Semiconductor curve tracer

A semiconductor curve tracer is a specialised piece of electronic test equipment used to analyze the characteristics of discrete semiconductor devices such as diodes, transistors, and thyristors. Based on an oscilloscope, the device also contains voltage and current sources that can be used to stimulate the device under test (DUT).

The function is to apply a swept (automatically continuously varying with time) voltage to two terminals of the device under test, and measuring the amount of current that the device permits to flow at each voltage. This so-called V-I (voltage versus current) graph is displayed on an oscilloscope screen. Configuration includes the maximum voltage applied, the polarity of the voltage applied (including the automatic application of both positive and negative polarities), and the resistance inserted in series with the device. The main terminal voltage can often be swept up to several thousand volts, with load currents of tens of amps available at lower voltages.

For two terminal devices (such as diodes and DIACs), this is sufficient to fully characterize the device. The curve tracer can display all of the interesting parameters such as the diode's forward voltage, reverse leakage current, reverse breakdown voltage, and so on. For triggerable devices such as DIACs, the forward and reverse trigger voltages will be clearly displayed. The discontinuity caused by negative resistance devices (such as tunnel diodes) can also be seen. This is a method for finding electrically damaged pins on integrated circuit devices.

Three-terminal devices such as transistors and FETs also use a connection to the control terminal of the device being tested such as the Base or Gate terminal. For transistors and other current based devices, the base or other control terminal current is stepped. For field effect transistors, a stepped voltage is used instead. By sweeping the voltage through the configured range of main terminal voltages, for each voltage step of the control signal, a group of V-I curves is generated automatically. This group of curves makes it very easy to determine the gain of a transistor, or the trigger voltage of a thyristor or TRIAC.

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