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13

• Bell signal detection
• ON/OFF hook and pulse dial circuit
• Side tone circuit

In the idle mode, Q141 is open to cut the DC loop current and decrease the ring load. When ring voltage appears at the Tip (T)
and Ring (R) leads (When the telephone rings), the AC ring voltage is transferred as follows:
T 

 R111  C110  Q111  BBIC pin 5 [BELL]

When the CPU (BBIC) detects a ring signal, Q141 turns on, thus providing an off-hook condition (active DC current flow through
the circuit). Following signal flow is the DC current flow.
T 

 D101  Q141  Q161  R163  D101  P101  R

Q141 is open, Q141 is connected as to cut the DC loop current and to cut the voice signal. The unit is consequently in an on-
hook condition.

Pin 6 of BBIC turns Q141 ON/OFF to make the pulse dialing.

Basically this circuit prevents the TX signal from feeding back to RX signal. As for this unit, TX signal feed back from Q161 is
canceled by the canceller circuit of BBIC.

PULSE_MUTE

BELL

HOOK

NL_CID

R121

390k

R122

390k

C120

1000p

+3.0V

+3.0V

C331

NC

VDDC

L2R

L1R

L1T

L2T

*R123

NC

*R124

10

*Q140

B1ABCE000009

R141

100k

R142

2.7k

*R144

NC

C143

NC

C142

0.01u

Q161

C152

0.01u

*C164

0.1u

C181

NC

R117

100k

R115

5.6M

R116

5.6M

R118

100k

C115

100n

C116

100n

*Q141

Q111

D133

D132

D113

C161

10u

*C166

NC

C178

0.1u

Q171

*C141

N

C

R114

68k

*R14

8

10k

*R149

680

*R16

2

NC

R165

27k

C113

0.01u

0

7

2

0

6

1

R

*

*R159

1.5

k

4

6

1

R

*

k

2

.

2

k

1

7

7

1

R

R113

22k

R111

1M

R112

47k

*C167 2700p

R158 4.7k

RA151

1k

1

2

3

4

C101 680p

C102

680p

C121 680p
C122 680p

D101

1

4

3

2

R176

1k

C103

NC

*C104

NC

*R103

1.2k

R163

39(0.5W)

GAP

1

2

C110

0.1u

C112

0.1u

R171

220

R172

680k

R175

3.9k

*R104

NC

R167

NC

C173

0.027u

C175

560p

*D142

SA102

NC

2

1

*SA101

2

1

P101

C176

1u

R151

100k

R152

130k

D143

NC

L101

27n

C476

NC

*C475

10pF

2

4

1

Q

4

8

1

C

u

1

C507

2.2u

*D141

R131

NC

R133

NC

C132

NC

*R154

NC

*R153

NC

*Q144

NC

*C479

10pF

*R16

9

39k

*R145

2.2k

*C171

0.033u

DC Monitor

Caller ID

Bell detection

P

in 28 of IC501

P

in 25 of IC501

P

in 24 of IC501

P

in 16 of IC501

P

in 18 of IC501

P

in 19 of IC501

P

in 17 of IC501

Pin 6 of IC501

Pin 5 of IC501

HOOK

BELL

14

• 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_Main
and Interface Box)(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_Main and Interface Box)(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 Q140.

15

QSPI

FLASH MEMORY

IC4

Reset

Reset

Pin 71

SPEAKER

RECEIVER

MIC

CHARGE

CIRCUIT

Q2, Q3, Q4,

Q9, R8

CHARGE

CONTACTS

CHARGE(+)

CHARGE_CTRL

CHARGE_DET

BATTERY

TERMINAL

R45

VBAT

BATT-

Q1

1.8 V

LCD

CD

RESET

CS

SID

 SCL

CPU

Analog

Front

End

D/A

A/D

35

37

21

22

17

18

34

33

 32

24

44

45

73

63

64

77

76

ADPCM

Codec

Filter

DSP

Speech

Decoding

Speech

Encoding

BMC

Burst

Decoding

ANT1

Burst

Encoding

RF

PLL

MOD/DEMOD

1

2

87

86

RXn

RXp

TXp

TXn

7

8

XTAL

X1

10.368

MHz

BATTERY

46

ON SWITCH

KEYPAD

Charge

Pump

ROWS

COLUMNS

CP3V

CP4V

57, 58, 59, 60

11

, 12, 13, 14, 25, 55

47, 48, 51, 53 QSPI-IO 0-3

BBIC

 65

LCD-BACK  LIGHT

KEY

 LED

61

LDO_CTRL

1.8 V

CP3V

QSPI

Control

52 QSPI-SCK

49 QSPI-CS

 LCD_LED0

CP4V

CP3V

1.8 V

GND

Ringer LED

79

80

BELL_LED1

BELL_LED2

KX-TGKA31 BLOCK DIAGRAM (HANDSET)

16

Handset consists of the following ICs as shown in Block Diagram (Handset) (P.15).

• 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
- Following information data is stored

- Settings
ex: ID code, user setting

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

 Q1 (1.8 V), IC1-44pin (CP3V)

The Reset signal generates IC1 (71 pin) and 1.8 V.

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

DC+(5.5 V) 

 R371  D362  CHARGE+(Base)  CHARGE+(Handset)  

 

 Q3  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/Reset Circuit (P.16).

“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.

1.8V

Battery +

Reset 
(IC1_71 pin)

Q2
R8