Table of Contents
Advertisement
Attenuator, Comparator and Attenuator Control. The circuit analyzes whether the TX(transmit) or
the RX(receive) signal is louder, and then it processed the signals such that the louder signal is
given precedence.
The Voice Detector provides a DC input to the Attenuator Control corresponding to the TX signal.
The Comparator receives a TX and a RX signal, and supplies a DC input to the Attenuator Control
corresponding to the RX signal.
The Attenuator Control provides a control signal to the TX and the RX attenuator to switch the
appropriate signals on and off. The Attenuator Control also detects the level of the volume
control to automatically adjust for changing ambient conditions.
1. Transmission/Reception signal path:
Refer to SP-PHONE TX/RX in
2. Transmission/Reception switching
The comparison result between TX and RX outputs as a DC level
of pin 25 of IC401.TX level is high ...... pin 26 = pin 22 - 6mV RX
level is high ...... pin 25 = pin 21 - 150mVComparator output is
connected to the attenuator control inside of IC601.
3. Voice detector
The output of the mic amp (pin 10 of IC401) is supplied to pin 14 of
IC401 as a control signal for the voice detector.
4. Attenuator control
The attenuator control detects the setting of the volume control
through pin 23 of IC401 to automatically adjust for changing
ambient conditions.
12.6. Bell Detection Circuit and Bell Generation Circuit
Circuit Operation: ( )...Line 2
When the bell signal is received from the line, it passes through C101 (C201) and R102 (R202),
turning PC5 (PC6) ON. As a result, pin 1 (pin 80) of IC801 becomes Low level. In this way, a ringer
tone which corresponds to each line is generated from
pin 25 of IC801.
This tone passes through the following path: pin 25 of IC801
R438
R466
the generated signal causing the tone ringer to produce a ringing tone.
12.7. Hold Circuit
Function:
This circuit is designed to hold a line which is IN USE in the handset mode or speakerphone
mode. In this case, the LED indication will change from a steady glow to a flashing indication.
Circuit Operation: ( )...Line 2
C467
pin 20 of IC401
SIGNAL ROUTE
R432
pin 16 of IC401
46
().
C446
R441
C469
Speaker,
C433
Advertisement
Table of Contents
