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

level. This has the effect of varying thc “noise” gain of the

amplifier, 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-

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

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

4

3

2

INPUT VOLTAGE – Volts

V

V

T

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

27

24

21

18

15

12

9

6

ATTENUATION – dB

* *

* * *

* *

*

* *

* * *

**

*

*

*

* ** *

* ** *

**

*

* *

* * * * **

*

* * *

* *

*

V

T

Figure 7. Typical Attenuation Error for 0.75 dB Steps

1.0

–1.0

078

0.5

–0.5

6

0.0

66

72

60

48

42

36

30

24

18

12

54

84

ATTENUATION – dB

T

T

DD

V

= +5V

Figure 8. Typical Attenuation Error for 3 dB Steps vs.

Temperature

Figure 9. Accuracy Specification for K/B/T Grade Devices