Panasonic KX-TG4221N

15
KX-TG4221N/KX-TG4222N/KX-TG4223N/KX-TG313SK/KX-TG4224N/KX-TG4225N/KX-TGA421N
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.
C120
1000p
R131 10M
L1R
R133 330k
VDDC
C111 0.047u
R141
100k
C142 K0.01u
C124
NC
L1T
C132 K0.01u
+3.0V
R112 100k
R113 10k
C186
10p
R142
2.7k
C123
NC
R145 2.2k
R111 100k
C113
K0.68u
R121 390k
R122 390k
C112 0.047u
Q142
B
C
E
*SA101
300V
SA103
NC
21
Q111
D113
AK
D133
AK
D153 NC
AK
R164
2.7k
R161
100k
C168 NC
R151
100k
C152
0.01u
R177
1k
Q171
Q161
B
C
E
C161
10u
R165 27k
+3.0V
C164
NC
RA151
1k
1
2
3 4
C181 NC
C184
1u
C163 NC
D101
1
43
2
C101 680p
C102 680p
C121 680p
C122 680p
R163 39
R152
130k
R176
1k
R175
3.9k
R172
680k
C176 1u
R114
47k
1
2
*D142
25V
C173
0.1u
C167
1000pC171
0.022u
C175
560p
C178
0.033u
R160
820
R171 220
R168
4.7k
*R115
NC
*C115
NC
*P101
*Q141
*D143
NC
*SA102
NC
*R162
47k
HookHook
BELLBELL
Pin 5 of IC501
Pin 6 of IC501
Pin 18 of IC501
Pin 17 of IC501
Pin 16 of IC501
Pin 25 of IC501 Pin 24 of IC501
Pin 28 of IC501