Article published Oscilloscope
Splitting signals to see them more clearly
Researchers have developed a patented process for accurately displaying a high-amplitude electrical signal on an oscilloscope.
High-amplitude electrical signals cannot always be displayed on an oscilloscope. The increased bandwidth of today's instruments is often achieved at the expense of dynamic range (signal-to-noise ratio). “That means it is impossible to measure a high-amplitude signal on the same input and in the same range of an oscilloscope with the required accuracy: the signal is either cut off at the top or the bottom,” points out Loïc Patissou, a researcher at CESTA*. A dynamic signal splitting system has been developed to overcome this problem by splitting the signal into several parts that can be displayed in the window. To put it more precisely, the electrical pulse, converted into an optical signal, is split into four replicas that are attenuated by a patented optical coupling system. In this system, three couplers work in a cascade configuration, each one acting rather like a “garden hose that has been split into two to reduce the water flow rate.” The most attenuated pulse is used to observe the top of the signal, while the least attenuated pulse displays the bottom part. This produces four images which are then combined using a computer program, which the researchers have specially designed and patented, to obtain an accurate reconstruction of the entire electrical signal. Optical fibres of varying length are used to obtain a time shift and allow acquisition of the various parts of the original pulse in succession on a single oscilloscope. This overcomes the need for several acquisition channels, thus avoiding the risk of measurement discrepancies. The applications of this invention chiefly concern high-power lasers.
* Centre d'études scientifiques et techniques d'Aquitaine.
