Panasonic KX-TCD220SLT, Service Manual

Page: 73 / 111

22.3. Telephone Line Interface
<Function>
·
Bell signal detection
· Clip signal detection
· ON/OFF hook circuit
·
Audio circuits
· DTMF tone signal circuits
Bell & Clip (: Calling Line Identification Presentation: Caller ID) signal detection:
In the standby mode, Q4 is open to cut the DC loop current and decrease the ring load.
When ring voltage appears at the TP2 (A) and TP3 (B) leads (when the telephone rings), the AC ring voltage is transferred as
follows;
·
A
→
C13
→
R17
→
R24
→
IC8 Pin 60 (CID INp)
· B
→
C12
→
R16
→
R32
→
IC8 Pin 52 (CID INn)
ON/OFF hook circuit:
In the standby mode, Q4 is open, and connected as to cut the DC loop current and to cut the voice signal. The unit is
consequently in an off-hook condition.
When IC2 detects a ring signal or press the TALK Key onto the handset, Q5 turns on and then Q4 turns on, thus providing an
off-hook condition (active DC current flow through the circuit) and the following signal flow is for the loop current.
· A
→
D3
→
Q4
→
Q8
→
R45
→
R46
→
D3
→
B [OFF HOOK]
22.4. Transmitter/Receiver
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.77).
22.4.1. Transmitter Block
The voice signal input from the TEL LINE interface goes to RF Module (IC2) through DECT BBIC (IC8) as shown in BLOCK
DIAGRAM (BASE UNIT) (P.70)
The voice signal passes through the analog part of IC8 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.
In IC2, the carrier frequency is changing, and frequency modulated RF signal is generated and amplified, and radiated from
antenna. Handset detects the voice signal or data signal in the circuit same as the following explanation of Receiver Block.
22.4.2. Receiver Block
The signal of 19.2 MHz band (18.81792 MHz ~ 18.97344 MHz) which is input from antenna is input to IC2 as shown in BLOCK
DIAGRAM (BASE UNIT) (P.70).
In IC2, the signal of 19.2 MHz band is downconverted to 864 kHz signal and demodulated, and goes to IC8 as GAP (Generic
Access Profile) standard DECT frames. It passes through the decoding section burst switch controller where it separates out
the frame information and performs de-encryption and de-scrambling as required. It then goes to the DSP section where it is
turned back into analog audio. This is amplified by the analog front end, and goes to the TEL LINE Interface.
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KX-TCD220SLT / KX-TCA122EXT / KX-TCA121EXT