AD633 Analog Devices, AD633 Datasheet - Page 5

• Manufacturer Part Number: AD633
• Description: Low Cost Analog Multiplier
• Manufacturer: Analog Devices

the basis of voltage controlled integrators and oscillators as will
be shown later in this Applications section. The transfer func-
tion of this circuit has the form
Linear Amplitude Modulator
The AD633 can be used as a linear amplitude modulator with
no external components. Figure 10 shows the circuit. The car-
rier and modulation inputs to the AD633 are multiplied to
produce a double-sideband signal. The carrier signal is fed
forward to the AD633’s Z input where it is summed with the
double-sideband signal to produce a double-sideband with carrier
output.
Voltage Controlled Low-Pass and High-Pass Filters
Figure 11 shows a single multiplier used to build a voltage con-
trolled low-pass filter. The voltage at output A is a result of
filtering, E
trol input. The break frequency, f
and the rolloff is 6 dB per octave. This output, which is at a
high impedance point, may need to be buffered.
The voltage at output B, the direct output of the AD633, has
same response up to frequency f
filter,
then levels off to a constant attenuation of f
For example, if R = 8 k and C = 0.002 F, then output A has
a pole at frequencies from 100 Hz to 10 kHz for E
from 100 mV to 10 V. Output B has an additional zero at 10 kHz
(and can be loaded because it is the multiplier’s low impedance
output). The circuit can be changed to a high-pass filter Z inter-
changing the resistor and capacitor as shown in Figure 12 below.
REV. B
MODULATION
CARRIER
I
E
f
O
2
f
C
1
INPUT
INPUT
sin
E
M
S
Figure 10. Linear Amplitude Modulator
R
2
t
1
20
. The break frequency is modulated by E
V
1
X
RC
E
1
C
RC
X
10
1
2
3
4
2
X1
X2
Y1
Y2
V
AD633JN
Y
1
Y
+V
–V
2
W
Z
S
S
1
, the natural breakpoint of RC
2
8
7
6
5
–15V
, equals
+15V
0.1 F
0.1 F
1
W = 1+
/f
2
= E
C
10V
E
C
(Equation 7)
(Equation 8)
(Equation 9)
M
/10.
ranging
C
, the con-
E
C
sin
t
–5–
Voltage Controlled Quadrature Oscillator
Figure 13 shows two multipliers being used to form integrators
with controllable time constants in a 2nd 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, E
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 out-
put from the second integrator (10 V sin t) has the lowest
distortion.
AGC AMPLIFIERS
Figure 14 shows an AGC circuit that uses an rms-dc converter
to measure the amplitude of the output waveform. The AD633
and A1, 1/2 of an AD712 dual op amp, form a voltage con-
trolled amplifier. The rms 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 k variable resistor,
sets the circuit’s output level. Feedback around the loop forces
the voltages at the inverting and noninverting inputs of A2 to be
equal, thus the AGC.
CONTROL
INPUT E
INPUT E
SIGNAL
CONTROL
INPUT E
INPUT E
Figure 12. Voltage Controlled High-Pass Filter
Figure 11. Voltage Controlled Low-Pass Filter
SIGNAL
C
, connected to the Y inputs, varies the integrator gains
C
S
C
S
1
2
3
4
X1
X2
Y1
Y2
1
2
3
4
AD633JN
X1
X2
Y1
Y2
AD633JN
+V
–V
W
S
Z
S
+V
–V
W
8
7
6
5
Z
S
S
–15V
+15V
8
7
6
5
–15V
0.1 F
+15V
0.1 F
0.1 F
0.1 F
–6dB/OCTAVE
0
dB
R
C
OUTPUTA
OUTPUT B =
OUTPUT A =
f1
0
OUTPUTA
dB
f2
R
C
T
T
+6dB/OCTAVE
f2 f1
OUTPUT B
OUTPUT A
2
OUTPUTB
1
=
=
AD633
W
W
1
1
1
2
1 + T
1 + T
1 + T
f
OUTPUTB
= RC
=
1
E
C
1
2
2
10
R
P
P
P
f
C