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Tech Note |
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AN700: Digital Filtering Using XA Revision 0.11 |
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This report describes a method of implementation of FIR filters using Philips XA microcontroller. Appended with this application note is a generic routine that could be used to implement a N-point FIR filter.
The term “digital filter” refers to the computational process or algorithm by which a digital signal or sequence of numbers (acting as input) is transformed into a second sequence of numbers termed the output digital signal. Digital filters involve signals in the digital domain (discrete-time signals) and are used extensively in applications such as digital image processing, pattern recognition, and spectral analysis.
Digital Signal Processing (DSP) is concerned with the representation of signals (and information they contain) by sequences of numbers and with the transformation or processing of such signal representations by numeric computational procedures. In order to be considered a DSP microcontroller, a part must be able to quickly multiply two values, and add the result to an accumulator register. this is a minimum requirement. “Quickly” implies MAC (Multiply and Accumulate). Typically, the multiply and accumulate path operates on 16-bit values with a 32-bit result. Figure 1 shows a typical Digital Signal Processing hardware used in digital filtering. Although XA currently does not have a hardware MAC unit, it is quite suitable for some DSP applications, due to its relatively high computational power, and high I/O throughput. This application note is intended to demonstrate such DSP power of the XA through implementation of FIR and IIR digital filters. It is to be noted, though, that this application note is not intended as a learning tool for DSP. It is assumed that the reader is familiar with DSP and filtering basics.
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