MLT04GBC AD [Analog Devices], MLT04GBC Datasheet - Page 3

• Manufacturer Part Number: MLT04GBC
• Description: Four-Channel, Four-Quadrant Analog Multiplier
• Manufacturer: AD [Analog Devices]

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.
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.
Details of each multiplier’s output-stage amplifier are shown in
Figure 5. The output stages idles at 200 A, and the resistors in
series with the emitters of the output stage are 25 . 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
INTERNAL
Figure 5. Equivalent Circuit for MLT04 Output Stages
BIAS
GND
V
V
Figure 3. Functional Block Diagram of Each MLT04
Multiplier
X
Y
G1, G2, G3, G4
EE
X1, X2, X3, X4
Y1, Y2, Y3, Y4
CC
IN
IN
Figure 4. Equivalent Circuit for the MLT04
200µA
22k
200µA
0.4
200µA
22k
+V
–V
S
S
200µA
25
25
MLT04
V
V
W
OUT
EE
CC
200µA
22k
W1, W2, W3, W4
resistor.
200µA
SCALE
FACTOR
W
OUT
–3–
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:
where:
Executing the algebra to simplify the above expression yields
expressions for all the errors in an analog multiplier:
Term
KV
V
V
X
Z
ƒ(X, Y)
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
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.
KV
X
Y
OS
50 mV, and the scale factor is internally adjusted to 2.5% of full
OS
Y
X
V
Figure 6. Optional Offset Voltage Trim Configuration
X
Y
OS
OS
V
Y
O
OS
V
Y
Y
50k
K
V
X
V
Y
Z
ƒ(X, Y) = Nonlinearity
( K
K
OS
X
Y
OS
Description
True Product
Scale-Factor Error
Linear “X” Feedthrough
Due to Y-Input Offset
Linear “Y” Feedthrough
Due to X-Input Offset
Output Offset Due to X-,
Y-Input Offsets
Output Offset
Nonlinearity
OS
–V
+V
S
S
K ){(V
50k
= Multiplier Scale Factor
= Scale Factor Error
= X-Input Signal
= X-Input Offset Voltage
= Y-Input Signal
= Y-Input Offset Voltage
= Multiplier Output Offset Voltage
X
X
I
OS
)(V
Y
±100mV
FOR X
CONNECT TO SUM
NODE OF AN EXT OP AMP
Y
Dependence on Input
Goes to Zero As Either or
Both Inputs Go to Zero
Goes to Zero at V
Proportional to V
Proportional to V
Independent of V
Independent of V
Depends on Both V
Contains Terms Dependent
on V
and Cross Products
OS
OS
)
X
, Y
, V
OS
Z
Y
OS
, Their Powers
TRIM
MLT04
f ( X , Y )}
X
Y
X
X
X
, V
, V
, V
X
, V
Y
Y
Y
= 0
Y
.