SOLID-STATE CHARACTERISTIC CURVE TRACER ATTACHMENT FOR OSCILLOSCOPES

摘要

1275071 Testing transistors W G DILLEY 14 May 1969 [27 May 1968] 24684/69 Heading G1U [Also in Division H3] A curve tracer attachment for use with an oscilloscope to enable the oscilloscope to display characteristic curves of a device under test incorporates a staircase waveform generator (which includes a differential amplifier with positive feedback for converting a sine wave to a square wave, a differentiator for converting the square wave to a pulse train and means for converting the pulse train to a staircase waveform) close output waveform is applied to the device under test e.g. as a base current drive, to produce a resultant waveform indicative of device characteristics. The attachment incorporates arrangements for converting the resultant waveform (representing e.g. collector current and voltage waveforms) to horizontal and vertical waveforms suitable for application to the horizontal and vertical deflection systems of an oscilloscope, arrangements for supplying power to the test device and to the staircase generator and arrangements including a polarity selector for applying power to the system by which the staircase waveform is applied to the test device. The staircase waveform is preferably synchronised to the line scan frequency of the oscilloscope. The arrangement shown enables a test transistor Q9 to be tested under a wide range of voltage, load and current drive conditions. Although the transistor is shown as being tested in common emitter configuration other configurations may obviously be used. The arrangement may be made as a plug in unit, for use with oscilloscopes accepting such units, in which case all its power supplies are derived from the oscilloscope and it contains a vertical amplifier to replace that in the oscilloscope as shown Fig. 1. The overall organisation of the test system is shown schematically in Fig. 2, with the attachment included within dashed lines. Alternatively, it may be made as an attachment requiring a separate low voltage power supply Fig.3 (not shown), or a separate console, using none of the oscilloscope facilities Fig. 13 (not shown). In the embodiment of Figs. 1 and 2 the transistor Q9 under test is connected in a test station where its emitter is earthed. Its collector receives power from a sampling unit designed to provide rectified but unsmoothed pulses of adjustable amplitude. This unit receives A. C. from the oscilloscope power supply via transformer Tl, and provides an output in two ranges, 0-50 the maximum being set by R22, or -50 to +50, by changing the switch S3. One side of this output is applied to the transistor collector via a selected load resistor S2. The other side is connected to earth via a resistor S1 selected according to the measuring range to detect the collector current. The voltages appearing across the selected resistor S1 represents the collector current and is relative to ground: it is applied to a vertical amplifier and thence to the vertical plates of the oscilloscope. The voltage at the transistor collector is applied to the horizontal plates of the oscilloscope. Details are given in the specification relating to the structure of the staircase waveform base drive generator and the vertical amplifier. (See Division H3).