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1.1.12. Line Monitor Circuit
The Line Monitor Circuit consists of an operational amplifier, analog master 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 and is
then input to the Analog SW2 for volume control. The signal is then input to the Speaker Amplifier, 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
RX signal
TX signal
Hybrid Circuit
Speaker
Amplifier
Electronic Volume
Analog SW2
Buzzer Signal from Panel
AGC
Analog SW1
Gain Switch
Amplifier
Ain(M)
Aout(M)
Aout(V)
Analog Front-End DSP
LPF Fc:4.5KHz
LPF Fc:7.8KHz
HYBSR
Analog Master
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