Re: 7T11 trace shifting left as time/div rotated.
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Albert,
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I can only think I'm not interpreting what I'm seeing on the 'scope screen correctly. I'm probing TP286 (output of TTH) with Sweep Range set to 50nS, 5nS/div in sequential mode. I have the viewing timebase set for 5uS/div. The signal I see at high scan rates is similar to waveform capture 11 in the 7T11 and 7T11A manuals except that the top of the bright zone starts ABOVE 0V, and the bottom of it is about 5.6V below there. The picture of this signal manuals however clearly has the top of this signal at 0V with nothing above I can't reconcile what I see with the descriptions in the manual that say the TTH ramp starts at 0V and goes more negative until stopped by the slewing ramp comparator. How can the TTH ramp voltage ever be +ve in sequential mode???? I could possibly understand the bright zone moving down as you turn the Time Position controls CCW if the individual trace line in the brightened zone represents the value of the TTH ramp after it has been stopped by the slewing ramp comparator for this sample (I now think this is the case). But I cannot see how it can end up above zero! If you turn the Scan control fully CCW, you can actually see the voltage ramp down and then jump back up. D. -----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On Behalf Of Albert Sent: 23 January 2012 19:27 To: TekScopes@... Subject: [TekScopes] Re: 7T11 trace shifting left as time/div rotated. Hi David, Our start and stop terminology is confusing since both are stop levels of the THT. The "start" is the stop level corresponding to the left most dot at the trace (start of the trace), the "stop" is the stop level corresponding to the right most dot of the trace (end of the trace). The start level of the Miller circuit is always the same, like you say. About 0 V. But the stop level for first dot of the trace varies from 0 V to -5 V if you rotate Position from fully CW to fully CCW. At the 50 ns range, the stop level of the last dot in the trace is 5 V more negative (at 5 ns/div), 2 V more negative (at 2 ns/div) and so on. The Slow Ramp Inverter (which is responsible for the level shifts) sends an opposite level change to the horizontal amplifier input to cancel the shift. Also at faster time/div the horizontal gain is increased to cancel the decrease in TTH level differences. At CCW position all curves at the TTH test point have the ramp from 0 V to -5 V in common. Hence you will see this ramp very bright. Albert
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David C. Partridge