Rohde & Schwarz, a leading manufacturer of test & measurement, communications and broadcasting equipment, has developed an oscilloscope that ensures high-signal fidelity when measuring the dynamic “on” resistance of power FETs (field-effect transistors).
Providing fast overdrive recovery, low front-end noise, and the highest effective number of bits (ENOB) available in its class, the advanced R&S®RTO Series oscilloscope allows users to overload the scope without distorting the measurement. The R&S®RTO Series oscilloscope features a sophisticated A/D converter for acquiring signals, which significantly reduces distortion and provides a high voltage per division setting, while enabling an ENOB value of seven.
“Two primary performance characteristics when measuring the dynamic “on” resistance of a power FET are the overdrive recovery and internal noise level. One of the key elements in high-efficiency power supplies for LED drivers, hybrid/electric cars and other electronic devices is the switching transistors that regulate voltage. These devices must be as efficient as possible, and efficiency is related to the resistance in the “on” state when the devices dissipate power. Lower resistance means lower dissipated power, and consequently results in higher efficiency, said Mike Schnecker, business development manger at Rohde & Schwarz.
The measurements required span a broad range. The dynamic resistance is determined by measuring the voltage across the transistor in the “on” state, which tends to be extremely small (a few hundred mV); yet at the same time the “off” voltage can be hundreds of volts. Allowing the signal to overload the scope front end allows the operator to use a lower volt per division setting, which dramatically improves the accuracy of the measurement, Schnecker explained.
Featuring a fast and accurate acquisition system that captures even rare events, the R&S®RTO Scope Series provides a gain range of one-millivolt per division. In addition, the oscilloscope uses a real-time digital trigger that employs a common signal path for both the trigger and acquired data. This eliminates time and amplitude offset between the trigger and signal, enabling signals to be displayed with the least possible trigger jitter and allowing precise results to be achieved when measuring complex waveforms.
Analog triggers typically have a long re-arm cycle, and while re-arming, the instrument cannot react to trigger events, which means signal properties that should act as triggers are masked. Because the R&S®RTO Scope Series’ digital trigger does not need to re-arm, every sample can trigger data acquisition to avoid missing events.