Panasonic KX-TCD420GS Service Manual page 64

signal. The unit is consequently in an off-hook condition.
When IC8 detects a ring signal or press the TALK Key onto the handset, Q4 turns on and then Q2
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 JMP9 D6 Q2 R13 Q4 D6 B [OFF HOOK]
20.4. 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 Pass:
*Refer to SIGNAL ROUTE ().
20.4.1. Transmitter Block
The voice signal input from the TEL LINE interface goes to RF Module (IC9) through DECT BBIC (IC8)
as shown in BLOCK DIAGRAM (BASE UNIT) ()
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 IC3, 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.
20.4.2. Receiver Block
The signal of 1.152 MHz band (1.881792 MHz ~ 1.897344 MHz) which is input from antenna is input to
IC9 as shown in BLOCK DIAGRAM (BASE UNIT) ().
In IC3, the signal of 1.152 MHz band is downconverted to 864 kHz signal and demoduleted, and goes
to IC2 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.
21. BLOCK DIAGRAM (HANDSET)
22. CIRCUIT OPERATION (HANDSET)
22.1. Outline
Handset consists of the following ICs as shown in BLOCK DIAGRAM (HANDSET) ().
- DECT BBIC (Base Band IC): IC1
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