Can Capacitors Make Noise?


Capacitors are components commonly found in most electrical circuits and have the useful property of storing electrical charge. A capacitor's capacitance (C) measures the element's ability to store charge and is measured in Farads. Due to their unique properties, capacitors have uses ranging from smoothing varying DC power supply currents to coupling different circuits in devices such as loudspeakers.

Circuit Noise

  • Circuits are made up of materials that either contain or interact with electrical charges. These charges arise due to the motion of electrons, and each circuit has inherent vibrations due to ambient temperature. For all temperatures greater than absolute zero (0 Kelvin), these vibrations hamper electron movement and result in circuit noise. It is important to note that it is the fundamental nature of materials to induce noise, and this noise can never be completely removed.

Problems Related to Circuit Noise

  • Circuit noise often manifests itself as variations in the circuit current. If the current, and hence the circuit voltage, fluctuate, sensitive components might get damaged and cause the circuit to malfunction. In addition, if the circuit is being utilized to measure or monitor the performance of another device, these fluctuations or ripples in the current can result in incorrect measurements. Consequently, minimizing circuit noise improves the sensitivity and the output signal to noise ratio of the circuit.

Active and Passive Elements

  • Electrical elements can be classified as either active or passive. Active elements are those that can deliver energy. Examples of active elements include current and voltage generators, such as a battery. Passive elements, on the other hand, are those that dissipate or store energy, such as resistors and capacitors.

Capacitor Noise

  • Since capacitors are passive elements, they do not contribute to the electrical noise within a circuit. In fact, a type of capacitors known as "bypass capacitors" are actually used to filter out the electrical noise from a circuit. Bypass capacitors work by filtering out voltage ripples, resulting in a cleaner and more uniform direct current. They can be found on most digital circuits and can be easily identified by their "cap"-like appearance.

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