MC1494P ONSEMI [ON Semiconductor], MC1494P Datasheet - Page 10

• Manufacturer Part Number: MC1494P
• Description: LINEAR FOUR-QUADRANT MULTIPLIER INTEGRATED CIRCUIT
• Manufacturer: ONSEMI [ON Semiconductor]

three adjustment potentiometers, eliminating one of the input
offset adjustments. For instance, if the “X” input offset
adjustment is eliminated,
offset (V iox ) but y is adjustable to the extent that the ( x + y )
term can be zeroed. Then the output offset adjustment is
used to adjust the V oo term and thus zero the remaining error
terms. An AC procedure for nulling with three adjustments is:
A. AC Procedure:
B. DC Procedure:
Divide
their special problems. Classic feedback theory teaches that
if a multiplier is used as a feedback element in an operational
amplifier circuit, the divide function results. Figure 22
illustrates the theoretical simplicity of such an approach and
a practical realization is shown in Figure 23.
latch–up. One way it can occur is if V X is allowed to go
negative, or in some cases, if V X approaches zero.
10
This shows that all error terms can be eliminated with only
Divide circuits warrant a special discussion as a result of
The characteristic “failure” mode of the divide circuit is
1. Connect oscillator (1.0 kHz, 15 Vpp) to input.
2. Monitor output at 2.0 kHz with tuned voltmeter and
3. Tune voltmeter to 1.0 kHz and adjust P1 for a minimum
4. Ground input and adjust P3 (output offset) for
5. Repeat steps 1 through 4 as necessary.
1. Set V X = V Y = 0 V and adjust P3 (output offset
2. Set V X = V Y = 1.0 V and adjust P1 (Y input offset
3. Set V X = V Y = 10 Vdc and adjust P4 (load resistor)
4. Set V X = V Y = –10 Vdc and check that V O = –10 V.
5. Repeat steps 1 through 4 as necessary.
adjust P4 for desired gain ( Be sure to peak
response of voltmeter).
output voltage.
0 Vdc out.
potentiometer) such that V O = 0 Vdc.
potentiometer) such that the output voltage is
– 0.100 V.
such that the output voltage is –10 V.
V
10 pF
510
x is determined by the internal
10
9
16 k
11
+
+
1
3
30 k
6
12
MC1494
Figure 21. MC1494 Squaring Circuit
13
Output
Offset
7
4
62 k
51 k
20 k
20 k
P1
+
8
MC1494
2
P3
Offset
Input
15
14
5
+15 V –15 V
function through the multiplier is noninverting. Its output is fed
to the inverting input of the op amp Thus, operation is in the
negative feedback mode and the circuit is DC stable.
the multiplier becomes inverting, the amplifier has positive
feedback and latch–up results. The problem resulting from
V X being near zero is a result of the transfer through the
multiplier being near zero. The op amp is then operating with
a very high closed–loop gain and error voltages can thus
become effective in causing latch–up.
of the op amp exceeding the rated common mode input
voltage of the multiplier. The input stage of the multiplier
becomes saturated, phase reversal results, and the circuit is
latched up. The circuit of Figure 23 protects against this
happening by clamping the output swing of the op amp to
approximately
are used to assure adequate output swing but still limit the
output voltage of the op amp from exceeding the common
mode input range of the MC1494.
operation is somewhat different from the procedure for the
multiplier itself. One approach, however, is to break the
feedback loop, null out the multiplier circuit, and then close
the loop.
Figure 22 illustrates why this is so. For V X > 0 the transfer
Should V X change polarity, the transfer function through
The other mode of latch–up results from the output voltage
Setting up the divide circuit for reasonably accurate
Figure 22. Basic Divide Circuit Using Multiplier
V Z
3
2
P4
50 k
+
–15 V
–
+
KV X V Y
MC1456
10 pF
4
10.7 V. Five percent tolerance, 10 V zeners
MOTOROLA ANALOG IC DEVICE DATA
–
+15 V
22 k
7
+
–
+
MC1494
V X
6
+
+
V O =
V Y
–V 2
10
V Z = –KV X V Y
V O
V O =
or
KV X
–V Z