US 4,727,318 A · Apparatus for measuring characteristics of electronic devices

Abstract

An electronic device measurement apparatus measures a characteristic of an electronic device under test (DUT) by applying a sine-wave voltage to the DUT, detecting the voltage across the DUT as well as the current flowing through the DUT and displaying a characteristic curve in accordance with the detected voltage and current. The sine-wave voltage is generated in phase with an AC line voltage but the amplitude thereof is independent of the line voltage, and consequently the circuits in the measurement apparatus are not affected by variations in phase and amplitude in the line. Moreover, the generated sine-wave voltage is symmetrical, whereby display distortion is substantially eliminated. A voltage limiter and a current limiter are provided for limiting the voltage and current to be applied to the DUT to values determined by a display window, for protecting a current detecting resistor and a voltage divider connected to the DUT.

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Claims18

Dependent claims

An apparatus for measuring characteristics of electronic divices, comprising:

generator means for synthesizing a symmetrical alternating voltage in phase with an AC line voltage, said generator means including a variable frequency signal generator, a frequency divider for producing a plurality of divided output signals by dividing an output frequency of said variable frequency signal generator, a phase comparator for comparing one of the divided output signals from said frequency divider with the AC line voltage and controlling an oscillation frequency of said variable frequency signal generator in response to the comparison result, converter means for converting an input signal into the alternating voltage in response to the divider output signals from said frequency divider, and a voltage comparator for comparing a voltage corresponding to the alternating voltage from said converter means with a reference voltage so as to generate the input signal to said converter means;
voltage supply means for supplying said alternating voltage from said generator means to an electronic device under test;
voltage detector means for detecting the voltage across said electronic device;
current detector means for detecting the current flowing through said electronic device;
and
display means for displaying the characteristic of said electronic device in accordance with output signals from said voltage detector means and said current detector means.

3 more elements

Dependencies are inferred from the claim text.

Description8,213 words

Summary2,793 words

#The present invention relates to an apparatus for measuring the characteristics of electronic devices, such as transistors, diodes, etc.

#An electronic device measurement apparatus, generally known as a curve tracer, is useful to measure characteristics of electronic devices such as transistors, diodes, etc. A conventional electronic device measurement apparatus of this type is illustrated in FIG. 1, wherein an AC voltage from a line source is applied through a switch 10 to power supply circuit 12 as well as to variable transformer 14. The power supply circuit 12 produces DC voltages for each circuit of the measurement apparatus, while the variable transformer 14 supplies an AC voltage having a controlled amplitude to a primary winding of transformer 16. A plurality of taps are provided on the secondary winding of the transformer 16, and one of these taps, excluding the lowest position tap, is selected by a switch 18 for connection to the anode of diode 20 which half-wave rectifies the selected AC voltage. The elements 14-20 provide a collector supply circuit 21. The cathode voltage of diode 20 is applied to a first terminal of a device under test (DUT), e.g., to the collector of a transistor 26 through a load resistor 24 selected by a switch 22. The base of the transistor 26 receives a stepped bias signal from a bias supply circuit 28, while the emitter thereof, comprising a second terminal of the DUT, is grounded. The lowest tap of transformer 16 is connected to the emitter of the transistor 26 through a collector current detector resistor 32 as selected by a switch 30. Furthermore, a voltage divider 36 is selected by switch 34 and divides down the collector voltage Vc of the transistor 26 for application to a horizontal deflection plate of cathode ray tube (CRT) 40 via an amplifier 38 having a high input impedance. Differential amplifier 42 operates as a high input impedance voltage detector which detects a voltage across a resistor 32 (being substantially proportional to the collector current Ic) and couples this voltage to a vertical deflection plate of CRT 40. The CRT 40 displays the Vc-Ic characteristic curve of the transistor 26 as shown in FIG. 2, as the voltage thereacross is varied in response to half cycles of line voltage. In FIG. 1, the DUT 26 comprises a common emitter connected transistor. However, another electrode of the transistor may be grounded, or the DUT may comprise another electronic device such as a diode. In any case, the voltage-current characteristic of the DUT is displayed on CRT 40.

#The conventional measurement apparatus as shown in FIG. 1 has many disadvantages. For example, the collector supply circuit consisting of elements 14-20 uses the external line voltage directly, the line voltage waveform desirably comprising a sine-wave. It should be noted, however, that a pure sine-wave consists of only one frequency component while the waveform of the external line voltage is not a pure sine-wave, i.e., it is not a symmetrically repeated waveform, but rather includes various distortions. In other words, the repeated voltage waveform applied to the DUT, not being a pure sine-wave, is not symmetrical but rather contains differing frequency components, and it is found a forward trace of the characteristic curve displayed on the CRT 40 (during a rising period of the rectified sine-wave voltage) is different from a back trace thereof (during a falling period of the rectified sine-wave voltage). Therefore, the characteristic of the DUT cannot be measured exactly, but a phenomenon occurs called display distortion in this specification. Moreover, the peak amplitude of the line voltage is not constant but varies within a predetermined range. As a result of the variation, the peak amplitude of the repeat waveform voltage applied to the DUT varies in response to the line voltage, producing further inaccuracies in measurement.

Brief description of the drawings13 figures

#FIG. 1 is a block diagram of a conventional electronic device measurement apparatus;

#FIG. 2 comprises characteristic curves of a transistor under test displayed by an electronic device measurement apparatus;

#FIG. 3A is a circuit diagram of a part of a first preferred embodiment according to the present invention for illustrating a repeat waveform voltage generator employed therein;

Detailed description5,147 words

#Referring to FIGS. 3A and 3B (hereinafter jointly referred to as FIG. 3) there is shown a circuit diagram of a part of a first preferred embodiment according to the present invention. An AC line voltage is applied through a power switch 10 to a primary winding of a transformer 41 provided in a power supply circuit 12. A plurality of secondary windings of transformer 41 are connected to DC voltage regulator circuits (not shown) of the power supply circuit 12 for generating regulated DC voltages for each of circuits in the electronic device measurement apparatus. An AC voltage across the lowest position secondary winding of the transformer 41 is divided by resistors 43 and 45. A voltage comparator 47 compares the divided AC voltage with ground voltage for generating a pulse signal f.sub.L whose level is inverted every time the line voltage crosses ground voltage. It should be noted that this pulse signal f.sub.L is a reference signal having the same frequency and phase as the line voltage.

#An oscillation frequency of a variable frequency oscillator (voltage controlled oscillator or VCO) 51 is 2.sup.n (n is a positive integer) times the frequency of pulse signal f.sub.L, e.g., 4096(=2.sup.12) times the pulse signal f.sub.L. An output signal (4096 f.sub.L) from the VCO 51 is applied to a clock terminal of a counter 52 operating as a frequency divider. The frequency divider 52 divides the frequency of the output signal from the VCO 51 so as to generate signals 16f, 8f, 4f, 2f and f whose frequencies are sixteen, eight, four, two and one times the pulse signal f.sub.L, respectively. Bars over "16f", "8f", "4f" and "2f" represent that the signals are inverted in phase with respect to the input signal to the frequency divider 52. A phase comparator 49 compares the phase of the pulse signal f.sub.L with that of the output pulse signal f from the frequency divider 52 and controls the oscillation frequency of the VCO 51 such that the phase of the pulse signals f.sub.L and f are equal to each other. Thus, a phase locked loop consists of phase comparator 49, VCO 51 and frequency divider 52, and each of the output pulses from the frequency divider 52 is synchronized with the AC line voltage.

#An encoder circuit for encoding the output pulses from the frequency divider 52 includes four exclusive OR (XOR) gates 54-60, wherein XOR gate 54 receives the pulse signals 16f and 2f, XOR gate 56 receives the pulse signals 8f and 2f, XOR gate 58 receives the pulse signals 4f and 2f, and XOR gate 60 receives the pulse signals 2f and f. Thus, the phase of the output pulse signal S from XOR gate 60 is delayed by ninety degrees with respect to the pulse signal f, namely, f.sub.L, and the output pulses A-C construct a three-bit digital signal changing sequentially from "000" to "111" and from "111" to "000" every ninety degrees (a quarter period) of the pulse signal S. The phase relation of these signals is shown in FIG. 4.

Facts

Application

06/780,957Filed 27 Sep 1985

Priority

JP 59-2087914 Oct 1984

Granted

23 Feb 1988

Term ended

27 Sep 2005

Estimated · how

Pre-1995 term; greater of 17 years from grant or 20 years from filing when eligible. Maintenance-fee lapses, terminal disclaimers and statutory extensions have not been checked. The continuity chain may be incomplete; this is not an enforceability determination.

Classification3 codes

G01R 31/2603
Apparatus or methods therefor: for curve tracing of semiconductor characteristics, e.g. on oscilloscope
G01R 31/2607
Testing of individual semiconductor devices: circuits therefor
G01R
Measuring electric variables

Apparatus for measuring characteristics of electronic devices

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Apparatus for measuring characteristics of electronic devices

Life of this patent

Life of this patent

Abstract

Drawings

Drawings

Claims18

Description8,213 words

Description8,213 words

Drawings

Classification3 codes

Life of this patent