Working with ADS chips and oscilliscopes
rwgast_logicdesign
Posts: 1,464
Ok so ive been hard at work on multiple prop projects and one of them is a multi-functional piece of testing equipment. This whole thing is in the research stage and at the moment the only things I feel comfortable with is a cap tester, frequency meter and voltage meter. I had never planned to add a scope to the project and still cant say I have any real intentions too. I see all these kit scopes around or even something like the prop scope and i just dont understand what anyone would really want one for, at least anyone doing digital electronics. From my research i found the prop scope is lucky to measure waves around 2mhz, what are seriously going to need to measure thats under 2mhz when working on things like propeller based boards. I know I know some people out there may be able to use a prop scope for certain applications.
Im still a hardware newb and the reason id love to own a scope is to test my board layouts, learn how to read wave forms, just generally see whats going on, on my circuit boards. I think a scope can really boost the learning process and give one a better understanding of what there projects are doing. Anyways at this point in time i would need about a 300mhz scope. I looked all over the net at scope kits, projects, and diy articles. The best thing I could find was an fpga based 100mhz scope that was about 100 bucks to build. For 100 bucks I could get a used 300mhz bench scope. I went looking at new scopes in the 300mhz range and those things are all over a grand. I didnt even bother pricing a new 1ghz scope. Theres all kinds of DIY tools out there almost any test tool i can think I can find a homemade version based on some sort of micro. So what is the deal with scopes why is there no diy scopes out there over a few mhz?? Is it just as exspensive to make one as buy one, are they just to complicated or require some special fab that DIYers dont have access too??
I came across 3 of these ADS chips today there pretty slick, http://search.digikey.com/us/en/products/ADS1210UG4/ADS1210UG4-ND/1689106, and kinda spendy. I dont know anything about using an ADS except for how to read voltages with some prewritten code for a totally different ads. Are all ADS's kind of based on a standard like you would hook up this ads the same as a different 4 channel ads, code wirtten for one ads will work with another? What are some good resources for getting started with these things and making a few little projects. At some point id like to use it for a scope, even if it is a useless 500khz scope.. just to learn how a scope works. Thats another thing I couldnt find, just some info about how a scope works, i mean something more detailed than an ads sends it signal to a controller. I feel like if I could get the basics down i could maybe build a nice scope one day, or at least know why I cant build a 300mhz scope. Other than the propscope whos software isnt open, there is no propeller scope projects or code on obex, maybe there was one using java for pc software but there project page link was broke (this coulda been something else i was searching for too idk). If anyone knows of just a basic scope project hardware and software based on the prop, please tell. Anyways any info or good links on ADS's or basics of how to build a scope would be greatly appreciated. Most any info I find on this stuff is sorda connect this to that upload the hex file to a pic and tada.
Im still a hardware newb and the reason id love to own a scope is to test my board layouts, learn how to read wave forms, just generally see whats going on, on my circuit boards. I think a scope can really boost the learning process and give one a better understanding of what there projects are doing. Anyways at this point in time i would need about a 300mhz scope. I looked all over the net at scope kits, projects, and diy articles. The best thing I could find was an fpga based 100mhz scope that was about 100 bucks to build. For 100 bucks I could get a used 300mhz bench scope. I went looking at new scopes in the 300mhz range and those things are all over a grand. I didnt even bother pricing a new 1ghz scope. Theres all kinds of DIY tools out there almost any test tool i can think I can find a homemade version based on some sort of micro. So what is the deal with scopes why is there no diy scopes out there over a few mhz?? Is it just as exspensive to make one as buy one, are they just to complicated or require some special fab that DIYers dont have access too??
I came across 3 of these ADS chips today there pretty slick, http://search.digikey.com/us/en/products/ADS1210UG4/ADS1210UG4-ND/1689106, and kinda spendy. I dont know anything about using an ADS except for how to read voltages with some prewritten code for a totally different ads. Are all ADS's kind of based on a standard like you would hook up this ads the same as a different 4 channel ads, code wirtten for one ads will work with another? What are some good resources for getting started with these things and making a few little projects. At some point id like to use it for a scope, even if it is a useless 500khz scope.. just to learn how a scope works. Thats another thing I couldnt find, just some info about how a scope works, i mean something more detailed than an ads sends it signal to a controller. I feel like if I could get the basics down i could maybe build a nice scope one day, or at least know why I cant build a 300mhz scope. Other than the propscope whos software isnt open, there is no propeller scope projects or code on obex, maybe there was one using java for pc software but there project page link was broke (this coulda been something else i was searching for too idk). If anyone knows of just a basic scope project hardware and software based on the prop, please tell. Anyways any info or good links on ADS's or basics of how to build a scope would be greatly appreciated. Most any info I find on this stuff is sorda connect this to that upload the hex file to a pic and tada.
Comments
Why do you think you need a 300MHz scope ?
Even with a 50-100MHz bandwidth, with a fast sampler you can check timing skews down to 1ns.
I have no application that toggles pins above 100Mhz but I DO have a need to check skews.
Depends what you mean by DIY.
There is an open source FPGA design that comes in a nice case with screen for ~ $185 See DSO203 on eBay.
Above that, and the memory-ADC coupling gets tough. Not to mention screen and case, so you need to reality check against something like UTD2102CEL ~ $350, which sports a high res LCD ( 7" 800x 480 from memory) and they also claim 100MHz bandwidth, and 1Gs/s with 50Gs/s equivalent, (whatever that really means).
Includes a 6 digit frequency counter too, nice looking units.
If they really can deliver 1ns 'dots' (even repetitive), and some sort of 20ps 'equivalent' that would be
more than useful.
Has anyone used these Uni Trend scopes on a real problem ?
http://www.uni-trend.com/UTD2052CL.html
Delta-sigma converters don't handle high slew-rates, which is exactly what you need from a scope on digital circuitry. Delta-sigma is really a trick to get high resolution A->D conversion on the assumption that you are less interested in resolution at the higher frequencies - great for audio and anti-aliasing filters.
For a fast scope you need a high-imput impedance input stage to a fast (probably flash) ADC, and then dealing with the 100's MB/s raw data that results. Neither the fast ADC nor the memory system are cheap I believe.
[edit: had a quick look at Farnell for 250MSPS ADCs with 10bits+ and the minimum price was GBP 52, or about $80 - and that only gets 100MHz or so]
Take a look under "Prop Lab Equipment" in post #5 of my index. Perry has a "Poor Man's Oscilloscope". It's not going to have the speed you're looking for though.
Lawson