Re: filter designing
ananya.M,
Choice of active or passive is influenced by the frequency of interest. In general, low frequency filters are not practical, since inductors must be used (except for very simple filters). Inductors are physically quite large for low frequency filters. For very high frequency filters, op amps are not available that have sufficient bandwidth. In this case passive filters are the only choice. Of course, passive filters have the advantage that no power supply is required.
.
The order of the filter and filter type depend on the required performance. The performance is defined by the required passband attenuation, and stopband attenuation. For example, if you require a maximum passband attenuation of 1 db at a specified passband frequency, and a required attenuation of 20 db in the stopband at a specified frequency, these two parameters partially specify the performance. The selection of filter type depends on several additional requirements, such as:
. Is ripple allowed in the passband?
. Is ripple allowed in the stopband?
. Is phase linearity important?
"Electrical Networks and Filters" by G.H Tomlinson gives a good introduction to both passive and active filters. For a good beginners book on active filters, see Don Lancaster's "Active Filter Cookbook".
Regards,
Kral