Low Pass vs High Pass Filter | Explanation and Comparison

The frequency range that low pass vs high pass filter pass is the most significant distinction between them.

When we talk about a high pass filter, we’re talking about a circuit that allows high frequencies to flow through while blocking low frequencies.

Low pass filter, on the other hand, is an electrical circuit that allows low-frequency signals to flow through while blocking high-frequency signals.

You could be wondering which frequency range is high and which is low. Cut-off frequency is a word used to describe filters that presume a threshold value.

What is a Filter

Filters are electronic circuits that eliminate a portion of an AC signal. A capacitor filter is one type of filters.

A low pass filter allows signals lower than a cut-off frequency to pass, whereas a high pass filter allows signals higher than a cut-off frequency to pass.

The frequency of the cutoff is governed by the circuit’s components.

It’s critical to understand that filters don’t generate signals or modify the frequency of an object. A high-pass filter, for example, cannot produce the high frequencies that it outputs.

Instead, the input waveform has a mix of high and low frequencies, with the low frequencies being blocked by the high-pass filter.

Active filters have amplifiers that increase the filter’s output, giving the impression that the filter is creating a signal that didn’t exist in the input waveform.

However, in the filter circuit, unwanted frequencies are filtered away, while desired frequencies are amplified.

Attenuation is the process of removing undesirable frequencies. High frequencies are primarily attenuated by a low pass filter, while low frequencies are mostly attenuated by a high pass filter.

A combination of a resistor and a capacitor is used in both low pass and high pass filters. Both resistors and capacitors contribute to the circuit’s overall impedance in an AC circuit.

Resistors, much like in DC circuits, contribute resistance. The capacitive reactance of capacitors is dependent on the frequency of the incoming AC signal. The sum of the resistance and reactance is the total impedance.

Low Pass vs High Pass Filter Definition

Signals with frequencies above this cut-off frequency have low reactance, whereas signals with frequencies below this cut-off frequency have high reactance.

The low pass filter has a low reactance to signals with frequencies below the cut-off frequency, allowing low frequencies to pass, but a high reactance to high-frequency signals, preventing them from passing.

Let’s start with the filter’s components before moving on to the filter’s operational mechanism. Electronic components such as a resistor, capacitor, amplifier, and others are required for creating a filter, whether it is a high pass filter (HPF) or a low pass filter (LPF).

The important thing to remember here is that if you use passive components like a resistor or a capacitor, the resulting filter is referred to as a passive filter. If you want to use the amplifier in your filter circuit to boost the gain of the filtered signal, you’re constructing an active filter.

So far, we’ve looked at the key differences between high-pass and low-pass filters, as well as the components that determine whether they’re active or passive. Let’s look at some more noteworthy distinctions using a comparison chart.

What is Cutoff Frequency

Both low pass and high pass filters use a resistor and a capacitor combination. In an AC circuit, both resistors and capacitors contribute to the overall impedance.

Resistance is provided by resistors, just as it is in DC circuits. The frequency of the incoming AC signal affects the capacitive reactance of capacitors. Total impedance is the sum of resistance and reactance.

Because capacitive reactance is proportional to the frequency of the signal, filters can be built to raise reactance considerably above or below the cut-off frequency.

The reactance of a low-pass filter will increase above the cut-off frequency, with little or no reactance below the cut-off frequency.

A high pass filter will be designed to boost reactance below the cut-off frequency while having little or no reactance above it.

What is Low Pass Filter

In a low pass filter, the capacitor and resistor positions are switched around to get the desired output. When the input signal is applied to a low pass filter circuit, the resistance acts as a constant blockage, but the output signal is affected by the position of the capacitor.

low pass vs high pass filter 1

If a high-frequency signal is placed into a low-pass circuit, it will pass through resistance, which will provide the usual resistance, but the capacitor will provide zero resistance. This is because the capacitor’s resistance to high-frequency signals is zero, but its resistance to low-frequency signals is unlimited.

Any frequency component over the cut-off frequency would be blocked by an ideal low pass filter, however low pass filters aren’t perfect.

Both high and low pass filters employ a resistor and capacitor combination, although the order is inverted in each. The input signal is supplied directly to the resistor in a low pass filter, and the output is monitored across the capacitor:

low pass vs high pass filter 2

The circuit design clearly shows that if a high-frequency signal hits the low pass filter circuit, the capacitor will allow it to pass and the signal will be sent to ground. The output voltage obtained in this case is zero since the full voltage is transmitted to ground.

However, if a low-frequency signal enters a low-pass filter circuit, the output will be generated because the resistance will supply the same obstruction as a high-frequency signal, but the capacitor will provide infinite resistance.

As a result, the signal cannot pass through the capacitor circuit in this situation. As a result, the output terminal receives the complete low-frequency signal.

The low pass filter’s properties are determined by the interaction of capacitive reactance and resistance, both of which contribute to the overall impedance.

The resistor’s contribution to impedance (i.e. resistance) is unaffected by frequency, but capacitive reactance is inversely proportional to frequency.

The capacitive reactance is high at low frequencies and low at high frequencies, and this value can be expressed with the equation below,

    \begin{align*}X_c=\frac{1}{\omega C}=\frac{1}{2\pi fC}\end{align*}

Where:

XC = reactance of the circuit
f = cutoff frequency
C = capacitance of the capacitor

The capacitive reactance and its effect on the voltage drop across the capacitor, which is the output voltage, is a simple way to think about low pass filters.

The capacitive reactance is low at high frequencies. The capacitor permits the signal to travel to ground without causing a large voltage drop across it.

The capacitive reactance is high at low frequencies, though, and the capacitor has a significant voltage drop across it. A higher voltage drop indicates a higher circuit output voltage.

Read also : types of capacitors

What is High Pass Filter

A high pass filter attenuates low frequencies preferentially, allowing high frequencies to pass while low frequencies are blocked.

Only high-frequency signals pass through a high pass filter, which attenuates low-frequency signals. Although it attenuates high-frequency signals as well, the attenuation factor is so minimal that it can be overlooked.

low pass vs high pass filter 3

You’re probably wondering what goes into the design of a High Flow filter, what makes it enable high-frequency signals to pass through while blocking low-frequency sounds. The characteristics of the capacitor and resistor can be used to achieve this.

The input signals are applied to the capacitor, and the output voltage is acquired by measuring the voltage across the resistor. The resistance of the resistor and the resistance of the capacitor are referred to as reactance.

Any frequency component below the cut-off frequency would be blocked by an ideal high pass filter, however high pass filters aren’t perfect.

Both high and low pass filters employ a resistor and capacitor combination, although the order is inverted in each. The input signal is supplied directly to the capacitor in a high pass filter, and the output is monitored across the resistor:

low pass vs high pass filter 4

The role of capacitive reactance and resistance, which both contribute to total impedance, determines the characteristics of the high pass filter.

The resistor’s contribution to impedance (i.e. resistance) is unaffected by frequency, but capacitive reactance is inversely proportional to frequency.

The capacitive reactance is high at low frequencies and low at high frequencies, and this value can be expressed with the equation below,

    \begin{align*}X_c=\frac{1}{\omega C}=\frac{1}{2\pi fC}\end{align*}

The reactance is inversely proportional to the cutoff frequency, as shown in the preceding equation. When the frequency of the input signal is high, the reactance will be reduced. However, if the signal’s frequency is low, the reactance will be large.

The capacitive reactance and its effect on the voltage drop across the resistor are an easy way to think about high pass filters.

The capacitive reactance is large at low frequencies, and the capacitor has a significant voltage drop across it. As a result, the majority of the voltage drop happens across the capacitor, leaving only a little voltage loss across the resistor.

The capacitive reactance is low at high frequencies. As a result, the resistor has the majority of voltage drop, resulting in a large output voltage at high frequencies.

I hope you now understand why a high pass filter allows high frequencies to flow through while preventing low frequencies from passing through.

Low Pass vs High Pass Filter Table Comparison

Below is the table comparison for low pass vs high pass filter.

low pass vs high pass filter table

Low Pass vs High Pass Filter : What’s the Difference?

  1. The main difference between a high pass and a low pass filter is that the former passes signals with frequencies higher than the cutoff frequency, whereas the latter passes signals with frequencies lower than the cutoff frequency.
  2. The circuit design of the high pass and low pass filters differs as well; the high pass filter has a capacitor followed by resistance in parallel. The low pass filter circuit is made up of a resistor and a capacitor.
  3. The low pass filter is employed as an anti-aliasing filter, whereas the high pass filter is used in audio amplifiers to remove distortions caused by low-frequency signals like noise.

Conclusion

Because they use passive components, the high pass and low pass filters we explained previously are passive filters. When we include amplifiers in the filter circuit to boost the signal’s gain, the filter becomes an active filter.

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