Panasonic KX-TS105LXW Service Manual page 20

In talk status, L1 RLY output from pin 25 of IC801 changes to low level, causing Q103, Q101 to
turn on and resulting in a line loop.The loop current flows from D101(+) Q101 Q108
R124 D106 in that order, A pulse signal that repeated switches between high and low logic is
output from pin 26 of the CPU.This switches the line loop on and off, generating the dial pulse
signal.
11.3. MODULE BLOCK DIAGRAM
11.3.1. Speakerphone Circuit
11.3.1.1. Function
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.
11.3.1.2. Circuit Operation
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 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
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