Charting High-Resolution Oscilloscope Performance

Eric Bogatin, Signal Integrity Evangelist, Teledyne LeCroy

Figure 1. 8-bit vs. 12-bit oscilloscope waveforms.

There are hundreds of different oscilloscope models from a dozen different vendors. How do you make sense of all of their different features to pick the one instrument right for your application?  Here is a simple way of comparing high-resolution oscilloscopes.

High-resolution usually refers to the vertical resolution, the quantization of a waveform into a fixed number of vertical levels measured by the oscilloscope's Analog-to-Digital Converter (ADC). The more bits of vertical resolution, the more levels and the more detailed the waveform rendered. The earliest digital storage oscilloscopes (DSO) started as 8-bit resolution, or 256 vertical levels. But in the last ten years, as ADC chip technology got faster, higher resolution appeared in the industry, pioneered by Teledyne LeCroy.  Now, many oscilloscopes come with 10-bit and 12-bit vertical resolution. Why would you want higher resolution? The answer: the ability to see lower level signals and better dynamic range. An example of the difference between the same signal measured with an 8-bit and 12-bit oscilloscope is shown in Figure 1. 

The Resolution Revolution In Oscilloscopes

Figure 1: Teledyne LeCroy's WavePro HD exemplifies
today's high-resolution, high-bandwidth instruments

Oscilloscopes have been around for a very long time now, and older oscilloscope users will remember the heyday of those analog boat anchors of the '60s and '70s. Many have survived and are still usable if you don't need much bandwidth (and have the means to calibrate them if necessary). I used to scout local hamfests looking for bargains on them. Many techs and engineers cut their teeth on those behemoths. You could learn a lot about design if you poked around inside them, too.

The Challenges of GFCI Measurements

Figure 1: An example
of a GFCI

The ubiquitous ground fault circuit interrupter (GFCI), a fast-acting circuit breaker, has saved countless individuals from serious injury or death when they've inadvertently entered the low-resistance ground path of an electrical device or outlet. It's important to measure precisely the amount of time that elapses from when the 60-Hz cycle is present to when the GFCI disables the ground path. Other tests include determining the start, stop, and duration of the GFCI's tripping time. Let's take a look at the challenges these measurements present.

An Overview of Oscilloscope Banner Specs

"Banner specs" is a term that oscilloscope makers use often. If you've ever met with one of the vendors' salespeople, you're likely to have heard it. But what are banner specs and what do they mean to you?

The Making of 12-Bit Scope Hardware

In many applications, the accuracy of a true 12-bit oscilloscope is not only desirable, but necessary. Going forward, this will become the case more and more often. When choosing one, it's a good idea to peek under the covers and gain a little insight into how the instrument operates. Having discussed in an earlier post the advantages of oscilloscopes with 12-bit vertical resolution, let's look at the ways in which that resolution is accomplished in hardware.