AD534 Analog Devices, AD534 Datasheet - Page 5

• Manufacturer Part Number: AD534
• Description: Internally Trimmed Precision IC Multiplier
• Manufacturer: Analog Devices

FUNCTIONAL DESCRIPTION
Figure 2 is a functional block diagram of the AD534. Inputs are
converted to differential currents by three identical voltage-to-
current converters, each trimmed for zero offset. The product
of the X and Y currents is generated by a multiplier cell using
Gilbert’s translinear technique. An on-chip “Buried Zener”
provides a highly stable reference, which is laser trimmed to
provide an overall scale factor of 10 V. The difference between
XY/SF and Z is then applied to the high gain output amplifier.
This permits various closed loop configurations and dramati-
cally reduces nonlinearities due to the input amplifiers, a domi-
nant source of distortion in earlier designs. The effectiveness of
the new scheme can be judged from the fact that under typical
conditions as a multiplier the nonlinearity on the Y input, with
X at full scale ( 10 V), is 0.005% of FS; even at its worst
point, which occurs when X = 6.4 V, it is typically only
on the other hand, is determined almost entirely by the multi-
plier element and is parabolic in form. This error is a major
factor in determining the overall accuracy of the unit and hence
is closely related to the device grade.
The generalized transfer function for the AD534 is given by:
where A = open loop gain of output amplifier, typically
In most cases the open loop gain can be regarded as infinite,
and SF will be 10 V. The operation performed by the AD534,
can then be described in terms of equation:
REV. B
0.05% of FS Nonlinearity for signals applied to the X input,
X
X
Y
Z
SF
Y
Z
2
2
1
1
2
1
AD534
X, Y, Z = input voltages (full scale = SF, peak =
SF = scale factor, pretrimmed to 10.00 V but adjustable
by the user down to 3 V.
V
+
+
+
–
–
–
V-1
V-1
V-1
OUT
70 dB at dc
Figure 2. Functional Block Diagram
( X
1.25 SF)
1
TRANSLINEAR
REFERENCE
A
MULTIPLIER
0.75 ATTEN
ELEMENT
AND BIAS
STABLE
X
( X
2
) (Y
1
1
X
Y
2
SF
TRANSFER FUNCTION
) (Y
2
V
) 10 V ( Z
O
= A
1
HIGH GAIN
OUTPUT
AMPLIFIER
A
Y
(X
2
1
– X
)
2
SF
1
) (Y
+V
–V
OUT
( Z
S
S
1
1
Z
– Y
2
2
)
)
Z
2
– (Z
)
1
– Z
2
)
–5–
The user may adjust SF for values between 10.00 V and 3 V by
connecting an external resistor in series with a potentiometer
between SF and –V
tance for a given value of SF is given by the relationship:
Due to device tolerances, allowance should be made to vary R
by 25% using the potentiometer. Considerable reduction in
bias currents, noise and drift can be achieved by decreasing SF.
This has the overall effect of increasing signal gain without the
customary increase in noise. Note that the peak input signal is
always limited to 1.25 SF (i.e., 5 V for SF = 4 V) so the overall
transfer function will show a maximum gain of 1.25. The per-
formance with small input signals, however, is improved by
using a lower SF since the dynamic range of the inputs is now
fully utilized. Bandwidth is unaffected by the use of this option.
Supply voltages of 15 V are generally assumed. However,
satisfactory operation is possible down to 8 V (see Figure 16).
Since all inputs maintain a constant peak input capability of
achieve output voltage swings in excess of 12 V when using
higher supply voltages.
OPERATION AS A MULTIPLIER
Figure 3 shows the basic connection for multiplication. Note
that the circuit will meet all specifications without trimming.
In some cases the user may wish to reduce ac feedthrough to a
minimum (as in a suppressed carrier modulator) by applying an
external trim voltage ( 30 mV range required) to the X or Y
input (see Figure 1). Figure 19 shows the typical ac feedthrough
with this adjustment mode. Note that the Y input is a factor of
10 lower than the X input and should be used in applications
where null suppression is critical.
The high impedance Z
sum an additional signal into the output. In this mode the out-
put amplifier behaves as a voltage follower with a 1 MHz small
signal bandwidth and a 20 V/ s slew rate. This terminal should
always be referenced to the ground point of the driven system,
particularly if this is remote. Likewise, the differential inputs
should be referenced to their respective ground potentials to
realize the full accuracy of the AD534.
1.25 SF some feedback attenuation will be necessary to
Y INPUT
X INPUT
12V PK
12V PK
10V FS
10V FS
Figure 3. Basic Multiplier Connection
SF
X
X
Y
Y
1
2
1
2
AD534
S
. The approximate value of the total resis-
R
2
OUT
SF
+V
–V
terminal of the AD534 may be used to
Z
Z
2
1
S
S
5.4K
+15V
–15V
10 SF
SF
OPTIONAL SUMMING
INPUT, Z,
=
OUTPUT ,
(X
1
– X
2
10V
) (Y
10V PK
AD534
1
12V PK
– Y
2
)
+ Z
2
SF
;