What Is a Curve Tracer?
A curve tracer is a device that displays the relationship between the voltage applied to a semiconductor device and the current flowing through it.
It is called a curve tracer because it traces a graph (curve) of the voltage-current characteristic and displays it on a display. In semiconductor devices, the relationship between the applied voltage and the flowing current is non-linear and not proportional, like a resistor.
Therefore, measuring the voltage vs. current characteristics of semiconductors and electronic devices requires procedures such as changing the voltage, measuring the current value, and plotting the results on a sheet of paper. With a curve tracer, however, the voltage-current characteristic can be directly displayed on a display.
Uses of Curve Tracers
Curve tracers are used to measure the characteristics of semiconductor devices during development, to inspect devices in manufacturing departments, and to verify the operation of circuits using semiconductors. The main measurement targets are semiconductor devices such as diodes, bipolar transistors, and FETs.
In semiconductors, the voltage applied to the target device is gradually varied and the current flowing at that time is measured. On the other hand, the display of the curve tracer shows the voltage value on the X-axis and the current value on the Y-axis, thus depicting the relationship between the voltage and the current value as a graph.
Optional power supplies are available for high voltage application and high current flow, and the equipment is ready to accommodate a variety of devices.
Principle of Curve Tracers
1. Measurement of Diodes
If the measurement object is a diode, connect a power supply for driving the device between the anode and cathode, set the maximum and minimum applied voltage values Vmax and Vmin, and the power supply will automatically sweep the voltage between them at a frequency of 50Hz to 60Hz. It also measures the current value flowing through the diode at this time.
The horizontal sweep circuit of the CRT uses the voltage of the power supply for driving the semiconductor device as the input signal, while the vertical sweep circuit uses the current flowing through the diode as the input signal, so that the current characteristic (V-I characteristic) against the applied voltage is drawn on the CRT.
2. Transistor Measurement
For bipolar transistor/FET measurements, a current/voltage source using a step generator is connected to the base/gate electrodes. The device drive power supply is connected between the emitter/source and collector/drain, and the maximum and minimum values of the applied voltage, Vmax and Vmin, are set.
For Bipolar Transistors
If the base current is varied stepwise with a step generator and the voltage between emitter and collector and collector current at that time is displayed on the CRT, the static characteristic curve of the transistor is drawn.
In the Case of FET
When the gate voltage is varied stepwise with a step generator, a static characteristic curve of a FET is drawn, showing the relationship between the voltage between source and drain and the drain current.
Curve tracers are designed based on the assumption that a CRT is used for the display. However, since CRTs are rarely produced anymore, the conventional type of curve tracer has disappeared.
Instead, a curve tracer that draws characteristic curves on a display by importing voltage-current characteristic data into a PC is now commercially available.
Structure of a Curve Tracer
A curve tracer consists of a power supply for driving devices, a step generator for controlling transistor base current and FET gate voltage, a CRT and its horizontal sweep and vertical sweep circuits, etc.
Other Information on Curve Tracer
Semiconductor Parameter Analyzer
Curve tracer is a very effective measuring instrument for understanding the basic characteristics of semiconductors, and was a basic measuring instrument utilized in all processes from research and development to product inspection, especially by device manufacturers. They are also used in user acceptance testing of semiconductor devices, and although several Japanese manufacturers used to produce them, all but a few have now withdrawn from the market.
On the other hand, curve tracers, which were developed for solar panel evaluation, are now being sold. In addition, semiconductor parameter analyzers have replaced curve tracers.
These are equipped with multiple voltage and current sources, and the voltage and current are controlled by a controller (PC) to measure the characteristics of semiconductors.