Blog Post

RSS

The third Electronic Design Innovation Conference (EDICON), was held Oct 17-18, 2018 in Santa Clara. The attendees were treated to two days of technical talks, tutorials and tradeshow with the overlapping topics of RF, SI, PI and EMI. This is a unique combination, allowing cross fertilization between these otherwise separate fields.

We usually associate problems with the power distribution network (PDN) as from excess VRM noise, or from transient current draw from the core or I/O drivers. But that’s not the only source of PDN noise. Some failures can arise from dull, boring, mundane problems at DC.

Eric Bogatin reviews a presentation by Terence Regan, and shares his thoughts on the topic of high-performance interconnect design and fabrication.

I have lost count of the number of times I have been asked to fix an EMC problem, only to find that a shielding box has been designed or purchased to provide XdB up to fMAX. Or a filter has been designed or purchased with a similar specification, but to reduce cost the filter has been mounted on a printed circuit board (PCB) inside the box, with a cable from it entering or exiting the box through a plain connector.

For this project, we will use an Atmel 328 microcontroller demo board, prepared with firmware to control it explicitly for our purposes, and with coaxial cables connected between the I/O pins and the input to the active probes of the scope. This interconnect provides a high bandwidth transmission line path for the signals.

If the die's I/O power rails are shared by the core power rails, here's a way to get your core power-rail measurements anyway.

How do you achieve high bandwidth in your measurements while minimizing current load on your DUT? Given that your DUT is a power rail, you really don't want to draw too much current from it., or your measurement system will distort the rail. But these two measurement criteria are at loggerheads with each other. It's a quandary, and it has to do with the fundamental nature of signals on interconnects.

Measuring the noise on a power rail seems to be a straightforward task. However, there are some basic pitfalls that can cause incorrect, or even downright strange, results. Let's look at one of these challenges: RF pickup. We'll demonstrate the effect of RF pickup on a power-rail measurement, and then we'll show you an effective means of mitigating that effect.

Eric Bogatin explains the figures of merit in the time and frequency domain, and he steps through how to get a rough measure of the highest frequency components in a signal.