MLT04GBC AD [Analog Devices], MLT04GBC Datasheet - Page 10

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

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.
Squaring and Frequency Doubling
As shown in Figure 44, squaring of an input signal, V
by connecting the X-and Y-inputs in parallel to produce an output
of V
will be positive.
When the input is a sine wave given by V
circuit behaves as a frequency doubler because of the trigonometric
identity:
+5V
IN
V
0.1µF
2
IN
/2.5 V. The input may have either polarity, but the output
Figure 43. Basic Multiplier Connections
Figure 44. Connections for Squaring
W2
W1
GND
X1
Y1
Y2
X2
(V
X
Y
IN
2.5V
sin t )
+
+
W
1
2
4
5
7
8
9
3
6
1–4
2
Y2
X2
GND1
X1
Y1
V
GND2
W2
W1
0.4
CC
= 0.4 (X
MLT04
2.5V
1 2 3 4 5 6 7 8 9 1 8
17
16
15
14
13
12
11
10
V
–5V
+5V
IN
2
1/4 MLT04
1–4
GND4
GND3
0.1µF
V
0.1µF
W4
W3
X4
Y3
X3
•
Y4
EE
1
2
Y
1–4
IN
(1 cos 2 t )
18
17
16
15
14
13
12
10
11
sin t, the squaring
)
W
W4
Y4
X4
Y3
X3
W3
IN
W = 0.4 V
, is achieved
0.1µF
IN
2
–5V
–10–
The equation shows a dc term at the output which will vary
strongly with the amplitude of the input, V
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.
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:
Here, the multiplier operates as a voltage-controlled potentiometer
that adjusts the loop gain of the op amp relative to a control signal,
V
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
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
X
IN
. As the control signal to the multiplier decreases, the output of
Figure 45. Frequency Doubler with Input Offset Voltage
Trims
–5V
–5V
500k
500k
10k
10k
R1
R3
R5
R6
50k
50k
P1
P2
A1, A2 = 1/2 OP285
2
6
Y
3
5
X
OS
X
OS
+
+
10k
A1
A2
10k
R2
R4
is increased, the output of the multiplier
TRIM
V
TRIM
+5V
+5V
O
1
7
2.5 V
3
4
2
R2
R1
+
+
0.4
1/4 MLT04
IN
V
. The output dc offset
V
IN
X
1
W1
100pF
C1
REV. B
10k
R
L
V
O