My Experience with "Noise"

For any electronics engineer involved in board design, working with digital circuits running at medium/high speed (clock frequency > ~10Mhz) or SMPS circuit design, "noise" is a nightmare. For any of the new designs, the first question appears in my mind is obviously whether it will work or not. The second question is whether my board will pass the EMC (Electro Magnetic Compliance) tests or not. The first could be more confidently answered than the second. I have most of my experience in digital and mixed circuit design, but I've also seen people struggling for several months to resolve EMC issues on SMPS boards. So far, I've seen SMPS designers having hard time to pass conducted and radiated emission tests, where as digital designers struggle to pass ESD (Electro Static Discharge), EFT (Electrical Fast Trasient) or RF susceptability tests. When I was a novice designer (That doesn't mean that I'm an expert now), I used to ask myself an "open-ended" question before starting a design: What all measures and design practices shall I follow in order to not get stuck due to EMC issues. As I gained experience over time, I've learned that it is better to ask myself a couple of questions:

1. What are the EMC tests that my product needs to pass?
2. Can I have the necessary measures and design practices implemented in order to pass those applicable tests?

If I have answered the above two questions satisfactorily, I have experienced a much better success rate.

The generic electromagneic compliance standard IEC 61000-6-2 specify the EMC tests to be conducted and alse specifies the test levels. This is important for an organization to get its products certified by agencies to obtain CE marking on its products. The generic standard IEC 61000-6-2 again calls various standards mentioned below, which are specific to the different EMC tests to be conducted. The following standards documents the detailed testing & measurement techniques for difference EMC tests.

• IEC 61000-4-1: Over view of IEC 61000-4 series
• IEC 61000-4-2 : Electro Static Discharge (ESD) Test
• IEC 61000-4-3: Radio Frequesncy (RF) Immunity Test
• IEC 61000-4-4: Electric Fast Transient (EFT) Immunity Test
• IEC 61000-4-5 High Voltage Surge Immunity Test
• IEC 61000-4-6: Immunity to Conducter Radio Frequency (RF)
• IEC 61000-4-8: Power frequency magnetic field immunity test.
• IEC 61000-4-10: Damped oscillatory magnetic field immunity test.
• IEC 61000-4-11: Voltage dips, short interruptions and voltage variations immunity tests.

There are some more. The tests specified in the above international EMC standards are designed for testing the products in a harsh environment simulating the real world EMI situations. Hence if we approach from understanding the tests specified in those standards and then take necessary precausions in our design in order to pass those tests, it is highly likely that our product will also work in real life environment.

Let us now focus on each of those EMC tests standards by standard. Let's start with ESD: IEC 61000-4-2.

(To Be Continued In Part II...)