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| Tektronix 1-3 GHz touch screen color DSO back in 1989 ! |
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| David Hess:
--- Quote from: tggzzz on June 16, 2024, 03:09:43 pm --- --- Quote from: David Hess on June 16, 2024, 02:57:51 pm ---Sampling oscilloscope are almost uniquely useful for doing transient response calibration. The input stage of a sampling oscilloscope is immune to overload, so they are also very good for making settling time measurements at high sensitivities that other oscilloscopes simply cannot do. --- End quote --- Just so. Unfortunately that doesn't stop some salesmen claiming otherwise. https://www.eevblog.com/forum/testgear/choosing-between-entry-level-12-bit-dsos/msg5433389/#msg5433389 But advances in ADC and front ends are continuing to eroding that advantage. --- End quote --- ADCs and front ends have been trying to solve the overload problem for decades, (1) and greater sensitivity makes it worse. It along with the settling time problem are hard problems, which a sampling input completely solves. Jim Williams wrote about these two problems, which are linked. He spent a lot of effort designing a circuit to prevent oscilloscope overload and then used a sampling oscilloscope to verify its performance. Oscilloscopes that have input offset controls may make an attempt to solve this. The Tektronix 7A13 differential comparator uses feedback to clamp the input, so does better than most oscilloscope inputs. I think this was also a feature of the differential comparator Tektronix made for their 11k series of mainframe oscilloscopes, which includes DSOs. Jim Williams talked about the issues here: https://www.analog.com/media/en/technical-documentation/application-notes/an47fa.pdf (1) Not really - hardly anybody cares about overload performance. |
| tggzzz:
--- Quote from: David Hess on June 16, 2024, 06:00:21 pm --- --- Quote from: tggzzz on June 16, 2024, 03:09:43 pm --- --- Quote from: David Hess on June 16, 2024, 02:57:51 pm ---Sampling oscilloscope are almost uniquely useful for doing transient response calibration. The input stage of a sampling oscilloscope is immune to overload, so they are also very good for making settling time measurements at high sensitivities that other oscilloscopes simply cannot do. --- End quote --- Just so. Unfortunately that doesn't stop some salesmen claiming otherwise. https://www.eevblog.com/forum/testgear/choosing-between-entry-level-12-bit-dsos/msg5433389/#msg5433389 But advances in ADC and front ends are continuing to eroding that advantage. --- End quote --- ADCs and front ends have been trying to solve the overload problem for decades, (1) and greater sensitivity makes it worse. It along with the settling time problem are hard problems, which a sampling input completely solves. Jim Williams wrote about these two problems, which are linked. He spent a lot of effort designing a circuit to prevent oscilloscope overload and then used a sampling oscilloscope to verify its performance. Oscilloscopes that have input offset controls may make an attempt to solve this. The Tektronix 7A13 differential comparator uses feedback to clamp the input, so does better than most oscilloscope inputs. I think this was also a feature of the differential comparator Tektronix made for their 11k series of mainframe oscilloscopes, which includes DSOs. Jim Williams talked about the issues here: https://www.analog.com/media/en/technical-documentation/application-notes/an47fa.pdf (1) Not really - hardly anybody cares about overload performance. --- End quote --- Yes. The improvements in ADC and front ends appears to be just an increased number of bits (effective or otherwise) at high sampling rates. That enables software "select rectangle and zoom in" functions, i.e. without hardware fiddling with large DC offsets. |
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