HA1-2556/883 INTERSIL [Intersil Corporation], HA1-2556/883 Datasheet - Page 12

• Manufacturer Part Number: HA1-2556/883
• Description: Wideband Four Quadrant Analog Multiplier (Voltage Output)
• Manufacturer: INTERSIL [Intersil Corporation]

DESIGN INFORMATION
The information contained in this section has been developed through characterization by Intersil Semiconductor and is for use as
application and design information only. No guarantee is implied.
Applications Information
Operation at Reduced Supply Voltages
The HA-2556 will operate over a range of supply voltages,
input and output voltage ranges. See “Typical Performance
Curves” for more information.
Offset Adjustment
X and Y channel offset voltages may be nulled by using a
20K potentiometer between the V
and B and connecting the wiper to V-. Reducing the channel
offset voltage will reduce AC feedthrough and improve the
multiplication error. Output offset voltage can also be nulled
by connecting V
tied between V+ and V-.
Capacitive Drive Capability
When driving capacitive loads >20pF a 50
be connected between V
put (see Figure 1). This will prevent the multiplier from going
unstable and reduce gain peaking at high frequencies. The
50
capacitive load and the inductance of the output at pin 8.
Gain accuracy will be maintained because the resistor is
inside the feedback loop.
Theory of Operation
The HA-2556 creates an output voltage that is the product of
the X and Y input voltages divided by a constant scale factor
of 5V. The resulting output has the correct polarity in each of
the four quadrants defined by the combinations of positive
and negative X and Y inputs. The Z stage provides the
means for negative feedback (in the multiplier configuration)
and an input for summation into the output. This results in
the following equation, where X, Y and Z are high imped-
ance differential inputs
5V to 15V. Use of supply voltages below 12V will reduce
resistor will dampen the resonance formed with the
-15V
V
NC
NC
NC
FIGURE 1. DRIVING CAPACITIVE LOAD
Y
+
Z
- to the wiper of a potentiometer which is
1
2
3
4
5
6
7
8
V
OUT
REF
+
-
.
50
OUT
+
=
-
and V
+
+
X x Y
--------- -
-
-
5
16
15
14
13
12
11
10
9
YIO
Z
+, using V
–
V
or V
Z
1K
NC
NC
NC
V
Z
+15 V
V
-
X
Z
+
+
XIO
(Continued)
resistor should
Z
adjust pin A
+ as the out-
V
20pF
OUT
HA2556
8-18
To accomplish this the differential input voltages are first con-
verted into differential currents by the X and Y input transcon-
ductance stages. The currents are then scaled by a constant
reference and combined in the multiplier core. The multiplier
core is a basic Gilbert Cell that produces a differential output
current proportional to the product of X and Y input signal cur-
rents. This current becomes the output for the HA-2557.
The HA-2556 takes the output current of the core and feeds
it to a transimpedance amplifier, that converts the current to
a voltage. In the multiplier configuration, negative feedback
is provided with the Z transconductance amplifier by con-
necting V
current which is subtracted from the multiplier core before
being applied to the high gain transimpedance amp. The Z
stage, by virtue of it’s similarity to the X and Y stages, also
cancels second order errors introduced by the dependence
of V
The purpose of the reference circuit is to provide a stable
current, used in setting the scale factor to 5V. This is
achieved with a bandgap reference circuit to produce a tem-
perature stable voltage of 1.2V which is forced across a NiCr
resistor. Slight adjustments to scale factor may be possible
by overriding the internal reference with the V
scale factor is used to maintain the output of the multiplier
within the normal operating range of 5V when full scale
inputs are applied.
The Balance Concept
The open loop transfer equation for the HA-2556 is:
where;
An understanding of the transfer function can be gained by
assuming that the open loop gain, A, of the output amplifier
is infinite. With this assumption, any value of V
generated with an infinitesimally small value for the terms
within the brackets. Therefore we can write the equation:
which simplifies to:
This form of the transfer equation provides a useful tool to
analyze multiplier application circuits and will be called the
Balance Concept.
V
0
OUT
BE
=
V
X+
on collector current in the X and Y stages.
---------------------------------------------------------------- -
=
OUT
V
–
A
X+
A = Output Amplifier Open Loop Gain
V
5V = Fixed Scale Factor
V
X
to the Z input. The Z stage converts V
---------------------------------------------------------------------------
X-
, V
–
V
X+
V
Y
, V
X-
–
Z
V
= Differential Input Voltages
V
5
X-
Y+
V
5
–
Y+
V
V
Spec Number
Y-
Y+
–
V
–
Y-
V
=
Y-
5 V
–
–
V
Z+
V
Z+
REF
Z+
511063-883
OUT
–
–
–
V
pin. The
OUT
V
V
Z-
can be
Z-
Z-
to a