High Pass Filter Calculator
Table of contents
How do I use the highpass filter calculator?What is a highpass filter?Different highpass filters — passive vs. active highpass filtersRC highpass filterRL highpass filterInverting opamp highpass filterNoninverting opamp highpassfilterFAQsWelcome to the high pass filter calculator. If you want to remove some lowfrequency noise or you're trying to get more treble, you've come to the right place. Together, we'll learn:
 What a highpass filter is;
 The different types of highpass filter circuits;
 Passive highpass filters and active highpass filters;
 How to tell highpass and lowpass filters apart; and
 How capacitors can be used in highpass filters.
How do I use the highpass filter calculator?
Using the highpass filter calculator is easy! Here's how:

Select the filter type you're designing. The highpass filter calculator covers the following filter types:

RC highpass filter;

RL highpass filter;

Noninverting opamp highpass filter; and

Inverting opamp highpass filter.


Input the values for which you are designing. The passive RC and RL filters (both RLC circuits) let you finetune the component values and the desired cutoff frequency, while the active (opamp) filters also let you adjust the gain on your output.
Keep reading if you want to learn how they work!
💡 The highpass filter calculator lets you enter whatever values you know, and it will calculate the other values for you. It adjusts its equations according to your choice of filter type.
What is a highpass filter?
A highpass filter is an electronic circuit that removes lowfrequency components from a given AC signal. In other words, it blocks low frequencies and lets high frequencies pass through it. That's why we call it a "highpass filter".
What does this mean in practice? Take a look at the Bode plot for highpass filters below.
A Bode plot (like the one above) illustrates a circuit's frequency response, which is another word for how it amplifies signals of certain frequencies and damps others. A highpass filter's frequency response suppresses lowfrequency signals, which we can see all the way up to $f = f_c$. That frequency is called the cutoff frequency, and it's what defines any highpass filter:
 Frequencies below $f_c$ are damped; and
 Frequencies above $f_c$ are left untouched.
💡 The Bode plot above has two lines, one representing ideal theoretical filter behavior and the other representing realworld filter behavior. Ideal filters would slope straight down at $f_c$. For realworld filters, the cutoff frequency is the frequency at which a signal is damped to $3\ \text{dB}$.
The slope at which the frequency response drops for increasingly low frequencies is $20\ \text{dB}/\text{decade}$. This means that every time the frequency is reduced by a factor of 10, the amplitude is reduced by 20 decibels. This slope is made even steeper if the order of the filter is increased: firstorder filters have a 20decibel slope, secondorder filters slope at 40 decibels, thirdorder descends at 60, etc.
Realworld signals rarely consist of just one frequency, and that's partly why we need highpass filters in signalhandling circuits. Here's how a highpass filter affects signals comprised of more than one frequency:
Different highpass filters — passive vs. active highpass filters
There are two main categories of highpass filters:
 Passive highpass filters exclusively use passive components (which are resistors, capacitors and inductors). The two common passive highpass filters are RC highpass filters and RL highpass filters.
 Active highpass filters use some active component, typically an operational amplifier (or "opamp"). Thanks to their adjustable gains, they can be modified more than passive filters.
RC highpass filter
The RC highpass filter consists of a resistor and a capacitor in the configuration shown below.
It's probably the most wellknown yet basic highpass filter, partly thanks to the easy formula for its cutoff frequency:
The RC highpass filter works thanks to its capacitor. A capacitor's impedance $Z_c$ decreases with frequency, making it act like a shortcircuit for highfrequency signals. Inversely, a capacitor acts as an open circuit for low frequencies.
where $j$ is the unit imaginary number.
Thanks to this frequencydependent impedance, we can use capacitors for highpass filters.
💡 Engineers frequently bridge their constant voltage rails to ground with capacitors, which act as highpass filters and remove any shakiness in the voltage supply.
RL highpass filter
The RL highpass filter uses an inductor and a resistor in the configuration below:
Its cutoff frequency is also very simple to calculate:
An inductor $L$ acts the opposite way a capacitor does: An inductor becomes a shortcircuit for lowfrequency signals and an open circuit for high frequencies. Because of this, any lowfrequency components of $v_\text{in}$ pass through the inductor, but highfrequency components are blocked. Instead, highfrequency components must travel through the load at $v_\text{out}$ instead. Here is the equation for the impedance of an inductor:
Inverting opamp highpass filter
The inverting opamp highpass filter is an active filter that incorporates an operational amplifier (opamp). The opamp feeds back into itself with the feedback resistor $R_f$, with the highpass filtering performed by the capacitor $C$. It's designed as follows:
Its cutoff frequency is calculated much like the RC filter's but with the feedback resistor $R_f$.
And the gain $G$ introduced by the opamp is calculated with
See that minus sign in the equation for $G$? It means that we're flipping the signal around the timeaxis, or in more technical terms, we're introducing a 180° phase shift. If this behavior is undesirable, then head on over to the next section on NONinverting opamp highpass filters.
Noninverting opamp highpassfilter
The noninverting opamp highpass filter is more complicated than its inverting sibling, but it has the useful property of not inverting the input. We connect an RC highpass filter to the negative input of the opamp and create a feedback loop between the opamp's output $v_\text{out}$ and the opamp's positive input. See its circuit diagram below:
Because the only filtering is done by the passive RC circuit at $v_\text{in}$, we can calculate the filter's cutoff frequency by:
And we can calculate $G$ (the gain from $v_\text{in}$ to $v_\text{out}$) with:
Note that $G$ is positive, but also that $G \ge 1$, as resistance can never be negative.
What components do I need for a 1 kHz highpass filter?
To build an RC highpass filter with a cutoff frequency of 1 kHz, use a 3.3kΩ resistor and a 47nF capacitor. Such a highpass filter circuit will have a cutoff frequency of precisely.
f_{c} = 1 / (2π × 3.3 kΩ × 47 nF) = 1.0261 kHz
Remember to keep components' tolerances in mind — consider measuring them with a multimeter!
How do I tell a highpass filter from a lowpass filter?
You can differentiate highpass vs. lowpass filters in a few ways.
 Analyze the circuit. Using techniques like Laplacian transformation, calculate the frequencydependent impedance of each component and determine the filter's frequency response.
 Test it with signals. Feed waveforms of varying frequencies to the circuit and monitor the amplitudes at the outputs.
 Compare the circuit to known filter layouts. If you see your circuit matches a wellknown filter design, you can guess what filter type it is.
How do I build a highpass filter?
To build a highpass filter, follow these easy steps:
 Select a suitable filter type (RC, RL, opamp, etc.).
 Determine your desired cutoff frequency, f_{c}.
 Calculate the components' values based on the above choices. The equations are dependent on the filter type you selected.
If you need more help, come to omnicalculator.com's highpass filter calculator!