The Picotest J2111A Current Injector, together with the Bode 100, allows direct measurement of the output impedance, group delay and Q of the system. Using this information, the phase margin of the system can be calculated without breaking the feedback loop of the controller. This method is, therefore, considered “non-invasive.” In this application note, the results of the non-invasive measurement are compared to the “classical” Bode plot loop gain measurements.

This application note also shows how the phase margin of a linear voltage regulator (LM317) can be measured using the Bode 100 and additional accessories. The same techniques can be used to measure switching regulators as well. The measurements are performed on the PICOTEST Voltage Regulator Test Standard (VRTS) testing board.