Line Monitor Circuit - Panasonic Panafax UF-885 Service Manual

6.2.6

Line Monitor Circuit

The Line Monitor Circuit consists of an operational amplifier (IC100), analog master (IC91) and its peripheral circuits. Its function is
to monitor the dial tone, DTMF tone, response signals, etc. over the speaker. It also sounds the output of the key touch tones, alarm
tones, etc. from the panel CPU over the speaker. The received signal from the Ain (M) passes through an AGC circuit and is
conditioned by the Analog Front-End DSP (IC90) and is then input to the Analog SW2 for volume control. The signal is then input
to the Speaker Amplifier (IC100, Q91, 92), where it is amplified to a level sufficient to drive the speaker. The key touch tones and
Buzzer Signals from the panel are input to the Analog SW2 for volume control and then input to the Speaker Amplifier. The monitor
tone from the phone line and the buzzer tone from the panel can be adjusted from the Control Panel.
HYSIG
HYBSR
Speaker Amplifier
IC100, Q91, 92
Speaker
RX signal
LPF Fc: 7.8 KHz
TX signal
LPF Fc: 7.8 KHz
Analog Master IC91
Analog SW1
Analog SW2
Buzzer Signal
from Panel
System Description
Analog Front-End DSP
(IC90)
Ain(M)
AGC
Aout(M)
Aout(V)
210