Circuit Description Of Tel/Liu Pwb - Sharp FO-77 Service Manual

[3] Circuit description of TEL/LIU PWB

(1) TEL/LIU block operational description
1) Block diagram
L1
CML
M
C
L2
B
CI
HANDSET
RX
TX
BIT7 BIT6 BIT5 BIT4 BIT3
DAC
L/O E SPKR E
MIC GAIN
IACR1
GAIN
TXRX LINEOUT
IACR2
LOOP ATTENUATION
IACR3
2) Circuit description
The TEL/LIU PWB is composed of the following 7 blocks.
1. Speech circuit section
2. Dial transmission section
3. Speaker amplifier section
4. Ringer circuit section
5. Externally connected TEL OFF HOOK detection circuit
6. CI detection circuit
7. Signal/DTMF transmission level
TEL/LIU PWB CONTROL PWB
TXOUT
RXIN
TELIN
TELMUTE
TELOUT
SPEAKER
BIT2 BIT1 BIT0
ADC
L/I E MIC E
GAIN
MICBIAS
RXTXLOOP
SEL
LINE SEL
SP OUT
ENABLE
SPKRP-P
SP
DRIVER
MIC
GAIN
MICP
0,20,25,30dB
LINEIN
RCV VOL
LINE
DRIVER
LINEOUT
MUTE,0,
LINEOUT
–6,–12dB
ENABLE
SPMUTE
Fig. 6
3) Block description
1. Speech circuit section
•
The receiver volume is an electronic volume type, this model is
switched in 2 steps.
2. Dial transmission section
•
D.P. transmission: The CML relay is turned on and off for control in
the DP calling system. (Refer to the attached sheet.)
•
DTMF transmission: It is formed in the modem, and is output.
3. Speaker amplifier section
•
Ringer volume : It is controlled by the combination of the attenuator
•
Speaker volume: It is controlled by the attenuator value of the LINE
4. Ringer circuit section
•
The ringer sound is formed in the tone of modem when CI signal is
detected. The amplifier circuit drives the speaker of the main body.
5 – 9
RTLOOP
(0:1)
MIC ENABLE
(1:0)
(0:0)
DAC
(1:1)
DAC GAIN
0,6dB
MIC
ENABLE
1
MIC IN
LPF 0
ADC
LINE IN
ENABLE
ADC GAIN
1
LINE IN
0,–4dB
LPF
0
LNINSEL
MODEM
(0:0)
FM209
(1:1)
(1:0)
BZOUT
CML
SPMUTE
RCVOL
VTHON
value of the LINE DRIVER in the modem and the
ringer sending level sent from the modem.
DRIVER in the modem.
FO-77U
UX-66U
SIN
SOUT
RHS
RANK
DRSNS
TXMUTE
TELMUTE
IA-RESET
CUTI
HS
CI
CSWI
PESNS
FRSNS
FAX
ORGSNS
ENGINE
PSNS
FC200
VREFCONT
MDMRST
LEDON