Operational amplifier high pass filter
-a summary of operational amplifier or op-amp active high pass filter
circuitry
Operational amplifiers lend themselves to being used for
active filter circuits, including a high pass filter circuit. Using a few
components they are able to provide high levels of performance.
The simplest circuit high pass filter circuit using an
operational amplifier can be achieved by placing a capacitor in series with one
of the resistors in the amplifier circuit as shown. The capacitor reactance
increases as the frequency falls, and as a result this forms a CR low pass
filter providing a roll off of 6 dB per octave. The cut off frequency or break
point of the filter can be calculated very easily by working out the frequency
at which the reactance of the capacitor equals the resistance of the resistor.
This can be achieved using the formula:
Xc = 2 pi f C
where:
Xc is the capacitive reactance in ohms
pi is the greek letter and equal to 3.142
f is the frequency in Hertz
C is the capacitance in Farads
Operational amplifier circuits with low frequency roll
off
Two pole low pass filter
Although it is possible to design a wide variety of filters with different
levels of gain and different roll off patterns using operational amplifiers, the
filter described on this page will give a good sure-fire solution. It offers
unity gain and a Butterworth response (the flattest response in band, but not
the fastest to achieve ultimate roll off out of band).
Operational amplifier two pole high pass filter
Simple sure fire design with Butterworth response and unity gain
The calculations for the circuit values are very
straightforward for the Butterworth response and unity gain scenario. Critical
damping is required for the circuit and the ratio of the resistor vales
determines this.
When choosing the values, ensure that the resistor values
fall in the region between 10 k ohms and 100 k ohms. This is advisable because
the output impedance of the circuit rises with increasing frequency and values
outside this region may affect he performance.
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