The AD7821 is a high speed, 8-bit, sampling, analog-to-digital converter that offers improved performance over the popular AD7820. It offers a conversion time of 660 ns (versus 1.36 s for the AD7820) and 100 kHz signal bandwidth (versus 6.4 kHz). The sampling instant is better defined and occurs on the falling edge of WR or RD. The provision of a VSS pin (Pin 19) allows the part to operate from 5 V supplies and to digitize bipolar input signals. Alternatively, for unipolar inputs, the VSS pin can be grounded and the AD7821 will operate from a single +5 V supply, like the AD7820.