Kenwood TK-3148 Service Manual page 18

TK-3148
• FFSK
The FFSK input signal from the IF IC is amplifi ed by IC300
(1/2) and goes to pin 5 of IC500. The signal is demodulated
by FFSK demodulator in IC500. The demodulated data goes
to the MCU for processing.
8. Power Supply Circuit
Battery +B is supplied via a 3A fuse from the battery ter-
minal connected to the TX-RX unit. After passing through
the power switch, power supply (SB) is applied to the three
AVRs. IC401 supplies 5V (5M) to the control circuit, and
IC403 supplies 5V (5C) to common circuits. IC402 supplies
to the TX circuit, the RX circuit and common circuits of
needless save mode. During transmission, 5TC becomes
Low and Q405 is turned ON to supply 5V (5T) to the TX
circuit. During reception, 5RC becomes Low and Q404 is
turned ON to supply 5V (5R) to the RX Circuit.
The power supply voltage monitor IC (IC404) monitors
power supply voltage (SB). If the voltage falls (less than 5V),
the VOUT port goes "LOW" level, the MCU INT port also
goes "LOW" level, and the MCU stops.
18
CIRCUIT DESCRIPTION /
IC500 IC303
AF IC BPF
IC300 IC306
AMP LPF
Fig. 11 Decode / 图 11 解码
+B
F400
SB
ON/OFF
D405
VOL
Fig. 12 Power supply circuit / 图 12 电源电路
电路说明
• FFSK
来自于中频芯片的 F F S K 输入信号被 I C300(1/2) 放大，然
后进入 IC500 的管脚 5。 此信号被 IC500 中的 FFSK 解调器解调。
已解调的数据进入 MCU 执行操作。
3
IC201
HSD IN
BPF
IC309
MCU
95
LSD IN
8. 电源电路
经由来自于连接到 TX-RX 单元的电池端点的 3A 保险丝提供
电池＋ B。通过电源开关后， 电源 (SB) 向 3 个 AVRs 提供电压。
I C401 向控制电路提供 5V (5M ) 电压，I C403 向共用电路提供
5V(5C) 电压。IC402 向 TX 电路，RX 电路和共用电路的保存模
式提供电压。在发送过程中，5T C 变为低电平，且 Q405 接通
并向 TX 电路提供 5V(5T) 电压。在接收过程中，5RC 变为低电
平，且 Q404 接通并向 RX 电路提供 5V(5R) 电压。
电源电压监测 IC(IC404) 监测电源电压 (SB)。如果电压下
降 ( 低于 5V)，则 VOUT 端口变为"低"电平，MCU INT 端口
也变为"低"电平，MCU 停止运行。
RF power amp (Q103 and Q106)
IC401
IC400
IC404
IC403
CE
Q405
IC402
CE
5TC
Q404
5RC
DT,CK,CE IC312
14
VCC
10
IC309
RESET
MCU
71
INT
5C
5T
5R
5CNS