HA-2546(2004) データシートの表示（PDF） - Intersil
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HA-2546 Datasheet PDF : 16 Pages
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HA-2546
Application Information
Theory Of Operation
The HA-2546 is a two quadrant multiplier with the following
three differential inputs; the signal channel, VY+ and VY-,
the control channel, VX+ and VX-, and the summed channel,
VZ+ and VZ-, to complete the feedback of the output
amplifier. The differential voltages of channel X and Y are
converted to differential currents. These currents are then
multiplied in a circuit similar to a Gilbert Cell multiplier,
producing a differential current product. The differential
voltage of the Z channel is converted into a differential
current which then sums with the products currents. The
differential “product/sum” currents are converted to a single-
ended current and then converted to a voltage output by a
transimpedance amplifier.
The open loop transfer equation for the HA-2546 is:
VOUT = A
(VX+
-
VX-) (VY+
SF
-
VY-)
-
(VZ+
-
VZ-)
where;
A = Output Amplifier Open Loop Gain
SF = Scale Factor
VX, VY, VZ = Differential Inputs
The scale factor is used to maintain the output of the
multiplier within the normal operating range of ±5V. The
scale factor can be defined by the user by way of an optional
external resistor, REXT, and the Gain Adjust pins, Gain
Adjust A (GA A), Gain Adjust B (GA B), and Gain Adjust C
(GA C). The scale factor is determined as follows:
SF = 2, when GA B is shorted to GA C
SF ≅ 1.2 REXT, when REXT is connected between
GA A and GA C (REXT is in kΩ)
SF ≅ 1.2 (REXT + 1.667kΩ), when REXT is
connected to GA B and GA C (REXT is in kΩ)
The scale factor can be adjusted from 2 to 5. It should be
noted that any adjustments to the scale factor will affect the
AC performance of the control channel, VX. The normal
input operating range of VX is equal to the scale factor
voltage.
The typical multiplier configuration is shown in Figure 2. The
ideal transfer function for this configuration is:
VOUT =
(VX+
-
VX-) (VY+
2
-
VY-)
+
VZ-,
when
VX
≥
0V
0
, when VX < 0V
The VX- pin is usually connected to ground so that when VX+
is negative there is no signal at the output, i.e. two quadrant
operation. If the VX input is a negative going signal the VX+
pin maybe grounded and the VX- pin used as the control
input.
1
NC 2
NC 3
REF
NC 4
VY + 5
6
+
-
Y
V- 7
8
16 NC
15
14
+
X-
13 VX +
12
11 V+
+
Σ-
10
-
Z+ 9
50Ω
1kΩ
VOUT
50pF
FIGURE 2.
The VY- terminal is usually grounded allowing the VY+ to
swing ±5V. The VZ+ terminal is usually connected directly to
VOUT to complete the feedback loop of the output amplifier
while VZ- is grounded. The scale factor is normally set to 2
by connecting GA B to GA C. Therefore the transfer equation
simplifies to VOUT = (VX VY) / 2.
Offset Adjustment
The signal channel offset voltage may be nulled by using a
20kΩ potentiometer between VYIO Adjust pins A and B and
connecting the wiper to V-. Reducing the signal channel
offset will reduce VX AC feedthrough. Output offset voltage
can also be nulled by connecting VZ- to the wiper of a 20kΩ
potentiometer which is tied between V+ and V-.
Capacitive Drive Capability
When driving capacitive loads >20pF, a 50Ω resistor is
recommended between VOUT and VZ+, using VZ+ as the
output (see Figure 2). This will prevent the multiplier from going
unstable.
Power Supply Decoupling
Power supply decoupling is essential for high frequency
circuits. A 0.01µF high quality ceramic capacitor at each
supply pin in parallel with a 1µF tantalum capacitor will
provide excellent decoupling. Chip capacitors produce the
best results due to the close spacing with which they may be
placed to the supply pins minimizing lead inductance.
Adjusting Scale Factor
Adjusting the scale factor will tailor the control signal, VX, input
voltage range to match your needs. Referring to the simplified
schematic on the front page and looking for the VX input
stage, you will notice the unusual design. The internal
reference sets up a 1.2mA current sink for the VX differential
pair. The control signal applied to this input will be forced
across the scale factor setting resistor and set the current
flowing in the VX+ side of the differential pair. When the
7
FN2861.6
November 19, 2004
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