Chapter 2 Analog InputE Series User Manual 2-8 ni.comDitherWith 12-bit E Series devices, you can improve resolution by enabling theGaussian dither generator and averaging acquired samples. Dithering is afeature on all 12-bit E Series devices. When you enable dithering, you addapproximately 0.5 LSBrms of white Gaussian noise to the signal to beconverted by the ADC. This addition is useful for applications involvingaveraging to increase device resolution, as in calibration or spectralanalysis. In such applications, noise modulation decreases and differentiallinearity improves with the addition of dithering. When taking DCmeasurements, such as when checking device calibration, enable ditheringand average about 1,000 points for a single reading. This process removesthe effects of quantization and reduces measurement noise, resulting inimproved resolution. For high-speed applications not involving averagingor spectral analysis, you may want to disable dithering to reduce noise. Thesoftware enables and disables the dithering circuitry.Figure 2-3 illustrates the effect of dithering on signal acquisition. Graph Ashows a small (±4 LSB) sine wave acquired with dithering off. The ADCquantization is clearly visible. Graph B shows 50 such acquisitionsaveraged together; quantization is still plainly visible. Graph C shows thesine wave acquired with dithering on. There is a considerable amount ofvisible noise, but averaging about 50 such acquisitions, as shown in graphD, eliminates both the added noise and the effects of quantization.Dithering has the effect of forcing quantization noise to become azero-mean random variable rather than a deterministic function of the inputsignal.
