Resolution
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This tutorial recommends tips and techniques for using National Instruments high-speed digitizers to build the most effective data sampling system possible. In this tutorial, you will learn fundamental information about the underlying theory of sampling with a high-speed digitizer and various methods to optimize the performance of your data sampling. This section of the tutorial covers resolution.
The best way to understand the concept of resolution is by comparison with a yardstick. Divide a 1 meter yardstick into millimeters. What is the resolution?
The smallest “tick” on the yardstick is the resolution. Yes, you might be able to interpolate between these, but in the absence of this sophisticated guessing process the resolution is 1 part out of 1000.
The resolution of a n-bit analog-to-digital Converter (ADC) is a function of how many parts the maximum signal can be divided into. The formula to calculate resolution is 2^n. For example, a 12 bit ADC has a resolution of 2^12 = 4,096. Therefore, our best resolution is 1 part out of 4,096, or 0.0244% of the full scale.
An ADC takes an analog signal and turns it into a binary number. Thus, each binary number from the ADC represents a certain voltage level. Resolution is the smallest input voltage change a digitizer can capture. Resolution can be expressed in bits (LSB), in proportions, or in percent of full scale.
Resolution limits the precision of a measurement. The higher the resolution (number of bits), the more precise the measurement. An 8-bit ADC divides the vertical range of the input amplifier into 256 discrete levels. With a vertical range of 10 V, the 8-bit ADC cannot ideally resolve voltage differences smaller than 39 mV. In comparison, a 14-bit ADC with 16,384 discrete levels can ideally resolve voltage differences as small as 610 µV.
Let us examine how a sine wave would look if it is passed through ADCs with different resolutions. We will compare a 3-bit ADC and a 16-bit ADC. A 3-bit ADC can represent 8 discrete voltage levels. A 16-bit ADC can represent 65,536 discrete voltage levels. As you can see, the representation of our sine wave with 3-bit resolution looks more like a step function than a sine wave. However, the 16-bit ADC gives us a clean looking sine wave. Note that if you are using a 3-bit ADC, minute voltage fluctuations in the incoming signal will not be detected.
Another way to think of resolution is by considering your television screen. The higher the resolution of the screen, the more pixels you have to show the picture, so you get a better picture.
Related Links:
Fundamentals of High-Speed Digitizers
Utilizing Deep Memory on High-Speed Digitizers and Oscilloscopes
Reader Comments | Submit a comment »
The explaination is simple and easy to
understand. THX
- Suong Lee, US Navy, Seal Beach. suong.lee@navy.mil - Sep 20, 2005
Reqiured resolution Calculation
Topic is very clear to understand but it
would be better if you explain clearly with
an example with a solved problem.
- mynampati@gmail.com - Apr 4, 2005
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