MLT04 Datasheet, PDF(11/12 Page) Analog Devices – Four-Channel, Four-Quadrant Analog Multiplier

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MLT04 Datasheet, PDF (11/12 Pages) Analog Devices – Four-Channel, Four-Quadrant Analog Multiplier

◁

MLT04

1/4 MLT04 +

0.4

2 GND1

10k

VIN

OP113 6

VIN

VO = â2.5V â¢ VX

1/4 MLT04

1N4148 W1

0.4

10k

VIN

OP113 6

VO = â2.5V â¢ VIN

Figure 46. âInverted-Multiplierâ Configuration for

Analog Division

AVOL

OP113

VX = 0.025V

VX = 0.25V

VX = 2.5V

100

10k

100k

10M

FREQUENCY â Hz

Figure 47. Signal-Dependent Feedback Makes Variables

Out of Amplifier Bandwidth and Stability

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 MLT04âs 8 MHz bandwidth.

Connection for Square Rooting

Another application of the âinverted multiplierâ 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:

VO =

â2.5

ï£«

ï£ï£¬

R2ï£¶

R1 ï£¸ï£·

Ã VIN

the

input

signal

voltage

limited

the

range

â2.5

â¤

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.

Figure 48. Connections for Square Rooting

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, ÏO, will be directly

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

circuitâs transfer function is given by:

ï£±

ï£¼

ï£´

VIN

âï£«ï£ï£¬

ï£¶

ï£¸ï£·

ï£²ï£´

ï£´

ï£³ï£´

s ï£«ï£ï£¬

R2 + R1ï£¶ ï£«

R1 ï£¸ï£· ï£ï£¬

2. 5 RC

ï£¶

ï£¸ï£·

ï£½ï£´

ï£´

ï£¾ï£´

In this circuit, the ratio of R2 to R1 sets the passband gain, and the

break frequency of the filter, ÏLP, is given by:

ÏLP

ï£«

ï£ï£¬

R1 + R

ï£¶

ï£¸ï£·

ï£«

ï£ï£¬

2. 5 RC

ï£¶

ï£¸ï£·

GND1

+ 1/4 MLT04

W1 10k

0.4

80pF

A1 1

10k

VIN

10k

A1 = 1/2 OP285

=â

VIN

5RC

1 + S VX

fLP = VX ; fLP = MAX @ VX = 2.5V

Ï10ÏRC

Figure 49. A Voltage-Controlled Low-Pass Filter

For example, if R1 = R2 = 10 kâ¦ , R = 10 kâ¦ , and C = 80 pF,

REV. B

â11â

▷