Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
  • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
  • G01R31/26—Testing of individual semiconductor devices
  • G01R31/2607—Circuits therefor
  • G01R31/2621—Circuits therefor for testing field effect transistors, i.e. FET's
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
  • G01R15/04—Voltage dividers
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
  • G01R19/0084—Measuring voltage only
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
  • G01R31/26—Testing of individual semiconductor devices
  • G01R31/2607—Circuits therefor
  • G01R31/2637—Circuits therefor for testing other individual devices
  • G01R31/2639—Circuits therefor for testing other individual devices for testing field-effect devices, e.g. of MOS-capacitors
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
  • G01R31/26—Testing of individual semiconductor devices
  • G01R31/2607—Circuits therefor
  • G01R31/2608—Circuits therefor for testing bipolar transistors
  • G01R31/2617—Circuits therefor for testing bipolar transistors for measuring switching properties thereof

Definitions

• This relates generally to measuring transistor operating characteristics, and more particularly to systems and circuits to measure voltages across high-voltage transistors during switching to determine on-state impedances during switching.
• Gallium nitride (GaN) and aluminum gallium nitride (AlGaN) high electron mobility transistors (HEMTs), silicon carbide (SiC) and other high voltage transistors are becoming popular for high voltage power conversion applications, due to high breakdown voltages and low on state resistance and reduced conduction losses.
• Electron trapping in AlGaN/GaN HEMTs causes current collapse and increased drain-source on-state resistance (RDSON) in certain dynamic conditions.
• RDSON drain-source on-state resistance
• measuring the dynamic RDSON performance of HEMTs is difficult. Measurements by semiconductor testers do not simulate the true device conditions in actual power electronics circuits. For example, switching transistors in typical power converters undergo a hard-switching transition before turning on.
• the transistors also switch at high frequencies, typically hundreds of KHz, and thereby the measurement needs to reflect the RDSON value within a very short time after turn on, such as a microsecond in some instances. These conditions are very difficult to replicate in semiconductor testers, particularly for testing multiple devices. Improved circuits and techniques for measurement of the dynamic RDSON under the operating conditions of real power electronics circuits are therefore desired, particularly for HEMTs such as high-voltage AlGaN/GaN and SiC transistors.
• One approach is to measure the on-state drain-source voltage and the corresponding transistor current during dynamic operation. However, the drain voltage in high voltage applications varies between hundreds of volts in the off state and millivolts in the on state.
• the system includes a drive circuit to turn the high-voltage transistor on and off in a high voltage circuit, a subjecting circuit to subject the high-voltage transistor to a hard-switching transition, and a current sense circuit to provide a signal representing a current flowing through the high-voltage transistor during switching.
• the system includes a measurement circuit with attenuator and differential amplifier circuitry to provide an amplified sense voltage signal representing the voltage of the high-voltage transistor during switching, and a high-speed analog signal digitizer, such as an oscilloscope, to provide an on-state impedance value based on the slope of the current sense signal and the slope of the amplified sense voltage signal.
• the measurement circuit includes an attenuator circuit to generate an attenuator output signal representing a voltage across the high voltage transistor when the high voltage transistor is turned on, and a differential amplifier to provide an amplified sense voltage signal according to the attenuator output signal.
• the attenuator circuit includes a clamp transistor coupled with the high voltage transistor to provide a sense signal to a resistive voltage divider circuit to provide the attenuator output signal, and a first clamp circuit to limit the sense signal voltage when the high voltage transistor is turned off.
• a second clamp circuit in certain embodiments conditions the attenuator output signal, including a low capacitance diode to limit the voltage of the attenuator output node, and a compensation capacitor can be included to compensate a capacitance of the differential amplifier input for fast signal settling time.
• the resistive voltage divider circuit is adjustable in certain examples to facilitate measurement of a wide dynamic range of drain-source voltage and other parameters associated with the DUT RDSON.
• FIG. 1 is a schematic diagram of a high voltage transistor device under test and a test pod including an attenuator circuit and a differential amplifier circuit.
• FIG. 2 is a schematic diagram of a second test by example.
• FIG. 3 is a schematic diagram of a motherboard including a plurality of test pods and multiplexer circuits.
• FIG. 4 is a system diagram showing a plurality of motherboards providing signals to first and second levels of multiplexers to provide input signals to an oscilloscope to analyze devices under test.
• FIG. 5 is a simplified system diagram showing a high voltage transistor device under test (DUT) undergoing measurement of drain voltage and source current during switching in a high voltage subjecting circuit in the system of FIG. 4.
• DUT high voltage transistor device under test
• FIG. 6 is a graph showing gate voltage, drain voltage and source current waveforms for analyzing drain-source on resistance using voltage and current slope analysis for a high voltage transistor device under test in the system of FIG. 4.
• FIG. 7 is a graph showing oversampling and linear curve fitting for drain voltage and source current data in the system of FIG. 4.
• FIG. 8 is a graph showing signal waveforms in the system of FIG. 5.
• Couple includes indirect or direct electrical connection or combinations thereof. For example, if a first device couples to or is coupled with a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via one or more intervening devices and connections.
• Example embodiments include systems to determine high-voltage transistor RDSON, and measurement circuitry to measure the transistor drain voltage during switching.
• the circuitry facilitates high-resolution measurement of dynamic characteristics of drain-source voltages of AlGaN/GaN and SiC devices or other high voltage transistors.
• the apparatus and techniques are useful in hard-switching and other high-voltage circuits, including a high voltage transistor device under test (DUT) undergoing switching.
• DUT high voltage transistor device under test
• FIG. 1 shows a measurement circuit 100 including an attenuator circuit 102 and an amplifier circuit 120 to measure a drain voltage of a high voltage transistor M0.
• the attenuator circuit 102 generates an attenuator output or drain voltage clamp signal VDCLAMP at an attenuator output node 121.
• the attenuator output signal VDCLAMP represents the voltage across the transistor M0 when M0 is turned on, and is provided as an input to the amplifier circuit 120.
• the transistor MO can be any suitable high-voltage transistor, such as a gallium nitride, aluminum gallium nitride, silicon, or silicon carbide high voltage transistor. As shown in FIG.
• the transistor MO includes a drain terminal (D) connected via line 106 to a high voltage Vd through a subjecting circuit (not shown in FIG. 1), a source terminal (S) coupled with a constant voltage node GND through a current sense resistor Rl 1 for measurement of a DUT current IDUT (e.g., the source current of MO).
• a DUT current IDUT e.g., the source current of MO
• the current sense resistor Rl l is a very low impedance device, such as 0.1 ohms.
• the current IDUT can be sensed using a current probe (not shown).
• the DUT transistor M0 further includes a gate control terminal (G) which receives a switching control signal from a gate drive circuit 104.
• G gate control terminal
• a supervisory controller can operate the gate driver circuit 104 to provide switching operation of the DUT 103 while on-state drain voltage measurements are obtained via the measurement circuit 100 and conveyed through one or more multiplexers to a signal digitizing instrument such as an oscilloscope.
• the high-voltage transistor M0 is positioned as a device under test (DUT) 103 in a test fixture or pod to complete a switching or subjecting circuit, such as a high-voltage hard-switching circuit illustrated and described hereinbelow in connection with FIG. 5.
• the measurement circuitry 100 provides signal conditioning for amplification and transmission of an amplified voltage sense signal VO through cables and multiplexers to allow a single digitizing instrument or oscilloscope to characterize RDSON according to measured on-state drain voltages of multiple DUTs 103 and according to corresponding current sense signals IS.
• each DUT transistor M0 is driven by a corresponding gate drive circuit 104, and each transistor current IDUT is sensed by a corresponding current sense circuit 130 to provide a corresponding current sense signal IS.
• the attenuator circuit 102 includes a clamp transistor Ml with a drain or first terminal D coupled with the drain terminal 106 of the high voltage transistor M0 through a first resistor Rl to sense the drain voltage of M0.
• the first resistor Rl is a low resistance component, such as 10 ohms.
• a second (e.g., source) terminal S of Ml provides a sense signal VSENSE to a first internal node 110 of the attenuator circuit 102.
• Ml includes a gate control terminal G that receives a first bias signal at an internal node 114 from a bias circuit 112 based on a first supply voltage VI .
• the bias circuit 112 turns the clamp transistor Ml on when the high voltage transistor MO is turned on.
• the first bias circuit 112 includes a second resistor R2 coupled between VI and the node 114 at the control terminal G of the clamp transistor Ml, and a third resistor R3 coupled between the control terminal node 114 and the constant voltage node GND.
• the circuit 112 further includes a bias circuit capacitor CI coupled between the node 114 and GND to reduce voltage spikes and to stabilize the voltage on the control terminal G of Ml during switching of the high voltage transistor MO.
• the first resistor Rl is 10 ohms to provide a slight amount of impedance between the sensed drain line 106 of the DUT 103 and the drain line 108 of the clamp transistor Ml .
• Ml is an N-channel field effect transistor (FET) having a low gate-drain capacitance Cgd, which in combination with the bias circuit capacitor CI provides stable sensing through the drain-source channel of Ml even in the presence of high voltage transients at the drain line as M0 is switching.
• Ml is a IXTY02N120P 1200 V enhancement mode FET with a rated drain current of 200 mA, maximum rated voltage VDSS of 1200 V, and an RDSON of 75 ohms, although other suitable clamp transistors can be used, preferably having low capacitance between the drain D and both gate G and source S terminals.
• R2 is 1 kohm
• R3 is 10 kohm
• CI is 1 ⁇ for a first supply voltage VI of 12 V, although other suitable component values can be used in other embodiments.
• the attenuator circuit 102 also includes a first voltage divider circuit 116 formed by resistors R4 and R5 connected in series with one another between the first internal node 110 and GND.
• the voltage divider resistors R4 and R5 are connected to one another at an attenuator output node 121 to provide the attenuator output signal VDCLAMP based on the sense signal VSENSE from the clamp transistor Ml .
• R4 and R5 are preferably matched resistors having values of 10 kohms to provide a low current attenuator output signal VDCLAMP, with good thermal matching between the resistors R4, R5.
• R4 is adjustable.
• R4 in such embodiments can be implemented as a trim pot, or the resistance R4 may be implemented as a set of multiple switchable resistors configured in any suitable series, parallel and/or a combination series/parallel configurations to implement a switch selectable adjustable resistance R4.
• An adjustable resistance R4 in certain embodiments can be used to provide a tunable gain for the attenuation circuit 102, alone or in combination with an adjustable gain of the amplifier circuit
• the attenuator circuit 102 also includes a first clamp circuit to limit the voltage of the resistive voltage divider circuit R4, R5 between the first internal node 110 and G D when the high voltage transistor M0 is turned off.
• the first clamp includes a 12 V Zener diode Zl coupled between the first internal node 110 and GND. In operation, Zl increases the reliability of the attenuator circuit 102 by protecting the clamp transistor Ml against spikes on the first internal node 110 during switching operation of M0.
• Zl passes any spike current to GND by clamping the voltage at the node 110 to approximately 12 V to stabilize the attenuator output signal VDCLAMP against voltage spikes coupled through the drain-source capacitance Cds of the clamp transistor Ml .
• Zl also improves the robustness of the attenuator circuit 102 by preventing high gate-to- source voltages from appearing across clamp transistor Ml .
• the voltage at the gate node 114 of Ml is biased to a voltage less than or equal to VI (e.g., less than or equal to 12 V) by the bias circuit 1 12, and the nominal source voltage at the internal node 110 (VSENSE) will be the gate voltage at node 114 minus the threshold voltage (Vt) of Ml while the DUT transistor M0 is turned off, and Zl prevents the sense voltage VSENSE from spiking above 12 V when M0 is turned off.
• the voltage divider circuit 116 including the clamping Zener Zl provides a stable attenuator output signal VDCLAMP from the attenuator output node
• the example attenuator circuit 102 in FIG. 1 also includes a second clamp circuit 118 to condition the attenuator output signal VDCLAMP.
• the second clamp circuit 118 in this example includes a second voltage divider circuit formed by resistors R6 and R7 connected in series with one another between a second supply voltage V2 (e.g., 5 V) and the constant voltage node GND to provide a bias voltage signal at a second internal node 119.
• the second clamp circuit 118 also includes a low capacitance diode Dl with an anode coupled with the attenuator output node 121, and a cathode coupled with the second internal node 119.
• Dl is a low capacitance BAT 15-03W silicon Schottky diode.
• the second clamp circuit 118 limits the voltage VDCLAMP of the attenuator output node 121.
• VDCLAMP voltage of the attenuator output node 121.
• MO is in the on state, and Dl does not affect the attenuation or amplification of the VDCLAMP signal.
• Dl is chosen to have a low capacitance value, usually less than lpf to improve the settling time and accuracy of the drain voltage measurement in the first microsecond after turn on.
• the amplifier circuit 120 in one example includes a differential amplifier 124, with a first input (+) coupled with the attenuator output node 121 to receive the attenuator output signal VDCLAMP, and a second input (-) coupled connected to G D via line 122.
• the (-) input into the differential amplifier 124 is coupled to the source of the DUT MO, and the shunt resistor value does not need to be accounted for in the RDSON measurement.
• the differential amplifier 124 includes an output to provide an amplified sense voltage signal VO along line 126 via an output resistor RIO representing the voltage across the high voltage transistor MO when MO is turned on.
• the output resistor RIO is a 50 ohm resistor to advantageously provide a matched output impedance for use with a 50 ohm coaxial cable as described further hereinbelow in connection with FIGS. 3-7.
• the use of a differential amplifier 124 advantageously facilitates removal or mitigation of offset effects and to provide common mode noise rejection of signals due to ground inductance by providing a ground reference close to the DUT 103.
• the differential amplifier 124 is a Texas Instruments VCA824 ultra wideband adjustable gain fully differential amplifier having a low input capacitance to facilitate fast settling time and amplification of the attenuator output signal VDCLAMP to provide the amplified sense voltage signal VO for further processing to determine RDSON of the DUT M0.
• the gain of the amplifier 124 is set by a gain resistance R8.
• the gain of the amplifier 124 is adjustable in certain implementations through an adjustable resistor R8.
• the amplifier circuit 120 also includes a feedback resistor R9, and is provided with a gain adjustment bias voltage V3 in one example.
• another embodiment includes a compensation capacitor C3 to compensate a capacitance of the first input (+) of the differential amplifier 124.
• the compensation capacitor C3 includes a first terminal connected to the first internal node 110, and a second terminal connected to the attenuator output node 121.
• the input capacitance of the (+) input is on the order of 1 pF
• the compensation capacitor C3 is 1 pF in order to compensate the amplifier input capacitance. This effectively creates a pole to cancel the zero of the amplifier input capacitance, thereby shortening the input signal settling time and enhancing the bandwidth of the measurement system.
• the high switching rates of gallium nitride high-voltage transistors MO is an attractive feature for power converters or other high voltage switching systems.
• the high bandwidth and low settling times achieved by the measurement circuitry 100 facilitates measurement of the highly dynamic operating parameters of the DUT MO, while providing protection and/or immunity against voltage spikes and noise associated with the high voltage switching operation of MO in a high voltage system.
• the circuitry 100 thus presents significant advantages compared with oscilloscope probes and conventional clamping circuits to facilitate accurate characterization of the performance of the DUT M0 for production testing, life testing, and other applications.
• FIGS. 3-7 illustrate application of the attenuator circuit 102 and the differential amp circuit 120 in a multiple DUT system application for test and/or measurement of multiple DUTs 103 during switching operation thereof in high voltage tests circuits, along with characterization of RDSON for the tested DUTs 103 using a slope comparison technique based on the amplified sense voltage signals Vd associated with the individual tested devices 103.
• FIG. 3 shows a motherboard 300 that can be rack-mounted along with a number of other identical motherboards 300 in a test set up to form a system for RDSON measurement of gallium nitride , aluminum gallium nitride and/or silicon carbide or silicon high-voltage transistors (e.g., FETs, HEMTs, BJTs) during switching operation and corresponding high-voltage circuits.
• the motherboard 300 includes an integer number "M” modules or "pods", each pod constituting an integer number "N” measurement circuits e.g., 100, each with its output.
• two measurement circuits per pod are used to determine RDSON, one for the drain voltage measurement, and one for the current measurement as described, and each measurement circuit uses a differential amplifier.
• the illustrated embodiment has one DUT 103 per pod, with the attenuated and clamped drain voltage signal output and the device current signal output. Accordingly, the illustrated pods individually include one DUT 103, one attenuator circuit 102 and one differential amplifier circuit 120 to provide a corresponding amplified sense voltage signal VO on a corresponding line 126 as shown.
• each motherboard 300 has N multiplexers 302, and each multiplexer 302 has M inputs.
• each motherboard will have M pods and N outputs, with each multiplexer multiplexing the same type of measurement signal from each pod.
• the attenuated and clamped drain signals, VO from all M pods in one example are connected to one multiplexer, and the corresponding DUT sense current signals IS (from the corresponding current sense circuits 130 is shown in FIGS. 2 and 3) as output signals, are connected to another multiplexer.
• the multiplexers on the mother board in one example allow the coaxial outputs to be connected to the pod being sampled.
• the motherboard accommodates 4 pods, each with four signals, so there are four 4: 1 multiplexers per mother board.
• the motherboard 300 includes a number of multiplexer circuits 302, in this example 4: 1 multiplexers (MUXs), that each receive 4 input signals and provide a multiplexer output 304 to a coaxial cable (COAX, not shown).
• MUXs multiplexers
• the motherboards 300 each provide the multiplexed sense voltage signals 304 using matched-length coaxial cables to a first set of N X: 1 multiplexers, where X is the number of motherboards connected to each multiplexer shown as quad 4: 1 multiplexers 401.
• X is the number of motherboards connected to each multiplexer shown as quad 4: 1 multiplexers 401.
• four quad 4: 1 multiplexers 401 each receive four multiplexed inputs 304 from a corresponding set of four motherboards 300, and the quad multiplexers 401 each provide four-way multiplexed outputs 402 through corresponding matched-length coaxial cables to a second level N Y: l, e.g.
• the multiplexer 403, provides a multiplexed N-channel (e.g. 4-channel) output 404 to a digitizing instrument e.g., four-channel oscilloscope 406 via a coaxial cable.
• the digitizing instrument 406 is configured to capture a slope of the amplified sense voltage signal VO as described further hereinbelow in connection with FIGs. 6 and 7 for a processing unit to compute and provide an on-state impedance value (e.g., RDSON) for the individually measured DUTs 103.
• an on-state impedance value e.g., RDSON
• FIG. 5 shows a high voltage transistor DUT 103 (MO) undergoing measurement of drain voltage and source current during switching in a high voltage test circuit 504 in the system 400 of FIG. 4.
• the high-voltage test circuit 504 is a hard switching subjecting circuit including a high voltage DC supply or power source 504 (e.g., 400-600 V in one example) with a capacitance C4 and a load inductance L connected in series with a resistor R12 (e.g., 0.1 to 5 ohms) between the positive (+) output of the source 502 and the drain line 106 (Vd) of the DUT 103.
• the high-voltage circuit 504 further includes a second diode D2 with an anode connected to the line 106 and a cathode connected to the positive (+) output of the source 502.
• Other subjecting circuits may also be used, such as a soft- switching subjecting circuit.
• the corresponding gate driver circuit 104 of the pod drives the DUT gate terminal in order to selectively turn M0 on and off to alternately conduct and block current from the high voltage supply 502.
• a low switching control signal turns on the DUT 103 (M0), allowing buildup or increase in an inductor current IL flowing in the inductor L.
• the attenuator circuit 102 and the differential amplifier circuit 120 measure the drain voltage of the DUT 103 to provide the sense voltage signal VO when the transistor M0 is on.
• the current sense circuit 130 provides the current sense signal IS to represent the DUT current IDUT flowing from the source of M0 through the current sense resistor Rl l when the transistor M0 is turned on.
• the oscilloscope 406 receives the Vd and IS signals (e.g., through one or more multiplexers as described hereinabove) and processes these signals to provide an output signal or value 500 representing the RDSON of the tested DUT transistor M0.
• the Vd and IS signals in one example are processed for a given DUT 103 using a computer connected to the oscilloscope or another digitizing instrument to analyze the digital samples of the received analog signals, and perform curve fitting as needed, along with slope determination to compute or estimate RDSON for the DUT 103.
• FIG. 6 provides a graph 600 of a gate voltage curve or signal voltage waveform VS used to drive the DUT gate, a drain voltage curve Vd and a source current curve IS used by the oscilloscope 406 to analyze drain source on resistance RDSON using voltage and current slope analysis in the system of FIG. 4.
• a gate voltage curve or signal voltage waveform VS used to drive the DUT gate
• Vd drain voltage curve
• a source current curve IS used by the oscilloscope 406 to analyze drain source on resistance RDSON using voltage and current slope analysis in the system of FIG. 4.
• any suitable computer or processor-based analytical system can be used.
• a first slope SI is determined by the computer or other data processing device which corresponds to the slope of the Vd signal
• a second slope S2 is determined which corresponds to the slope of the IS signal during the time when the VS signal is high indicating that the high-voltage transistor DUT MO is on.
• the drain-source voltage represented by the Vd signal and the source current represented by the IS signal ramp as the inductor L in the high-voltage circuit 500 charges in response to MO turning on.
• the data processing device 406 determines the first and second slopes S I and S2 and computes RDSON as (S 1/S2) - Rl l (FIGS. 1 and 2).
• FIG. 7 provides a graph 700 showing samples obtained from an analog-to-digital (AID) converter of the oscilloscope 406 in the system 400 of FIGS. 4 and 5, including a series of samples 702 related to the Vd signal and a series of samples 704 associated with the IS signal.
• the data processing device 406 in one example is configured, rather than sampling a single measurement, to instead sample the signal over a configurable period of time and perform linear curve fitting to apply a linear curve in post-processing to determine a curve fit Vd from the samples 702, and to determine the corresponding first slope S I from the fitted curve Vd.
• curve fitting is also applied to the current sample 704 to determine a curve IS and determines the second slope S2 from the fitted curve IS in FIG. 7.
• the act of curve-fitting enables both noise reduction due to the averaging of multiple samples, and also an increase in the effective number of bits of the AID converter of the data processing device 406, due to the fitting over multiple digital quantization units of the converter.
• FIG. 8 provides a graph 800 of signal waveforms in the system of FIG. 5, including an inductor current waveform 802 representing the current IL flowing in the inductor L of the test circuit 504, and a curve 804 representing the drain voltage 106, Vd of transistor M0 (103).
• a curve 806 in FIG. 8 represents the switching control signal (VS) provided to the drive circuit 104 that drives the gate control terminal of the DUT 103 (M0).
• the drive circuit 104 provides the switching control signal to the gate of M0 as a first sequence of short pulses indicated at 821 in FIG.
• the first sequence of pulses 804 may be performed for any suitable duration, with a sufficient number of switching pulses to ensure that the DUT 103 is operating within specified end-use current, temperature and voltage conditions.
• the first set of pulses during the first sequence 821 have a short on-time duration 808, such as about 250 ns, and the first sequence of short pulses are provided at a switching period of approximately 45 corresponding to a switching frequency of approximately 22 kHz.
• the first sequence 821 is followed by a second sequence 822 in which the drive circuit 104 provides the switching control signal in a low state to turn the high voltage transistor M0 off.
• the second sequence 822 is a few milliseconds long, allowing the inductor current IL (e.g., curve 802 in FIG. 8) to decrease to a predetermined value, such as zero in the illustrated example. Allowing full or at least partial discharge of the inductor L facilitates use of a longer on-time pulse duration 814 to turn the high voltage transistor M0 on in a subsequent third sequence 823 to obtain the current sense signal IS and the amplified sense voltage signal VO, and to allow the analysis system 406 to compute the on-state impedance value RDSON of the high voltage transistor M0.
• Discharging the inductor to a predetermined value also allows the RDSON measurement to be repeatable for different stress currents.
• the on-time duration in the third sequence 823 in one example is greater than a duration 816 of approximately 1 or more during which the attenuator circuit 102 and the differential amplifier circuit 124 described hereinabove measure and provide the amplified sense voltage signal Vd, including any suitable settling time of the circuits 102, 124.
• the drive circuit 104 is configured to provide the switching control signal to the DUT 103 such that the first sequence 821 of short pulses individually have a first on-time 808 that is less than the on-time 814 of the third sequence 823.
• the first sequence of short pulses 821 facilitates simulated operation of the DUT 103 in a switching power converter with the inductor current 802 representing real-life switching converter conditions, while also minimizing both inductor current ripple and energy usage, while the second sequence 822 facilitates full or partial discharge of the inductor L for a duration 812 of a few milliseconds to reduce the inductor current level IL, and the subsequent third sequence 823 thereafter provides the test pulse to turn on M0 for the on-time duration 814 to allow sufficient measurement time to measure the drain voltage of the DUT 103 while the inductor current is sufficiently low to mitigate the possibility to overstress the DUT 103 during on-state impedance measurement and for the RDSON measurement to be taken in the FET linear region (saturation region for BJT).
• the transistor is held under high voltage so that interface or bulk traps of the DUT 103 remain charged, and the RDSON value is measured during the measurement pulse during the time period 816 in FIG. 8 so that the determined RDSON reflects the presence of charged traps in the DUT 103.
• the drive circuit 104 resumes switching operation in the first sequence 821 as described hereinabove.
• the third sequence 823 allows a sufficient time 820 for the inductor current IL to again ramp down to zero or some other determine value, before the next sequence 821 of short pulses begins. As shown in FIG.
• the inductor current curve 802 again begins to ramp up with successive charging and discharging cycles through the resumed switching operation of the DUT 103, and the next instance of the second and third sequences 822 and 823 in one example is repeated after the inductor current curve 802 has again resumed a normal operating level and sufficient stress time has elapsed to warrant a measurement.
• the illustrated test sequence can be implemented by individual gate drive circuits 104 of a plurality of the pods and motherboards 300, with a centralized controller (not shown) coordinating the switching test operation of the individual DUTs 103 and measurement of the corresponding drain voltages and transistor currents via the multiplexers 302, 401, 403 and matched-length cables such that a single analysis system (e.g., scope 406) can perform slope-based RDSON computations on converted analog signals from the individual motherboards 300.
• a single analysis system e.g., scope 406

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