• • • POWER SUPPLIES • • •
simulate disturbances and unstable operating conditions. Compared to conventional power supplies, the
R&S NGU source measure units offer two additional features that are important for practical measurements:
True current regulation Standard lab power supplies only provide fast ?voltage regulation. While a current limit can be set and the device appears to provide current regulation in constant ?current mode, it is inherent in the design that this regulation is considerably slower than the voltage regulation. This results in large current overshoots under switch-on and load change conditions. Sensitive loads such as laser diodes frequently suffer damage from these overcurrents. To avoid this risk, the power supplies of the R&S NGU series feature true current regulation, with a load recovery time (< 50 µs) nearly as short as that for voltage regulation, and reducing overshoots to a minimum.
High-capacitance mode The capacitor typically provided at the DUT input is a frequent source of error when measuring supply current and voltage. Together with the leads connecting the power supply to the DUT, it forms a lowpass filter that distorts measurement results. The R&S NGU units feature a capacitance mode adjustable in steps, compensating the input capacitance, so that the current measured is the true current flowing into the DUT.
Summary Power supplies offering high measurement accuracy and the ability to handle currents and voltages in the nanoampere and microvolt ranges are needed to develop battery-powered mobile and IoT devices. The R&S NGU series adds a class of precision source measure units to the Rohde?&?Schwarz portfolio of general purpose lab
Figure 3: Standard power supplies are optimized for fast voltage changes. This is at the expense of large current overshoots (left), which can damage sensitive DUTs such as LEDs. The current priority mode selectable on the R&S NGU power supplies resolves this issue (right).
Figure 4: The capacitance present at the inputs of many circuits distorts measurement results by filtering the supply current (red). The high-capacitance mode offered by the R&S NGU ensures that the current measured is the true current flowing into the circuit (green).
DC power supplies. The R&S NGU201 two- quadrant model targets wireless applications, while the R&S NGU401 four-quadrant model is the specialist for semiconductor tests. Along with a wealth of features that make testing simpler, the units have generously dimensioned
heat sinks and barely audible fans, making them extremely quiet – a feature that is often overlooked but very much appreciated by lab engineers. These units are indispensable for anyone who develops sensitive circuits or autonomous IoT devices.
With the two-quadrant R&S NGU201 and its four-quadrant counterpart R&S NGU401 (shown here), Rohde & Schwarz has entered the market for precision power supplies (source measure units)
26 ELECTRICAL ENGINEERING • DECEMBER 2021/JANUARY 2022
electricalengineeringmagazine.co.uk
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