PicoScope 7 Software
Available on Windows, Mac and Linux
IMD measurement and signal generator
IMD measurement and signal generator
I'm using Picosope 4262 to do some THD% and IMD measurements. The signal generator of picoscope can easily generate sine-signals, but is it somehow possible to make the signal generator to generate sum of two different frequencies for IMD measurements?
Re: IMD measurement and signal generator
Hi teemumm,
The answer to your question is yes. However, you need to use the Arbitrary Waveform Generator to do it.
Probably the easiest method would be create the waveforms in Excel over a column length equal to the length of the AWG waveform buffer (4096 for PicoScope 4262), then save them as a CSV file and import that file into the AWG. In Excel the waveforms will need to be of equal magnitude, and then algebraically summed, but with the following conditions:
1/ They must not be Harmonically related (i.e. neither waveform should be a harmonic of the other, otherwise you will be measuring harmonic distortion not IMD)
2/ Both waveforms must be continuous over the total width of the waveform buffer. To put it another way, both waveforms (with their unrelated number of cycles) must have their first cycle starting at the first Row, and their last cycle finishing at the last Row + 1 (so that when the AWG repeats the next set of cycles it picks up the next set exactly where it left off the last set) otherwise you will have sharp edges in your waveform creating distortion from spectral leakage, not IMD.
To create continuous sinewaves in Excel you just use the formula:
SIN((2*PI()*Number_of_cycles*(ROW()-First_row_number))/Total_number_of_rows)
where 'Number_of_cycles' are the non harmonically related numbers that you want to use, and then sum the columns together and normalize the sum column to the maximum ±1V range of the AWG (i.e. divide the sum column by its +ve and -ve peak values).
When performing the measurements, you should also, first of all apply the Sig Gen directly to an Input Channel to establish the Amount of IMD created by the Scope Channel itself (so that you can subtract it from the IMD of your DUT).
Regards,
Gerry
The answer to your question is yes. However, you need to use the Arbitrary Waveform Generator to do it.
Probably the easiest method would be create the waveforms in Excel over a column length equal to the length of the AWG waveform buffer (4096 for PicoScope 4262), then save them as a CSV file and import that file into the AWG. In Excel the waveforms will need to be of equal magnitude, and then algebraically summed, but with the following conditions:
1/ They must not be Harmonically related (i.e. neither waveform should be a harmonic of the other, otherwise you will be measuring harmonic distortion not IMD)
2/ Both waveforms must be continuous over the total width of the waveform buffer. To put it another way, both waveforms (with their unrelated number of cycles) must have their first cycle starting at the first Row, and their last cycle finishing at the last Row + 1 (so that when the AWG repeats the next set of cycles it picks up the next set exactly where it left off the last set) otherwise you will have sharp edges in your waveform creating distortion from spectral leakage, not IMD.
To create continuous sinewaves in Excel you just use the formula:
SIN((2*PI()*Number_of_cycles*(ROW()-First_row_number))/Total_number_of_rows)
where 'Number_of_cycles' are the non harmonically related numbers that you want to use, and then sum the columns together and normalize the sum column to the maximum ±1V range of the AWG (i.e. divide the sum column by its +ve and -ve peak values).
When performing the measurements, you should also, first of all apply the Sig Gen directly to an Input Channel to establish the Amount of IMD created by the Scope Channel itself (so that you can subtract it from the IMD of your DUT).
Regards,
Gerry
Gerry
Technical Specialist
Technical Specialist