Digital to analog conversion in microelectronics

This paper describes the design advantages and limitations of a hybrid digital-to-analog converter that is capable of a 12-bit resolution with an accuracy that is better than one-half the least significant bit. Through advances made in the research and applications of tantalum - nitride and nickel - chromium resistors, analog conversion systems can be designed to be compatible in size, weight, and power to monolithic digital and linear circuits. The system described here, also indicates why the hybrid circuit design is necessary for obtaining the accuracy required and where the monolithic design joins to optimize the characteristics of both fabrication methods. The basic elements that make up a digital-to-analog converter are the ladder network and the semiconductor switches. In order to produce output voltage steps that are accurate to +0.0122%, the tolerances and matching characteristics of tantalum - nitride resistors are required. It is also extremely vital to have an ideal switch having very low resistance to connect the reference voltage to the ladder. This requirement is best satisfied through the use of low offset chopper transistors and can presently be optimized only in hybrid form. Resolution and accuracy -- two of the most important requirements in digital-to-analog conversion, can be made presently available, only when the advantages of monolithic and hybrid technologies are joined under the conditions described in this paper.