oscilloscope 8bit adc ??! - Page 1
Forum section: electronics / beginners

author: 5282
author_rank: Regular Contributor
timestamp: December 17, 2016, 06:32:25 pm
content: HIIII,i have questionthe most popular oscilloscope is 8bit ADC that mean it's 256level voltage stepsthat's means you need 256 pixel to show the 8bit ADC signal.in this picture the sine wave is drawing in <256pixel then why he using 8bit ADC!!

author: Twoflower
author_rank: Frequent Contributor
timestamp: December 17, 2016, 07:03:21 pm
content: Because higher resolution ADCs are more expensive. Especially the surrounding parts needs to be much better if you really want to get useful data out of a 12bit ADC and not 8 bit data + 4 bit noise.The screen-resolution is so big: Sometimes it's just easier to see things if they're bigger even if it not contain additional data. Especially if the screen is small. A second point is if you want to display multiple traces stacked (not overlay each other). If you have a 4 channel scope it can get very messy very easy and you have to reduce the x-axis gain to fit them in.

author: 5282
author_rank: Regular Contributor
timestamp: December 17, 2016, 07:18:19 pm
content: thank youyes he reduce vertical resolution to fit in LCD display then why not using 6bit ADC instead of 8bit ?

author: Simon
author_rank: Unknown
timestamp: December 17, 2016, 07:23:54 pm
content: Input resolution and screen resolution will be totally different things. Input resolution will be more meaningful for measurements and no doubt the output is a processed image not a direct representation of the input.

author: wraper
author_rank: Unknown
timestamp: December 17, 2016, 07:25:04 pm
content: And on what basis you decided that sine waveform signal amplitude is the maximum what that scope can show?

author: Paul Moir
author_rank: Frequent Contributor
timestamp: December 17, 2016, 07:30:47 pm
content: 1 Because the A/D converter came with 8 bits.2 You need headroom for DC offsets and you may want to zoom in to a particular feature on your signal. There's nothing illegal about having your waveform going off the screen.(Headroom - I don't know if that will translate well. It directly means the space between your head and the ceiling so you don't bump your head. But what I mean is that you need a comfortable gap before you run into the limits of the A/D converter.)

author: wraper
author_rank: Unknown
timestamp: December 17, 2016, 07:31:37 pm
content: Quote from: 5282 on December 17, 2016, 07:18:19 pmIf you decide to use 128x64 pixel display, then it might make sense. I's not like those 8 bits are perfect either, you might get something like 6.5 ENOB (effective number of bits) from 8 bit ADC (some are better, other worse), anything below that is more or less noise.https://en.wikipedia.org/wiki/Effective_number_of_bits

author: David Hess
author_rank: Super Contributor
timestamp: December 18, 2016, 06:19:26 am
content: The standard Tektronix uses or at least used to use except for their very early DSOs is that 8 bits of input resolution applies to 10 vertical divisions or more even though only 8 divisions can be displayed. Usually they arranged this so the digitizer resolution maps to the screen resolution without aliasing. This prevents clipping of waveforms which are just beyond the border which would otherwise cause measurement errors or interfere with digital add and invert differential measurements.For similar reasons, the analog operating position range is greater than the display range and usually by a significant amount so the position control operates as a low range offset control.It is very difficult to make fast vertical input amplifiers which have better than 8 bit linearity and settling time so digitizer resolution beyond 8 bits is usually wasted unless input bandwidth is much lower. Even 8 bits is pushing it at 100 MHz and higher.

author: Simon
author_rank: Unknown
timestamp: December 18, 2016, 08:28:41 am
content: Quote from: David Hess on December 18, 2016, 06:19:26 amAnd for example the Rigol 1054Z can do oversampling to increase effective resolution although no doubt you get a lower bandwidth but you would be looking as low frequency signals anyway.

author: David Hess
author_rank: Super Contributor
timestamp: December 19, 2016, 12:36:00 am
content: Quote from: Simon on December 18, 2016, 08:28:41 amAs far as I know, the Rigol DS1000Z series always return 8-bit data from the digitizer and always produces an 8-bit result so resolution cannot be increased. Averaging and high resolution mode still decrease noise.All of my DSOs return the ADC samples in 16-bit memory for processing so averaging and filtering does produce a visibly higher resolution display record.