System and method for determining probe skew
A system for determining an amount of time skew between two measurement probes includes a first probe and a second probe and one or more processors configured to measure a current signal from a Device Under Test (DUT) through the first probe, measure a voltage signal from the DUT through the second probe, generate a modeled voltage signal from the measured current signal, compare the modeled voltage signal to the measured voltage signal, and determine the amount of time skew between the first and the second probe from the compared signals. Methods are also described.
1 . A system for determining an amount of time skew between two measurement probes, the system comprising:
a first probe and a second probe coupled to a Device Under Test (DUT) having at least one semiconductor device; and
one or more processors configured to:
measure a current signal from the at least one semiconductor device of the DUT through the first probe,
measure a voltage signal from the at least one semiconductor device of the DUT through the second probe,
generate a modeled voltage signal from the measured current signal using the following formula:
V_
(
ds_low
)
=
V_eb
-
〚
(
I
〛
_d
*
R_probe
)
-
(
L
〛
eff
*
dI
d
d
t
)
wherein V ds_low is the modeled voltage signal, V eb is a constant bias voltage for the at least one semiconductor device of the DUT, I d is the current signal measured with the first probe, R probe is a resistance of the first probe, and L eff is an effective inductance,
compare the modeled voltage signal to the measured voltage signal,
determine the amount of time skew between the first and the second probe from the compared signals,
set a skew value in the system to the determined amount of time skew, and display the skew value.
2 . The system according to claim 1 , in which the one or more processors are further configured to:
generate an overlapping plot of the modeled voltage signal and the measured voltage signal.
3 . The system according to claim 2 , in which the one or more processors are further configured to:
measure a horizontal distance between the modeled voltage signal and the measured voltage signal.
4 . The system according to claim 3 , in which the one or more processors are further configured to:
modify a parameter used to generate the modeled voltage signal, in which the parameter includes one of probe resistance, bias voltage, differential order, and effective inductance,
generate a new modeled voltage signal using the modified parameter, and
compare the new modeled voltage signal to the measured voltage signal.
5 . The system according to claim 4 , in which system repeatedly modifies the parameter, generates a new modeled voltage signal using the modified parameter, and compares the new modeled voltage signal to the measured voltage signal until a difference between the new modeled voltage signal and the measured voltage signal is below a skew threshold amount.
6 . The system according to claim 2 , in which the one or more processors are further configured to:
measure a vertical distance between the modeled voltage signal and the measured voltage signal.
7 . The system according to claim 6 , in which the one or more processors are further configured to determine an amount of effective inductance in a DUT measuring circuit coupled with the first and second probes based on the vertical distance.
8 . The system according to claim 7 , in which determining the amount of effective inductance is determined iteratively.
9 . The system according to claim 1 , in which the one or more processors are further configured to:
perform a frequency transform on the measured voltage signal,
perform a frequency transform on the modeled voltage signal, and
compare the transforms in the frequency domain.
10 . The system according to claim 1 , in which the one or more processors are further configured to:
simultaneously display the measured voltage signal and the modeled voltage signal to a user as the amount of time skew between the first and the second probe is being iteratively determined.
11 . The system according to claim 1 , in which the first probe or the second probe includes a probe selected from the group of shunt resistor probe, hall effect probe, and Rogowski coil probe.
12 . The system according to claim 1 , in which the at least one semiconductor device of the DUT is an IGBT formed of SiC, GaN, GaN-HEMT, vertical GaN, and GaN-cascode.
13 . The system according to claim 1 , in which the one or more processors are configured to iteratively determine the amount of time skew between the first and the second probe from the compared signals.
14 . A method, comprising:
measuring a current signal of at least one semiconductor device of a Device Under Test (DUT) through the first probe,
measuring a voltage signal of the at least one semiconductor device of the DUT through the second probe,
generating a modeled voltage signal from the measured current signal using the following formula:
V_
(
ds_low
)
=
V_eb
-
〚
(
I
〛
_d
*
R_probe
)
-
(
L
〛
eff
*
dI
d
d
t
)
wherein V ds_low is the modeled voltage signal, V eb is a constant bias voltage for the at least one semiconductor device of the DUT, I d is the current signal measured with the first probe, R probe is a resistance of the first probe, and L eff is an effective inductance,
comparing the modeled voltage signal to the measured voltage signal, determining the amount of time skew between the first and the second probe from the compared signals,
setting a skew value in the system to the determined amount of time skew, and
displaying the skew value.
15 . The method according to claim 14 , further comprising generating an overlapping plot of the modeled voltage signal and the measured voltage signal.
16 . The method according to claim 15 , further comprising:
measuring a horizontal distance between the modeled voltage signal and the measured voltage signal.
17 . The method according to claim 16 , further comprising:
modifying a parameter used to generate the modeled voltage signal, in which the parameter includes one of probe resistance, bias voltage, differential order, and effective inductance,
generating a new modeled voltage signal using the modified parameter, and
comparing the new modeled voltage signal to the measured voltage signal.
18 . The method according to claim 17 , further comprising repeatedly modifying the parameter, generating a new modeled voltage signal using the modified parameter, and comparing the new modeled voltage signal to the measured voltage signal until a different between the new modeled voltage signal and the measured voltage signal is below a skew threshold amount.
19 . The method according to claim 15 , further comprising:
measuring a vertical distance between the modeled voltage signal and the measured voltage signal.
20 . The method according to claim 19 , further comprising determining an amount of effective inductance in a DUT measuring circuit coupled with the first and second probes based on the vertical distance.
21 . The method according to claim 20 , in which determining the amount of effective inductance is determined iteratively.
22 . The method according to claim 14 , further comprising:
transforming the measured voltage signal from a time domain to a frequency domain;
transforming the modeled voltage signal from the time domain to the frequency domain; and
comparing the transforms in the frequency domain.
23 . The method according to claim 14 , in which determining the amount of time skew between the first and the second probe from the compared signals is determined iteratively.