A 20 Bit + Sign, Relay Switched D/A Converter

摘要

A multirange, 20-bit + sign, voltage output d/a converter is described. The converter exhibits less than 1 ppm (of full scale range) linearly error, and temperature coefficients of gain, offset and linearly of less than 0.5 ppm/C. The design is based on the R-2R ladder network in the current steering mode, using miniature latching relays with mercury wetted contacts for switching. Ten buffered, temperature-controlled unsaturated standard cells comprise the voltage reference. Techniques with design details are presented for minimizing errors due to relay thermal emf's, for implementing a self-calibration of linearity errors, and for obtaining optional coding formats. Calibration techniques are discussed and representative calibration data are presented.