AD8531/AD8532/AD8534
DIRECT ACCESS ARRANGEMENT FOR TELEPHONE
LINE INTERFACE
P1
Tx GAIN
ADJUST
R2
Figure 46 illustrates a 5 V only transmit/receive telephone line
interface for 600 Ω transmission systems. It allows full duplex
transmission of signals on a transformer-coupled 600 Ω line in
a differential manner. A1 provides gain that can be adjusted to
meet the modem output drive requirements. Both A1 and A2
are configured to apply the largest possible signal on a single
supply to the transformer. Because of the high output current
drive and low dropout voltage of the AD8531/AD8532/AD8534,
the largest signal available on a single 5 V supply is approximately
4.5 V p-p into a 600 Ω transmission system. A3 is configured as
a difference amplifier for two reasons: it prevents the transmit
signal from interfering with the receive signal, and it extracts
the receive signal from the transmission line for amplification
by A4. The gain of A4 can be adjusted in the same manner as
that of A1 to meet the input signal requirements of the modem.
Standard resistor values permit the use of single in-line package
(SIP) format resistor arrays.
9.09kΩ
C1
0.1µF
R1
10kΩ
TRANSMIT
TxA
TO TELEPHONE
LINE
2kΩ
R3
360Ω
2
1
1:1
A1
3
R5
10kΩ
6.2V
6.2V
Z
O
600Ω
5V DC
R7
T1
R6
10kΩ
6
5
MIDCOM
671-8005
7
10kΩ
A2
R8
10kΩ
10µF
R9
10kΩ
R10
10kΩ
P2
Rx GAIN
ADJUST
R13
R14
RECEIVE
RxA
2
3
10kΩ 14.3kΩ
R11
10kΩ
1
A3
2kΩ
C2
0.1µF
6
R12
10kΩ
7
A4
5
A1, A2 = 1/2 AD8532
A3, A4 = 1/2 AD8532
Figure 46. Single-Supply Direct Access Arrangement for Modems
Rev. F | Page 16 of 20
ADI [ ADI ]
