Characterisation of oscilloscopes with time domain measurement and spectrum analyser functions
Many lab-quality oscilloscopes have spectrum analyser capabilities in addition to time-domain measurements. Due to the increasing prevalence of telecoms applications in today's design environments, modern oscilloscopes have also added some functionality similar to dedicated spectrum analysis.
Many factors have contributed to the increased accuracy and resolution of measurement instruments. For example, 8-bit oscilloscopes with floating-point FFT operations can observe signals down to -100 dBm (about 2 µV). However, at this level some oscilloscopes also show large harmonics, whereas spectrum analysers do not.
A good spectrum analyser
There are three metrics that can be used to determine the performance of an oscilloscope-based spectrum analyser: resolution bandwidth (RBW), noise floor and dynamic range. These three metrics can be used to compare dedicated spectrum analysers with oscilloscopes.
* Resolution Bandwidth
RBW determines the ability of neighbouring signals to be distinguished, the smaller the RBW index the better the ability to distinguish adjacent frequencies. the smaller the RBW the better.
* Noise floor
The noise floor of an instrument is its own inherent noise. The noise floor determines the minimum level of the input signal that can be observed. If the input signal is to be distinguished from the noise floor as a valid input, it must have a higher amplitude than the noise floor. The smaller the noise floor, the better.
* Dynamic Range
This is the maximum ratio of the amplitude of the input signal to the amplitude of the noise floor, and the greater the dynamic range, the better.
These three parameters, as well as some other instrument characteristics, must be considered. In addition, relatively important characteristics related to the application should not be ignored. With the recent stage of development of data acquisition technology, there have been some oscilloscope platforms comparable to the top spectrum analysers.
These three parameters, as well as some other instrument characteristics, must be considered. In addition, the relatively important characteristics related to the application should not be ignored. With the recent stage of development of data acquisition technology, some oscilloscope platforms comparable to the top spectrum analysers have emerged.
