basic circuit of a dso

[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]

1.how do they change the analog input form channel 1 to 2
or do they have the same circuit made for each channel

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.

2.how do they sample high voltages when their adc is capable of only 1v p-p

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]

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

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.

[Simon]

if your trying to say it can't work your a bit late, we all use them and have had no problems 

[abhimanyu]

okk
So in a 1Ghz sampling rate dso when we are using  both the channels actually the sampling rate of each channel is 500Mhz which makes it a total of 1Ghz
hope I got it right!!!

[alm]

Yep, and each channel consists of a bunch of ADCs (5?), all interleaved.

[Simon]

no each channel is multiplexed into a set of 5 chips that have 2 AD's each, if you watch daves review of it it's all explained, the chips are 2 X 40 MHz ADC's that have been overclocked to 100 MHz X 2 per IC X 5 IC's = 1000 MHz = 1GHz interleaved

[abhimanyu]

@all
thank you
this information was very useful..
thanx once again