What is Passive Low Pass Filter


A passive low pass filter is an electronic circuit that allows low-frequency signals to pass through while attenuating high-frequency signals. The filter achieves this by using only passive components such as resistors, capacitors, and inductors. The passive low pass filter is widely used in various electronic circuits such as audio signal processing, power supplies, and communication systems.

Characteristics of Passive High Pass Filter:

  • Attenuates low-frequency signals and passes high-frequency signals.
  • The cutoff frequency is determined by the values of the resistor and capacitor.
  • Does not provide gain or amplification to the filtered signal.
  • Has a high output impedance.
  • Has a flat response at high frequencies and a roll-off response at low frequencies.
  • Used in audio crossover networks, tone control circuits, and power supply circuits.


The passive low pass filter circuit consists of a resistor and a capacitor connected in series. The input signal is applied across the resistor, and the output signal is taken across the capacitor. The resistor and capacitor values determine the frequency range that the filter allows to pass through.


In a passive low pass filter, the resistor limits the current flowing through the circuit, and the capacitor blocks high-frequency signals by offering a low impedance path. As the frequency of the input signal increases, the capacitor impedance decreases, and the amount of signal attenuation increases. The filter cutoff frequency is determined by the product of the resistor and capacitor values, and it determines the frequency at which the filter starts attenuating the input signal.


Some of the applications of passive low pass filters are:

  • Audio signal processing in music systems and amplifiers
  • Power supplies to filter out high-frequency noise
  • Antenna filters in communication systems
  • Electronic crossovers in speakers and subwoofers
  • Signal conditioning in sensor circuits
  • Frequency response shaping in equalizers
  • Medical equipment signal processing and filtering.

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