Tiefpass- / Hochpassfilter-Rechner
-3 dB Grenzfrequenz für RC- und RL-Filter
Required Parameters
Waiting for input data...
Quick Answer
The -3dB cutoff frequency (fc) is where the signal power drops by half. For RC filters: fc = 1 / (2πRC). For RL filters: fc = R / (2πL).
High Pass Filter Calculator
Design a first-order passive high-pass filter and compute the -3 dB cutoff frequency from resistor and capacitor (or inductor) values — or enter any two of R, C, L, fc to solve for the third.
Quick start: Select RC High Pass, enter R and C → instant fc. 10 kΩ and 0.1 µF → ≈ 159 Hz. Switch Target Variable to find C for a desired cutoff.
RC high pass filter formula
fc = 1 / (2π × R × C)
| Symbol | Meaning |
|---|---|
| fc | Cutoff frequency (Hz) — -3 dB point |
| R | Resistance (Ω) |
| C | Capacitance (F) |
Rearranged:
- C = 1 / (2π fc R) — pick C when you know target fc and R
- R = 1 / (2π fc C) — pick R when fc and C are fixed
Time constant: τ = RC = 1 / (2π fc)
A series capacitor and shunt resistor is the usual RC high-pass. DC is blocked; frequencies above fc pass.
RL high pass filter formula
fc = R / (2π × L)
Use RL when an inductor is already in the path (power or RF). Capacitors dominate most signal-level designs because they are smaller and cheaper.
What a high pass filter does
A high-pass filter passes frequencies above fc and attenuates those below, including DC. Below fc, a first-order high-pass rises at +20 dB per decade. Applications:
- DC blocking / AC coupling into an amplifier or ADC
- Audio rumble / thump removal
- Sensor high-side conditioning (kill offset and 1/f)
- Break frequency design on a Bode plot — another name for fc
Worked example — 1 kHz RC high pass
Target fc = 1 kHz, choose R = 3.3 kΩ:
- C = 1 / (2π × 1000 × 3300) ≈ 48.2 nF
- Nearest E12: 47 nF → actual fc ≈ 1.03 kHz
- Use C0G/NP0 ceramics; Y5V parts shift badly with bias
Use Target Variable → Find capacitance (C) with R = 3.3 kΩ and fc = 1 kHz.
High-pass vs low-pass
| Type | Passes | Blocks | Slope (1st order) |
|---|---|---|---|
| High-pass | Above fc | Below fc (incl. DC) | +20 dB/decade below fc |
| Low-pass | Below fc | Above fc | −20 dB/decade above fc |
Same fc = 1/(2πRC) formula — only the capacitor/resistor placement changes. Need the other topology? Use the low pass filter calculator.
Common mistakes
- Reading fc as a brick wall — first-order filters roll off gently; expect ±20 dB/decade, not instant blocking.
- Ignoring source impedance — if the driver already has 10 kΩ output Z, your effective R is higher than the printed resistor.
- Y5V/Z5U capacitors — capacitance can collapse under DC bias; cutoff shifts badly. Prefer C0G/NP0.
- Wrong topology — this page is passive first-order RC/RL high-pass. Active / Sallen-Key stages use different equations.
Related tools
- Low Pass Filter Calculator — RC & RL low-pass
- RC Filter Calculator — RC low-pass and high-pass only
- RC/LC Filter Cutoff Calculator — all four RC/RL modes
- Reactance Calculator — Xc and XL at any frequency
- RC Time Constant Calculator — τ = RC step response
Design Notes
First-order passive filters only roll off at -20dB per decade. They are great for simple noise filtering, anti-aliasing before a slow ADC, or debounce circuits, but inadequate for separating close frequencies. When designing RC filters, avoid using extremely large resistors (e.g., >1MΩ) because the input bias current of the next stage (like an Op-Amp or ADC) will cause a DC voltage error. Conversely, avoiding extremely small resistors (<100Ω) will save power and prevent overloading the driving source.
Common Mistakes
- 1
Expecting a sharp cutoff from a simple RC filter. It's a gentle curve, not a brick wall.
- 2
Not balancing the source impedance. If your signal source already has 10kΩ output impedance, and you use a 1kΩ series resistor for your filter, your effective R is 11kΩ.
- 3
Ignoring capacitor tolerances. Cheap Y5V or Z5U ceramic capacitors can vary by +20%/-80% with temperature and DC bias, completely ruining your cutoff frequency.
Engineering Handbox
1. Identify variables: R = 10,000, C = 0.0000001 2. Multiply R × C = 0.001 seconds (Time Constant τ) 3. Multiply by 2π: 0.001 × 6.283 = 0.006283 4. Divide 1 by result: 1 / 0.006283 = 159.15 Hz
Knowledge Base
Was ist die -3dB Grenzfrequenz?
Der Punkt, an dem die Ausgangsleistung auf die Hälfte sinkt (Spannung auf 70,7%). Universelle Definition in Elektronik, Audio und HF-Technik.
Was ist die Formel für RC-Tiefpass?
fc = 1 / (2π × R × C). Beispiel: R = 10kΩ, C = 100nF ergibt fc = 159,15 Hz.
Was ist der Unterschied zwischen Tiefpass und Hochpass?
Tiefpass lässt tiefe Frequenzen durch und dämpft hohe. Hochpass ist umgekehrt. Gleiche Grenzfrequenz-Formel, nur vertauschte Bauteile.
Wie steil ist die Flanke eines Filters erster Ordnung?
-20 dB/Dekade bzw. -6 dB/Oktave. Für steilere Flanken mehrere Stufen kaskadieren.
Welcher Kondensatortyp für Filter?
C0G/NP0 für Präzisionsfilter. X7R für allgemeine Filterung. Y5V/Z5U vermeiden – deren Kapazität ändert sich stark mit Temperatur und Spannung.
Related Engineering Tools
Low Pass / High Pass Filter Calculator
-3 dB cutoff for RC and RL filters
Reactance Calculator
Inductive and capacitive reactance
Time Constant Calculator
RC and RL transient constant
Series and Parallel Capacitor Calculator
Equivalent capacitance from a capacitor list
Frequency to Wavelength Conversion
Convert frequency and wavelength with velocity factor