The present invention relates to testing electronic components such as discrete, analog components, and more specifically, is directed to methods and apparatus for acquiring and graphically displaying component test data.
Passive components such as resistors and capacitors as well as semiconductor junctions can be tested by applying an appropriate stimulus signal to a device under test (DUT), and then measuring circuit parameters such as voltage and/or current. One problem in the prior art test equipment is the limited range of capacitance values that can measured. Because prior art devices, such as the Huntron instrument described below, use analog oscillators as a source of test stimulus signals, their stimulus frequency range is limited. Accordingly, high capacitance components cannot be tested without a high-voltage stimulus source which in many applications is not practical. Moreover, stimulus signals generated using analog oscillators have only a limited selection of discrete frequencies available.
Graphical display of component test data, such as Lissajous patterns, is particularly useful in many applications. In the prior art, however, complex and expensive equipment such as an oscilloscope is required to generate such patterns. For example, using an oscilloscope, an X-channel can be used to acquire voltage data while a Y-channel is used to acquire current data. By displaying X versus Y with a common trigger to synchronize the display, Lissajous patterns or the like may be generated. This is not possible in simpler, hand-held instruments such as a digital multimeter (DMM) which have only a single channel "front-end".
A semiconductor test instrument known commercially as the "Huntron Tracker" is described in U.S. Pat. No. 4,074, 195. It is used for determining operating states of a semiconductor junction, and displaying a trace representative of the characteristics of the junction. One of the problems with the Huntron type of apparatus is that it requires a multi-tap transformer and voltage dividers for providing a range of AC test stimulus signals. More specifically, the prior art teaches a transformer driving a set of vertical voltage dividers to provide test signals for vertical deflection of the display, together with a set of horizontal voltage dividers to provide test signals for horizontal deflection of the display. See FIG. 1 of the `195 patent and column 4. The `195 system therefore requires constant AC power for operation, a heavy transformer, and a two-channel (vertical and horizontal) high-voltage display system like an oscilloscope. That technology, therefore, is not useful in lightweight, portable test equipment which is desirable for field use, for example by a repair technician.
The need remains, therefore, to provide new methods and apparatus for component testing which do not require high power or bulky equipment, yet provides wide range and high accuracy, at minimum cost.