AD826
HIGH PERFORMANCE ADC BUFFER
1k
V
S
0.1 F
1k
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.
V
IN
500mV
p-p MAX
50
COAX
CABLE
52.5
1/2
AD826
V
INA
AD872
12-BIT
10MSPS
ADC
1k
5V
100 F
25V
COMMON
100 F
25V
–5V
–V
S
V
S
1/2
AD826
0.1 F
V
INB
–V
S
1k
Figure 42. A Differential Input Buffer for High
Bandwidth ADCs
Figure 43. FFT, Buffered A/D Converter
REV. B
–13–
AD [ ANALOG DEVICES ]
