Re: 7T11 trace shifting left as time/div rotated.
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I also note at least one transcription error!! The Start V for .5nS in the second half should of course be 90mV.
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Very well spotted on the systematic nature of the offset BTW. I'd been banging my head on the wall (so to speak) with this problem for so long that I completely missed that! Regards, David Partridge -----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On Behalf Of Albert Sent: 21 January 2012 23:06 To: TekScopes@... Subject: [TekScopes] Re: 7T11 trace shifting left as time/div rotated. Hi David, It takes some time to remember what all those circuits in the 7T11 are doing! The shift in output of U512A in a 5-2-1 sequence corresponds nicely (as should be) to the increase in feedback resistors 10k-25k-50k, ratio 2:3. At 1 ns/div the shift is about 0.5 V and that same shift will appear at the input R647 to the Dot Position Memory. This memory should detect that systematic error and send a correction to the Slow Ramp Inverter. That in turn would (finally) result in a shift of the THT output range to correct the error. This doesn't seem to happen, or not not enough. At the faster sweep speeds U512B and D get switched in and introduce their own offsets. Again the Dot Pos Mem should correct for this. Maybe you can check its operation/calibration. I remember it's not an easy calibration and a lot of compromise is needed. Albert (BTW your packet calculator needs some attention as well...) In equivalent time, sequential mode, the trace is shifting left as I rotate the time/div knob. ------------------------------------ Yahoo! Groups Links |
David C. Partridge