8/21/97 4:00 PM

OP297

–10–

REV. D

NONLINEAR CIRCUITS

Due to its low input bias currents, the OP297 is an ideal log

amplifier in nonlinear circuits such as the square and square-

root circuits shown in Figures 34 and 35. Using the squaring

circuit of Figure 34 as an example, the analysis begins by writing









+V









=V









+V









All the transistors of the MAT04 are precisely matched and at

× I

Exponentiating both sides of the equation leads to:

× 10. Substituting (V

R2









R1









2

A similar analysis made for the square-root circuit of Figure 35

leads to its transfer function:

R1

Figure 34. Squaring Amplifier

33k

Ω

1/2

OP-297

2

3

8

1

4

V–

V+

100pF

100pF

33k

Ω

1/2

OP-297

6

5

7

MAT-04E

1

3

2

14

12

13

7

5

6

8

10

9

50k

Ω

50k

Ω

–15V

–

+

–

+