Don't forget your decoupling caps, kids...

Give me any electronic device right now, and I bet the most common component on it is the decoupling/bypass capacitor. 

What is that? Why is it everywhere? Why do you hate yourself?

While I can't answer some of life's more perplexing questions, I CAN answer the decoupling capacitor question.  Let's unravel the surprisingly simple mystery of these indispensible little charge stores.

What are decoupling capacitors?

In simple terms, they are capacitors used for filtering out voltage spikes and stabilizing the power supply to ICs or other active components.

I like to think these capacitors handle the 'dirty' side of electronics and keep things running smoothly. 

The power supply lines, which we like to think are just one smooth and stable voltage, are anything but. They're filled with electrical noise – pesky little voltage spikes and drops that wreak havoc on sensitive ICs or components. There can be noticeable voltage dips as an IC suddenly increases its power draw for a moment. 

Decoupling capacitors act like lil shock absorbers for these ICs, ensuring they get a clean, stable power supply. Without these capacitors, your ICs would be getting jolted with every spike in the supply voltage. This could lead to erratic behavior in electronics, like a processor skipping instructions or a sensor giving incorrect readings.

How do you practically implement Decoupling Caps in designs?

In the real world of circuit design, decoupling caps aren't just scattered around randomly on the power lines. There's a method to the madness. For e.g. they're strategically placed as close as possible to the physical power pins of ICs/components they're supporting. Why? 

Short, simple answer: The shorter the distance, the more effective they are at doing their job – minimizing noise and voltage spikes. 

Long Answer: It's all about minimising loop area, connection impedance. Just read this post for a proper technical dive, or accept it as fact.

The typical setup you'd see in many commercial circuits is the combined use of the capacitor duo: bulk capacitors and high-frequency capacitors.
The bulk capacitors, are larger (1 µF to 100 µF), and handle the slower, low-frequency changes in the power supply. On the other hand, the smaller value capacitors (0.01 µF to 0.1 µF) tackle high-frequency noise. This tag team ensures that a wide range of noise frequencies is kept in check.

When it comes to what you should be looking to decouple, it's basically just these:

1. Power Supply Rail

Directly on the output for DC supplies, you need to have sufficient decoupling; this is often done with the duo capacitor strategy.
On the output of your buck/boost converters, there has to be decoupling or else they might not even function properly in delivering a stable output.

2. Power Supply Rail - but close to power-hungry or sensitive ICs

Next to EVERY single important active component, there should be at least one 0.1uF capacitor. 

E.g. If you have some digital IC, make sure you shove a decoupling capacitor on the power pins to maintain its input voltage stability.

E.g. If you have a component that has huge power draw bursts (buzzer or actuator circuitry etc.), they all need good decoupling to prevent big voltage dips.

How to pick the correct value for a decoupling capacitor?

Picking good values for decoupling capacitors boils down to the following factors:    

1. IC Requirements: Each IC has its own power supply needs. So, first step is to check the datasheet which could have explicit values already stated and should just be followed.

2. Frequency Range: Usually though, it's up to you to determine values. We've spoken about capacitor value and frequency operation range; High frequencies typically need smaller capacitance values for low impedance, whereas lower frequencies benefits from larger values. So for high frequencies, think 0.01-0.1uF while for lower frequencies you'd find 1uF-100uF.

3. Parasitic Elements: Real-world capacitors come with parasitic inductance and resistance, known as Equivalent Series Resistance (ESR) and Equivalent Series Inductance (ESL). In high-frequency applications, it's important to choose capacitors with low ESR and ESL to ensure effectiveness.

Conclusion

Decouple your circuits, don't be silly.