Data Sheet

AD633

Rev. K | Page 11 of 20

For example, if R = 8 kΩ and C = 0.002 μF, then Output A has a

pole at frequencies from 100 Hz to 10 kHz for EC ranging from

100 mV to 10 V. Output B has an additional 0 at 10 kHz (and

can be loaded because it is the low impedance output of the

multiplier). The circuit can be changed to a high-pass filter Z

interchanging the resistor and capacitor as shown in Figure 21.

AD633JN

X1

1

X2

2

Y1

3

Y2

4

+VS 8

W 7

Z 6

–VS 5

CONTROL

INPUT EC

SIGNAL

INPUT ES

0.1µF

0.1µF

+15V

–15V

R

C

OUTPUT B

OUTPUT A

dB

f1 f2

f

+6dB/OCTAVE

OUTPUT A

OUTPUT B

0

Figure 21. Voltage-Controlled, High-Pass Filter

VOLTAGE-CONTROLLED QUADRATURE OSCILLATOR

Figure 22 shows two multipliers being used to form integrators

with controllable time constants in second-order differential

equation feedback loop. R2 and R5 provide controlled current

output operation. The currents are integrated in capacitors C1

and C2, and the resulting voltages at high impedance are applied

to the X inputs of the next AD633. The frequency control input, EC,

connected to the Y inputs, varies the integrator gains with a

calibration of 100 Hz/V. The accuracy is limited by the Y input

offsets. The practical tuning range of this circuit is 100:1. C2

(proportional to C1 and C3), R3, and R4 provide regenerative

feedback to start and maintain oscillation. The diode bridge, D1

through D4 (1N914s), and Zener diode D5 provide economical

temperature stabilization and amplitude stabilization at ±8.5 V

by degenerative damping. The output from the second integrator

(10 V sin ωt) has the lowest distortion.

AUTOMATIC GAIN CONTROL (AGC) AMPLIFIERS

Figure 23 shows an AGC circuit that uses an rms-to-dc

converter to measure the amplitude of the output waveform.

The AD633 and A1, half of an AD712 dual op amp, form a

voltage-controlled amplifier. The rms-to-dc converter,

an AD736, measures the rms value of the output signal. Its

output drives A2, an integrator/comparator whose output

controls the gain of the voltage-controlled amplifier. The

1N4148 diode prevents the output of A2 from going negative.

R8, a 50 kΩ variable resistor, sets the output level of the circuit.

Feedback around the loop forces the voltages at the inverting

and noninverting inputs of A2 to be equal, thus the AGC.

AD633JN

X1

1

X2

2

Y1

3

Y2

4

+VS 8

W 7

Z 6

–VS 5

0.1µF

0.1µF

C1

0.01µF

+15V

–15V

AD633JN

X1

1

X2

2

Y1

3

Y2

4

+VS 8

W 7

Z 6

–VS 5

0.1µF

+15V

–15V

R5

16kΩ

R3

330kΩ

R4

16kΩ

C3

0.01µF

C2

0.01µF

(10V) sin ωt

0.1µF

R2

16kΩ

R1

1kΩ

D5

1N5236

D1

1N914

D2

1N914

D3

1N914

D4

1N914

f =

EC

10V

= kHz

(10V) cos ωt

EC

Figure 22. Voltage-Controlled Quadrature Oscillator