REV. D

–10–

AD843

equal. Alternatively, an autocalibration circuit using two D/A

converters can be employed. This can also be used to calibrate

out the effects of offset voltage drift over temperature.

The switch choice, for U1s, is critical in this type of design. The

DG542 utilizes “T” switching techniques on each channel for

exceptionally low crosstalk and for high isolation. The part fur-

ther improves these specifications by using ground pins between

the signal pins. With an input frequency of 5 MHz, crosstalk

and isolation are –85 dB and –75 dB, respectively. A limitation

of this switch is that it operates from a maximum –5 V negative

supply, making bipolar operation more difficult. It is recom-

mended that amplifiers A1, A2 and A3 operate from the same

–5 V supply to minimize any potential latch-up problems.

Figure 26. A Ping-Pong Sample-and-Hold Amplifier

Figure 27. Settling Time Test Circuit