DOWNLOAD Panasonic KX-TG8551CAB / KX-TG8561CAB / KX-TGA855RUB Service Manual ↓ Size: 8.49 MB | Pages: 103 in PDF or view online for FREE

13

• Bell signal detection
• Clip signal detection
• ON/OFF hook circuit

In the standby mode, Q141 is open to cut the DC loop current and decrease the ring load.
When ring voltage appears at the L1T (A) and L1R (B) leads (when the telephone rings), the AC ring voltage is transferred as
follows;

• B 

→ P101 → C106 → R106 → R107 → IC501 (CID INp) 

• A 

→ C105 → R105 → R108 → IC501 (CID INn)

In the standby mode, Q104 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 IC501 detects a ring signal or press the TALK Key onto the handset, Q142 turns on and then Q141 turns on, thus
providing an off-hook condition (DC current flows through the circuit) and the following signal flow makes the loop current.

• B 

→ P101 →D101 → Q141 → Q161 → R163 → R167 → D101 → A

• 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.

*Refer to Signal Route (P.17).

The voice signal input from the TEL LINE interface goes to DECT BBIC (IC501) as shown in Block Diagram (Base Unit) (P.8)
The voice signal passes through the analog part of IC501 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 IC501, the carrier frequency is changing, and frequency modulated RF signal is generated.In IC501,RF signal is amplified,
and radiated from antenna. Handset detects the voice signal or data signal in the circuit same as the following explanation of
Receiver Block.

The signal of 1900 MHz band (1881.792 MHz ~ 1897.344 MHz) which is input from antenna is input to IC501 as shown in Block
Diagram (Base Unit) (P.8).
In IC501, the signal of 1900 MHz band is downconverted to 864 kHz signal and demodulated, 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.

During pulse dialling the hookswitch (Q141, Q142) 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 Q144.

14

QSPI

FLASH MEMORY

IC4

Re

s

et

Re

s

et

pin 62

SPEAKER

RECEIVER

Headset Jack

CN4

MIC

CHARGE

Power Failer Mode

Power Supply SW

CIRCUIT

Q2, Q3, Q4,

Q9, R8

CHARGE

CONTACTS

CHARGE(+)

CHARGE_CTRL

BATTERY_ON

CHARGE_DET

EEPROM

SCL

SDA

BATTERY

TERMINAL

R45

VBAT

BATT-

1.8 V

Q1

1.8 V

CP 2.8 V

LCD

CD

RESET

CSB

SDA

 SCL

CPU

Analog

Front

End

D/A

A/D

34

36

23

24

19

20

21

29

33

32

58

59

 85

26

43

44

64

55

56

69

67

ADPCM

Codec

Filter

DSP

Speech

Decoding

Speech

Encoding

BMC

Burst

Decoding

ANT1

Burst

Encoding

RF

PLL

MOD/DEMOD

5

2

3

79

78

RXn

RXon

ANT1

DA801

RXp

TXp

TXn

TXon

9

10

XTAL

X1

10.368

MHz

BATTERY

45

ON SWITCH

KEYPAD

Charge

Pump

ROWS

COLUMNS

CP3V

D3

CP2.8V

CP_LED

49, 50, 51, 52

13, 14, 15, 16, 27,47

90, 92, 94, 96 QSPI-IO 0-3

BBIC

 57

LCD-BACK  LIGHT

KEY   LED

BELL  LED

53

72

80

LDO_CTRL

CP 3.0 V

CP3V

QSPI

Control

 91 QSPI-SCK

 95 QSPI-CS

TGA855 only

71

Q10, Q11, Q12, R10

70

KX-TGA855 BLOCK DIA

GRAM (H

a

nd

s

et)

15

Handset consists of the following ICs as shown in Block Diagram (Handset) (P.14).

• DECT BBIC (Base Band IC): IC1

- All data signals (forming/analyzing ACK or CMD signal)
- All interfaces (ex: Key, Detector Circuit, Charge, DC/DC Converter, EEPROM, LCD, RF Power Amp.)
- PLL Oscillator
- Detector
- Compress/Expander
- Reception
- Integrated 1.9 GHz PA for DECT

• QSPI FLASH MEMORY: IC4

- Main Program D/L Area

• EEPROM: IC3

- Temporary operating parameters (for RF, etc.)

When power on the Handset, the voltage is as follows;
BATTERY(2.2 V ~ 2.6 V: BATT+) 

→ F1 → Q1 (1.8 V), IC1-43pin (3.0V)

The Reset signal generates IC1 (62 pin) and 1.8 V.

When charging the handset on the Base Unit, the charge current is as follows;

DC+(5.5 V) 

→ R371 → R372 → R373 → CHARGE+(Base) → CHARGE+(Handset) → 

 

→ Q3 → F1 → BATTERY+...

Battery... 
BATTERY- 

→ R45 → GND → CHARGE-(Handset)→ CHARGE-(Base) → GND → DC-(GND)

In this way, the BBIC on Handset detects the fact that the battery is charged.
The charge current is controlled by switching Q9 of Handset.
Refer to Fig.101 in Power Supply Circuit (P.12).

“Battery Low” and “Power Down” are detected by BBIC which check the voltage from battery.
The detected voltage is as follows;

• Battery Low

Battery voltage: V(Batt)   2.25 V ± 50 mV

The BBIC detects this level and "

" starts flashing.

• Power Down

Battery voltage: V(Batt)   2.0 V ± 50 mV
The BBIC detects this level and power down.

The hands-free loudspeaker at SP+ and SP- is used to generate the ring alarm.

1.8 V

Reset 
(IC1_62pin)

Battery +

Q2
R8

16

The power supply is as shown.

In case that power from AC adaptor is lost and lose radio waves, BBIC (IC1) turn Q11 ON since handset perfume that base units’s
power is failed.
Base unit detects that power voltage of AC adaptor +5.5V is OFF at IC351, then turns Q351ON.
It’s possible to use the units during the power failure, supplying power to VBAT of base unit from battery of handset through Q10
CHG terminal and Q351.

D1

R2

R1

TP1

TP2

J1

AC Adaptor

F1

R355

Q351

Vbat

CHG+

R45

Q11

R11

Q10

R12

R13

㪙㪙㪠㪚

㪠㪚㪈

㪎㪈

Battery

CHG-

HANDSET

BASE

R354

R352

IC351

VOUT

VIN

VSS

+5.5V

R351