Its And Monitor Section - Panasonic KX-F900 Service Manual

8. ITS (Integrated telephone System) and MONITOR SECTION
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KX-F900
8-1. GENERAL
The general ITS operation is executed by the special iC109. This IC has a speakerphone circuit and a handset circuit in 1
chip, and control to each mode is executed from the outside (IC151). At the time of speakerphone operation the speaker output
passes through the power amplifier (IC241). The DTMF signal and the bell tone are output from the modem (IC11 : digital
board). The alarm tone, the key tone, and the beep are outputted from the gate array IC151 (digital board). At the time of pulse
dial operation, the monitor tone is outputted from the gate array IC151.
8-2. SPEAKER PHONE CIRCUIT
(1)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.
(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 IC109 and consists of voice detector, TX attenuator, RX attenuator, compara tor and
attenuator control. The circuit analyzes whether the TX (transmit) or the RX (receiver) signal is louder, and then it
processes 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 RX signals 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.
(Transmission Signal Path)
The input signal from the microphone is sent through the circuit via the following path:
MIC --* J270 --* C138 --* IC109 (13-27) --, R145 ---*IC151 (75-63) _ C203 _ R210 ---* IC201 (2-1) --, C202 -* R201 --*
T101 --* TEL LINE
(Reception Signal Path)
Signals received from the telephone line are outputted at the speaker via the following path.
TEL LINE --, T101 --* R202 --, C205 ---*IC201(6-7) --, C210 --* C173 --, R172 --, R173 --* C174 --, IC151(59-71) --* C142
-* R143 _ IC109 (22-30) --* C145 --, IC109 (4-7) --* R146 ---*C146 -,. IC151 (40-38) ---,R245 ---* C245 _ IC241 (4-5,8)
--* SPEAKER
(Control Signal Path)
Control signals for transmission and reception are inputted to IC109 via following path.
(Transmission Control Signal Path)
MIC --* J270 --, C138 _ IC109 [(13) --* MC AMP --* SW4 --* (31)] --* C130 --* R130 --* IC109 [(1) _ AMP --, Comparator]
(Reception Control Signal Path)
TEL LINE --* NCU Section [IC201(6-7)] -* C173 --* R172 --, R173 ---* C174 --* IC151(59-71) --* C142 -* R143
IC109[(22) -," SW3 ---, RX ATT -* (30)] --* C145 --* IC109 [(4) -* SW5 -_ SP AMP -," (7)] -.. C132 --* R131 ---* IC109 [(3)
--* AMP --* Comparator]
(Voice Detector)
The transmission signal given as input from the microphone to IC109 pin (1) passes through the built-in amplifier and en-
ters the voice detection circuit for judgment of voice noise. In case of noise, the TX attenuator is made effective via the at-
tenuator control.
(Attenuator Control)
The attenuator control detects the setting of the volume control through pin 11 of IC109 to automatically adjust for changing
ambient conditions.
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