Thursday, July 28, 2011

How to accurately measure vertical noise on a real-time oscilloscope

My introduction to the world of being a field applications engineer was a frantic call from a sales person.  His customer had been told that a competitor's oscilloscope was "lower noise" due to Faraday cage shielding, something that presumably my product did not have.  Now, I recognize marketing hype when I hear it, but I had to understand the misperception in detail to explain it to the customer.  Every scope has "faraday cage shielding" - it's a standard part of designing high bandwidth front-ends.  Michael Faraday died in 1867, so it amazed me that anybody would act like using a metal shield was something revolutionary, but here it was in marketing literature.

At first I suspected the customer was concerned a small difference in noise that really didn't matter.  But when the customer said we had twice the noise of our competition, I had to understand what was going on. 

How do you measure noise on an oscilloscope?