Decoupling capacitors are used to maintain stable voltage levels and filter out noise. They are used to isolate sensitive components from power supply fluctuations and interference, ensuring that the circuit performs reliably.
Calculator
This tool calculates the capacitor value for the following inputs:
- Frequency of noise (Hz)
- Impedance (ohm)
Formula
C = 1/(2ฯ*fn*Xc)
- Xc is the circuit impedance
- fn is the frequency
Example Calculation
Letโs assume you are working with a microcontroller operating at 16 MHz. To ensure reliable operation, you want the impedance to be below 1 ohm at this frequency.
- Input Frequency: 16 MHz (16,000,000 Hz)
- Target Impedance: 1 ohm
Using the calculator, the cap value is found to be 9.95 nF
So, a 10 nF capacitor would provide the required impedance to filter noise at 16 MHz. In practice, engineers often use 0.1 ยตF (100 nF) capacitors as decoupling capacitors because they cover a wide range of high frequencies and are readily available.
What is a Decoupling Capacitor?
A decoupling capacitor isolates components (such as microcontrollers, operational amplifiers, and ICs) from voltage variations in the power supply, preventing interference between parts of the circuit. The capacitor stores energy and releases it when needed to compensate for sudden changes in voltage, ensuring that each component receives a stable voltage level.
In essence, decoupling capacitors:
- Filter high-frequency noise from power lines.
- Stabilize voltage by compensating for fluctuations.
- Isolate components from one another to prevent cross-interference.
While they share similarities with bypass capacitors, decoupling capacitors are primarily intended to stabilize voltage within specific components, rather than filter out noise across the entire circuit.
How Does a Decoupling Capacitor Work?
In an electronic circuit, voltage drops can occur when components switch states or consume varying amounts of power. These sudden changes can introduce electrical noise, affecting the performance of nearby components. The decoupling capacitor, placed between the power supply and ground, acts like a buffer by temporarily storing energy and discharging it to maintain a stable voltage.
In high-frequency circuits, the decoupling capacitor offers a low impedance path for unwanted noise, redirecting it to the ground. This ensures that sensitive components (like microcontrollers or ICs) are isolated from power supply fluctuations.