AD8531/AD8532/AD8534

Rev. F | Page 16 of 20

DIRECT ACCESS ARRANGEMENT FOR TELEPHONE

LINE INTERFACE

6.2V

6.2V

TRANSMIT

TxA

RECEIVE

RxA

C1

0.1µF

R1

10kΩ

R2

9.09kΩ

2kΩ

P1

Tx GAIN

ADJUST

A1

A2

A3

A4

A1, A2 = 1/2 AD8532

A3, A4 = 1/2 AD8532

R3

360Ω

1:1

T1

TOTELEPHONE

LINE

1

2

3

7

6

5

2

3

1

6

5

7

10µF

R7

10kΩ

R8

10kΩ

R5

10kΩ

R6

10kΩ

R9

10kΩ

R14

14.3kΩ

R10

10kΩ

R11

10kΩ

R12

10kΩ

R13

10kΩ

C2

0.1µF

P2

Rx GAIN

ADJUST

2kΩ

600Ω

5V DC

MIDCOM

671-8005

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.

Figure 46. Single-Supply Direct Access Arrangement for Modems