–3–

REV. B

FUNCTIONAL DESCRIPTION

The MLT04 is a low cost quad, 4-quadrant analog multiplier with

single-ended voltage inputs and voltage outputs. The functional

block diagram for each of the multipliers is illustrated in Figure 3.

Due to packaging constraints, access to internal nodes for externally

adjusting scale factor, output offset voltage, or additional summing

signals is not provided.

Figure 3. Functional Block Diagram of Each MLT04

Multiplier

Each of the MLT04’s analog multipliers is based on a Gilbert cell

multiplier configuration, a 1.23 V bandgap reference, and a unity-

connected output amplifier. Multiplier scale factor is determined

through a differential pair/trimmable resistor network external to

the core. An equivalent circuit for each of the multipliers is shown

in Figure 4.

Figure 4. Equivalent Circuit for the MLT04

Details of each multiplier’s output-stage amplifier are shown in

Figure 5. The output stages idles at 200

µA, and the resistors in

series with the emitters of the output stage are 25

Ω. The output

stage can drive load capacitances up to 500 pF without oscillation.

For loads greater than 500 pF, the outputs of the MLT04 should

be isolated from the load capacitance with a 100

Ω resistor.

Figure 5. Equivalent Circuit for MLT04 Output Stages

ANALOG MULTIPLIER ERROR SOURCES

Multiplier errors consist primarily of input and output offsets, scale

factor errors, and nonlinearity in the multiplying core. An expres-

sion for the output of a real analog multiplier is given by:

V

O

= (K +∆K ){(V

f ( X , Y )}

where:

K

=

Multiplier Scale Factor

∆K

=

Scale Factor Error

V

X

=

X-Input Signal

X

OS

=

X-Input Offset Voltage

V

Y

=

Y-Input Signal

Y

OS

=

Y-Input Offset Voltage

Z

OS

=

Multiplier Output Offset Voltage

ƒ(X, Y) =

Nonlinearity

Executing the algebra to simplify the above expression yields

expressions for all the errors in an analog multiplier:

Term

Description

Dependence on Input

KV

True Product

Goes to Zero As Either or

Both Inputs Go to Zero

∆KV

Scale-Factor Error

Goes to Zero at V

V

Linear “X” Feedthrough

Proportional to V

X

Due to Y-Input Offset

V

Linear “Y” Feedthrough

Proportional to V

Y

Due to X-Input Offset

X

Output Offset Due to X-,

Independent of V

Y-Input Offsets

Z

OS

Output Offset

Independent of V

ƒ(X, Y)

Nonlinearity

Depends on Both V

Contains Terms Dependent

on V

and Cross Products

As shown in the table, the primary static errors in an analog

multiplier are input offset voltages, output offset voltage, scale

factor, and nonlinearity. Of the four sources of error, only two are

externally trimmable in the MLT04: the X- and Y-input offset

voltages. Output offset voltage in the MLT04 is factory-trimmed to

±50 mV, and the scale factor is internally adjusted to ±2.5% of full

scale. Input offset voltage errors can be eliminated by using the

optional trim circuit of Figure 6. This scheme then reduces the net

error to output offset, scale-factor (gain) error, and an irreducible

nonlinearity component in the multiplying core.

Figure 6. Optional Offset Voltage Trim Configuration

MLT04

W

OUT

25

Ω

25

Ω

INTERNAL

BIAS

GND

W

OUT

22k

200µA

200µA

22k

22k

200µA

200µA

200µA

200µA

SCALE

FACTOR

50k

Ω

–V

S

50k

Ω

+V

S

±100mV

FOR X

OS

, Y

OS

TRIM

CONNECT TO SUM

NODE OF AN EXT OP AMP

I

0.4

+V

S

–V

S

X1, X2, X3, X4

G1, G2, G3, G4

Y1, Y2, Y3, Y4

W1, W2, W3, W4

MLT04