Sampling rate conversion in digital signal processing

Multirate processing, sampling rate conversion, or interpolation and decimation as it is known, is a clever technique in DSP. As analog and mixed signal design engineers we have learned to use this technique in various product designs for our customers. It offers an added degree of freedom in the design of mixed signal integrated circuits that may be of help to other professionals such as us.

Multirate processing finds use in signal processing systems where various sub-systems with differing sample or clock rates need to be interfaced together. At other times multirate processing is used to reduce computational overhead of a system. For example, an algorithm requires k operations to be completed per cycle. By reducing the sample rate of a signal or system by a factor of M, the arithmetic bandwidth requirements are reduced from kfs operations to kfs/M operations per second. fs is the sampling rate. M is the decimation factor.

In other applications, resampling a signal at a lower rate will allow it to pass through a channel of limited bandwidth. In another application a high accuracy delta-sigma A/D converter can be made with very high modulation rate at the front end followed by a decimator ( down converter) to reduce the sampling rate and provide converted samples at or near the Nyquist rate.

Applications for this technique abound, if understood by the practitioner. The challenge is that it is not easy to pick up a book or a paper on DSP and understand Decimation and Interpolation to an intuitive extent. This causes hesitation in usage.

A tutorial paper has been written to aid in further understanding of this fascinating topic. Read it at http://www.signalpro.biz/sampling_rate_conv.pdf.