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In order to disable call waiting and stutter tone functions when using telephones connected in parallel, it is necessary to have a
circuit that judges whether a telephone connected in parallel is in use or not. This circuit determines whether the telephone
connected in parallel is on hook or off hook by detecting changes in the T/R voltage.

Parallel connection detection when on hook:
When on hook, the voltage is monitored at pin 17 of IC501. There is no parallel connection if the voltage is 
0.54 V or higher, while a parallel connection is deemed to exist if the voltage is lower.

Parallel connection detection when off hook:
When off hook, the voltage is monitored at pin 18 of IC501; the presence/absence of a parallel connection is determined by
detecting the voltage changes.
If the Auto disconnect function is ON and statuses are Hold, receiving ICM, OGM transmitting, BBIC disconnects the line after
detecting parallel connection is off hook.

Q141

Q161

R141

R142

Q142

R117

R115

R116

19 pin

IC501 DCIN 3

IC501 DCIN 1 17 pin

R118

R151

R145

Pin 18 of IC501 

DCIN2

HOOK 

Pin 6 of IC501

C101

D101

C102

SA101

P101

TEL  JACK

3

4

2

1

R163

R167

L1T

L1R

R152

C152

RA151

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• 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.18).

The voice signal input from the TEL LINE interface goes to through DECT BBIC (IC501) as shown in Block Diagram (Base
Unit_Main) (P.7)
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. 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) (P.7).
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 (Q3, Q4) 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 Q2.

15

SPEAKER

RECEIVER

MIC

CHARGE

CIRCUIT

Q4, Q9, R7Q

4

, 

Q

9

, 

R

7

CHARGE

CONTACTS

CHARGE(+)

CHARGE(-)

CHARGE_CTRL

CHARGE

EEPROM

SCL

SDA

BATTERY

TERMINAL

D7

R45

VBAT

BATT+

BATT-

1.8 V

Q2Q

2

1.8 V

LCD

CD

RESET

CSB

SDA

 SCL

CPU

Analog

Front

End

D/A

A/D

33

35

15

16

19

20

32

31

57

58

 36

13

43

42

63

54

55

66

ADPCM

Codec

Filter

DSP

Speech

Decoding

Speech

Encoding

BMC

Burst

Decoding

RF PA

ANT1

Burst

Encoding

RF 

PLL

MOD/DEMOD

5

3

4

3

6

7

8

9

2

77

78

75

RXn

RXon

ANT1

DA801

RXp

TXp

TXn

Pon 

PSEL

TXon

VDD-PADRY

9

10

XTAL

X1

10.368

MHz

BATTERY

44

ON SWITCH

KEYPAD

Charge

Pump

ROWS

COLUMNS

CP3.0V

CP4.0V

48, 49, 50, 51

22, 23, 24, 25, 26

BBIC

 56

LCD-BACK  LIGHT

KEY   LED

BELL  LED

52

68

73

74

80

LDO_CTRL

KX-TGA650/651 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

• RF Power Amp: IC801

- Amplifier for transmission

• 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 → Q2 (1.8 V), IC1-43pin (2.5V)

The Reset signal generates IC1 (61 pin) and 1.8 V.

When charging the handset on the Base Unit, the charge current is as follows;
DC+(6.5 V) 

→ R56 → R55 → D22 → CHARGE+(Base) → CHARGE+(Handset) → Q4 → D7→ 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/Reset Circuit (P.10).

“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_61pin)

Battery +