A 12-Mc, Nine-Bit Digital Function Generator

This paper describes some developed equipment found very useful in evaluating circuits that require digital inputs. For example, D-A converters are generally tested by using their associated A-D converter as a test-signal source. Since the A-D converter itself introduces errors, the measurement of analog input and output indicates over-all performance but not individual converter performance. The digital function generator allows separate evaluation of D-A converters by synthesizing useful test functions from discrete samples. Comparison of the known input with the output gives an accurate performance check. The present equipment generates up to sixteen different samples, represented by nine-bit words in parallel form, at a word rate of 12 Mc. A discussion of useful test functions for determining D-A converter linearity and transient response will include discussion of digital sine waves, ramps, and step functions. Although D-A converter evaluation is stressed, the equipment is also useful for other tasks.