KlausST
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How many samples: Nyquist says at least twice the signal frequency.
to get the information about the complex impedance of the load you need to simultaneously sample "voltage" and "current".
By the way, maybe Matlab would be a good environment to look at those aspects?Nyquist says: MORE than twice the signal frequency.
So using 2.000.000 samples/second with a 1.000.000 Hz signal won't work.
And when you use 2.000.000 samples/second on a 999.000 Hz signal you need to take 2000 samples into account for full information.
You may use some Excel calculations/simulations to see what happens.
Klaus
This is wrong.as far as I know the Nyquist fs/2 rule only applies for getting the frequency information of a square-wave
some additional information:and as Klaus keep referring to, 10MHz sample rate is what is needed to get the amplitude/phase information of a 1MHz sine-wave.
Didn't review the preceding sample rate discussion from the start, but to mention a simple point: If the excitation signal is periodical with zero or low modulation bandwidth, undersampling is of course an option. Nyquist rate has to be related to the actual signal bandwidth, not the carrier frequency. https://en.wikipedia.org/wiki/Undersampling
some additional information:
For a clean sinewave without overtones..
* two points per fullwave don´t give enough information.
* three points give full information.
How do you calculate amplitude and frequency?A sine wave (a*sin(w*t+b)) is specified by amplitude and frequency. Two points are sufficient to determine the amplitude and the frequency.
The OP wants to determine a complex load. LCRZ meter.The phase is sometimes important and we will need a reference to determine the phase. In such a case, three points are needed for the complete description.
--> Yes, the benefit of the lock_in_amplifier is you don´t need 10Msamples ADC. The input to the ADC (= output of the filtered lock_in_amplifier) is almost DC, therefore 100 samples/second is enough. (no kilosamples, no megasamples). You may use a high resolution I2C or SPI ADC. But you get full amplitude and phase information.I think I have been presented with two different techniques to accomplish my goals while avoiding ADCs with sample rates of something like 10MHz/10MSPS, because that is the point of the Lock-in Amplifier idea in this situation right?
Are you aware that with a (auto) balancing bridge ... you need to balance with a complex load.going with the Opamp Auto-Balancing Bridge was a appropriate choice
The output of the LIA is independent of even harmonics..., but then I thought "why would I care?", the beauty of the LIA is that the harmonics will not influence the LIA right?
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