AD797

Rev. F | Page 17 of 20

*

7

*

*

*

AD797

26.1Ω

26.1Ω

6

3

4

2

AD600

*USE THE POWER SUPPLY BYPASSING SHOWN IN FIGURE 35.

Professional Audio Signal Processing—DAC Buffers

The low noise and low distortion of the AD797 make it an ideal

choice for professional audio signal processing. An ideal I-to-V

converter for a current output DAC would simply be a resistor

to ground, were it not for the fact that most DACs do not operate

linearly with voltage on their output. Standard practice is to

operate an op amp as an I-to-V converter, creating a virtual

ground at its inverting input. Normally, clock energy and current

steps must be absorbed by the op amp output stage. However, in

frequency energy to ground while correctly reproducing the

desired output with extremely low THD and IMD.

Figure 50. An Ultrasound Preamplifier Circuit

Amorphous (Photodiode) Detector

7

*

*

AD797

82pF

6

2

C1

2000pF

4

100Ω

3kΩ

AD1862

DAC

3

*USE THE POWER SUPPLY BYPASSING SHOWN IN FIGURE 35.

detectors (amorphous Si) have optimum performance when used

in conjunction with amplifiers with very low voltage (rather than

very low current noise). Figure 51 shows the AD797 used with

voltage noise amplified by the ac noise gain. The AD797’s excellent

input noise performance gives 27 μV rms total noise in a 1 MHz

bandwidth, as shown by Figure 52.

*

7

*

AD797

10kΩ

100Ω

50pF

1000pF

6

3

4

2

*USE THE POWER SUPPLY BYPASSING SHOWN IN FIGURE 35.

Figure 53. A Professional Audio DAC Buffer

7

AD797

6

2

4

3

1

5

–IN

+IN

20kΩ

Figure 51. Amorphous Detector Preamp

Figure 54. Offset Null Configuration

100M

1k

100

100

0

60

20

40

80

10M

1M

100k

10k

FREQUENCY (Hz)

–80

–30

–50

–70

–60

–40

NOISE

of Amorphous Detector Preamp