MC1494 데이터 시트보기 (PDF) - ON Semiconductor
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MC1494 Datasheet PDF : 16 Pages
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MC1494
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).
Offset and Scale Factor Adjustment Procedure
The adjustment procedure for the circuit of Figure 18 is:
A. X Input Offset
1. Connect oscillator (1.0 kHz, 5.0 Vpp sinewave)
to the ‘‘Y’’ input (Pin 9).
2. Connect ‘‘X’’ input (Pin 10) to ground.
3. Adjust X–offset potentiometer, P2 for an AC null
at the output.
B. Y Input Offset
1. Connect oscillator (1.0 kHz, 5.0 Vpp sinewave)
to the ‘‘X’’ input (Pin 10).
2. Connect ‘‘Y’’ input (Pin 9) to ground.
3. Adjust Y–offset potentiometer, P1 for an AC null
at the output.
C. Output Offset
1. Connect both ‘‘X’’ and ‘‘Y’’ inputs to ground.
2. Adjust output offset potentiometer, P3 until the
output voltage VO is 0 Vdc.
D. Scale Factor
1. Apply +10 Vdc to both the ‘‘X’’ and ‘‘Y’’ inputs.
2. Adjust P4 to achieve –10 V at the output.
3. Apply –10 Vdc to both ‘‘X’’ and ‘‘Y’’ inputs and
check for VO = –10 V.
E. Repeat steps A through D as necessary.
The ability to accurately adjust the MC1494 is dependent on
the offset adjust potentiometers. Potentiometers should be
of the “infinite” resolution type rather than wirewound. Fine
adjustments in balanced–modulator applications may
require two potentiometers to provide “coarse” and “fine”
adjustment. Potentiometers should have low temperature
coefficients and be free from backlash.
Temperature Stability
While the MC1494 provides excellent performance in
itself, overall performance depends to a large degree on the
quality of the external components. Previous discussion
shows the direct dependence on RX, RY and RL and indirect
dependence on R1 (through I1). Any circuit subjected to
temperature variations should be evaluated with these
effects in mind.
Bias Currents
The MC1494 multiplier, like most linear ICs, requires a
DC bias current into its input terminals. The device cannot
be capacitively coupled at the input without regard for this
bias current. If inputs VX and VY are able to supply the small
bias current (≈ 0.5 µA) resistors R can be omitted (see Figure
18). If the MC1494 is used in an AC mode of operation and
capacitive coupling is used the value of resistor R can be any
reasonable value up to 100 kΩ. For minimum noise and
optimum temperature performance, the value of resistor R
should be as low as practical.
Parasitic Oscillation
When long leads are used on the inputs, oscillation may
occur. In this event, an RC parasitic suppression network
similar to the ones shown in Figure 18 should be connected
directly to each input using short leads. The purpose of the
network is to reduce the “Q” of the source–tuned circuits
which cause the oscillation.
Inability to adjust the circuit to within the specified
accuracy may be an indication of oscillation.
AC OPERATION
General
For AC operation, such as balanced modulation,
frequency doubler, AGC, etc., the op amp will usually be
omitted as well as the output offset adjust potentiometer. The
output offset adjust potentiometer is omitted since the output
will normally be AC coupled and the DC voltage at the
output is of no concern providing it is close enough to zero
volts that it will not cause clipping in the output waveform.
Figure 19 shows a typical AC multiplier circuit with a scale
factor K ≈ 1. Again, resistor RX and RY are chosen as
outlined in the previous section, with RL chosen to provide
the required scale factor.
3.0 k
6.2 k
+15 V -15 V
1
RX 12
1
7 RY
8
15
9
ey
+
5
14
eo
R
MC1494
ex
10 +
1
16 k
RL
4.7 k
CO
R6
13 4
3
51 k 2
20 k
K=1
20 k
ex (max) = ey(max) = 1.0 V
Figure 19. Wideband Multiplier
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