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basic circuit of a dso

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abhimanyu:
hi
i have some doubts about the circuit design of the ossiloscope shown in this video
http://www.eevblog.com/2009/10/12/eevblog-37-rigol-ds1052e-oscilloscope-teardown/

1.how do they change the analog input form channel 1 to 2
or do they have the same circuit made for each channel
2.how do they sample high voltages when their adc is capable of only 1v p-p

GeoffS:
I think the only people who could tell you this for sure are Rigol and they're unlikely to reveal their design secrets  ;)

abhimanyu:
@tumutbound
i feel David would have surely looked into it when when he had opened that dso

alm:

--- Quote from: abhimanyu on August 26, 2010, 08:17:39 am ---1.how do they change the analog input form channel 1 to 2
or do they have the same circuit made for each channel

--- End quote ---
I'm sure both channels have separate analog front-ends, the ADCs from both channels can be combined for double the sample rate, they probably use some kind of analog switch.


--- Quote from: abhimanyu on August 26, 2010, 08:17:39 am ---2.how do they sample high voltages when their adc is capable of only 1v p-p

--- End quote ---
Compensated voltage dividers (parallel RC so the ratio of the impedance is constant, regardless of the frequency). They divide the voltage down within the range of the vertical amplifiers.

Tektronix published a lot about oscilloscopes (search for the Concepts series), but this was way before the modern DSO. By the time the DSO came around, companies had stopped publishing detailed technical explanations. But apart from the digitizer/CRT, many parts are similar in DSOs and CROs.

EEVblog:

--- Quote from: abhimanyu on August 26, 2010, 08:17:39 am ---hi
i have some doubts about the circuit design of the ossiloscope shown in this video
http://www.eevblog.com/2009/10/12/eevblog-37-rigol-ds1052e-oscilloscope-teardown/

1.how do they change the analog input form channel 1 to 2
or do they have the same circuit made for each channel
2.how do they sample high voltages when their adc is capable of only 1v p-p

--- End quote ---

1. It's done in software and hardware multiplexing. The input signal can be switched through to either 1 or 2 ADC channels depending on the speed required. Both channles can be sampled at once, and the software can simply ignore one channel.

2. That's the function of the "analog front end" or "vertical amplifier/attenuator" (the bit inside the metal can). Every oscilloscope has one, it is designed to scale the input to the 1V range of the ADC. It is done with a software programmable gain amplifier and/or attenuator.

Dave.

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