5 Best Practices for Maximizing DC Measurement Performance
Whether you are testing power management ICs or RF power amplifiers, taking quality DC measurements is a cornerstone of testing semiconductor chips. Improve measurement accuracy and product quality by applying these foundational best practices.
1. Use Remote Sense to Offset the Effects of Lead Resistance
In a typical 2-wire measurement, the resistance of your leads is unaccounted for. This results in a voltage drop across the lead and introduces error in measurements. The effects of lead resistance are especially noticeable when taking low-resistance and low-voltage measurements. Remote sense is a 4-wire measurement setup designed to counteract the effects of lead resistance. With remote sense, one set of leads carries the output current while another set of leads measures voltage directly at the device-under-test (DUT) terminals. This allows the instrument to compenstate for the voltage drop and improve measurement results.
2. Compensate for Offset Voltage
A common source of offset voltage error is thermal EMF, which is produced when two dissimilar metals at different temperatures come in contact with each other. This forms a thermocouple that produces voltage in the measurement circuit. Error due to thermal EMF is typically in the range of microvolts, which makes this an important consideration when making low-voltage or low-resistance measurements. Offset compensation and current reversal are two methods that eliminate offset voltage and improve the accuracy of results.
3. Minimize External Noise
A variety of sources like electromagnetic interference or parasitic capacitance can introduce noise into your measurement system. Electromagnetic interference can come from things like AM/FM radio, TV, or power lines. Parasitic capacitance occurs when a charged object is close to your measurement circuit. This can show up as an oscillating noise or an offset to your measurement. Adding shielding to your measurement setup reduces these sources of error, which results in a cleaner signal for your instrument to measure.
4. Guard Against Leakage Current
A guard is a conductive layer added between the HI and LO terminals of your measurement device that is driven to the same voltage potential as the HI terminal. Whereas shielding protects against external sources of electromagnetic interference, guarding prevents leakage current from flowing between the shield and the measurement circuit. This is especially critical for low-current measurements. As an added benefit, the guard layer reduces the effects of parasitic capacitance from the shield, which improves your signal's settling time.
5. Understand the Importance of Calibration
Calibration is necessary for your instrument to achieve its warranted specifications. Many are familiar with external calibration where your device is sent to a metrology lab to correct for drift over time, but another form of calibration called self-calibration is just as important and helps the instrument perform consistently as the device temperature changes. Simple changes in the room temperature of your lab or testing your device over its operating temperature range can have major effects on your measurements. Self-calibration ensures your measurements are accurate every time.
Technical White Paper
Maximizing DC Measurement Performance
Maximizing DC Measurement Performance
In this guide, learn how you can improve measurement accuracy and product quality for power management ICs, RF power amplifiers, and other ICs. Dive deeper into the 5 best practices outlined above, and learn about the following topics:
- Source measure unit theory of operation
- Measurement accuracy
- Accuracy versus speed trade-off
- The effects of pulsing