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■ Wide/Narrow Changeover Circuit
The Wide port (pin 92) and Narrow port (pin 91) of the
CPU is used to switch between ceramic filters. When the
Wide port is high, the ceramic filter SW diodes (D13, D15)
cause CF1 to turn on to receive a Wide signal.
When the Narrow port is high, the ceramic filter SW diodes
(D13, D15) cause CF2 to turn on to receive a Narrow signal.
■ AF Signal System
The detection signal from IF IC (IC5) goes to D/A con-
verter (IC3) to adjust the gain and is output to AF filter (IC10)
for characterizing the signal. The AF signal output from IC10
and the DTMF signal, BEEP signal are summed and the re-
sulting signal goes to the D/A converter (IC3). The AFO out-
put level is adjusted by the D/A converter. The signal output
from the D/A converter is input to the audio power amplifier
(IC102). The AF signal from IC102 switches between the
internal speaker and speaker jack (J1) output.
CIRCUIT DESCRIPTION / 电路说明
IF_IN
D13
Narrow
IC6 91pin
Fig. 3 Wide/Narrow changeover circuit /
图3 宽／窄转换电路
IC5
IC3
DEO
D/A
IF IC
CONV.
FIg. 4 AF signal system / 图4 音频信号系统
■ 宽／窄转换电路
CPU的宽端口 (管脚 92) 和窄端口 (管脚 91) 用于陶瓷滤波器
之间的切换。当宽端口为高电平时, 陶瓷滤波器 SW 二极管
(D13, D15) 使 CF1 导通来接收宽带信号。
当窄端口为高电平时, 陶瓷滤波器 SW 二极管 (D13, D15) 使
CF2 导通来接收窄带信号。
IC5
IF System
MIX_O
R73
CF1
(Wide)
R77
CF2
(Narrow)
D15
■ 音频信号系统
来自于IF IC (IC5) 的检测信号进入数/模转换器 (IC3) ，调整
增益并输出到AF滤波器 (IC10) 来表示信号的特征。从IC10输出
的AF信号，DTMF 信号和BEEP 信号被累加，并且将获得的信
号送到数/模转换器(IC3). AFO 输出电平被数/模转换器调整。从
数/模转换器输出的信号被输入到音频功率放大器 (IC102). 来
自于IC102的AF信号在内部扬声器和扬声器插口 (J1) 输出之间
变换。
IC10
IC3
IC102
AF
D/A
AF PA
Filter
CONV.
TK-8108
Wide
IC6 92pin
SP
17
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