The gain in dB is given as 20log (A max) = 20log (10) = 20 dB Assume that at low frequencies this circuit has a voltage gain of 10. Let us consider a non-inverting active low pass filter having cut off frequency at 160 Hz and input impedance as 15kΩ. Magnitude of the voltage Gain= Active Low Pass Filter Example We know that, for non-inverting amplifier circuit the magnitude of the voltage gain is obtained by its feedback resistor R 2 divided by its corresponding input resistor R 3. By this filter circuit, the output signal amplitude is increased by the pass band gain of the filter. When the input signals are at low frequencies the signals will pass through the amplifying circuit directly, but if the input frequency is high the signals are passed through the capacitor C1. Thus,we use below circuit to provide high voltage gain. The above active low pass filter circuit does not provide more than unity gain. Active Low Pass Filter with High Voltage Gain Even for this circuit also the output power is high since the input impedance is low. The main drawback of this configuration is voltage gain is unity. This circuit will provide high stability to filter. The output impedance of the op-amp which is connected in the circuit is always low.
Even though the input impedance of the op-amps high below the cut-off frequency, this input impedance is limited by the series impedance which is equal to R+ 1⁄jωC. This circuit has more input impedance value. The amplifier acts as a buffer circuit providing unity gain output. This RC circuit will provide a low frequency path to the input of the amplifier. A simple RC Passive Filter connected to the non-inverting terminal of an operational amplifier is shown below. A Passive Low Pass Filter connected to either inverting or non-inverting op-amp gives us a simple Active Low Pass Filter.įirst order active filter is formed by a single op-amp with RC circuit. In order to overcome this disadvantage of passive filter, active filter is designed. the amplitude of the output signal is lesser than amplitude of the input signal in the passive circuit. The maximum frequency response of the filter depends on the amplifier used in the circuit design. The amplifier component in this filter circuit will increase the output signal’s amplitude.īy this action of the amplifier, the output signal will become wider or narrower. The operational amplifier will take the high impedance signal as input and gives a low impedance signal as output. Active filters are introduced to overcome the defects of passive filters.Ī simple active low pass filter is formed by using an op-amp. These filters are very effective when compared with the passive filters. Rather than using the passive components alone, the Active Low Pass Filter is formed by active components like Op-Amps, FETs and transistors in combination with Passive Components. So this filter is also called as high-cut filter or treble cut filter. Stop band region means the area where the attenuation occurs mostly to the input signals. Transition region means the area where falloff occurs. Practically the signal will not drop suddenly but drops gradually from transition region to the stop band region.Ĭut-off frequency means the point where the response drops -3 dB or 70.7% from the pass band. In ideal case, the frequency response curve drops at the cut-off frequency.
Low Pass filter is a filter which passes all frequencies from DC to upper cut-off frequency fH and rejects any signals above this frequency.
Applications Of Active Low Pass Filters.Active Low Pass Filter with High Voltage Gain.