AD734
Table I. Component Values for Setting Up Nonstandard
Denominator Values
AD734
X – INPUT
10V FS
1 X1
2 X2
3 U0
VP 14
DD 13 NC
W 12
Z1 11
Z2 10
ER 9 NC
VN 8
0.1 F
(X
1
– X
2
)(Y
1
– Y
2
)
+ Z
2
W=
10V
LOAD
L
GROUND
Z
2
OPTIONAL
L
0.1 F
SUMMING INPUT
±10V
FS
+15V
Denominator
5V
3V
2V
1V
R1 (Fixed)
34.8 kΩ
64.9 kΩ
86.6 kΩ
174 kΩ
R1 (Variable)
20 kΩ
20 kΩ
50 kΩ
100 kΩ
R2
120 kΩ
220 kΩ
300 kΩ
620 kΩ
4 U1
5 U2
Y – INPUT
10V FS
6 Y1
7 Y2
The denominator can also be current controlled, by grounding
Pin 3 (U0) and withdrawing a current of Iu from Pin 4 (U1).
The nominal scaling relationship is U = 28
×
Iu, where u is
expressed in volts and Iu is expressed in milliamps. Note,
however, that while the linearity of this relationship is very good,
it is subject to a scale tolerance of
±
20%. Note that the common
mode range on Pins 3 through 5 actually extends from 4 V to
36 V below VP, so it is not necessary to restrict the connection
of U0 to ground if it should be desirable to use some other
voltage.
The output ER may also be buffered, re-scaled and used as a
general-purpose reference voltage. It is generated with respect to
the negative supply line Pin 8 (VN), but this is acceptable when
driving one of the signal interfaces. An example is shown in
Figure 12, where a fixed numerator of 10 V is generated for a
divider application. There, Y
2
is tied to VN but Y
1
is 10 V above
this; therefore the common-mode voltage at this interface is still
5 V above VN, which satisfies the internal biasing requirements
(see Specifications table).
OPERATION AS A MULTIPLIER
–15V
Figure 5. Basic Multiplier Circuit
of 32 Hz. When a tighter control of this frequency is needed, or
when the HP corner is above about 100 kHz, an external resis-
tor should be added across the pair of input nodes.
At least one of the two inputs of any pair must be provided with
a dc path (usually to ground). The careful selection of ground
returns is important in realizing the full accuracy of the AD734.
The Z2 pin will normally be connected to the load ground,
which may be remote, in some cases. It may also be used as an
optional summing input (see Equations (3) and (4), above)
having a nominal FS input of
±
10 V and the full 10 MHz
bandwidth.
In applications where high absolute accuracy is essential, the
scaling error caused by the finite resistance of the signal source(s)
may be troublesome; for example, a 50
Ω
source resistance at
just one input will introduce a gain error of –0.1%; if both the
X- and Y-inputs are driven from 50
Ω
sources, the scaling error
in the product will be –0.2%. Provided the source resistance(s)
are known, this gain error can be completely compensated by
including the appropriate resistance (50
Ω
or 100
Ω,
respectively,
in the above cases) between the output W (Pin 12) and the Z1
feedback input (Pin 11). If Rx is the total source resistance
associated with the X1 and X2 inputs, and Ry is the total source
resistance associated with the Y1 and Y2 inputs, and neither Rx
nor Ry exceeds 1 kΩ, a resistance of Rx+Ry in series with pin
Z1 will provide the required gain restoration.
Pins 9 (ER) and 13 (DD) should be left unconnected in this
application. The U-inputs (Pins 3, 4 and 5) are shown
connected to ground; they may alternatively be connected to
VN, if desired. In applications where Pin 2 (X2) happens to be
driven with a high-amplitude, high-frequency signal, the
capacitive coupling to the denominator control circuitry via an
ungrounded Pin 3 can cause high-frequency distortion. However,
the AD734 can be operated without modification in an AD534
socket, and these three pins left unconnected, with the above
caution noted.
+15V
All of the connection schemes used in this section are essentially
identical to those used for the AD534, with which the AD734 is
pin-compatible. The only precaution to be noted in this regard
is that in the AD534, Pins 3, 5, 9, and 13 are not internally
connected and Pin 4 has a slightly different purpose. In many
cases, an AD734 can be directly substituted for an AD534 with
immediate benefits in static accuracy, distortion, feedthrough,
and speed. Where Pin 4 was used in an AD534 application to
achieve a reduced denominator voltage, this function can now be
much more precisely implemented with the AD734 using alter-
native connections (see Direct Denominator Control, page 5).
Operation from supplies down to
±
8 V is possible. The supply
current is essentially independent of voltage. As is true of all
high speed circuits, careful power-supply decoupling is impor-
tant in maintaining stability under all conditions of use. The
decoupling capacitors should always be connected to the load
ground, since the load current circulates in these capacitors at
high frequencies. Note the use of the special symbol (a triangle
with the letter ‘L’ inside it) to denote the load ground.
Standard Multiplier Connections
AD734
X – INPUT
10V FS
1 X1
2 X2
3 U0
4 U1
5 U2
Y – INPUT
10V FS
6 Y1
7 Y2
VP 14
DD 13 NC
W 12
Z1 11
Z2 10
ER 9
VN 8
NC
0.1 F
L
Figure 5 shows the basic connections for multiplication. The X
and Y inputs are shown as optionally having their negative
nodes grounded, but they are fully differential, and in many
applications the grounded inputs may be reversed (to facilitate
interfacing with signals of a particular polarity, while achieving
some desired output polarity) or both may be driven.
The AD734 has an input resistance of 50 kΩ
±
20% at the X,
Y, and Z interfaces, which allows ac-coupling to be achieved
with moderately good control of the high-pass (HP) corner
frequency; a capacitor of 0.1
µF
provides a HP corner frequency
–6–
I
R
S
W
=
(X – X ) (Y
1
– Y
2
)
1
2
10V
1
1
+
R
S
50k
0.1 F
L
LOAD
I
W
10mA MAX FS
10V MAXIMUM
LOAD VOLTAGE
–15V
L
Figure 6. Conversion of Output to a Current
REV. C
AD [ ANALOG DEVICES ]
