Method and apparatus for increasing effective resolution of analog output of digital-to-analog converter (dac) having predetermined digital word size, where dac drives plant

Abstract

In one embodiment, one or more less significant input bits (LSB's) of a digital-to-analog converter (DAC) are pulsed or otherwise modulated at a frequency substantially higher than the response cutoff frequency of a driven analog plant (e.g., a finely positioned mechanical table). The band pass characteristics of the driven analog plant convert the high frequency energy content of the pulses applied to the DAC's input into a smoothed response having a substantially lower frequency (e.g., an essentially DC response). By varying the duty cycle of the high frequency pulses, the system can be controlled to make it appear as if the DAC has a greater number of input bit nodes than it actually has. The analog plant can then be driven with finer resolution than that provided by the limited number of input bit nodes of the DAC.