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PicoScope and oscilloscope primer
12
Copyright 2006 Pico Technology Limited. All rights reserved. PSW044-2.0
5.8
Oversampling
Oversampling is a technique of capturing samples n times faster than the requested
sampling rate, then replacing each group of n adjacent samples with the average of
that group. If the signal contains a small amount of noise, the result of oversampling
is a waveform with increased effective resolution. The amount of oversampling
available depends on how fast your scope device can sample.
Procedure
First make sure that the Oversampling control is displayed on the Scope Setup
toolbar . If it is not, add this control to the toolbar as explained in the "Toolbars
" topic.
Use the Oversampling control to adjust the oversampling factor (n). PicoScope
allows oversampling factors in the range 1 (no oversampling) to 256.
How to choose the oversampling factor
To obtain an increase in effective resolution of n bits, you should choose an
oversampling factor of 4
n
. Conversely, an oversampling factor of f will give an
increase in effective resolution of log(f) / n log(4).
For example, if a scope device has a stated resolution of 8 bits, then an oversampling
factor of 4 will, under ideal conditions, increase this to 9 bits. An oversampling factor
of 16 will increase the effective resolution to 10 bits, and a factor of 256 will increase
it to 12 bits.
These calculations assume that the noise is Gaussian (follows a normal distribution).
This is approximately true for noise from natural sources, such as thermal noise in
resistors and sensors, but not be true for man-made noise such as radio interference
and mains (line) hum. The scope device itself often produces enough low-amplitude
noise to make oversampling successful.
The benefit of oversampling comes at the cost of having to increase the sampling rate.
If your scope device is already running at its maximum sampling rate in order to
capture high-frequency details in the signal, then it will not be able to oversample.
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