In the standby mode, Q2 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 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 P
rofile) 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.
20.5. Pulse Dialing
During pulse dialing the hookswitch (Q2,Q3) 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 dialpulses, the PULSE_DIAL signal turns on Q10.
58
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1/2/2015
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