Our Signal Integrity, Power Integrity, EMC Philosophy.


...Symptoms of Signal Integrity Power Integrity and EMC failure.
Symptoms of SI, PI & EMC design failures include flaky boards, hardware software wars, poor manufacturing yield, high warranty return rate, FCC & CISPR regulatory failure, extra pre-production board design turns, established products suddenly becoming hard to manufacture, excessive EMI shielding, and generally unexplainable strangeness. Designing with poor SI EMC hygiene is like leaving food on the kitchen counter in south Florida. A seemingly infinite number of roaches will converge on your kitchen. The purpose of our training is to teach methods of design that will keep the electronic roaches out of your product.



War Story..
A major telecommunications manufacturer documented their experience in trying to solve this problem. When they began measuring their process, they found that 94% of the time they needed to redesign the PCB in order to solve high speed problems. After implementing a new process with appropriate tools, they reduced the redesign to less than 1%. They also maintained that rate over a base of 1300+ PCB designs. At the end of the study, they had so few rework problems that it became standard practice to convene a formal process review any time a board failed. FCC certification became routine. Design cycles and product shipments became far more predictable. Redesign and rework costs were poured into new product development. The benefits to the organization were massive.



Foundation is Board Stack Up & Power Delivery.
The foundation of proper SI EMC design is the board stack up and power delivery system. The board in combination with the bypass capacitor array provides the current for the drivers and also provides the path for the return current. Digital designers often think only in terms of signal current since that is the path displayed on the schematic. Return current is the other half of the circuit. If you can not point at you design and determine precisely where the return current is flowing, you are in trouble. Nothing else will be predictable. Remember, the return current has the same rise time at the signal current, therefore this analysis must be correct over a fairly wide frequency range.



Triage Signals
Triage your signals into clocks, high speed busses, and status signals. Clocks must always be analyzed for proper distribution, delay, clearance, and termination. They are the single greatest source of SI EMC problems. Next look at the high speed busses. They do not have as high of a repetition rate as clocks, but they generally switch synchronously with fast edge rates. These signals must be analyzed like the clock signal, but in addition you must consider the fact that the synchronous nature of the switching will cause significant ground bounce if the power deliver system is not adequate. Status signals are low repetition rate signals that will generally not cause any problems as long as they are not effected by cross talk from a clock or high speed buss. Create a budget for ringing, cross talk, and ground bounce that will guarantee that your signal settling requirements will be met even if those vectors add up in phase. The nature of flaky boards is that they work 99.999% of the time. The 0.001% failure only comes up 1000 times per second at modern clock speeds. Design the clock distribution, termination, etc to make sure it works. Do the same for the high speed busses.

Implement a Signal Integrity Power Integrity & EMC Design Process
The design process we teach will result in layout, termination, and topology rules that are adequate to ensure success for both signal integrity as well as radiated emissions. In other words, it ensures a solid design with adequate noise and timing margins so the product works reliably. It will have a high manufacturing yield, low warranty return rate, and it will pass FCC / CISPR radiated emissions tests on the first try. Remember, if you fail radiated emissions, you can not ship an otherwise properly working product. If you can not ship the product, you do not get paid and life gets ugly.

Regardless of the method you implement, it will never work unless you close the loop. If you have any unexpected results with SI, PI, or EMC, you must find the source of the error and correct your process.

Perspectives on Radiated Emissions
There are two basic ways of controlling radiated emissions. You can either suppress it at the source or you can attempt to contain it. The difficulty with containing it is that it can get very expensive and it can be quite unpredictable. If you suppress noise at its source, you do not need to chase it. Suppressing noise at the source is the classy way to go. The same types of things one does to suppress radiated emissions at its source are in most cases, identical to the things one would do to attain good signal integrity performance. The methods used will save money in board turns. It will also make the entire process more predictable. It will always leave you with the option to add shielding and filtering if necessary.

Generally, it is far easier to get a board to work reliably than it is to get the board to be quiet. The only way to succeed on a regular basis is to solve noise problems at their source.