Typically, pulsed semiconductor testing involves I-V (current-voltage) device characterization using an SMU with pulse generator functionality. A pulsed voltage stimulus is applied to the device and the resulting current measured. Alternatively, a pulsed current source supplies the stimulus and voltage measurements are taken.. Therefore, two high-speed analog-to-digital converters (ADCs) are needed, one for voltage and one for current, to digitize fast pulses. These ADCs should have at least 18-bit resolution. Integrating ADCs may also be needed for precision DC measurements and should provide 22-bit resolution.Many SMUs can deliver only an averaged result from a pulsed measurement, but it is highly desirable to have the flexibility to Wholesale USB Flash Memory examine the raw data at high sampling rates. To accomplish this, high-performance SMUs have high-speed ADCs that allow a 1MHz burst sampling rate similar to high-end data acquisition systems. Usually, the readings are stored periodically in an on-board non-volatile reading buffer before being transferred to the system controller for analysis.The availability of two high-speed ADCs in a single instrument provides an accurate and economical way to make simultaneous measurements at a true 1MHz sampling rate for both voltage and current. Theres no degradation in sample rate or signal integrity when the application requires sampling both signals at once. This type of SMU design can also produce a current waveform without the use of an oscilloscope and current probe.Its also important that both the high-speed and integrating ADCs support asynchronous measurements. With this type of design, users wont be limited to source-delay-measure test sequencing; they can set the pulse measurement trigger Wholesale wherever they desire in relation to the pulse. This greater trigger model flexibility allows users to trigger the measurement before the pulse, during the pulse, after the pulse, or across the pulse.These and additional pulse measurement features are available in the latest pulsed SMU designs, such as the Keithley Model 2651A SourceMeter instrument. Here are a few ways to use this flexibility with pulsed measurements:> The high-speed ADCs can digitize the top of the pulse when the measurements are made synchronously with the source. The ability to characterize the slope of the measured voltage at the top of the pulse is important for evaluating pulse amplitude flatness. For LEDs, the slope of the measured forward voltage (VF) indicates whether there is significant device self-heating.> Analysis software is often used to average sampled data to improve accuracy. Look for an SMU with averaging and median filters that can be applied to readings from the high-speed ADC to obtain spot mean measurements. Applications include studying the thermal impedance of power semiconductor devices. For example, changes in the VF of the source-drain diode, along with external temperature measurements of the device package and surrounding environment, indicate how the semiconductor junction temperature changes whenever a high power pulse passes through it, and how the heat the device generates is transferred out of the packaging. > For a variety of applications, it is useful to characterize how a pulse is transmitted through a device or system, which requires digitizing the entire pulse, including the rising and falling edges. This measurement is possible using high-speed ADCs to measure asynchronously with the source operation.> Pre-pulse characterization, which involves triggering measurements before the pulse occurs, is another useful sourcing and measurement mode. Pulses are sometimes used to provide power stresses to the device. It is useful to note the device state before the stress is applied. This can be done by programming a pulse with a non-zero idle level and triggering the measurements Plastic Model Kit before the pulse. For this you want an instrument that allows users to specify how long before the pulse the measurements should be made.> Post-pulse characterization requires triggering measurements after the pulse occurs. When using pulse testing to stress a device, the device must also be characterized after the stress is applied. This is typically done by sourcing a pre-defined test voltage or current after the pulse. The test level is chosen so as not to cause any additional thermal or electrical stress to the device. The measurement can be made by sourcing a pulse with a non-zero idle level and using high-speed ADCs to perform the measurement. The results from the high-speed ADCs indicate how the device recovers from the stress.For device designers and others involved in enhancing semiconductor device efficiency, high-speed ADCs in SMUs such as Keithleys Model 2651A provide a more detailed look at the measurements of pulsed Unique USB Accessories waveforms than ever before available within a single instrument. As a result, they can be used for a variety of transient characterization applications that were previously impractical with commercially available SMUs.References. To learn more about the advantages of SMUs with high-speed ADCs, download a free copy of the application note: Measuring Pulsed Waveforms with High Speed Analog-to-Digital Converters.
