AD7821
SIMULTANEO US SAMP LING A/D CO NVERTERS
T he 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.
O UTLINE D IMENSIO NS
D imensions shown in inches and (mm).
20-P in P lastic D IP (N-20)
20-P in Cer dip (Q -20)
20-Ter m inal P lastic Leaded Chip Car r ier
(P -20A)
Figure 22. Sim ultaneous Sam pling A/D Converters
T he actual sampling instant, which is the instant at which VIN 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. T his 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-Ter m inal Leadless Cer am ic Chip Car r ier
(E-20A)
–12–
REV. A
ADI [ ADI ]
