Panasonic KX-TCD287UAT / KX-TCA128UAT Service Manual ▷ View online
14 BLOCK DIAGRAM (BASE UNIT)
Analog
Front
End
To TEL_LINE
A
B
CN3
Bridge
Rect D3
D3
Hook Switch
Q4,Q5
Q4,Q5
Audio
Bell/Caller ID
Interface
Analog
Switch
Switch
CPU
59
54
54
61
52
60
56
60
56
55
BELL
HOOK
Off-Hook Line Voltage
64 ADCO
D/A
A/D
ADPCM
Codec Filter
DSP
Speech Decoding
Speech Encoding
BMC
Burst Decoding
Burst Encoding
RF
Interface
18
19
TXDA
RXDA
15
21
20
22
RSSI
SYCL
SYDA
SYEN
SYCL
SYDA
SYEN
ANT1
ANT2
ANT2
RF Module
18
16
2
31
8
21
14
13
12
12
12
11
XTAL
X1
X1
10.368
MHz
MHz
EEPROM
SCL
SDA
6
5
To AC Adaptor
CN1
Limit
Resistor
CHARGE
CONTACT
CONTACT
VUNREG
3.3V
Reg.
Reg.
IC1
IC1
2.5V
Reg.
Reg.
Q2
Q2
1.8V
Reg. Q3
Reg. Q3
Q3
3.3V
2.5V
1.8V
BBIC
IC3
IC11
IC8
IC2
KX-TCD287 BLOCK DIAGRAM (BASE UNIT)
KX
-T
CD2
87UAT
/
K
X
-T
CA1
28UAT
45
15 CIRCUIT OPERATION (BASE UNIT)
15.1. Outline
Base Unit consists of the following ICs as shown in BLOCK DIAGRAM (BASE UNIT) (P.45).
•
DECT BBIC (Base Band IC): IC8
−
Handling all the audio, signal and data processing needed in a DECT base unit
−
Controlling the DECT specific physical layer and radio section (Burst Module Controller section)
−
ADPCM code filter for speech encoding and speech decoding (DSP section)
−
Echo-cancellation and Echo-suppression (DSP section)
−
Any tones (tone, sidetone, ringing tone, etc.) generation (DSP section)
−
DTMF receiver (DSP section)
−
Clock Generation for RF Module
−
ADC, DAC, timer, and power control circuitry
−
All interfaces (ex: RF module, EEPROM, LED, Analog Front End, etc.)
•
RF Module: IC2
−
PLL Oscillator
−
Detector
−
Compress/Expander
−
First Mixer
−
Amplifier for transmission and reception
•
EEPROM: IC3
−
Temporary operating parameters (for RF, etc.)
•
Additionally,
−
Power Supply Circuit (+3.3V, +2.5V, +1.8V output)
−
Crystal Circuit (10.368MHz)
−
Charge Circuit
−
Telephone Line Interface Circuit
46
KX-TCD287UAT / KX-TCA128UAT
15.2. Power Supply Circuit
The power is supplied to the DECT BBIC, RF Module, EEPROM and Charge Contact from AC Adaptor (+6V) as shown in
Fig.101. The power supply is as follows;
Fig.101. The power supply is as follows;
•
DECT BBIC (IC8):
CN1 (+6V)
→
D1
→
IC1
→
Q2
→
IC8
CN1 (+6V)
→
D1
→
IC1
→
Q3
→
IC8
•
RF Module (IC2):
CN1 (+6V)
→
D1
→
IC1
→
Q2
→
IC2 (PLL)
CN1 (+6V)
→
D1
→
IC1
→
Q6
→
IC2 (Power AMP)
•
EEPROM (IC3):
CN1 (+6V)
→
D1
→
IC1
→
Q2
→
IC3
•
Charge Contact (TP15):
CN1 (+6V)
→
D1
→
R4, R5
→
TP15
<Fig.101>
47
KX-TCD287UAT / KX-TCA128UAT
15.3. Telephone Line Interface
<Function>
•
Bell signal detection
•
Clip signal detection
•
ON/OFF hook circuit
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 TP28 (A) and TP27 (B) leads (when the telephone rings), the AC ring voltage is transferred
as follows;
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 off, and connected as to cut the DC loop current and to cut the voice signal. The unit is consequently
in an on-hook condition.
in an on-hook condition.
When pressing the TALK Key onto the handset, Q5 turns on and then Q4 turns on, thus providing an off-hook condition (DC
current flows through the circuit) and the following signal flow makes the loop current.
current flows through the circuit) and the following signal flow makes the loop current.
•
A
→
D3
→
Q4
→
Q8
→
R45
→
R46
→
D3
→
B [OFF HOOK]
15.4. Transmitter/Receiver
•
Audio Circuits and DTMF tone signal circuits.
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.53).
15.4.1. 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.45)
DIAGRAM (BASE UNIT) (P.45)
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.
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.
antenna. Handset detects the voice signal or data signal in the circuit same as the following explanation of Receiver Block.
15.4.2. Receiver Block
The signal of 1900 MHz band (1881.792 MHz ~ 1897.344 MHz) which is input from antenna is input to IC2 as shown in BLOCK
DIAGRAM (BASE UNIT) (P.45).
DIAGRAM (BASE UNIT) (P.45).
In IC2, the signal of 1900 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.
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.
15.5. Pulse Dialing section
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 Q12.
during pulses. To force the line impedance low during the “pause” intervals between dial pulses, the PULSE_DIAL signal turns
on Q12.
48
KX-TCD287UAT / KX-TCA128UAT
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