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 μs 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. The AD7821 has a built-in track-and-hold function capable of digitizing full-scale signals up to 100 kHz max. It also uses a half-flash conversion technique that eliminates the need to generate a CLK signal for the ADC. The AD7821 is designed with standard microprocessor control signals （CS， RD， WR， RDY， INT） and latched， three-state data outputs capable of interfacing to high speed data buses. An overflow output （OFL） is also provided for cascading devices to achieve higher resolution. The AD7821 is fabricated in Linear Compatible CMOS （LC2 MOS）， an advanced， mixed technology process combining precision bipolar circuits with low power CMOS logic. The part features a low power dissipation of 50 mW..