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參數(shù)資料
| 型號： | MC1494 |
| 廠商： | ON SEMICONDUCTOR |
| 英文描述： | LINEAR FOUR-QUADRANT MULTIPLIER INTEGRATED CIRCUIT |
| 中文描述： | 線性四象限乘法器集成電路 |
| 文件頁數(shù)： | 7/16頁 |
| 文件大小： | 319K |
| 代理商： | MC1494 |
MC1494
7
MOTOROLA ANALOG IC DEVICE DATA
Figure 18. Typical Multiplier Connection
+15 V
+15 V
15
5
RL
50 k
22 k
10 pF
2
3
3
14
1
R1
16 k
P4
6
4
7
10
11
30 k
RX
12
13
9
8
7
6
4
2
P1 20 k
P2
P3
20 k
50 k
R*
510
10 pF
510
10 pF
R*
62 k
RY
MC1494
+
+
–
–
+
–
+
–
+
MC1456
VO
0.1
μ
F
+15 V
–15 V
VO = –VX VY
10
–10 V
≤
VX
≤
+10 V
–10 V
≤
VY
≤
+10 V
*R is not necessary if inputs are DC coupled.
0.1
μ
F
0.1
μ
F
0.1
μ
F
VX
VY
It should be pointed out that there is nothing magic about
setting the scale factor to 1/10. This is merely a convenient
factor to use if the VX and VY input voltages are expected to
be large, say
±
10 V. Obviously with VX = VY = 10 V and a
scale factor of unity, the device could not hope to provide a
100 V output, so the scale factor is set to 1/10 and provides
an output scaled down by a factor of ten. For many
applications it may be desirable to set K = 1/2 or K = 1 or even
K = 100. This can be accomplished by adjusting RX, RY and
RL appropriately.
The selection of RL is arbitrary and can be chosen after
resistors RX and RY are found. Note in Figure 18 that RY is
62 k
while RX is 30 k
. The reason for this is that the “Y”
side of the multiplier exhibits a second order nonlinearity
whereas the “X” side exhibits a simple nonlinearity. By
making the RY resistor approximately twice the value of the
RX resistor, the linearity on both the “X” and “Y” sides are
made equal. The selection of the RX and RY resistor values is
dependent upon the expected amplitude of VX and VY inputs.
To maintain a specified linearity, resistors RX and RY should
be selected according to the following equations:
RX
≥
3 VX (max) in k
when VX is in Volts,
RY
≥
6 VY (max) in k
when VY is in Volts.
For example, if the maximum input on the “X” side is
±
1.0 V,
resistor RX can be selected to be 3.0 k
. If the maximum
input on the “Y” side is also
±
1.0 V, then resistor RY can be
selected to be 6.0 k
(6.2 k
nominal value). If a scale factor
of K = 10 is desired, the load resistor is found to be 47 k
. In
this example, the multiplier provides a gain of 20 dB.
Operational Amplifier Selection
The operational amplifier connection in Figure 18 is a
simple but extremely accurate current–to–voltage converter.
The output current of the multiplier flows through the
feedback resistor RL to provide a low impedance output
voltage from the op amp. Since the offset current and bias
currents of the op amp will cause errors in the output voltage,
particularly with temperature, one with very low bias and
offset currents is recommended. The MC1456 or MC1741
are excellent choices for this application.
Since the MC1494 is capable of operation at much higher
frequencies than the op amp, the frequency characteristics of
the circuit in Figure 18 will be primarily dependent upon the
operational amplifier.
Stability
The current–to–voltage converter mode is a most
demanding application for an operational amplifier. Loop gain
is at its maximum and the feedback resistor in conjunction
with stray or input capacitance at the multiplier output adds
additional phase shift. It may therefore be necessary to add
(particularly in the case of internally compensated op amps)
a small feedback capacitor to reduce loop gain at the higher
frequencies. A value of 10 pF in parallel with RL should be
adequate to insure stability over production and temperature
variations, etc.
An externally compensated op amp might be employed
using slightly heavier compensation than that recommended
for unity–gain operation.
Offset Adjustment
The noninverting input of the op amp provides a
convenient point to adjust the output offset voltage. By
connecting this point to the wiper arm of a potentiometer
(P3), the output offset voltage can be adjusted to zero (see
Offset and Scale Factor Adjustment Procedure).
The input offset adjustment potentiometers, P1 and P2 will
be necessary for most applications where it is desirable to
take advantage of the multiplier’s excellent linearity
characteristics. Depending upon the particular application,
some of the potentiometers can be omitted (see Figures 19,
21, 24, 26 and 27).
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