9

LT1169

S

APPLICATI

I FOR ATIO

R2

OUTPUT

R1

TRANSDUCER

OUTPUT

TRANSDUCER

LT1169 • F03

Q = CV;

dQ

 dt

= I = C

dV

 dt

Reduced Power Supply Operation

To take full advantage of a wide input common-mode

range, the LT1169 was designed to eliminate phase rever-

sal. Referring to the photographs in Figure 4, the LT1169

supplies with the input swinging

±5.2V. The output of the

LT1169 clips cleanly and recovers with no phase reversal,

unlike the competition as shown by the last photograph.

This has the benefit of preventing lockup 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

LT1169 Output

Input:

±5.2 Sine Wave

OPA2111 Output

LT1169 • F04a

LT1169 • F04b

LT1169 • F04c

Figure 3. Inverting and Noninverting Gain Configurations

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 5

illustrates these concepts. Output offset is a function of the

difference between the two halves of the LT1169. 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

The difference between these two currents (

is the offset current of the instrumentation amplifier. Com-

mon-mode and power supply rejections will be

dependent only on the match between the two amplifiers

(assuming perfect resistor matching).

The concepts of common mode and power supply

rejection ratio match (

∆CMRR and ∆PSRR) are best dem-

onstrated with a numerical example: