MLT04GBC AD [Analog Devices], MLT04GBC Datasheet - Page 11

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

Although this technique works well with almost any operational
amplifier, there is one caveat: for best circuit stability, the unity-
gain crossover frequency of the operational amplifier should be
equal to or less than the MLT04’s 8 MHz bandwidth.
Connection for Square Rooting
Another application of the “inverted multiplier” configuration is the
square-root function. As shown in Figure 48, both inputs of the
MLT04 are wired together and are used as the output of the
circuit. Because the circuit configuration exhibits the following
generalized transfer function:
the input signal voltage is limited to the range –2.5 V
prevent circuit latchup due to positive feedback or input signal
polarity reversal, a 1N4148-type junction diode is used in series
with the output of the multiplier.
REV. B
Figure 47. Signal-Dependent Feedback Makes Variables
Out of Amplifier Bandwidth and Stability
Figure 46. “Inverted-Multiplier” Configuration for
Analog Division
V
IN
90
80
70
60
50
40
30
20
10
0
Figure 48. Connections for Square Rooting
100
10k
R1
10k
R2
V
V
V
X
X
X
= 0.025V
= 0.25V
= 2.5V
W1
1k
V
O
1
A
OP113
1/4 MLT04
VOL
V
O
FREQUENCY – Hz
2.5
10k
= –2.5V •
3
2
OP113
+
R2
R1
0.4
100k
V
6
V
+
+
IN
X
V
IN
4
3
2
Y1
GND1
X1
1M
+
V
V
O
IN
10M
V
< 0. To
X
–11–
Voltage-Controlled Low-Pass Filter
The circuit in Figure 49 illustrates how to construct a voltage-
controlled low-pass filter with an analog multiplier. The advantage
with this approach over conventional active-filter configurations is
that the overall characteristic cut-off frequency,
proportional to a multiplying input voltage. This permits the
construction of filters in which the capacitors are adjustable
(directly or inversely) by a control voltage. Hence, the frequency
scale of a filter can be manipulated by means of a single voltage
without affecting any other parameters. The general form of the
circuit’s transfer function is given by:
In this circuit, the ratio of R2 to R1 sets the passband gain, and the
break frequency of the filter,
For example, if R1 = R2 = 10 k , R = 10 k , and C = 80 pF,
V
IN
+
V
IN
Figure 49. A Voltage-Controlled Low-Pass Filter
V
GND1
X
10k
R1
X1
10k
R1
V
V
2
3
IN
O
4
1N4148
f
R2
10k
LP
Y1
D1
+
+
0.4
=
LP
10 RC
R2
R1
1/4 MLT04
V
W1
V
V
X
IN
O
1
= –
R1 R2
; f
s
1/4 MLT04
V
LP
LP
R2 R1
R1
1 + S
O
, is given by:
= MAX @ V
=
R1
2
3
1
OP113
+
1
W1
–2.5V • V
5RC
V
10k
R2
X
2.5RC
1
0.4
V
10k
R
6
X
2.5RC
X
= 2.5V
V
IN
A1 = 1/2 OP285
X
4
3
2
3
2
O
, will be directly
+
Y1
X1
A1
MLT04
1
80pF
C
1
V
O
V
O