Via Configurations Can Be Used to Connect Decoupling Capacitors

Due to the fact that input voltages in ICs can be unstable, decoupling capacitors are needed as solutions for keeping voltage stable when input voltage fluctuates. Also known as bypass capacitors, decoupling capacitors act as energy reserves to compensate for losses. These electronic components either provide needed energy or absorb excess energy. Using decoupling capacitors next to clocked digital ICs helps generate a smooth input voltage, drawing from large transient power supply currents.

Adjustments for Transient Energy

Circuit boards commonly experience excess electrical noise. The noises can be controlled with decoupling capacitors since they protect sensitive chips by filtering out noise. At the same time, they create a much steadier source of power. Without decoupling capacitors, a technician might waste valuable time troubleshooting.

It is possible for a microprocessor to draw currents on the level of 10 amps over a short time frame. The transient energy needs to be stepped up to a higher rate as the rise/fall time of the IC outputs is reduced. A voltage across inductance is generated when the digital IC's large transient current goes through inductance of the power and ground conductors. However, a constant voltage across the IC's power and ground pads is prevented due to the large transient power drops.

This problem can be resolved with a charge source that provides transient currents, which involves placing decoupling capacitors next to each logic IC. The circuit power routing renews the charge in the decoupling capacitor, which should provide all the high-frequency transient currents over a half a clock cycle. Separating the high-frequency energy from the power distribution traces allows for greater tolerance of inductance throughout the power distribution structure.

Managing Inductance in the Decoupling Loop

When the inductance of the decoupling loop is not strong enough, the logic IC attempts to gain energy through the power distribution structure. This inductance, however, must be minimized to avoid damaging other circuit components. Connecting decoupling capacitors to the PCB power and ground planes can be done via various configurations. Different configurations are used depending on whether currents flow in the opposite or same direction.