Circuit Description Of Cordless Pwb - Sharp FO-CC500 Service Manual

[4] Circuit description of Cordless PWB

(1) This 2.4GHz cordless machine use DSSS(Direct
Sequence Spread Spectrum) technology.
DSSS feature
• The communication is little influenced by noise.
• The ability of keeping a secret is high level.
And the communication using the radio frequency is performed TDD
operation between the sets of keeping a common system ID.
The system ID is stored nonvolatile memory of each set.
24
The ID code are kinds of 2
1) Transmission
Voice signal is inputted from mic and headset is adjusted the level of
signal and converted from analog signal to digital in the CODEC, and
is sent to Merlin (Baseband IC).
In Merlin, the inputted signal is converted ADPCM data and scram-
bled by XORed PN sequence.
The scrambled signal is differentially encoded and spreaded.
A 12chip spreading code is used to meet FCC part 15.247 require-
ments for a DSS(Digital Spread Spectrum) system.
The spreaded signal is modulated by DBPSK (Differential Binary Phase
Shift Keying) and is sent to RF109(2.4GHz Digital Spread Spectrum
Transceiver) into a RF MODULE.
RF109 generates the Local Oscillator(LO) frequencies using a
PLL(Phase Look Loop) frequency synthesizer and external 2.4GHz
VCO(Voltage Controlled Oscillator).
The baseband signal from Merlin is mixed LO frequency.
The mixed signal pass through Matching Network Circuits and is sent
to RF110(RF Power Amplifier).
The Amplified signal in RF110 pass through Antenna Matching Circuit
and is sent to Antenna.
2) Reception
The signal from radio pass through BPF (Band Pass Filter) of 2.4GHz
band width and is sent to RF109.
RF109 adjust the level of signal in LNA(Low Noise Amplifier) and
downconverted to Baseband I/Q signals.
Baseband I/Q signals is sent to the Merlin and despread, demodu-
lated and descrambled to ADPCM data.
The ADPCM data is converted analog signal in CODEC.
3) Stand-by
When the cordless handset(HS) put on the cradle, the system be-
come stand-by mode.
In this mode FAX(BS) monitor a present using channel and other chan-
nel to choice best channel.
HS is sleep mode. but it wakes up every 1second, and monitor the
signal from BS.
And it checks link establishment with BS every 10 second.
4) Serial communication with FAX ENGINE
The merlin and fax engine is connected by serial interface.
Example) If user push Talk key, the Talk command from merlin is sent
to fax engine through the serial interface and the fax engine control
the connection to line.
RF MODULE BLOCK DIAGRAM (TMX964A:UNIT1)
3-TERMINALS
VCC
REGULATOR
MATCHING
NETWORK
RF110
2450MHz
BPF
TX/RX SW
LPF
.
VCO
BALUN
TX DATA
RF109
RXI,RXQ
TXEN
RXEN
ANTENNA
ANTENNA
MATCHING
NETWORK
Fig. 7
(2) Audio data flow
Data flow in transmission and reception mode are shown as Fig. 8.
Example) FAX(BS)
TRANSMISSION
RECEPTION
5 – 13
FO-CC500A
FO-K01A
LINE
LIU
LINE IMPEDANCE
MATCHING
CODEC
MERLIN
RF MODULE
RF109 TRANSCEIVER
MATCHING NETWORK
RF110 POWER
AMPLIFIER
LPF
TX/RX SW
ANTENNA MATCHING
NETWORK
ANTENNA
ANTENNA
RF MODULE
ANTENNA MATCHING
NETWORK
TX/RX SW
2450MHz BPF
RF109 TRANSCEIVER
MERLIN
CODEC
LINE IMPEDANCE
MATCHING
LIU
LINE
Fig. 8