RChøypassfilter

RChøypassfilter, often written as RC højpassfilter in Scandinavian contexts, refers to a first‑order RC high‑pass filter used to attenuate low-frequency components while passing higher frequencies. The passive form typically consists of a capacitor in series with the input and a resistor to ground, with the output taken across the resistor. This configuration allows AC signals above a chosen cutoff to appear at the output while blocking DC and very low frequencies.

The transfer function of the standard RC high‑pass is Vout/Vin = ZR / (ZC + ZR) = R / (1/(jωC) + R) = (jωRC) / (1 + jωRC). Its magnitude is |H(jω)| = ωRC / sqrt(1 + (ωRC)²). The corner frequency, where the output is reduced to 1/√2 of the input, occurs at ωc = 1/RC, i.e., fc = 1/(2πRC). For frequencies much higher than fc, the filter passes the signal with little attenuation; for frequencies much lower than fc, the output is proportional to frequency and the signal is attenuated.

Design considerations include component tolerances, loading effects, and the need to buffer the stage if the following input impedance is not high relative to R. Loading can shift the effective resistance and alter fc. Variations include using an active high‑pass configuration with an operational amplifier to improve impedance matching or to achieve steeper roll‑offs with higher‑order stages. Practical notes cover capacitor voltage ratings, voltage coefficients, and parasitics at higher frequencies.

Applications span DC blocking, audio signal conditioning, sensor interfacing, and front‑end coupling networks where unwanted low‑frequency content must be suppressed before subsequent stages. See also RC low‑pass filters and active high‑pass implementations.