Current Topic: Good breadboarding techniques are what ultimately separate average circuits from instrumentation. That's what we used to call high-accuracy - high-definition circuits. A good design helps also of course.
Using Component Layout To Control Inter-Node (signal) Impedance...
Impedance is an unfortunately misunderstood, and thus misused, reference. To most it is interpreted as a purely resistive component. That may be true at pure DC but with all time varying signals (analog) extra physics effects apply. And their influence becomes greater as signal frequency increases. The beauty is that it is not so important to understand the underlying math when a more broader understanding will work for almost all circuit design.
Ok... Here's the thing with impedance. It is 'Not' unidimentional i.e. '8 ohms'. Proper impedance contains a second term which represents, for lack of a simpler definition, a phase angle. It is the charge relationship between the voltage and the current. This additional term is necessary to calculate the actual behavior at a given frequency.
But how often do you really need to consider that. Uh! Almost never. Fortunately a very basic understanding of transmission lines can be used to better understand impedance and help to design circuits which reduce many of the effects for all but the most specialized of circuits (which still benefit).
So What Are We Looking At Here...
All signals (wires, leads, circuit traces) have a pure resistive element to them but also have a reactive component as well. This additional component defines a relationship of how much the current will lead or lag the voltage as it passes through the signal (path) meaning how much capacitance or inductance is influencing the signal. Put these two elements together and you have 'Impedance'.
It is this (parasitic) effect that capacitors and inductors intensify to create filters (analog networks) for both simple and extreme analog signal processing. It is also this effect that limits the operating frequency range of these components.
The point being that every signal path needs to be considered when laying out a circuit as to minimize the influence that these effects have.
Reducing Coupling, Interference And Noise...
We need a little 'simple' theory here to understand transmission lines.
Armed with this information let's see how this applies and how to reduce said effects through proper layout techniques.
Capacitance : Is a property that holds a charge. The charge amount (rate) is proportional to the proximity of the plates. In other words the more area and the closer that one signal is to another the more capacitance.
Inductance : Is a property that creates a potential. The potential amount (energy) is proportional to the length of the conductor. It is further increased when the contuctor is coiled. Especially when the coil is wrapping an Iron core. The longer the conductor and or the number of coil turns. The more the inductance. And the more magnetic flux generated.
Proper Power Distribution Makes A Huge Difference...
High definition circuit performance additionally depends on good power supply decoupling techniques. Really? You would be surprised at how much noise and 'crosstalk' (coupling), between otherwise isolated circuit functions, occurs at the power supply level. Using a few extra, common, components to help isolate and condition the power supply can often improve the power and ground 'signal' quality by more then 20 db. And that can mean the difference between a circuit that exhibits a 70 - 80 db quality where it could be over 100 db.
Scale that down and it may even help a lot of crummy circuits work satisfactory. Hmm!
When decoupling the power supply it is important to not only recognize the demand of the local circuit but to also understand it's transient reflection back to the source and how that will also affect other circuits. Simple decoupling circuits can take care of both needs.
The best way to do this is to use a combination of capacitors and a resistor (or inductor for high currents). Create a node that is designated 'ground' for the local sub-circuit (function). Create a 'network' using a ceramic and an electrolytic (aluminum or preferably tantalum) at the source power supply with a resistor (preferably wirewound) in series with the power to the circuit and an additional ceramic capacitor at the circuit power input.
This technique is also easily extended to bipolar power supplies which many circuits require.
Ground And Signal Reference Nodes...
New copy.
Safely Powering Up A Circuit For The First Time...
New copy.
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