MLT04 Datasheet, PDF (10/12 Pages) Analog Devices – Four-Channel, Four-Quadrant Analog Multiplier

MLT04
APPLICATIONS
The MLT04 is well suited for such applications as modulation/
demodulation, automatic gain control, power measurement, analog
computation, voltage-controlled amplifiers, frequency doublers,
and geometry correction in CRT displays.
Multiplier Connections
Figure 43 llustrates the basic connections for multiplication. Each
of the four independent multipliers has single-ended voltage inputs
(X, Y) and a low impedance voltage output (W). Also, each
multiplier has its own dedicated ground connection (GND) which
is connected to the circuit’s analog common. For best perfor-
mance, circuit layout should be compact with short component
leads and well-bypassed supply voltage feeds. In applications where
fewer than four multipliers are used, all unused analog inputs must
be returned to the analog common.
W1
X1
Y1
+5V
0.1µF ^Y2
X2
W2
1 W1
W4 18
2 ^GND1
GND4 17
3 X1
X4 16
4 ^Y1 _MLT04 Y4 15
5 ^V_CC ^{123456789876543210}
V_EE 14
6 ^Y2
Y3 13
7 X2
X3 12
8 ^GND2
GND3 11
9 W2
W3 10
W_1–4 = 0.4 (X_1–4 • Y_1–4)
W4
X4
Y4
–5V
Y3
0.1µF
X3
W3
Figure 43. Basic Multiplier Connections
Squaring and Frequency Doubling
As shown in Figure 44, squaring of an input signal, V , is achieved
IN
by connecting the X-and Y-inputs in parallel to produce an output
of V ²/2.5 V. The input may have either polarity, but the output
IN
will be positive.
+5V
0.1µF
V_IN
X
GND
Y
+
0.4
+
1/4 MLT04
W
W = 0.4 V_IN2
0.1µF
–5V
Figure 44. Connections for Squaring
When
the
input
is
a
sine
wave
given
by
V
IN
sin
ωt,
the
squaring
circuit behaves as a frequency doubler because of the trigonometric
identity:
The equation shows a dc term at the output which will vary
strongly with the amplitude of the input, V . The output dc offset
IN
can be eliminated by capacitively coupling the MLT04’s output
with a high-pass filter. For optimal spectral performance, the
filter’s cutoff frequency should be chosen to eliminate the input
fundamental frequency.
A source of error in this configuration is the offset voltages of the X
and Y inputs. The input offset voltages produce cross products
with the input signal to distort the output waveform. To circum-
vent this problem, Figure 45 illustrates the use of inverting
amplifiers configured with an OP285 to provide a means by which
the X- and Y-input offsets can be trimmed.
ΩP1
50kΩ
–5V
+5V
ΩR5
500kΩ
X_OS TRIM
R2
10k
R1
10k
2
A1 ¹
3+
V_IN
A1, A2 = 1/2 OP285
5+
A2 ⁷
R3
6
10k
ΩR6
500kΩ
R4
10k
Y_OS TRIM
–5V
+5V
ΩP2
50kΩ
3 + ^{1/4 MLT04}
2 0.4
C1
W1 ^100pF
1
ΩR_L ^VO
10kΩ
4⁺
Figure 45. Frequency Doubler with Input Offset Voltage
Trims
Feedback Divider Connections
The most commonly used analog divider circuit is the “inverted
multiplier” configuration. As illustrated in Figure 46, an “inverted
multiplier” analog divider can be configured with a multiplier
operating in the feedback loop of an operational amplifier. The
general form of the transfer function for this circuit configuration is
given by:
V_O
=
−2.5 V
×


R2
R1 
× ^VIN
V_X
Here, the multiplier operates as a voltage-controlled potentiometer
that adjusts the loop gain of the op amp relative to a control signal,
V . As the control signal to the multiplier decreases, the output of
X
the multiplier decreases as well. This has the effect of reducing
negative feedback which, in turn, decreases the amplifier’s loop
gain. The result is higher closed-loop gain and reduced circuit
bandwidth. As V is increased, the output of the multiplier
X
increases which generates more negative feedback — closed-loop
gain drops and circuit bandwidth increases. An example of an
“inverted multiplier” analog divider frequency response is shown in
Figure 47.
(V_IN sin ωt )²
2. 5 V
=
V2
IN
2. 5 V


1
2
₍₁
−
cos
2
ωt
)
–10–
REV. B