Telephone Line Interface - Panasonic KX-TGF340B Service Manual

4.6.6.

Telephone Line Interface

Telephone Line Interface Circuit:
Function
• Bell signal detection
• ON/OFF hook and pulse dial circuit
• Side tone circuit
Bell (RINGING) signal detection and OFF HOOK circuit:
In the idle mode, Q141 is open to cut the DC loop current and decrease the ring load. When ring voltage appears at the Tip (T)
and Ring (R) leads (When the telephone rings), the AC ring voltage is transferred as follows:
L1T  C105  R105  R110  R11 1 R112  BBIC pin18(RINGING)
When the CPU (BBIC) detects a ring signal, Q141 turns on, thus providing an off-hook condition (active DC current flow through
the circuit). Following signal flow is the DC current flow.
T  D101  Q141  Q161  R163  D101  P101  R
ON HOOK Circuit:
Q141 is open, Q141 is connected as to cut the DC loop current and to cut the voice signal. The unit is consequently in an on-
hook condition.
Pulse Dial Circuit:
Pin 19 of BBIC turns Q141 ON/OFF to make the pulse dialing.
Side Tone Circuit:
Basically this circuit prevents the TX signal from feeding back to RX signal. As for this unit, TX signal feed back from Q161 is
canceled by the canceller circuit of BBIC.
C173
RX
Pin25 of IC501
R178
TX
Pin27 of IC501
HOOK
Pin19 of IC501
RINGING
Pin18 of IC501
CIDOUT
Pin24 of IC501
CIDINn
RA101
Pin23 of IC501
CIDINp
RA101
Pin21 of IC501
LSRn
Pin28 of IC501
KX-TGF340/KX-TGF342/KX-TGF343/KX-TGF344/KX-TGF345/KX-TGF372/KX-TGF373/KX-TGF374/KX-TGF375/KX-TG585/KX-TGFA30
R160
Q151
+
C
B
E
C163
C165
TP9
R164 R161
TP10
C184
R111
C113
R151
C107 C103
R103 R101
R105 C105
C108 C104
R104 R102
R106 C106
17
Q141
R141
C101
D101
Q142
C
B
+
3 2
E
_
1
4
C102
L1T
L1R
P101