![]() ![]() The calculation of this filter can be done by working on the frequency at which the capacitor reactance can equal the resistance of the resistor. This circuit has an effect when the frequency increases for enhancing the feedback level then the capacitor’s reactive impedance falls. The circuit of the low pass filter using op-amp uses a capacitor across the feedback resistor. The circuit diagram of the single pole or first order active low pass filter is shown below. First Order Active LPF Circuit using Op-Amp The applications of op-amp LPFs are used in different areas of power supplies to the outputs of DAC (Digital to Analog Converters) for eliminating alias signals as well as other applications. The feedback loop of an op-amp can be incorporated with the basic elements of a filter, so the high-performance LPFs are easily formed by using the required components except for inductors. Op-Amps or operational amplifiers supply very efficient low pass filters without using inductors. Generally, the frequency response of a low pass filter is signified with the help of a Bode plot, & this filter is distinguished with its cut-off frequency as well as the rate of frequency roll off Low Pass Filter Using Op Amp The low pass filter bode plot is shown below. This is a low pass filter of second order and the roll of is at -12 dB per octave. If frequency doubles output isc1/4th.(- 12 dB for every doubling of frequency or – 12 dB per octave). Output reduces (attenuates) inversely as the square of the frequency. Therefore transfer function is a second order equation. The second order low pass filter is shown in the figure. ![]()
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