Panasonic KX-TCA151AXM Service Manual page 77

20.3. Telephone Line Interface
<Function>
• • • • Bell signal detection
• • • • Clip signal detection
• • • • ON/OFF hook circuit
• • • • Audio 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 TP21 (A) and TP19 (B) leads (when the telephone rings), the signal is transferred as follows;
• • • • A → C13 → R17 → R24 → IC2 Pin 107 (CID IN +)
• • • • B → C12 → R16 → R32 → IC2 Pin 112 (CID IN -)
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 on-hook condition.
When IC2 detects a ring signal or press SP Key or pick up Curl Cord Handset 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 → R34 → Q8 → R45 → R46 → D3 → B [OFF HOOK]
20.4. Transmitter/Receiver
Base Unit and Cordless Handset mainly consist of RF Module and DECT BBIC.
Base Unit and Cordless Handset transmit/receive voice signal and data signal through the antenna on carrier frequency.
Signal Pass:
*Refer to SIGNAL ROUTE (P.81).
20.4.1. Transmitter Block
The voice signal input from the TEL LINE interface goes to RF Module (RFM1) through DECT BBIC (IC2) as shown in BLOCK
DIAGRAM (BASE UNIT) (P.74)
The voice signal passes through the analog part of IC2 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 RFM1, the carrier frequency is changing, and frequency modulated RF signal is generated and amplified, and radiated from
antenna. Cordless 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 19.2 MHz band (18.81792 MHz ~ 18.97344 MHz) which is input from antenna is input to RFM1 as shown in
BLOCK DIAGRAM (BASE UNIT) (P.74).
In RFM1, the signal of 19.2 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.
20.5. Pulse Dialing
During pulse dialing the hookswitch (Q4, Q5) is used to generate the pulses using the HOOK control signal, which is set high
during pulses. To force the line impedance low during the "pause" intervals between dial pulses, the PULSE_DIAL signal turns
on Q9.
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KX-TCD530AXM / KX-TCA151AXM