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| FeelTech/FeelElec FY8300S Quick Tear Down |
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| CDaniel:
Normally the square wave is generated digital from FPGA , but an older FY generator has jitter like in your oscillogramme with trigger ... for allmost all frequencies except for some that divide exactly with the clock |
| TurboTom:
On today's "Magic Pulse", "SiFi II", or whatever the manufacturer may call their version of edge accuracy improvement technology, the slopes don't consist of a single "step" of the DAC output (i.e. outputting a series of -1V samples and the next series of samples directly outputting +1V -- this would permit much faster slopes), but the edges are "stitched up" of a certain amount of samples, ususally 2..3 and the manufacturer makes use of the reconstruction filter to smooth that out to a "more or less" steep, homogenous edge. To compensate for the mis-match of the sample frequency with the signal frequency, the arrangement of these "slope samples" is calculated (or looked up) new for each edge. As a result of this approach, you will always find some slope steepness wobble with these generators (which may be more or less pronounced on a certain instrument, I emphasized on it quite a little on my "rants" on the SDG6000X which permits outputting faster slopes in certain modes than what the reconstruction filter is designed for), yet with the zero crossing (or centerline crossing) of the signal being virtually jitter-freeand thus resulting in the very good phase jitter figures. This approach may also lead to some ringing on the "plateaus" of the square (quite visible with the Rigol DG800 / DG900 series) and as it appears, with the AWG that's the subject here as well. Did anybody test if this three-channel AWG permits outputting full length 8kSa arbitrary signals simultaneously on all outputs? To tell from the FPGA specs, this shouldn't be possible (only enough internal ram to store slightly more than 2* 8kSa, and I don't find any external sample memory attached to the FPGA - unless it's located on the other side of the PCB). |
| grizewald:
That sounds like exactly what is being done on this generator. In the shot where I'm triggering off the sync output, I think you can see each edge of the square wave on channel 1 being adjusted slightly on each pulse. The sync output is unadjusted, and the original 4ns jitter still appears to be present there. I'll try installing the software and uploading a waveform of my own to check all three channels at the same time. Are there any features you think I should include in the waveform? |
| edigi:
Thank you for the detailed tear down. As a result, I've pulled the trigger on one of the FY8300S (financially it's a bad idea to read reviews ;) ). It's on its way now. Trading the jitter for interpolated edges (varying rise/fall time) is an acceptable compromise for me. I could not justify even the cheapest Siglent/Rigol generator so far (still significantly more expensive although much better DAC and probably logic as well) as I suspect it will see too little use with me, but it's good to have one sometimes. It's a pity that they don't include a decent PSU even in this variant, but luckily there is plenty of space for a replacement (that I'm not very keen to do though). It's really good that finally they use a standard 10 MHz clock (so that it can be easily replaced with a better one), although allowing for an external reference is really a missed opportunity. For a little cost quite much value could have been gained... |
| grizewald:
Don't forget to give it a good shake when it arrives. You don't want a screw shorting out the supply or anything else first time you power it up! I also noticed that the rear panel is just a little bit too thick and this makes it very difficult to connect a BNC connector to any of the rear BNC plugs. I'm not sure how I'll address that problem yet. |
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