Patent ID: 7283076

Claim:
A sigma-delta digital-to-analog converter system for performing a non-integer sample rate conversion, comprising: an interpolation filter having an input to receive a digital input signal with a first sampling rate and to generate a digital output signal with a second sampling rate on its output, said second sampling rate being increased by a predetermined upsampling integer; a polyphase filter circuit coupled to the output of said interpolation filter and being used to upsample the digital output signal with the second sampling rate by a predetermined non-integer upsample ratio of a relatively large number so as to produce a third sampling rate; a modulator coupled to receive the digital output signal with the third sampling rate from said polyphase filter circuit and to generate a digital signal having the third sampling rate with the non-integer upsampling rate such that quantization noise is moved substantially beyond the band of the digital input signal; and said polyphase filter circuit being formed of a long zero-order hold and a short FIR filter so that only several branches associated with said polyphase filter circuit corresponding to output samples immediately after a transition of the digital input signal is required to be calculated.