8

This multiplier has the advantage over other AGC circuits, in

that the signal bandwidth is not affected by the control signal

gain adjustment.

Voltage Controlled Amplifier

A wide range of gain adjustment is available with the Voltage

Controlled Amplifier configuration shown in Figure 16. Here

the gain of the HFA0002 can be swept from 20V/V to a gain

of almost 1000V/V with a DC voltage from 0V to 5V.

Wave Shaping Circuits

Wave shaping or curve fitting is another class of application

for the analog multiplier. For example, where a nonlinear

sensor requires corrective curve fitting to improve linearity

the HA-2556 can provide nonintegral powers in the range 1

to 2 or nonintegral roots in the range 0.5 to 1.0 (refer to

References). This effect is displayed in Figure 17.

A multiplier can’t do nonintegral roots “exactly”, but it can

yield a close approximation. We can approximate

nonintegral roots with equations of the form:

This function can be easily built using an HA-2556 and a

potentiometer for easy adjustment as shown in Figures 19 and

20. If a fixed nonintegral power is desired, the circuit shown in

Figure 21 eliminates the need for the output buffer amp. These

nonintegral power or root.

FIGURE 15. AUTOMATIC GAIN CONTROL

FIGURE 16. VOLTAGE CONTROLLED AMPLIFIER

NC

NC

V-

V+

NC

NC

50

Ω

HA-2556

5k

Ω

10k

Ω

HA-5127

0.01

µF

10k

Ω

0.1

µF

1N914

5.6V

0.1

µF

+15V

20k

Ω

NC

NC

+

-

14

15

16

9

13

12

11

10

1

2

3

4

5

7

6

8

Σ

REF

Y

X

Z

NC

NC

V-

V+

NC

NC

HFA0002

5k

Ω

500

Ω

NC

NC

HA-2556

+

-

14

15

16

9

13

12

11

10

1

2

3

4

5

7

6

8

Σ

REF

Y

X

Z

0

0.2

0.4

0.6

0.8

1

0

0.2

0.4

0.6

0.8

1

INPUT (V)

FIGURE 17. EFFECT OF NONINTEGRAL POWERS / ROOTS

V

o

1

α

–

()V

IN

2

αV

IN

+

=

V

o

1

α

–

()V

IN

12

⁄

αV

IN

+

=

0

0.2

0.4

0.6

0.8

1

0

0.2

0.4

0.6

0.8

1

INPUT (V)

X

FIGURE 18. COMPARE APPROXIMATION TO NONINTEGRAL

ROOT

HA-2556