AD7111/AD7111A
REV. 0
–7–
Another error arises from the output amplifier s input offset
voltage. The amplifier is operated with a fixed feedback resis-
tance, but the equivalent source impedance (the AD7111/
AD7111A output impedance) varies as a function of attenuation
l
evel. This has the effect of varying thc “noise” gain of the
am
plifier, thus creating a varying error due to amplifier offset
voltage. It is recommended that an amplifier with less than
50 µV of input offset be used (such as the AD OP07 in dc appli-
cations. Amplifiers with higher offset voltage may cause audible
“thumps” in ac applications due to dc output changes.
The AD7111/AD7111A accuracy is specified and tested using
only the internal feedback resistor. Any gain error (i.e., mis-
match of R
FB
to the R-2R ladder) that may exist in the
AD7111/AD7111A D/A converter circuit results in a constant
attenuation error over the whole range. The AD7111/AD7111A
accuracy is specified relative to 0 dB attenuation, hence “Gain”
trim resistors—R1 and R2 in Figure 1—can be used to adjust
V
OUT
= V
IN
precisely (i.e., 0 dB attenuation) with input code
00000000. The accuracy and monotonic range specifications of
the AD7111/AD7111A are not affected in any way by this gain
trim procedure. For the AD7111/AD7111A L/C/U grades, suit-
able values for R1 and R2 of Figure 1 are R1 = 500 Ω, R2 =
180 Ω; for the K/B/T grades, suitable value are R1 = 1000 Ω,
R2 = 270 Ω. For additional information on gain error the reader
is referred to the “CMOS DAC Application Guide,” available
from Analog Devices, Inc., Publication Number G872b–8–1/89.
Typical Performance Characteristics
6
0
5
3
1
1
2
0
5
4
432
INPUT VOLTAGE – Volts
I
DD
– mA
V
IN
APPLIED TO ALL DATA INPUTS
V
DD
= +5V
T
A
= +25
°
C
CS = WR = 0V
Figure 6. Typical Supply Current vs. Logic Input Level
0.4
–0.6
30
0.0
–0.4
3
–0.2
0
0.2
27242118151296
ATTENUATION – dB
ERROR – dB
*
*
*
*
*
*
*
*
*
*
*
*
*
**
*
*
*
*
**
*
*
**
***
*
*
*
*
*
*
*
**
*
*
*
*
*
*
*
V
DD
= +5V
T
A
= +25
°
C
Figure 7. Typical Attenuation Error for 0.75 dB Steps
1.0
–1.0
078
0.5
–0.5
6
0.0
66 726048423630241812 54
84
ATTENUATION – dB
ERROR – dB
T
A
= +85
°
C
T
A
= +25
°
C
DD
V = +5V
Figure 8. Typical Attenuation Error for 3 dB Steps vs.
Temperature
Figure 9. Accuracy Specification for K/B/T Grade Devices
at T
A
= +25
°
C
