# What components can be placed not to close to the circuit like capacitors and still work fine?

I read that capacitors(especially decoupling ones) have to be placed as close as possible to their position. Does the same apply for resistor also? Can resistor be placed not close enough, lets say far, from a transistor for example or from an other circuit that resistor is part of it?

Does the distance of components only apply to capacitors or not only?

I am talking about components and not lets say feed line of antenna obviously.

• It has nothing to do with caps in particular but with the need for low inductance connections and minimizing the size of high impedance nodes Commented May 15, 2021 at 13:30
• It basically depends on what you are building if placement of components matters a lot or not. The wires that connect components themselves are small capacitors, inductors and resistors so sometimes it matters and sometimes it doesn't. But do you have a specific circuit in mind or just in general? Commented May 15, 2021 at 13:35
• generally.. for example generally decoupling capacitors can be placed as close as possible.. but what if I have a led on the one corner of the PCB and the other corner a resistor. distance 10cm. is that a problem? But not only for a led..lets say a transistor which has resistors..can resistor be 10cm away or it has to be as close as possible
– Kris
Commented May 15, 2021 at 13:37

Any component that has a high impedance can generally be extended by arbitrarily long wires, with only an increase in its impedance. So the effective value of the component will change slightly, but not the way it's expected to work. Sometimes capacitors are used in a high impedance mode for signal coupling, when the same applies.

Often capacitors are used for their low impedance when decoupling power supplies. Then any finite lead length degrades their performance.

Before you can answer whether long leads are permitted, you need to know how you are expecting the component to work in the circuit.

Long leads can also get us into trouble, regardless of the type of component that their extending.

They can enhance capacitive or inductive coupling between different parts of the circuit, and can make amplifiers unstable or degrade filter stopband performance.

A long lead can inject current into a part of the circuit remote from where it's being sourced. This current flowing in the board's return path can couple signals to other circuits, again causing problems in circuit operation, possibly even at DC.

You can see the effect of impedance in the fact that industrial control systems, at least the old analogue ones, use 4 to 20 mA current loops, where the sensor operates as a current sink, drawing a current related to the process variable. A current sink has a very high, ideally infinite impedance. As a result, such systems can work reliably over open wires of many hundreds of metres, sometimes kilometres, in length.

Small capacitors optimized for low series inductance work best when placed close to the device. There’s a ‘factor of ten’ rule of thumb about size vs. effectiveness: on-die is 10x of on package is 10x of on board is 10x of at power source.

Larger ones, not so much. They have so much series inductance that they don’t benefit as much from close placement, except to localize high-current loops (like in a switching regulator for example.)

Series Inductance is your friend to a point, unless it’s in series with the caps. It can be helpful as part of a pi filter for example.

When mixing cap values, take care to avoid anti-resonance, where the capacitor resonances actually work against each other and reduce the effectiveness of bypassing.

But really, that Murata doc covers this and more.