Method and apparatus for detection of non-linear electrical devices

Abstract

The present invention provides a system for applying a fixed level D.C. voltage and a square wave signal sequentially to a voltage divider including a resistor of a known impedance and the device under test. The square wave ranges from a value which is substantially equal to the ground level to a level that is substantially twice the nominal value of the fixed D.C. level, thus the average value of the square wave signal is substantially equal to the nominal value of the fixed level D.C. voltage. With each of these signals applied on at a time to the voltage divider, the voltage across the device under test is applied to a voltage detector via a low pass filter. The output of the low pass filter for each applied voltage signal is the average of the voltage signal which appears across the device under test. The value of these average voltages are stored and then compared. If the average values are substantially equal, then the device under test is linear, and knowing the average voltage value, the nominal voltage value, and value of the known resistor, the resistance value of the device under test can be calculated. If the average values of the voltages across the device under test varies from the application of the fixed level D.C. voltage and the square wave signal, the device under test is non-linear, e.g. a diode or transistor junction.