AD7112

REV. 0

–7–

Another error arises from the output amplifier’s input offset volt-

age. The amplifier is operated with a fixed feedback resistance,

but the equivalent source impedance (the AD7112 output im-

pedance) varies as a function of the attenuation level. This has

the effect of varying the noise gain of the amplifier thus creating

a varying error due to amplifier offset voltage. It is recom-

mended that an amplifier with less than 50

µV of input offset be

used (such as the AD712 or ADOP07) in dc applications. Am-

plifiers with a large input offset voltage may cause audible

thumps in audio applications due to dc output changes. The

AD7112 accuracy is specified and tested using only the internal

R–2R ladder) that may exist in the AD7112 D/A converter cir-

cuit results in a constant attenuation error over the whole range.

The AD7112 accuracy is specified relative to 0 dB attenuation,

cisely (i.e., 0 dB attenuation) with input code 00000000. For

further information on gain error refer to the “CMOS DAC Ap-

plication Guide” which is available from Analog Devices, Publi-

cation Number G872b-8-1/89.

TYPICAL PERFORMANCE CHARACTERISTICS

6

0

5

3

1

2

0

5

4

34

2

1

ALL DIGITAL INPUTS

TIED TOGETHER

Figure 6. Supply Current vs. Logic Input Level

FREQUENCY – Hz

OP275

C1 = 0pF

10

–30

0

–20

–10

OP275

C1 = 15pF

AD712

C1 = 0pF

AD712

C1 = 15pF

DATA INPUT CODE = 0000 0000

Figure 7. Frequency Response with AD712 and OP275

10

90

100

0%

200ns

5V

C1 = 0pF

C1 = 15pF

DATA CHANGE

FROM 00H TO 80H

5V

A1

0.8V

Figure 4. Response of AD7112 with AD712

10

90

100

0%

200ns

5V

C1 = 0pF

C1 = 15pF

DATA CHANGE

FROM 00H TO 80H

5V

A1

0.8V

Figure 5. Response of AD7112 with OP275