High Pass Filter Calculator

A high-pass filter passes rapidly changing signals while reducing low-frequency components and direct current. It is used to remove sensor drift, block DC between amplifier stages, reduce rumble, shape audio, and separate frequency bands in communication systems. This calculator models first-order passive RC and RL networks. It reports cutoff frequency and the ideal sinusoidal response at a selected input frequency, making component choices and frequency behavior easy to compare. An RC high-pass filter commonly places a capacitor in series with the signal and a resistor from the output to the reference node. Its cutoff frequency is one divided by two pi times resistance times capacitance. An RL high-pass can take output across the inductor in a series resistor-inductor circuit, giving cutoff resistance divided by two pi times inductance. The calculator converts microfarads and millihenries to base SI units before applying those relationships. Frequency response depends on the ratio of input frequency to cutoff. Ideal voltage gain is that ratio divided by the square root of one plus the ratio squared. At cutoff, gain is about 0.707 and the decibel response is minus 3.01 decibels. Well below cutoff, gain approaches zero and low-frequency content is strongly attenuated. Well above cutoff, gain approaches one and the output closely follows the input. Gain in decibels is twenty times the base-ten logarithm of voltage gain. The output leads the input in phase for this ideal high-pass transfer convention. Phase approaches ninety degrees far below cutoff, equals forty-five degrees at cutoff, and approaches zero at high frequency. Actual polarity and measured phase also depend on exactly where output is observed and how the network is connected. Source impedance and load impedance effectively modify the component values and must be included when they are not negligible. Real capacitors have tolerance, leakage, equivalent series resistance, and parasitic inductance. Real inductors have winding resistance, core loss, parasitic capacitance, and a self-resonant frequency. These effects can make the simple model inaccurate at frequency extremes. Use this result for first-pass selection, then include source and load impedances, component tolerances, and operating limits in a complete circuit analysis. Verify important designs with simulation and bench measurement, especially in radio-frequency, precision measurement, or safety-critical applications.