ANALYSIS OF ACTIVE FILTERS
A filter circuit , as the name suggests, is one that allows certain frequency energy (sinusoids) to pass through while it attenuates (/blocks)sinusoids of other frequencies. Filter circuits can be classified into passive or active. A passive filter makes use of resistors and capacitors only whereas active filters have the additional advantage of an operational amplifer (such as the Op Amp).
Active filters can further be classified into:
(A). Low-Pass Filters : This is the type of filter circuit whose capacitor acts like an open at low frequencies and acts like a short at high frequency.It thus generally allows frequencies below a certain frequency to pass through while attenuating any higher frequency. The general function form is;
V_0/V_t =H_(0ω_0 )/(S+ω_0 ) , Or |V_0/V_i |=|H_0 |ω_0/√(ω^2+ω_0^2 )
A LOW-PASS FILTER
(B). High-Pass Filter/LowCut: In this type of filter circuit, the capacitor acts like a short at low frequencies and like an open at hig frequencies. Therefore allowing frequencies higher than a certain frequency to pass, attenuating the lower frequencies. The general function form being;
V_0/V_i =H_0 s/(s+ω_0 ) , Or |V_0/V_i |=|H_0 |ω/√(ω^2+ω_0^2 )
A HIGH-PASS FILTER
(C). BandPass Filter: It is a combination of the above to whereby, frequencies above a certain point are rejected an d frequencies below a certain point are also rejected.Only signals around some ceratain frequency pass. The bandwidth region can vary.
A SIMPLE BAND PASS FILTER
(D).Switched Capacitors Filter:This is a type active filter ‘that takes advantage of integration to achieve very accurate filter characteristics that are electronically tunable’.(Cheever).
REFERENCES
Cheever, Erik. Engineering Department Swarthmore College.
Frequency Response and Active Filters.
www.swarthmore.edu/NatSci/echeeve1/REf/FilterBkgrnd/Filters.html
[10.45 pm, 30 October 2012.]
