I have test a little more and found that I can make with my AWG a burst of one cycle of a sinusoidal at frequencies up to 120 MHz. It has both channels synchronized so we can make phase shift measures of both channels, especially in the case of a 20 MHz channel limit (used here as an example) because it’s dependent on the channel and not globally to the scope, like the acquisition bit deep 8 bits and 10 bits. The small fixed AWG inter-channel was measured and accounted for, in the data appears as corr (correction) and was of 1.05 nS.
But all my measures of phase shift where made comparing Channel 1 with Full Bandwidth with Channel 2 with 20 MHz limited bandwidth. I used math channels for both real channels with averaging and the phase measures between different bandlimit channel can’t be made with the Measurements menu, they had to be done by hand.
Note: I don’t know why the scope doesn’t permit inter bandwidth limit vs full bandwidth channel measurements.
The amplitude was also measured for the same channel with and without the bandlimit.
The connection between the scope and the AWG was a BNC 50 Ohms coaxial cable.
Please see the image and the excel file for the data.
There are considerable amplitude attenuations and considerable phase shifts as was expected.
The simple idea that I proposed is the correction of this effect and in this case I think that it could give a correction for the 20 MHz band limit of at least up to 40 MHz. In a normal 1 G sample scope the 20 MHz would be the 100 Mhz scope bandwith and the 40 Mhz would be the 500 Mhz Nyquiest limit. You have to use your imagination here :-D Like I said this can be made for any scope, for any bandwith, because it is made against the frequency response of the scope.
I use the 20 MHz band limit as an example and not as the final object, that is to correct for 0 Hz up to 1 GHz (950 MHz), but I don’t have a signal generator capable of hitting those high frequencies, I’m limit to what I have and that is a 40 Mhz Siglent AWG hacked to 120 MHz.
But I think that there is a way to make the phase frequency characterization of up to 1 GHz using a signal generator of a one single channel.
The ideia is that a low frequency sinusoidal signal ex: a 50 Mhz (10 %) for a 580 MHz scope are only really residually affected by a phase shift, and that high frequency signal is highly affected (phase shifted). So we have to find a way to compare the delta in time of the slow frequency wave top to the high frequency phase top, but we have to take out the part that is related to the fact the one wave is faster than the other, so we have to take out 1/4 period of the high freq wave times the frequency ratio between freq_ref_slow and freq_fast. And configure the channel of the fast signal wave to deskew for that delta. The result phase shift will be the real phase shift between the signals of different frequencies. To better measure use coursers and invert the channel, comparing top Ref_A (slow) to Channel B (fast).
1 - First get the trigger to the oscilloscope from the trigger output port of the signal generator.
2 – Generate a 50 MHz tone with +13dBm (1.4 V, if you have more then better) in single cycle burst, do average and record it in REF_A.
3 – At all the frequencies in the freq range:
3.1 - Generate a sinusoidal of one cycle in a burst mode.
3.2 – Calculate the time delta for the frequency delta of the number of cycles for the relation between each signal A (REF_A low frequency and not affected by the scope frequency response) and Signal B (at 50 MHz, 100 MHz, 150, 200, …. 900, 950, 1 GHz )1/4 of Wave. Configure the scope channel skew to go backward in time only the number of cycles in the difference between frequencies ex: 50 Mhz to 100 Mhz or 1 GHz.
3.3 – Measure the time delta( then calculate the phase delta difference) difference between the two tops of the two sinusoids.
3.4 - Record the data.
Best regards,
João Carvalho
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