Filters Page
Making a Filter.
Here there is a coverage of the filter types that have been employed for different projects. Digital, analogue, passive, RF, microwave. It is intended as a practical pass through of different design approaches , not a theoretical filter design course. See Tools site for filter designs
FIR (Finite Impulse Response) Filter
A pure digital filter with many variants, commonly programmed into a DSP. Some DSP (see Analogue Devices, Sharc series) have hardware FIR co-processors which allow the burden of a FIR filter calculation to be off-loaded from the main DSP software flow. However all professional DSP incorporate specific commands to carry out the basic FIR filter calculation to be carried out in one clock cycle. However digital filters are non-monotonic in that the frequency response repeats at multiples of the sample frequency.
Here there is a multiplication, addition, and recovery of 2 pieces of data all in one clock cycle.
IIR (Infinite Impulse Response) Filter
A pure digital filter, commonly programmmed into a DSP. Some DSP (see Analogue Devices, Sharc series) have hardware FIR co-processors which allow the burden of a IIR filter calculation to be off-loaded from the main DSP software flow. Commonly derived from passive formats the IIR is a digital synthesis of a passive prototype.
Passive Filters
The classical LC filters with resistive terminations. Can be used to generate IIR prototypes or active filter prototypes. Nowadays the inherent loss in filters can be circumvented by incorporating op-amps. The toolbox site has a number passive filter design tools.
Microwave Filters
The microwave filter is a special passive filter that differs by the use of distrubuted components (ie: components that comport differently with frequency change). The toolbox site has a number passive filter design tools orientated to distributed filters.