Hello dear readers!

Here I am again to guide you in creating and designing a simple active low pass filter using passive components, resistor and a capacitor and one active component, the op-amp. I will also include some applications and significance of this topic to our technology today.

I will begin this topic with a little introduction of a filter

What is a filter?

A filter is a circuit that passes certain frequencies and attenuates or rejects all other frequencies.
The pass band of a filter is the range of frequencies that are allowed to pass through the filter with minimum attenuation (usually defined as less than of attenuation).

The critical frequency, (also called the cutoff frequency) defines the end of the passband and is normally specified at the point where the response drops (70.7%) from the passband response.

What is a low pass filter?

A low-pass filter is one that passes frequencies from dc to and significantly attenuates all other frequencies. The response drops to zero at frequencies beyond the pass band.

This ideal response is sometimes referred to as a “brick-wall” because nothing gets through beyond the wall. The bandwidth of an ideal low-pass filter is equal to the critical frequency.

For example, we have a cut off frequency of 20Khz, all the frequency below this cut off frequency can pass through, while frequency above 20Khz cannot.

What is an Active Filters?

Filters that include one or more op-amps in the design are called active filters. These filters can optimize the roll-off rate or other attribute (such as phase response) with a particular filter design.

In general, the more poles the filter uses, the steeper its transition region will be. The exact response depends on the type of filter and the number of poles.

The critical frequency of a low-pass RC filter occurs when Xc = R where fc =1/2pRC

How it works

The op-amp provides gain, so the signal is not attenuated as it passes through the filter.
The high input impedance of the op-amp prevents excessive loading of the driving source, and the low output impedance of the op-amp prevents the filter from being affected by the load that it is driving.

Active filters are also easy to adjust over a wide frequency range without altering the desired response.

Components needed for the circuit

♦ op-amp
♦ resistor
♦ capacitor
♦ oscilloscope (output)
♦ signal generator (input)

I already give a short description for the components in my last tutorial. Feel free to read those tutorial.

Construction of the circuit in the QUCS circuit simulator

1. Open the QUCS simulator

2. Click components menu. Then select all the necessary components needed.

3. Search of components. Then place it in the circuit area.

We need 3 resistors, 1 capacitor and 1 op-amp for our ciruit.

Arrange each component.

4. Now we can connect our circuit. Click the wire icon above.

Explanation of the circuit

Our circuit is composed of two circuits, one is the RC filter and the other is the non-inverting amplifier. In the figure below, it is the low pass filter in which the input signal is being connected. As the signal passes through the RC filter, the unwanted signal will be filtered out. The output of this filter is then fed to the non-inverting input of the op-amp.

The figure below is the non-inverting amplifier part of this active low pass.

If you noticed the circuit construction, we can conclude that it is called active low pass filter because the filtered signal is being amplified by an active component, the op-amp. It is necessary to amplify the filtered signal to have a better transmission or reception.

The output signal that can be display in the oscilloscope when it is connected to the output of the non-inverting amplifier will look like this below.

Significance of a filter to the field of communication

In the field of communication, it is necessary to have filters to filter out the unwanted signals that could mix into the desired signal as it travels in the air. This signal is then amplified to get a better and clear signal.

Thanks for the time everyone!

Hope you learn from it.

Yours Truly,

@rfece143

---

Posted on Utopian.io - Rewarding Open Source Contributors

---