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Oscilloscope Fundamentals

Posted by marius 26/07/2021 0 Comment(s) 406 Test & Measurement,

In this short post Rohde & Schwarz guides us on what are the five main characteristics to consider when choosing a digital oscilloscope.


Bandwidth is the most important oscilloscope attribute.
► Oscilloscopes can only accurately measure signals with frequencies less than the rated oscilloscope bandwidth; input signals greater than the oscilloscope bandwidth will not be captured and displayed
► The bandwidth of an oscilloscope is the frequency at which an input signal is attenuated by 3 dB;
at this frequency, a sine wave will have a displayed amplitude of 70.7% of the real signal amplitude
► To correctly measure digital signals, the oscilloscope’s bandwidth should be at least 5 times the signal frequency to capture the fundamental frequency plus the 3rd and 5th harmonic


Memory depth is the number of ADC samples stored per acquisition.
► Captured time = memory depth / sampling rate
► The more memory depth, the more time can be captured in an acquisition
► When sampling at the fastest rate and using all memory, the oscilloscope is forced to reduce the sampling rate when you acquire more time
► More memory is always better, but it can require additional processing time and slow down the acquisition rate


An oscilloscope’s sampling rate is the number of samples/s that the instrument can acquire.
► The oscilloscope’s ADC (analog to digital converter) determines the sampling rate
► To accurately reconstruct signals, the sampling rate needs to be at least twice the signal frequency; most scopes have a maximum sampling rate of 2.5 times the oscilloscope’s rated bandwidth
la maggior parte degli oscilloscopi ha una frequenza di campionamento massima di 2,5 volte la larghezza di banda nominale dell'oscilloscopio
► Aliasing occurs when the sampling rate is too slow


The vertical resolution of an oscilloscope is determined by the oscilloscope’s ADC.
► An 8-bit ADC can place an input signal into any of 256 (28) vertical levels, while a 10-bit ADC has 1024 (210) vertical levels
► Oscilloscope noise produces vertical values that deviate from the actual signal values by the amount of inherent noise
► For repetitive signals, averaging of acquisitions reduces noise
► The high resolution mode averages adjacent signals and can be used on all signals


Oscilloscopes with faster acquisition rates have less dead time between acquisitions.
► Oscilloscopes with faster acquisition rates feel more responsive when you turn knobs or push buttons
► Oscilloscopes with faster acquisition rates feel more responsive when you turn knobs or push buttons
► Acquisition rate slows down as the acquisition memory depth is increased, due to additional processing time
► Acquisition rate slows down when measurements and math are enabled




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