Panasonic KX-F1200 Service Manual And Technical Manual page 131

8. ITS (Integrated Telephone System) AND MONITOR SECTIONS
i_-i i _. _t._ _._
8-1. GENERAL
The general ITS operation is executed by the special IC2. This IC has a speakerphone circuit and a handset circuit in 1 chip,
and control to each mode is executed from the outside (ICl). At the time of speakerphone operation the speaker output
passes through the power amplifier (IC12). The DTMF signal is output from the DTMF generator or modem (IC405: digital
board). The alarm tone, the key tone, and the beep are outputted from the gate array IC404 (digital board). At the time of
pulse dial operation, the monitor tone is outputted from the gate array IC1.
8-2. SPEAKERPHONE 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 hads-free mode.
2) Circuit Operation
The speakerphone can only provide a one-way communication path.
In otherwords, itcan eithertransmitan outgoingsignalor receivean incoming signalat a giventime, but cannot do both si-
multaneously. T herefore,a switching cimuitis necessaryto controlthe flow ofthe outgoingand incomingsignals.
This switching circuitiscontainedin IC2 and consistsof voicedetector,TX attenuator,RX attenuator,comparatorand at-
tenuatorcontrol.
The circuit analyzeswhetherthe TX (transmit)or the RX (receiver)signal islouder,and then it processes the signalssuch
thatthe louder signalis given precedence.
The voice detectorprovidesa DC inputto the attenuatorcontrolcorresponding to the TX signal.The comparatorreceives a
TX and RX signalsand suppliesa DC inputto the attenuator controlcorresponding to the RX signal.
The attenuatorcontrolprovidesa controlsignalto the TX and the RX attenuator to switchthe appropriatesignals ON and
OFF. The attenuator controlalsodetectsthe level of thevolumecontrolto automatically adjustfor changingambientcondi-
tions.
(Transmission Signal Path)
The input signal from the microphone is sent through the circuit via the following path:
MIC --* Cl10 --, IC2[(13) --, MIC AMP -* SW4 --* TX ATT --* (27)] -* R160 _ R161 --, C122 --* IC18(2)(1) ---,C125 --*
IC3[(7) _ (15)] --, R29 --* C28 -* IC14(6)(7) -* R20 --* T1 --* Line1
(16)J -* R59 --, C58 --* IC15(6)(7) -* R50 --, T2 -* Line2
(Reception Signal Path) (ex. Line1)
Signals received from the telephone line are outputted at the speaker via the following path:
Telephone Line -* NCU Section[IC14(2)(1)] --* R173 -* C225 -* IC3[(5)(14)] -* Cl17 --* R152 -* IC2[(22) -* SW3 --*
RX ATT -* (30)] --* C98 -* IC2[(4) --* SW5 --* SP AMP --, (7)] --, R253 --* C185 --* IC12[(4) --* (5)(8) -* Speaker
(Control Signal Path)
Control signals for transmission and reception are inputted to IC2 via following path.
(Transmission Control Signal Path)
MIC -* Cl10 --, IC2[(13) --, MC AMP-* SW4 --* (31)]---* C95 _ R130--* IC2[(1) --* AMP -* Comparator]
(Reception Control Signal Path) (ex. Line1)
Telephone Line _ NCU Section [IC14(2)(1)] ---, R173 ---*C225 --* IC3[(5)(14)] _ Cl17 --, R152 --, IC2[(22) --* SW3 -*
RX A'I-I- --* (30)] --, C98 --" IC2[(4) --* SW5 --* SP AMP --, (7)] --, C99 --, R131 --, IC2[(3) -* AMP ---* Comparator]
(Voice Detector)
The transmission signal given as input from the microphone to IC2 pin (1) passes through the built-in amplifier and enters the
voice detection circuit for judgment of voice noise, in case of noise, the TX attenuator is made effective via the attenuator
control.
(Attenuator Control)
The attenuator control detects the setting of the volume control through pin 11 of IC2 to automatically adjust for changing am-
bient conditions.
8-3. HANDSET CIRCUIT
1) Transmission Signal
HandsetMIC -F,'- C86--, £124 --*IC21(6)--r _ (7)--*C93_ R128--*102[(26) --, Handset M ICAMP--, SW1-* (24)]--*R162--,C123 --*IC18(2)(1)
L
--*C125--* IC3[(71 (15)'_--, R29--*C28--, IC14(6)(7) - * R20--, T1 __Line1
C87--' R125--, IC21(5)--4 -_ (16).1--* R59--, C58-* IC15(6)(7)--*R50--*T2 Line2
--*NCUSection[IC7(13)(14)] -, Telephone Une
2) Reception Signal (ex. Linel)
Telephone Line --" NCU Section [1C14(2)(1)] --" R173 -* C225 --* IC3[(5)(14)] --, C117 --, R152 --, IC2[(22) --" SW2
Handset SP AMP --" (19)(20)] "-" Handset Speaker
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