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8

The power is supplied to the DECT BBIC, RF Module, EEPROM and Charge Contact from AC Adaptor (+6.5 V) as shown in
Fig.101. The power supply is as follows;

• DECT BBIC (IC7): 

CN2 (+6.5 V) 

→ IC1 → Q9 → IC7

CN2 (+6.5 V) 

→ IC1 → Q8 → IC7

• RF Module (IC10): 

CN2 (+6.5 V) 

→ IC1 → Q8 → IC10 (Radio Transceiver (Digital))

CN2 (+6.5 V) 

→ IC1 → Q9 → IC10 (Radio Transceiver (Analog))

CN2 (+6.5 V) 

→ IC1 → R125 → IC10 (Power AMP)

• EEPROM (IC5): 

CN2 (+6.5 V) 

→ IC1 → Q9 → IC5

• Charge Contact (TP16): 

CN2 (+6.5 V) 

→ R57 → R56 → R55 → D22 → TP16

<Fig.101>

9

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

In the standby mode, Q3 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;

• A 

→ C4 → R6 → R33 → IC7 Pin 60 (CID INp) 

• B 

→ C3 → R4 → R35 → IC7 Pin 52 (CID INn)

In the standby mode, Q3 is open, and connected as to cut the DC loop current and to cut the voice signal. The unit is conse-
quently in an on-hook condition. 
When IC7 detects a ring signal or press the TALK Key onto the handset, Q4 turns on and then Q3 turns on, thus providing an
off-hook condition (DC current flows through the circuit) and the following signal flow makes the loop current.

• A 

→ D3 → Q3 → Q5 → R21 → R22 → D3 → B [OFF HOOK]

• 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.13).

The voice signal input from the TEL LINE interface goes to RF Module (IC10) through DECT BBIC (IC7) as shown in Block Dia-
gram (Base Unit) (P.6)
The voice signal passes through the analog part of IC7 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 IC10, 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.

The signal of 1900 MHz band (1881.792 MHz ~ 1897.344 MHz) which is input from antenna is input to IC10 as shown in Block
Diagram (Base Unit) (P.6).
In IC10, the signal of 1900 MHz band is downconverted to 864 kHz signal and demodulated, and goes to IC7 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 dialing 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.

10

SPEAKER

RECEIVER

MIC

CHARGE
CIRCUIT

Q4,Q5,Q9
R7

CHARGE
CONTACTS

CHARGE(+)

CHARGE(-)

CHARGE

CHARGE DETECT

EEPROM

SCL

SDA

SWITCHED
SUPPLY

    Q1

Q1

BATTERY
TERMINAL

D7

VBAT1

DC/DC-SWITCH

J1

J2

2.5 V

Q3

1.8 V

Q2

3.3 V

2.5 V

1.8 V

LCD

RS

RESET

CS

SI

 SCL

CPU

Analog

Front

End

D/A

A/D

38

36

81

82
88

85

77

65

53

52

 73

69

  74

75

2

 22

23

95

98

ADPCM

Codec

Filter

DSP

Speech

Decoding

Speech

Encoding

BMC

Burst

Decoding

Burst

Encoding

RF

Interface

RF

Module

9

8

RXDA

TXDA

 5

 4

 3

SYDA
SYEN
SYCL

13

11

XTAL

X1

10.368
MHz

BATTERY

76

ON SWITCH

KEYPAD

ROWS

COLUMNS

25,47,97,100

6,7,43,44,45,95

BBIC

 24

LCD-BACK  LIGHT

KEY-BACK  LIGHT

 1

KX-TGA720 BLOCK DIAGRAM (HANDSET)

11

Handset consists of the following ICs as shown in Block Diagram (Handset) (P.10).

• 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 Module: IC4

- PLL Oscillator
- Detector
- Compress/Expander
- Amplifier for transmission and reception

• 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: J1) 

→ F1, L1, D1 → Q2 (1.8 V), Q3 (2.5 V), Q1 (3.3 V)

The Reset signal generates IC1 (66 pin) and 1.8 V.

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

→ R57 → R56 → R55 → D22 → CHARGE+(Base) → CHARGE+(Handset) → L4 → Q4 → D7→ F1 → BAT-

TERY+... Battery... 
BATTERY- 

→ L8 → R45 → GND → L5 → 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 Q5 of Handset.
Refer to Fig.101 in Power Supply Circuit (P.8).

“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.