Appreciate your work here; I’ve done a lot of surveying of mostly C measurements with a scope. Two things - I think there is something off in your phase calc in your first example. A 1.5us difference on a 100kHz signal is less than pi/2. It is 0.3*pi. Also, all methods that involve probing across the DUT introduces error from the probe itself. I use a different method with triangle waves for C measurement that is simpler, easier to measure and calculate, and takes the probe reactance out of the equation.
Thanks for your comment. I think you refer to the 1.596 usec measured at 5:39. That's for a phase difference theta between Vdut and Vin, both voltage signals. A computation is then needed to get phi, the phase difference between the current and Vdut. The Tek app note calls this "alpha" for some reason. It's the one that should be near (but not more than) pi/2. The ADALM2000 does not measure theta accurately enough for the small Resr though (likely about 10ns off), and it should be worse than a standard oscilloscope as far as probes go. You make a good point there. I get somewhat better results with my scope, but the angle measurement is still challenging for small Resr. The ADALM2000 actually has differential inputs and could measure the current signal across Rref directly, but the tek app note does not assume a differential probe. So, the ADALM2000 could use a more direct method, but the computations would change. I have not heard of a method for C using triangle waves. That's interesting, thanks.
I have not got any method to measure inductance so will be trying this for sure ....cheers.
Appreciate your work here; I’ve done a lot of surveying of mostly C measurements with a scope. Two things - I think there is something off in your phase calc in your first example. A 1.5us difference on a 100kHz signal is less than pi/2. It is 0.3*pi. Also, all methods that involve probing across the DUT introduces error from the probe itself. I use a different method with triangle waves for C measurement that is simpler, easier to measure and calculate, and takes the probe reactance out of the equation.
Thanks for your comment. I think you refer to the 1.596 usec measured at 5:39. That's for a phase difference theta between Vdut and Vin, both voltage signals. A computation is then needed to get phi, the phase difference between the current and Vdut. The Tek app note calls this "alpha" for some reason. It's the one that should be near (but not more than) pi/2. The ADALM2000 does not measure theta accurately enough for the small Resr though (likely about 10ns off), and it should be worse than a standard oscilloscope as far as probes go. You make a good point there. I get somewhat better results with my scope, but the angle measurement is still challenging for small Resr.
The ADALM2000 actually has differential inputs and could measure the current signal across Rref directly, but the tek app note does not assume a differential probe. So, the ADALM2000 could use a more direct method, but the computations would change.
I have not heard of a method for C using triangle waves. That's interesting, thanks.
Nice presentation and information. Thank you.