Analog Filters, Software-Based FILTERS

Analog Filters, Software-Based and
Owing to the way that analog and digital filters are physicallyimplemented, an analog filter is inherently more size-andpower-efficient, although more component-sensitive, than itsdigital counterpart - if it can be implemented in astraightforward manner. In general, as signal frequencyincreases, the disparity in efficiency increases.Characteristics of applications where digital filters are moresize and power efficient than analog filters are: linear phase,very high stop band attenuation, very low pass band ripple;the filter’s response must be programmable or adaptive; thefilter must manipulate phase and, very low shape factors (adigital filter’s shape factor is the ratio of the filter’s pass bandwidth plus the filter’s transition band width to the filter’s passband width).
General-purpose digital signal microprocessors, nowcommodity devices, are used in a broad range ofapplications and can implement moderately complex digitalfilters in the audio frequency range. Many standard signalprocessing algorithms, including digital filters, are availablein software packages from digital signal processor and thirdparty vendors. As a result, software development costs aretrivial when amortized over production quantities.The architectures of digital signal microprocessors areusually optimized to perform a sum-of-products calculationwith data from RAM or ROM. They are not optimized for anyspecific DSP function.
However, to get extended samplingrate performance from a digital filter requires hardwaredesigned to perform the intended filter function at thedesired sampling frequencies.For example, Intersil Corporation offers a family of standarddigital filter products with several others in development.Some hardware-specific digital filters can now sample atrates approaching 75 Megasamples Per Second (MSPS).Higher performance is possible for high volume applicationsby limiting the range of parameters. Standard filter productsstrike a balance between optimized filter architectures andprogrammability by offering a line of configurable filters. Thatis, these products are function-specific, with optimizedarchitectures and programmable parameters.