Speakerphone Circuit - Panasonic KX-T7730X Service Manual

C3 Q1 D1 Telephone Line
2) Reception Signal Path
The input signal from the telephone line is sent to the receiver through the following path:
Telephone Line D1 Q1 C3 T1 C4 Q3 R10 C8 R12 Q4 C26
R32 IC10 C32 R34 C27 R208 Q8 C31 JK3 JK2 Handset Speaker

7.6. SPEAKERPHONE CIRCUIT

Function:
This 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.
Circuit Operation:
The speakerphone can only provide a one-way communication path 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.
In other words, it can either transmit an outgoing signal or receive an incoming signal at a given
time, but cannot do both simuitaneousiy. Therefore, a switching circuit is necessary to control
the flow of the outgoing and incoming signals.
This switching circuit is contained in IC3 and consists of a Voice Detector, Tx Attenuator, Rx
Attenuator, Comparator and Attenuator Control. The circuit analyzes whether the Tx (transmit) or
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