AD7821
SIMULTANEOUS SAMPLING A/D CONVERTERS
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
The AD7821’s inherent track-and-hold and well-defined sam-
pling instant makes it useful, in such applications as sonar,
where a number of input channels are required to be sampled
simultaneously. Figure 22 shows a circuit for such an applica-
tion.
20-Pin Plastic DIP (N-20)
20-Pin Cerdip (Q-20)
20-Terminal Plastic Leaded Chip Carrier
(P-20A)
Figure 22. Simultaneous Sampling A/D Converters
The actual sampling instant, which is the instant at which V
IN
is
measured, occurs approximately 50 ns after the falling edge of
WR
or
RD
in the WR-RD or RD modes, respectively, due to in-
ternal logic delays. However, the internal logic delay and, there-
fore, the sampling instant can vary from device to device, but is
typically within
±
5 ns. This means that a maximum common in-
put sine wave of
±
2.5 V at 32 kHz, applied to any number of
AD7821s in the circuit of Figure 22, will yield a maximum dif-
ference between the converter outputs of typically
±
1/4 LSB.
20-Terminal Leadless Ceramic Chip Carrier
(E-20A)
–12–
REV. A
PRINTED IN U.S.A.
C1186–10–4/88
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