However, although the voltage gain is unity the power gain is very high as its output impedance is much lower than its input impedance.
While this configuration provides good stability to the filter, its main disadvantage is that it has no voltage gain above one. The advantage of this configuration is that the op-amps high input impedance prevents excessive loading on the filters output while its low output impedance prevents the filters cut-off frequency point from being affected by changes in the impedance of the load. The amplifier is configured as a voltage-follower (Buffer) giving it a DC gain of one, Av = +1 or unity gain as opposed to the previous passive RC filter which has a DC gain of less than unity. This first-order low pass active filter, consists simply of a passive RC filter stage providing a low frequency path to the input of a non-inverting operational amplifier. The simplest form of a low pass active filter is to connect an inverting or non-inverting amplifier, the same as those discussed in the Op-amp tutorial, to the basic RC low pass filter circuit as shown. Its principle of operation and frequency response is exactly the same as those for the previously seen passive filter, the only difference this time is that it uses an op-amp for amplification and gain control. The most common and easily understood active filter is the Active Low Pass Filter. Still, active filters are generally much easier to design than passive filters, they produce good performance characteristics, very good accuracy with a steep roll-off and low noise when used with a good circuit design. Unlike a passive high pass filter which has in theory an infinite high frequency response, the maximum frequency response of an active filter is limited to the Gain/Bandwidth product (or open loop gain) of the operational amplifier being used. Then the main difference between a “passive filter” and an “active filter” is amplification.Īn active filter generally uses an operational amplifier (op-amp) within its design and in the Operational Amplifier tutorial we saw that an Op-amp has a high input impedance, a low output impedance and a voltage gain determined by the resistor network within its feedback loop. They draw their power from an external power source and use it to boost or amplify the output signal.įilter amplification can also be used to either shape or alter the frequency response of the filter circuit by producing a more selective output response, making the output bandwidth of the filter more narrower or even wider. One way of restoring or controlling this loss of signal is by using amplification through the use of Active Filters.Īs their name implies, Active Filters contain active components such as operational amplifiers, transistors or FET’s within their circuit design. With passive filter circuits containing multiple stages, this loss in signal amplitude called “Attenuation” can become quiet severe. The main disadvantage of passive filters is that the amplitude of the output signal is less than that of the input signal, ie, the gain is never greater than unity and that the load impedance affects the filters characteristics.
#Voltage follower op amp series
Active filters such as an active low pass filter, are filter circuits that use an operational amplifier (op-amp) as the their main amplifying device along with some resistors and capacitors to provide a filter like performance at low frequencies.īasic first-order passive filter circuits, such as a low pass or a high pass filter can be constructed using just a single resistor in series with a non-polarized capacitor connected across a sinusoidal input signal.
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