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# High Pass Filter Low Frequency Interference

May 16, 2017

High-pass filter, also known as low-cut filter, low-impedance filter, allows a higher frequency than a certain frequency through the filter, and greatly attenuate the lower frequency of a filter . It removes unwanted low-frequency components from the signal or removes low-frequency interference.

The high-pass filter is a combination of devices such as capacitors, inductors and resistors that allow signal components above a certain frequency to pass through, and to suppress the signal components below the frequency. Its characteristics in the time domain and frequency domain can be used respectively impulse response and frequency response description. The latter is expressed as a function of the frequency as an independent variable. In general, it is a complex function with the complex variable jω as an independent variable, expressed as H (jω). Its modulus H (ω) and the amplitude φ (ω) are functions of the angular frequency ω, which are called the "amplitude-frequency response" and "phase-frequency response" of the system, respectively, which represent the signal components of different frequencies in the excitation source The system is encountered when the amplitude changes and phase changes. It can be shown that the "frequency response" of the system is the Fourier transform of the system "impulse response". When the linear passive system can be expressed by an N-th order linear differential equation, the frequency response H (jω) is a rational fraction, and its numerator and denominator correspond to the right and left sides of the differential equation, respectively.

Passive high-pass filter: only by the passive components (R, L and C) composed of the filter, which is the use of capacitive and inductance components with the frequency of the changes in the composition of the principle of change. The advantages of this filter is: the circuit is relatively simple, do not need DC power supply, high reliability; drawback is: the passband signal has energy loss, the load effect is more obvious, the use of inductance components easily lead to electromagnetic induction, when the inductance L larger filter size and weight are relatively large, in the low frequency domain is not applicable.

Active high-pass filter: composed of passive components (generally R and C) and active devices (such as integrated operational amplifiers). The advantages of this type of filter is: the signal within the passband is not only no energy loss, but also can be amplified, the load effect is not obvious, multi-level interaction with each other is very small, the use of cascading simple method is easy to constitute high-order filter And the filter is small in size and light in weight and does not require magnetic shielding (due to the absence of inductive components); the drawback is that the passband range is limited by the bandwidth of the active device (eg integrated operational amplifier) and requires a DC power supply and reliable As high as the passive filter, high voltage, high frequency, high power occasions are not applicable.