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High Resolution and Low Noise Oscilloscopes

Last Updated: Jan 28, 2019 10:35AM PST
Oscilloscopes continue to evolve and improve. One area of continued interest from the engineering community is the ability to visualize small signals within larger signals from a single capture event. 

The ability of a scope to make these small signals visible is achieved through a number of technologies. One of the most basic is the resolution of the oscilloscope's actual ADCs (Analog Digitial Converters). ADCs are specified by how many bits they have. More bits lead to more resolution. 



As an example a 10 bit ADC has 4 times as many levels as an 8 bit ADC.
This helps reduce quantization error - the unknown associated with the limit of resolution.

This improves signal to noise ratio, but this alone does not make it easy to zoom in on a signal and view it normally.


The second common approach to improving oscilloscope resolution is the use of a high resolution mode. 
The High Resolution Acquisition mode uses oversampling to improve the noise levels of a captured signal. This is a tradeoff between noise and bandwidth to be used when lower noise is more important for signal visualization:



While this technology can help with many signals it may still be effected by front end overdrive recovery  when trying to view small signal detail within a larger signal. This article was written by Agilent Technologies to describe the phenomenon:

https://www.evaluationengineering.com/home/article/13002378/overcoming-overdrive-recovery

Overdrive recovery is the ability of a scope to zoom in on small signal detail without distorting the signal even when other portions of the signal go well off the scope's display.

RIGOL's UltraVisionII Technology made significant improvements in this area. Here is an example of zooming in on a signal capture with the RIGOL MSO5000 vs. a Competitor's Oscilloscope.


RIGOL's MSO5000 zoomed in to 20 mV per division on the high res test signal


A competitor's scope zoomed in to 20 mV per division on the high res test signal

Under such demanding test applications many oscilloscopes show significant distortion from the front end of the scope's signal recovery. 

Because an Oscilloscope is a visual instrument the engineer's first test is to locate and zoom in on the signal to understand its characteristics. Advanced Overdrive recovery capabilities, like those in RIGOL's integrated front-end custom chipset are critical to accurate signal visualization.

One additional aspect of debugging small signals is often not specified in many oscilloscopes, especially in the value and mid-range segments. This is the actual noise floor of the oscilloscope. The amount of noise injected by the scope itself affects the engineer's ability to visualize these small details.

RIGOL UltraVisionII Oscilloscopes also have improved noise performance over our previous models. Noise performance is effected by instrument bandwidth, sampling, channel configuration, and more but here are a couple of examples showing the noise performance of a MSO5000 in its normal acquisition mode to give you an idea of signal level detail that can be visualized:


This image shows about 260 uV RMS noise on the 2 mV range.


This image shows about 300 uV RMS noise on the 10 mV range.


 
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