–13–

REV. D

OP162/OP262/OP462

= 1+

2

cuit gain to unity.

The fourth op amp, OP462-D, is optional and is used to im-

prove CMRR by reducing any input capacitance to the ampli-

fier. By shielding the input signal leads and driving the shield

with the common-mode voltage, input capacitance is eliminated

at common-mode voltages. This voltage is derived from the

midpoint of the outputs of OP462-A and OP462-B by using two

10 k

W resistors followed by OP462-D as a unity gain buffer.

It is important to use 1% or better tolerance components for the

2 k

W resistors, as the common-mode rejection is dependent on

their ratios being exact. A potentiometer should also be con-

nected in series with the OP462-C noninverting input resistor to

ground to optimize common-mode rejection.

The circuit in Figure 41 was implemented to test its settling

time. The instrumentation amp was powered with

±5V, so the

input step voltage went from –5 V to +4 V to keep the OP462

within its input range. Therefore, the 0.05% settling range is

when the output is within 4.5 mV. Figure 42 shows the positive

slope settling time to be 1.8

ms, and Figure 43 shows a settling

time of 3.9

ms for the negative slope.

10

0%

100

90

5mV

1 s

2V

Figure 42. Positive Slope Settling Time

10

0%

100

90

5mV

1µs

2V

10

0%

100

90

5mV

1 s

Figure 43. Negative Slope Settling Time

Direct Access Arrangement

Figure 44 shows a schematic for a +5 V single supply transmit/

receive telephone line interface for 600

W transmission systems.

It allows full duplex transmission of signals on a transformer

coupled 600

W line. Amplifier A1 provides gain that can be

adjusted to meet the modem output drive requirements. Both

A1 and A2 are configured so as to apply the largest possible

differential signal to the transformer. The largest signal available

on a single +5 V supply is approximately 4.0 V p-p into a 600

W

transmission system. Amplifier A3 is configured as a difference

amplifier to extract the receive information from the transmis-

sion line for amplification by A4. A3 also prevents the transmit

signal from interfering with the receive signal. The gain of A4

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 OP462 14-lead SOIC or TSSOP package and this

circuit can offer a compact solution.

6.2V

6.2V

TRANSMIT

TXA

RECEIVE

RXA

C1

0.1 F

R1

10k

R2

9.09k

2k

P1

TX GAIN

ADJUST

A1

A2

A3

A4

A1, A2 = 1/2 AD8532

A3, A4 = 1/2 AD8532

R3

360

1:1

T1

TO TELEPHONE

LINE

1

2

3

7

6

5

2

3

1

6

5

7

10 F

R7

10k

R8

10k

R5

10k

R6

10k

R9

10k

R14

14.3k

R10

10k

R11

10k

R12

10k

R13

10k

C2

0.1 F

P2

RX GAIN

ADJUST

2k

600

5V DC

MIDCOM

671-8005

Figure 44. A Single-Supply Direct Access Arrangement for

Modems