生用于接收的第一本地振荡信号和发射用的 RF
信号。
1) PLL
PLL 电路的频率步进是 5 或 6.25kHz。
16.8MHz 的参考振荡信号在 IC1 中被一个固定记数器分频。
振荡器 (VCO) 的输出信号由 Q9 缓冲放大,然后在 IC1 中被一
个可编程双模块记数器分频。分频的信号在 IC1 的相位比较
器中进行比较。生成的信号通过一个低通滤波器滤波后传送
到 VCO 控制振荡器频率。 （见图 6）
2) VCO
所使用的频率在发射模式时由 Q 6 生成，在接收模式时由
Q5 生成。
通过将从相位比较器所获得的 VCO 控制电压输送给可变二
极管 (在发射模式时为D4和D9， 在接收模式时为D3和D9) 来
控制振荡频率。在接收时 RX 脚被设定为高，控制 Q8 和 Q12
来关闭 Q6 接通 Q5。
发射时 TX 脚被设定为高。Q5 和 Q6 的输出被 Q9 放大并且传
送给 RF 放大器。
Q6
D4, 7
TX VCO
DOUBLER
Q9
BUFF AMP
Q5
D3, 9
RX VCO
Q8, 12
T/R SW
5kHz/6.25kHz
1/ N
PHASE CHARGE
COMPARATOR PUMP
1/ M
5kHz/6.25kHz
TK-3160
Q7
Q11
RF AMP
RX
TX
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