The information contained in this section has been developed through characterization by Intersil Semiconductor and is for use as

application and design information only. No guarantee is implied.

8-19

HA2556

Let’s first examine the Balance Concept as it applies to the

standard multiplier configuration (Figure 2).

Signals A and B are input to the multiplier and the signal W

is the result. By substituting the signal values into the Bal-

ance equation you get:

And solving for W:

FIGURE 2. MULTIPLIER

Notice that the output (W) enters the equation in the feed-

back to the Z stage. The Balance Equation does not test for

stability, so remember that you must provide negative feed-

back. In the multiplier configuration, the feedback path is

that takes place at the summing node just prior to the output

amplifier. Feedback is not restricted to the Z stage, other

feedback paths are possible as in the Divider Configuration

shown in Figure 3.

FIGURE 3. DIVIDER

Inserting the signal values A, B and W into the Balance

Equation for the divider configuration yields:

Solving for W yields:

Notice that, in the divider configuration, signal B must remain

≥0 (positive) for the feedback to be negative. If signal B is

positive feedback and the output will swing into the rail.

A

()

B

()

×

5W

()

=

W

AB

×

5

------------

=

HA-2556

1/5V

X

Y

Z

∑

W

A

B

+

-

+

-

A

+

-

+

-

HA-2556

1/5V

X

Y

Z

∑

W

A

B

+

-

+

-

+

-

A

+

-

W

–

()

B

()

×

5V

A

–

()

×

=

W

5A

B

-----

=

Signals may be applied to more than one input at a time as

in the Squaring configuration in Figure 4:

Here the Balance equation will appear as:

FIGURE 4. SQUARE

Which simplifies to:

The last basic configuration is the Square Root as shown in

Figure 5. Here feedback is provided to both X and Y inputs.

FIGURE 5. SQUARE ROOT (FOR A > 0)

The Balance equation takes the form:

Which equates to:

Application Circuits

The four basic configurations (Multiply, Divide, Square and

Square Root) as well as variations of these basic circuits

have many uses.

Frequency Doubler

For example, if ACos(

ωτ) is substituted for signal A in the

Square function, then it becomes a Frequency Doubler and

the equation takes the form:

And using some trigonometric identities gives the result:

A

()

A

()

×

5W

()

=

HA-2556

1/5V

X

Y

Z

∑

W

A

A

+

-

+

-

+

-

+

-

W

A2

5

-----

=

HA-2556

1/5V

X

Y

Z

W

A

∑

+

-

+

-

A

+

-

+

-

W

()

W

–

()

×

5A

–

()

=

W5A

=

ACos

ωτ

()

()

ACos

ωτ

()

()

×

5W

()

=

W

A2

10

ωτ

()

+

()

=

Spec Number

511063-883