REV. B

AD826

–13–

HIGH PERFORMANCE ADC BUFFER

Figure 42 is a schematic of a 12-bit high speed analog-to-digital

converter. The AD826 dual op amp takes a single ended input

and drives the AD872 A/D converter differentially, thus reduc-

ing 2nd harmonic distortion. Figure 43 is a FFT of a 1 MHz

input, sampled at 10 MHz with a THD of –78 dB. The AD826

can be used to amplify low level signals so that the entire range

of the converter is used. The ability of the AD826 to perform on

a

±5 volt supply or even with a single 5 volts combined with its

rapid settling time and ability to deliver high current to compli-

cated loads make it a very good flash A/D converter buffer as

well as a very useful general purpose building block.

1/2

AD826

52.5

0.1 F

1k

1k

1k

1k

AD872

12-BIT

10MSPS

ADC

50

COAX

CABLE

500mV

p-p MAX

COMMON

100 F

25V

1/2

AD826

0.1 F

100 F

25V

–5V

5V

Figure 42. A Differential Input Buffer for High

Bandwidth ADCs

Figure 43. FFT, Buffered A/D Converter