DIGITAL NON-INTEGER SAMPLE/HOLD IMPLEMENTED USING VIRTUAL FILTERING

摘要

A method and apparatus for implementing non-integer sample hold operations in a sigma-delta digital-to-analog converter system includes an interpolation filter, a polyphase filter circuit, and a modulator. The polyphase filter circuit is used to virtual upsample a digital input signal by a predetermined non-integer upsample ratio of a relatively large number. The polyphase filter circuit is formed of a long zero-order hold and a short FIR filter so that only several branches associated with the polyphase filter circuit corresponding to output samples immediately after a transition of the digital input signal is required to be calculated., thereby reducing the need to store a large number of filter coefficients and eliminating complex computations.