AD7821

REV. A

–12–

OUTLINE DIMENSIONS

Dimensions shown in inches and (mm).

20-Pin Plastic DIP (N-20)

20-Pin Cerdip (Q-20)

20-Terminal Plastic Leaded Chip Carrier

(P-20A)

20-Terminal Leadless Ceramic Chip Carrier

(E-20A)

SIMULTANEOUS SAMPLING A/D CONVERTERS

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.

Figure 22. Simultaneous Sampling A/D Converters

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.