DAC1009_15 Datasheet, PDF (4/4 Pages) Analog Devices – Low Cost Multipurpose Digitalt To Analog Converter

converter is used in the fixed reference mode, this output is
connected via a 50n trim pot (supplied by the user) to the
reference input terminal (pin 20) as shown in Figure 4.
50n
20 TURN
cw
25
20
The feed through characteristics of the DAC1009 can be
greatly enhanced by the addition of the simple external cir-
cuit shown in Figure 6.
With this circuit, feedthrough is reduced by a fa<;tor of ap-
proximately 10: 1. The following table lists typical values of
feedthrough for a -lmA sine wave input and a digital input
code of 000. . .00 for the 0 to -10V output range.
DAC1009
Feedthrough (mV)
Input Frequency
w/Circuit
w/o Circuit
l!)
......
Figure 4. Reference Connection
10kHz
1.6
6
l'
0
50kHz
100kHz
2.0
24
4.0
44
~
'^I"
(j)
Since the value of the reference input current ultimately de-
00
termines the magnitude of the converter's analog output, this
With full scale (-lmA) reference applied, each DAC1009 is
<:>
OBSOLETE ^{trim pot is used to make gain adjustments. An external refer-}
ence source capable of supplying -6.2 volts at -lmA may be
used in place of the internal reference.
MULTIPLYING OPERATION
When used as a multiplying DAC, the fixed reference input
ISreplaced by a signal which can vary in amplitude from 0 to
-lmA. The converter's output will then represent the product
of the digital and analog inputs. The use of a unipolar input
code produces one quadrant multiplication; a bipolar code
produces two quadrant multiplication. As a multiplier, the
DAC1009 has a small signal bandwidth of 950kHz, a full
power bandwidth of 125kHz and a half power bandwidth of
750kHz. With proper external circuitry, maximum feedthrough
is less than 1LSB at 50kHz.
The following simplified schematic (Figure 5) represents the
analog input circuit configuration.
carefully trimmed to eliminate minor errors in the weighting of
individual bits. These errors tend to reappear when the refer-
ence level decreases as it does during multiplying operatiqn.
The overall effect of these errors is a function of reference in-
put level as shown in Figure 7.
15
10
OUTPUT
ERROA
(mV)
.1.0
.0.5
0.0
ANALOG INPUT (mA)
INPUT
OTO.1mA
--119
R'N
Figure 7. Output Error vs. Analog Input
SIGNAL1
"::'
DAC1009
Maximum linearity is achieved when the analog input signal
remains close to full scale.
GAIN AND ZERO ADJUSTMENT
Figure 5. Analog Input Circuit
The proper connections of the user-supplied gain and zero
adjustment potentiometers are shown below in Figure 8 for
fixed reference voltage output operation. For current output
Pin 19 which is connected to the reference amplifier's summing ^{operation, the wiper of the zero adjustment potentiometer}
junction is essentially at ground potential. The inpu t resistance
should be connected via a 2.2Mn resistor to pin 22 instead of
necessary to yield -lmA with the peak input voltage applied can, ^{directly to pin 28 as shown in Figure 2.}
...;
~
therefore, be readHy calculated. Due to minor variations between
units, an initial adjustment of up to :!:2%in the value of the input
resistor may be necessary to produce the proper overall gain.
Z8
DAC1009
+15
cw
ZERO
ADJUST
20kn
.15
::>
z
0
w_I-
Z
INPUT
A'N
19
Z5
cw
GAIN
eax. :
2<J
ADJUST
5012
~ SIGNAL
6.8k
(5%)
DAC1009
Figure 8. Gain and Zero Adjustments
22
22k
15%1
10kn
'C=3.3pFx-
An
Figure 6. Feedthrough Reduction Circuit
With a digital code of 000. . .00 applied, adjust the zero pot
until the analog output is zero :!:1/10LSB for unipolar units
or +VFS :!:1!1OLSB for bipolar units. With a full scale digital
code of 111. . .11 (binary) or 100110011001 (BCD) applied,
adjust the gain pot until the analog output is within :!:1!10LSB
of Full Scale less 1LSB.
-4-
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