Telephone Line Interface; Transmitter/Receiver - Panasonic KX-TGCA20EX Service Manual

KX-TGC210/KX-TGC212/KX-TGC213/KX-TGC220/KX-TGC222/KX-TGCA20
4.4.5.

Telephone Line Interface

Telephone Line Interface Circuit:
Function
• Bell signal detection
• ON/OFF hook and pulse dial circuit
• Side tone circuit
Bell 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:
T  R111  C111  Q111  BBIC pin 5 [BELL]
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 6 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.
+3.0V
C173
R172 680k
0.1u
C175
560p
Q171
Pin 28 of IC501
R121
R122
C120
1000p
4.4.6.

Transmitter/Receiver

• Audio Circuits and DTMF tone signal circuits.
Base Unit and Handset mainly consist of RF Module and DECT BBIC.
Base Unit and Handset transmit/receive voice signal and data signal through the antenna on carrier frequency.
Signal Path:
*Refer to Signal Route(P.18).
4.4.6.1. Transmitter Block
The voice signal input from the TEL LINE interface goes to DECT BBIC (IC501) as shown in
Unit_Main)(P.8)
The voice signal passes through the analog part of IC501 where it is amplified and converted to a digital audio stream signal.
The burst switch controller processes this stream performing encryption and scrambling, adding the various other fields to
produce the GAP (Generic Access Profile) standard DECT frame, assigning to a time slot and channel etc.
R160
820
Q161
C
B
E
C163 NC
R177 R164 R161
1k 2.7k 100k
R151
100k
C184
1u
390k C121 680p
390k C122 680p
VDDC
*Q141
R141
100k
Q142
C
B
E
Hook Hook
Pin 6 of IC501
+3.0V
BELL BELL
Pin 5 of IC501
Q111
14
C101 680p
D101
1 2
4 3
C102 680p
NC
*C115
1
*R115
NC
2
Block Diagram (Base
L1T
*P101
L1R