Hi
This question has probably been asked a 1000 times. So here it is for 1001st time.
How do I go about implementing an adc to a fpga?
Hopefully someone can give me some areas to start in. Some links, reference materials, code etc. What are the most commonly interfaced adc's, and the buses they use?
I currently am working with a spartan 3s 1500mb development board, and using the xilinx edk. Im new to the area, but need to learn about interfacing asap.
thanks
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Regarding analog-to-digital converters, there are two important parameters you have to consider first: Accuracy ( = number of bits), and speed (number of conversion per second)
Accuracy can be 4 bits to 20 bits, and conversion rate can be between 1 kHz and 1 GHz. There is a lot of room for different types of interfaces...
Peter Alfke
Basically its for industrial sensors, like thermocouples, 0-10v, -5v-5v, 0-5v,
0-20ma, 4-20ma sensors.--
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0-20ma, 4-20ma sensors.
Go to
Look for A/D converters, and every data sheet you choose, based on desired ADC operation, will include detailed interface information.
Common busses are i2c, SPI, Parallel CMOS, Parallel LVDS. SPI is the simplest, with lowest pin count, but in the region of
1Msps it becomes too slow, and above that parallel busses are used. On really fast ( 2GHz+) ADCs, bus expanders are used, so 2Gsps@8bits fans-out to 500Msps@32bits, where it can (just) feed into a FPGA.-jg
thanks for that info.
So what is the best approach to learning how to do this?
Is it possible to elaborate a bit more on this "..so 2Gsps@8bits fans-out to 500Msps@32bits, where it can (just) feed into a FPGA..."
Cheers!
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I think you'll find that everyone is directing you to information on interfacing an FPGA to a separate ADC. It is very hard, and not worth the effort to create a high performance ADC using the FPGA fabric. Instead using an external ADC is the best option. If you really need an ADC integrated into some IC with extra logic, you'd have to look into utilising an ASIC. Though there might be an FPGA out there with a custom ADC block integrated into it, it's not the norm however.
Bevan
Yes i wish to interface to an external adc. Sorry if that was not clear.
Hopefully the interfacing to an external adc is not too complicated.
I wish to be able to connect industrial sensor(s) to an adc, and then acquire the value to the fpga for further processing. Maybe its better to use an asic or something else for interfacing an adc. I need to find out these things.
Regards.
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So, where's the hard part?
You choose an external ADC based on the analog requirements - sampling rate, precision, aperture jitter, analogue bandwidth, and so on. You will probably find a lot of devices that meet your needs, so you must then refine the choice based on package size, cost, and complexity of the digital interface. Since you are doing industrial sensing stuff, I guess the data rate will be fairly low and it is probably sensible to choose a device with a serial interface (SPI or similar) because this will give you a smaller ADC package, use fewer pins on the FPGA, and make the circuit board layout much easier.
OK, now you start to read the ADC data sheet carefully to decide what its digital data interface looks like. Now you have a straightforward digital design problem that can easily be solved in your FPGA. Use the FPGA to generate the ADC's clock (probably divided-down from your system clock), copy control register values out to the ADC, and read conversion results back.
It's almost trivially easy. It would get harder if any of the following conditions applies:
1) Sampling rate of any one ADC is greater than about 50M samples/sec 2) Very large number of analogue inputs 3) Very high precision requirements (more than about 14 bits) 4) Need to maintain some special timing relationship between ADC sampling and something else, such as the activity of a DSP deviceGo away and try it. If you have trouble with some part, come back here and I'm sure someone will try to help. The rather vague nature of the responses so far has been directly related to the rather vague nature of your request :-)
-- Jonathan Bromley, Consultant DOULOS - Developing Design Know-how VHDL, Verilog, SystemC, Perl, Tcl/Tk, Verification, Project Services Doulos Ltd. Church Hatch, 22 Market Place, Ringwood, BH24 1AW, UK Tel: +44 (0)1425 471223 mail:jonathan.bromley@doulos.com Fax: +44 (0)1425 471573 Web: http://www.doulos.com The contents of this message may contain personal views which are not the views of Doulos Ltd., unless specifically stated.
Thanks!
Yeah the problem is im a chemical engineer doing research with very basic electronic engineering knowledge.
I need a kick in the right direction. There is alot of stuff out there, i just need to figure out the right path. Current help and more is very much appreciated!
Cheers!
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ouch...
I have a nasty feeling that this is a bit the same as me asking you "please explain how I can build a plant to manufacture
10 tons of ammonia per week" - it's very well-established technology, very easy when you know how, but not something that you should try unless you have a clear idea of what you are doing :-)When I said "almost trivial", I meant "almost trivial for a reasonably well trained digital designer". I don't think it's a very productive use of your or our time to provide you with all the necessary background via Usenet. Get yourself a competent design contractor, watch what he/she does very closely, take their results and modify it as needed to suit your next project... it'll be a few thousand dollars well spent. If you're building industrial instrumentation, or planning to build it, then you have *some* budget surely?
This post sounds a bit negative. Apologies... but I strongly suspect that you are a bit too far away from success just yet for Usenet to be your rescue. Please forgive me if I've misjudged.
-- Jonathan Bromley, Consultant < oh, and speaking of competent contractors... > DOULOS - Developing Design Know-how VHDL, Verilog, SystemC, Perl, Tcl/Tk, Verification, Project Services Doulos Ltd. Church Hatch, 22 Market Place, Ringwood, BH24 1AW, UK Tel: +44 (0)1425 471223 mail:jonathan.bromley@doulos.com Fax: +44 (0)1425 471573 Web: http://www.doulos.com The contents of this message may contain personal views which are not the views of Doulos Ltd., unless specifically stated.
If you are building industrial instrumentation, you might want to spend the money the next time as well. Electronic design (not just the FPGAs) has lots of ways to produce less than ideal results. Ground loops, proper power bypassing, signal integrity, and a list of other issues can give you a circuit that doesn't work, or even worse works most of the time.
Can I do that here as well?
-- Phil Hays to reply solve: phil_hays at not(coldmail) dot com If not cold then hot
It's outside your Sensor reference area, but I included it as a limiting case, as an example. You can get ADCs ($$) that have 2 G samples/second, and that is above FPGA abilties - but FPGAs have lots of pins, so the solution is to create a wider, slower datapath out of the ADCs. [the opposite of a SPI interface, if you like ]
Physical connection is simple. 'Further processing' sounds like some software, ie a SoftCPU. There are truckloads of examples, of ADC uC connections, and the software needed to initialise the registers in the ADC, and then pump the data out. That software is portable to your FPGA CPU. You have chosen an ADC partnumber, and FPGA SoftCPU ?
-jg
You brought your question to the FPGA news group, and sure enough everyone is trying to help you on the issue of connecting ADCs to FPGAs. Let me try kicking you in a different direction, just in case it makes more sense :-)
Ok, here goes: Why are you trying to do this with an FPGA ???
which screams out that this is where you are headed (but I could be wrong :-)
If you are trying to build a custom, self contained ACQ system, then going out and buying chips (ADC, DAC, FPGA) may be the way you have to go. But, if the collected data is to processed on a "standard" PC, then you can save a huge amount of pain and suffering by just going out and buying a data acq board that plugs into your computer, or that connects to the computer over ethernet, or serial (rs232), or USB.
Look at products from:
National Instruments:
Get started at $25
All the best,
Philip Freidin
Philip Freidin Fliptronics
Has anyone looked at interfacing a Cyclone II or Stratix II with th
1Gsps, 8 bit A/D from National Semiconductor (ADC081000) ? I' looking for a reference design that will save me time rather tha creating my own..Wow. Good thing I looked at the rest of the thread before posting. I thought you were talking about adders using the carry chain (also known as ADC). Anyway....
A very good question.
Excellent advice, probably the most important kick-start the OP received - unless he's doing something really unusual. Most of the usual industrial plant-control applications are well covered by standard hardware these days.
-- Jonathan Bromley, Consultant DOULOS - Developing Design Know-how VHDL, Verilog, SystemC, Perl, Tcl/Tk, Verification, Project Services Doulos Ltd. Church Hatch, 22 Market Place, Ringwood, BH24 1AW, UK Tel: +44 (0)1425 471223 mail:jonathan.bromley@doulos.com Fax: +44 (0)1425 471573 Web: http://www.doulos.com The contents of this message may contain personal views which are not the views of Doulos Ltd., unless specifically stated.
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