Contents
Why do we need a decoupling capacitor in a digital circuit?
The capacitor stores a small amount of energy that can compensate for the voltage drop in the power supply conductors to the capacitor. In digital circuits, decoupling capacitors also help prevent radiation of electromagnetic interference from relatively long circuit traces due to rapidly changing power supply currents.
Where to place a decoupling capacitor in a NAND chip?
For the best results, the decoupling capacitor should be placed as close as possible to the chip. The following schematic illustrates the use of decoupling capacitors with a 7400 NAND logic gate (pin 14 is used for the positive supply voltage, while pin 7 is connected to ground):
How are capacitors used to reduce series inductance?
To reduce the effective series inductance, small and large capacitors are often placed in parallel; commonly positioned adjacent to individual integrated circuits. The capacitor stores a small amount of energy that can compensate for the voltage drop in the power supply conductors to the capacitor.
What happens when a capacitor is coupled to a power source?
As a result, the current drawn by the device fluctuates, generating noise which propagates back to the power source.
When does transient load decoupling need to be done?
Transient load decoupling as described above is needed when there is a large load that gets switched quickly. The parasitic inductance in every (decoupling) capacitor may limit the suitable capacity and influence appropriate type if switching occurs very fast.
When do you use parallel combinations of capacitors?
Sometimes parallel combinations of capacitors are used to improve response. This is because real capacitors have parasitic inductance, which distorts the capacitor’s behavior at higher frequencies. Transient load decoupling as described above is needed when there is a large load that gets switched quickly.
How are capacitors placed on the same supply pin?
When multiple capacitors are placed on the same supply pin, make sure that the smallest capacitor is closest to the IC, and place the rest of the capacitors away in ascending order. When placed close to the IC, the smallest capacitor will provide the fastest short for high-frequency noise.