11

LT1113

S

APPLICATI

I FOR ATIO

of magnitude. A further reduction of IR errors can be

achieved by using a DC servo circuit shown in the applica-

tions section of this data sheet. The DC servo has the

advantage of reducing a wide range of IR errors to the

millivolt level over a wide temperature variation. The

preservation of dynamic range is especially important

when reduced supplies are used, since input bias currents

can exceed the nanoamp level for die temperatures

over 85

°C.

To take full advantage of a wide input common mode

range, the LT1113 was designed to eliminate phase rever-

sal. Referring to the photographs shown in Figure 3, the

at

±5V supplies with the input swinging ±5.2V. The output

of the LT1113 clips cleanly and recovers with no phase

reversal, unlike the competition as shown by the last

photograph. This has the benefit of preventing lock-up in

servo systems and minimizing distortion components.

The effect of input and output overdrive on one amplifier

has no effect on the other, as each amplifier is biased

independently.

Advantages of Matched Dual Op Amps

In many applications the performance of a system

depends on the matching between two operational ampli-

fiers rather than the individual characteristics of the two op

amps. Two or three op amp instrumentation amplifiers,

tracking voltage references and low drift active filters

are some of the circuits requiring matching between two

op amps.

The well-known triple op amp configuration in Figure 4

illustrates these concepts. Output offset is a function of the

difference between the two halves of the LT1113. This

error cancellation principle holds for a considerable

number of input referred parameters in addition to

offset voltage and bias current. Input bias current will

be the average of the two noninverting input currents

is the offset current of the instrumentation amplifier.

Common mode and power supply rejections will be

dependent only on the match between the two amplifiers

(assuming perfect resistor matching).

INPUT:

±5.2V Sine Wave

LT1113 Output

OPA2111 Output