®

MPY100

7

FIGURE 1. MPY100 Functional Block Diagram.

(X

10

Attenuator

Z

2

Z

1

Multiplier

Core

Y

2

Y

1

X

2

X

1

V-I

V-I

V-I

A

Out

High Gain

Output Amplifier

Stable

Reference

and Bias

+V

S

–V

S

V

– (Z

Transfer Function

Substituting this into the original equation yields the overall

transfer function

which shows the output voltage to be the product of the two

voltage swing in the circuit. The errors associated with this

common-mode voltage can be eliminated by using two

differential stages in parallel and cross-coupling their out-

puts as shown in Figure 3.

FIGURE 3. Cross-Coupled Differential Stages as a Variable-

Transconductance Multiplier.

FIGURE 2. Basic Differential Stage as a Transconductance

Multiplier.

–+

V

O

+V

CC

R

L

R

L

I

1

I

2

R

E

I

E

–

+

V

2

Q

3

Q

2

Q

1

–

+

V

1

THEORY OF OPERATION

The MPY100 is a variable transconductance multiplier con-

sisting of three differential voltage-to-current converters, a

multiplier core and an output differential amplifier as illus-

trated in Figure 1.

The basic principle of the transconductance multiplier can

be demonstrated by the differential stage in Figure 2.

An analysis of the circuit in Figure 3 shows it to have the

same overall transfer function as before:

=

= e

The resultant nonlinearity can be overcome by developing

Figure 4.

provide a linear conversion of the input voltages to differen-

I

3

I

4

I

1

I

2

V

T

V

1

–

+

V

O

+V

S

R

L

+

V

2

Q

5

Q

2

Q

1

–

+

V

1

Q

4

Q

3

I

3

I

1

I

2

I

4

R

E

R

E

Q

6

–

I

T

–V

CC

R

L