Technical Insights > Benchtop

Oscilloscope ADC Bits and ENOB

2019-06-19  |  4 min read 

Many engineers rely on the number of analog-to-digital converter (ADC) bits in an oscilloscope to determine the overall quality of the instrument. However, you must keep in mind that an oscilloscope is made up of much more than an ADC. The truth is there are other critical specifications that tell you just how accurate an instrument really is.

Just as important as the number of ADC bits is the system’s effective number of bits (ENOB). The ENOB tells you how many bits are actually effective in making your measurements by considering the entire oscilloscope measurement system, not just the ADC.

Download the “Understanding ADC Bits and ENOB” Whitepaper

In all oscilloscopes, some number of ADC bits will be useless. The effective number of bits in the system will always be lower than the specified number of ADC bits. This means if you are selecting an oscilloscope purely based on ADC bits, you will likely be disappointed in the resulting measurement quality. If the quality is too poor, this leads you to make incorrect design assumptions and potentially a faulty product.

ENOB is a better indication of signal integrity because it takes system error into account.

If you haven’t heard of system ENOB before, I’m not surprised. This specification is often not highlighted by other vendors due to how poor it is in comparison to ADC bits. Designing for a high ENOB is not as easy as putting in a high-bit ADC. The front end and supporting circuitry around the ADC must be designed with a high degree of quality, which is no simple task.

The signal moves through much more than just the ADC, such as the probe, attenuator, amplifier, and other front end components.
Figure 1. The signal path of an oscilloscope from the probe to the ADC.

A high ADC specification is important. However, you need to make sure you are looking at the other important components that go into signal integrity as well. The ADC is just one part of the overall system. Be sure your oscilloscope has the ENOB you need to meet your testing requirements.

Learn about why you should care about ENOB, what number of bits means for your testing, and the difference between “system ENOB” and “ADC ENOB” in the whitepaper Understanding ADC Bits and ENOB.

High performance oscilloscopes, such as the Infiniium S-Series, offer high ENOB at all bandwidths. This ensures you are always making the most accurate measurements possible. However, ENOB is just one of the critical specifications you should consider when looking for an oscilloscope with high signal integrity. Learn about the other important aspect of an oscilloscope measurement system in the eBook How to Determine Oscilloscope Signal Integrity.