Storage Oscilloscope

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Storage Oscilloscope

Digital storage oscilloscope vertical resolution?

Anyone know the following specification about the vertical resolution 8 bits means? on the performance of a digital storage oscilloscope? Can someone explain it to me?

Vertical Resolution and Accuracy
The resolution and accuracy of an oscilloscope can affect measurements greatly, so it's important to understand these limitations. An oscilloscope with an 8-bit analog-to-digital converter (ADC) has 28 (256) levels available while a 16-bit ADC has 216 (65536) levels. Thus, a 16-bit oscilloscope has 256 times more resolution than an 8-bit oscilloscope. Since only finite levels are available to represent the signal, there is a quantization error of 1 least significant bit (LSB). To find the minimum detectable voltage change (code width), divide the input range by the number of levels. Figure 1 depicts a 16-bit oscilloscope digitizing an 8 Vpp square wave with a 100 mV ripple voltage. In this case, the oscilloscope's code width is (10/65536) 150 uV which allows it to produce a good representation of both the large and small signals. An 8-bit oscilloscope's code width would be only (10/256) 39 mV, so it could not show the 100 mV component adequately. Changing the input range setting to 250 mVpp would improve the performance, reducing the code width to (0.25/256) 1 mV.

The dynamic range of an oscilloscope refers to how well the instrument can detect small signals in the presence of large signals and is expressed in decibels (dB). It is limited by the quantization error and all other noise sources such as background noise, distortion, spurious signals, etc. The dynamic range of an oscilloscope refers to how well the instrument can detect small signals in the presence of large signals and is expressed in decibels (dB). It is limited by the quantization error and all other noise sources such as background noise, distortion, spurious signals, etc. The equation for computing the dynamic range is:
Vmax is the maximum voltage that must be acquired and Vres is the minimum resolution that can be seen. A good rule of thumb is that every bit of resolution equals 6 dB of dynamic range. An 8-bit instrument's theoretical maximum dynamic range is 48 dB, but it is significantly less once all limitations are considered.

Accuracy refers to the oscilloscope's ability to represent the true value of a signal. An oscilloscope with high resolution, does not necessarily translate into giving an accurate result. Accuracy and resolution are related though, because the achievable accuracy of an instrument is limited by the resolution of the ADC.

The factors that reduce the accuracy of an oscilloscope can be mostly lumped into high- and low-frequency errors. Noise is generally the cause of high-frequency errors, while low-frequency errors are caused by drift stemming from temperature, ageing, bias currents, etc. High-frequency errors can usually be removed by oversampling and averaging. Low-frequency errors often require the calibration of the instrument, either internally or through a factory calibration.

Reference:

http://tinyurl.com/4nssc6

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