Rohde & Schwarz has announced its entry into the source measurement unit (SMU) market, with two new instruments to analyze and optimize battery lifetime testing for internet of things (IoT) applications and for semiconductor component testing.
The new R&S NGU series of source measurement units (SMUs) launch with two models, R&S NGU201 and R&S NGU401. These units mark Rohde & Schwarz’s entry into a new market, offering products that enable simultaneous current and voltage generation and measurement. This is a class of instruments that can simultaneously deliver voltage or current in a well-controlled mode and measure the correspondence of voltage and current values on the device under test. The two-quadrant R&S NGU201 targets battery testing of wireless devices, while the four-quadrant R&S NGU401 can switch to negative voltages and supports a much wider voltage range, for semiconductor testing.
Philipp Weigell, director of product management and planning for power products, meters, sources, and audio analyzers at Rohde & Schwarz, said the true definition of a source measurement unit is one that provides very precise sourcing, loading and measuring functions. The higher-end NGU401 matches the strict definition of an SMU, in that it provides four quadrant source or sink operation with arbitrary polarity; this makes it ideally suited to testing and characterizing semiconductors. The other two key sectors addressed by the new SMUs are precision electronics, as well as research and education.
Defining the SMU
An SMU is an instrument that combines a signal-generation function and a measurement function on the same pin or connector. It can generate voltage or current and measure them simultaneously, effectively encompassing the capability of a power supply or waveform generator, a digital multimeter, a current source, and an electronic load.
SMU instruments are used in test systems to measure both voltage and current. They enable rapid measurements of currents (or voltages) as a function of variable voltage (or current) while having a graphical interface and multiple computing options and system buses such as GPIB, Ethernet, and USB.
SMUs enable the characterization of many semiconductors and, in particular, the accurate measurement of I-V parameters and characteristics of photovoltaic cells or LED diodes, including short-circuit current, open-circuit voltage, and maximum power point. Semiconductor characterization is an example of an application that requires current sensitivities in the nano- or micro-amp range. In addition, the demand for higher accuracy, high speed, remote voltage sensing, and four-quadrant measurements can make a traditional programmable power supply insufficient.
The SMU instrument is a precision sourcing element that provides a measurement resolution of less than 1 mV. They have four-quadrant outputs on an I-V plane, meaning they can provide positive voltage and current (Quadrant 1), negative voltage and positive current (Quadrant 2), negative voltage and negative current (Quadrant 3), or positive voltage and negative current (Quadrant 4).
The new units
Modern circuits require different levels of voltage and/or current in different operating states. For example, simulating a startup sequence of an embedded system requires particular voltage and current profiles. Profile analysis is critical to optimize current consumption.
The R&S NGU SMUs include six current ranges, from 10 µA with 100-pA resolution to 10 A with 10-µA resolution. For all ranges, accuracy down to 0.025% is achieved. Voltage is measured with a resolution of 10 µV in the 20-V range and 1 µV in the 6-V range. The R&S NGU features a variable capacitance mode that can be adjusted in steps from 1 µF to 470 µF, compensating the capacitance so that the current is displayed as if it were measured directly on the device under test. Devices up to 20 V, 8 A, and 60 W are supported.
The biggest market for the four-quadrant R&S NGU401 is in semiconductor testing. It provides measurements in the range of –20 V to 20 V. It includes a fast-current adjustment mode to avoid damage to sensitive devices such as LEDs. A dedicated output renders the instrument as an AC source for simulating glitches.
The two-quadrant R&S NGU201 is optimized for battery performance analysis for a range of IoT devices. Designers can use it to simulate real-world battery characteristics. With its maximum current of 8 A, the instrument also supports fast-charging applications.
Weigell highlighted how it is critical to simulate and test rechargeable batteries to deliver better performance in portable devices. Overcharging and intense discharge reduce battery life and could induce thermal issues such as overheating. “Many batteries are built by putting many cells in parallel,” said Weigell. “In these cases, it is critical to control the state of charge; different values can limit the overall capacity of the battery. Therefore, it is critical to test the battery management systems that monitor and control the state of the batteries. Tests must simulate all conditions that might occur during operation. To define a battery model, the battery’s data can be entered in a pre-defined table. The R&S NGU power supply simulates the real output performance of the battery.”
With an acquisition rate of up to 500 ksamples per second, voltage and current results are available every 2 µs. The R&S NGU uses current feedback amplifier technology for providing high accuracy, as indicated in the figure below.
Battery lifetime is a winning factor that can offer portable devices long operating life. High dynamic range (nA to A), time resolution (state switches), and simulation of different batteries are the main features that a typical instrumentation must have.
“The typical power supply would regulate the voltage, so if you regulate the voltage, the current goes up and might destroy your LED,” said Weigell. “So essentially, what you need is a power supply that regulates on the current, in current priority mode. And this is a thing you’ll also find in SMUs.”
In recent times, the increasing demand for more energy-efficient and environmentally friendly products has helped revitalize the power semiconductor industry. SMUs enable the characterization of many semiconductors and will find a place in the automotive and mobile markets for the characterization of batteries, which are becoming increasingly important.
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