KX-TS2368CAW - Panasonic Telephone Service Manual (repair manual). Page 11

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The circuit controls the automatic switching of the transmitted and received signals, to and from the telephone line, when the unit is 

used in the hands -free mode. 

The speakerphone can only provide a one-way communication path. 

In other words, it can either transmit an outgoing signal or receive an incoming signal at a given time, but cannot do both 

simultaneously. Therefore, a switching circuit is necessary to control the flow of the outgoing and incoming signals. 

This switching circuit is contained in IC601 and consists of a Voice Detector, TX Attenuator, RX Attenuator, Comparator and Attenu-

ator 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 signal path:

The input signal from the microphone is sent through the circuit via the following path:                                                                 
MIC 

 IC601 (9  10  3  4)  R601  C602  Q108  Tel line. 

2. Reception signal path:

Signals receive from the telephone line are outputted at the speaker via the following path:                                                          
Tel line 

 Q108  Q109  C112  R600  C603  IC601 (27  26  19  15)  Speaker. 

3. Transmission/Reception switching

The comparison result between TX and RX outputs as a DC level of IC601 (25), In short the voltage difference between IC601
(20) and IC601 (25) switches TX/RX. 

4. Voice detector

The output of the Mic Amp (IC601 (10)) is supplied to IC601 (13) as a control signal for the voice detector. 

5. Attenuator control

The attenuator control detects the setting of the volume control through IC601 (24) to automatically adjust for changing ambi-
ent conditions. 

6 mV

150 mV

“TX” mode

“RX” mode

Idle mode