Effective Number of Bits (ENOB) as a Measure of Digitizer Performance

Most engineers and scientists focus on sample rate and resolution when selecting high speed digitizer products. Those "banner specs" will usually narrow the pool of candidates in the final selection. To really understand the true overall digitizer performance, the best specification to use is ENOB, or Effective Number of Bits.

The most widely used definition for ENOB is:

  • ENOB = (SINAD – 1.76) / 6.02

Where all values above are given in dB. SINAD is the signal to noise and distortion ratio, again in dB.

The use of ENOB allows one to evaluate the entire performance of the digitizer under consideration. It includes errors and non-linearity in the data converter chip, the front end analog amplifier, sample clock jitter, and interleave function if used to extend the sample rate. To be used effectively in comparing digitizer products, one should look at ENOB versus frequency - ENOB is usually much better at lower frequencies.

Drawing on experience from the development of many generations of digitizer product, the engineers designing GaGe products have created proprietary methods and tests to maximize ENOB. Today GaGe digitizer products consistently have best in class ENOB specifications for a given resolution and sample rate.

Figure 1 below is a good example, comparing GaGe digitizers to similar competitive products from other suppliers. Note the ENOB specifications for the GaGe digitizer models remains almost flat at higher frequencies, versus the trend of other products to dramatically decrease as frequency increases. The GaGe 12-bit digitzers have much better ENOB than competitor "Z's" 16-bit product at test frequencies above 30 MHz!

Graph of 12-Bit Digitizer ENOB Performance: CompuScope EON

Figure 1 – ENOB vs. Frequency for 12-bit to 16-bit Digitizers

 

Figure 2 below shows another case of the ENOB comparisons between the GaGe 8-bit Cobra Digitizer and competitive products. Again, the GaGe ENOB remains fairly flat across frequency, and easily beats a competitor’s 10-bit design.

Graph of 8-Bit Digitizer ENOB Performance: CompuScope Cobra

Figure 2 – ENOB vs. Frequency for 8-bit to 10-bit Digitizers

 

Customers have acknowledged the GaGe difference in digitizer ENOB performance as well. Recently an engineer told us about ENOB tests they performed on many new 12-bit, 1 to 2 GS/s digitizer products. Their results showed the GaGe CS121G2 CompuScope 2 GS/s digitizer had 1.5 more effective bits than the other new models. This meant their system dynamic range was increased by about 9 dB by selecting GaGe.

If your company is pushing the limits, and wants the best measurement technology available today, look carefully at specifications beyond resolution and speed, and include ENOB in your final decision. Look to GaGe for the leading products in high speed digitizer technology.

Using Dynamic Parameters to Measure Digitizer Performance

Review featured GaGe article published in Embedded Technology for more information on ENOB and Digitizer performance:

High-Speed Digitizers / Oscilloscopes

GaGe high-performance digitizers are renowned for sustaining the maximum effective number of bits (ENOB) over a wide signal frequency range with quality signal conditioning and signal fidelity features.

High-Speed Digitizers High-Speed Digitizers

With sampling rates up to 6.0 GS/s and very deep onboard acquisition memory of up to 16 GB, our high speed PCIe and PCI digitizers provide optimal combinations of high sampling speeds with 8-bit, 12-bit, 14-bit, and 16-bit high resolution rates with large sampling memory options and high-speed data streaming capabilities.