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| Bode Plot Torture Test |
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| mawyatt:
This is an extension of this thread, so review first!! https://www.eevblog.com/forum/testgear/bode-plot-computational-time-for-various-dsos/ To add some additional information regarding the Bode Plotting capability we decided to conjure up an experiment to "see" just how good the frequency selectivity of the Bode implementation behaves with large interference sources. This was done with a simple RC LPF (1K and 0.01uF) as DUT. We directly connected two separate AWGs (SDG2042X & SDG6022X) outputs relying on the 50 ohm output Z to create a summation signal, one AWG (2042X) is controlled by the DSO (SDS2104X+) by LAN and the other AWG (6022X) is Independent. First off we set the Independent AWG as a Noise Source (PRNS) with Standard Deviation of 1V, and the Dependant AWG to 0.1Vrms. The Bode Parameters were Decade Sweep from 100Hz to 100KHz, 20pts/dec, 0.1Vrms, with CH1 and CH2 using 10X DSO Probes and 20MHz BW DSO limitation. First image shows the Bode result without any disturbance from the Noise Source. Second Image shows result with Noise Source active. Third shows Time Domain Plot, note the level of the Bode Signal to the Noise Signal (buried within the Noise)!! Next we changed the Independent "Noise" AWG to 1KHz SineWave at 1Vrms, Bode signal still at 0.1Vrms. Fourth shows with 1KHz "Noise" Source Next shows Time Domain Plot, note the level of the Bode Signal (smaller signal) to the 1KHz "Noise" Signal!! Anyway, this was quickly done just to "See" how things behave, and much more work/effort needs to be applied. Maybe some others might find this useful/interesting and post some results they've achieved. Edit: Added: 6th with "Noise" source at 10KHz @ 1Vrms 7th with "Noise" source at 10KHz @ 5Vrms!! 8th Time Domain plot of 7th, note the small signal is the Bode signal of interest!! Best, |
| balnazzar:
Dave should do a shootout >:D |
| TopQuark:
My contribution to "cursed" bode plot measurements. >:D Two diodes in parallel but of opposite direction, in series with a resistor. Drive the DUT with enough amplitude (5v p-p in my case) to activate the diode clamps and introduce non-linearities. The bode plot is now tracking the first harmonic of the distorted signal. The gain plot should be flat but of lower amplitude, the phase plot should stick close to 0. The Siglent performs well in this test. |
| nctnico:
I did a similar test with the RTM3004 (converted 100mV rms to 282mVpp). I used an external function generator with an RF splitter but didn't compensate for the 3dB loss in the splitter. Also I used an 820 Ohm resistor with 10nf (measures 9.-something-) so the -3dB cut-off point is a bit higher. Couldn't find a through hole 1k resistor quickly. I agree with TopQuark though; using non-linear devices is a much more realistic torture test because that is what you can expect when doing real life measurements and likely the signal processing used for the bode plot is optimised to deal with harmonics. |
| Someone:
The built in bode/FRA/sweep functions are effectively "toys" for the educational market. As black boxes of mystery its not possible to practically compare the different implementations without a huge amount of reverse engineering (over to you lot if you really want to do that rather than just the apples to grapes to bricks comparisons that usually end up). When you know what the noise/aggressor/non-ideal components that need to be avoided are then you select/design-in a suitable capture and processing method to minimise those effects, but that needs the flexibility of scripting/programming. 100dB of displayed dynamic range is easy when exploiting the front end attenuation and a benign DUT. But 100dB of dynamic range below the noise? that need some effort but is still possible. That level of interference/noise in the plot from mawyatt's first post would be "very poor"/low-effort from my experience. |
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