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參數資料
| 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： | 9/16頁 |
| 文件大小： | 319K |
| 代理商： | MC1494 |
MC1494
9
MOTOROLA ANALOG IC DEVICE DATA
Figure 19, the “X” input zero and “Y” input zero will be at
approximately 15 MHz and 7.0 MHz respectively.
It should be noted that the MC1494 multiplies in the time
domain, hence, its frequency response is found by means of
complex convolution in the frequency (Laplace) domain. This
means that if the “X” input does not involve a frequency, it is
not necessary to consider the “X” side frequency response in
the output product. Likewise, for the “Y” side. Thus, for
applications such as a wideband linear AGC amplifier which
has a DC voltage as one input, the multiplier frequency
response has one zero and one pole. For applications which
involve an AC voltage on both the “X” and “Y” side such as a
balanced modulator, the product voltage response will have
two zeros and one pole, hence, peaking may be present in
the output.
From this brief discussion, it is evident that for AC
applications; (1) the value of resistors RX, RY and RL should
be kept as small as possible to achieve maximum frequency
response, and (2) it is possible to select a load resistor RL
such that the dominant pole (RL, CO) cancels the input zero
(RX, 3.5 pF or RY, 3.5 pF) to give a flat amplitude
characteristic with frequency. This is shown in Figures 11 and
12. Examination of the frequency characteristics of the “X”
and “Y” inputs will demonstrate that for wideband amplifier
applications, the best tradeoff with frequency response and
gain is achieved by using the “Y” input for the AC signal.
For AC applications requiring bandwidths greater than
those specified for the MC1494, two other devices are
recommended. For modulator–demodulator applications, the
MC1496 may be used up to 100 MHz. For wideband
multiplier applications, the MC1495 (using small collector
loads and AC coupling) can be used.
Slew–Rate
The MC1494 multiplier is not slew–rate limited in the
ordinary sense that an op amp is. Since all the signals in the
multiplier are currents and not voltages, there is no charging
and discharging of stray capacitors and thus no limitations
beyond the normal device limitataions. However, it should be
noted that the quiescent current in the output transistors is
0.5 mA and thus the maximum rate of change of the output
voltage is limited by the output load capacitance by the
simple equation:
IO
T
Thus, if CO is 10 pF, the maximum slew rate would be:
VO
T
C
Slew Rate
VO=
=0.5 x 10– 3
10 x 10–12=50 V/
μ
s
This can be improved, if necessary, by the addition of an
emitter–follower or other type of buffer.
Phase Vector Error
All multipliers are subject to an error which is known as the
phase vector error. This error is a phase error only and does
not contribute an amplitude error per se. The phase vector
error is best explained by an example. If the “X” input is
described in vector notation as;
X= A
0
°
and the “Y” input is described as;
Y= B
0
°
then the output product would be expected to be;
VO= AB
0
°
(see Figure 20)
However, due to a relative phase shift between the ‘‘X’’ and
‘‘Y’’ channels, the output product will be given by:
VO = AB
φ
Notice that the magnitude is correct but the phase angle of
the product is in error. The vector (V) associated with this
error is the ‘‘phase vector error’’. The startling fact about the
phase vector error is that it occurs and accumulates much
more rapidly than the amplitude error associated with
frequency response. In fact, a relative phase shift of only
0.57
°
will result in a 1% phase vector error. For most
applications, this error is
Figure 20. Phase Vector Error
X = A
Y = B
0
°
0
°
V
φ
AB
φ
AB
0
°
meaningless. If phase of the output product is not important,
then neither is the phase vector error. If phase is important,
such as in the case of double sideband modulation or
demodulation, then a 1% phase vector error will represent a
1% amplitude error a the phase angle of interest.
Circuit Layout
If wideband operation is desired, careful circuit layout must
be observed. Stray capacitance across RX and RY should be
avoided to minimize peaking (caused by a zero created by
the parallel RC circuit).
DC APPLICATIONS
Squaring Circuit
If the two inputs are connected together, the resultant
function is squaring:
VO = KV2
where K is the scale factor (see Figure 21).
However, a more careful look at the multiplier’s defining
equation will provide some useful information. The output
voltage, without initial offset adjustments is given by:
VO = K(VX + Viox –VX off) (VY + Vioy –VY off) + VOO
(Refer to “Definitions” section for an explanation of terms.)
With VX = VY = V (squaring) and defining;
∈
x = Viox – Vx (off)
∈
y = Vioy – Vy (off)
The output voltage equation becomes:
VO = KVx2+ KVx (
∈
x +
∈
y) + K
∈
x
∈
y + VOO
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