CMOS Microprocessor-Compatible 12-Bit A/D Converter

The ADC912A is a monolithic 12-bit accurate CMOS A/D converter. It contains a complete successive-approximation A/D converter built with a high-accuracy D/A converter, a precision bipolar transistor high-speed comparator, and successive-approximation logic including three-state bus interface for logic compatibility.

The accuracy of the ADC912A results from the addition of precision bipolar transistors to Analog Devices' advanced-oxide isolated silicon-gate CMOS process. Particular attention was paid to the reduction of transition noise between adjacent codes achieving a 1/6 LSB uncertainty. The low noise design produces the same digital output for dc analog inputs not located at a transition voltage. NPN digital output transistors provide excellent bus interface timing, 125 ns access and bus disconnect time which results in faster data transfer without the need for wait states. An external 1.25 MHz clock provides a 10 µs conversion time.

In stand-alone applications, an internal clock can be used with external crystal.

An external negative five-volt reference sets the 0 V to 10 V input range. Plus 5 V and minus 12 V power supplies result in 95 mW of total power consumption.

* Low Cost * Low Transition Noise between Code * 12-Bit Accurate ±1/2 LSB Nonlinearity Error over Temperature No Missing Codes At All Temperatures * 10µ Conversion Time * Internal or External Clock