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Signal Integrity

Every electronic product designed today has potential issues caused by Signal Integrity effects. The question is whether they have been well understood and dealt with in the best way possible, or have been ignored and left to potentially cause problems with the product at some later stage.
If in your design you ignored them and have not yet been bitten by them, you are very lucky. Signal Integrity problems can cause erratic and unexpected behaviour or reduce the lifetime of your products.

What is Signal Integrity (SI)?

When Electronic circuits are joined together, there is a signal that can be defined by some voltage waveform and a current waveform. This signal is driven with a certain specification (level, speed, shape, timing) by the driver circuit, and must meet some requirements (level, timing) of a receiver circuit.

It used to be the case that the PCB trace that connected them could be thought of as a perfect (instantaneous) connection, so you could make your design using only the data sheets of the two circuits. If you connected them over a long cable (or radio channel etc.) then you needed to do a bit more than that because the connection was no longer perfect.

Some years ago, the electronic devices being used in most circuits became so fast (rise and fall time rather than clock rate) that even the PCB traces could no longer be assumed to be perfect. They became "Transmission lines" which come with their own behaviours that can be explained by simple science, but that most engineers don't even think about.

It is vitally important to understand the principles of transmission lines and the paths of the return currents as well as the signal currents to be able to properly design an electronic board or system. You must plan your system for good Signal Integrity from the start, so that you can achieve not only the function, but speed, reliability and Electromagnetic Compatibility (EMC).

SI Simulation results

Now because the driver and receiver circuits are no longer fully characterised by the data sheet, you need to simulate the connections using models of the driver, transmission line and receiver together. You also need confidence that the simulation results actually represents reality - otherwise you are wasting your time, then you need to be able to look at the simulation results and interpret if it is acceptable or not, and if not what can be done to make it acceptable.

We would be happy to discuss offering training in Signal Integrity (SI), or problem solving if you now have a problem that you cannot work out.

Of course any Custom Electronics work that we do for your project will bear SI in mind from start to finish to ensure that your system can be completely reliable.