Calculate the cutoff frequency of a passive RC high-pass filter.Real component tolerance (±5-10%) will shift cutoff frequency slightly.
A high-pass filter is an electronic filter that passes signals with a frequency higher than a certain cutoff frequency and attenuates signals with frequencies lower than the cutoff frequency.
In a simple RC (Resistor-Capacitor) high-pass filter, the capacitor is placed in series with the signal source, and the resistor is placed in parallel with the output.
Design a high-pass filter with 1 kHz cutoff frequency:
High-pass filters allow high frequencies through and block low frequencies. Low-pass filters do the opposite—they block high frequencies and allow low frequencies through. Their formulas are identical, but the application and component placement differ.
At the cutoff frequency, the filter's output power is reduced to 50% of the input power (a -3dB attenuation). It's the point where the circuit begins to significantly filter the signal and is the standard definition for cutoff frequency.
You can choose either R or C and calculate the other. For practical circuits: use standard resistor values (1k, 10k, 100k), then calculate the required capacitor. Standard capacitor values are easier to find, so this approach works well for most designs.
Yes, high-pass filters effectively remove DC (0 Hz). Since DC has zero frequency, it's well below any practical cutoff frequency and will be almost completely blocked, allowing only AC signals through.
Real components have tolerances (typically ±5-20%). Your actual cutoff frequency will vary by the product of component tolerances. Use higher-quality components if precise cutoff frequency is critical.
This calculator covers passive filters (R and C only). Passive filters don't require power and simplify circuit design, but they provide first-order (20dB/decade) rolloff. Active filters using op-amps can achieve steeper rolloff and gain.
Above cutoff, the filter still attenuates slightly (+20dB/decade for passive), but the effect diminishes. Your signal isn't fully passed; there's still attenuation, just less than below cutoff. Steeper filters (active or higher-order) improve this.
Yes, you can connect multiple high-pass filters in series to increase rolloff steepness (from 20dB/decade per stage) and achieve sharper frequency response. However, cascading increases component count and can introduce phase shift.