AD8531A Analog Devices, AD8531A Datasheet - Page 13

• Manufacturer Part Number: AD8531A
• Description: Low Cost, 250 ma Output Single-supply Amplifiers
• Manufacturer: Analog Devices

REV. 0
Direct Access Arrangement for Telephone Line Interface
Figure 42 illustrates a +5 V only transmit/receive telephone line
interface for 600
transmission of signals on a transformer coupled 600
differential manner. Amplifier A1 provides gain which can be
adjusted to meet the modem output drive requirements. Both
A1 and A2 are configured so as to apply the largest possible sig-
nal on a single supply to the transformer. Because of the
AD8531/AD8532/AD8534’s high output current drive and low
dropout voltage, the largest signal available on a single +5 V
supply is approximately 4.5 V p-p into a 600
tem. Amplifier A3 is configured as a difference amplifier for
two reasons: (1) It prevents the transmit signal from interfering
with the receive signal, and (2) it extracts the receive signal from
the transmission line for amplification by A4. A4’s gain can be
adjusted in the same manner as A1’s to meet the modem’s input
signal requirements. Standard resistor values permit the use of
SIP (Single In-line Package) format resistor arrays. Couple this
with the AD8531/AD8532/AD8534’s 8-pin SOIC or TSSOP
footprint and this circuit offers a compact, cost-sensitive solution.
transmission systems. It allow full duplex
transmission sys-
line in a
–13–
Figure 42. A Single-Supply Direct Access Arrange-
ment for Modems
TO TELEPHONE
600
Z
A1, A2 = 1/2 AD8532
A3, A4 = 1/2 AD8532
O
LINE
MIDCOM
671-8005
1:1
T1
6.2V
6.2V
10k
R11
10k
10k
R9
R12
360
R3
AD8531/AD8532/AD8534
2
3
A3
10k
10k
10k
R10
TX GAIN
ADJUST
R5
R6
P1
2k
1
1
7
A2
10k
A1
R13
9.09k
R2
6
5
2
3
14.3k
6
5
R14
A4
10k
R1
RX GAIN
ADJUST
10µF
2k
7
0.1µF
P2
C1
+5V DC
0.1µF
C2
R7
10k
R8
10k
TRANSMIT
RECEIVE
RXA
TXA