arm7 core with fast monolithic 12-bit ADC

As others have intimated, a vendor that excels in ADC's, is much more likely to offer a uC with better class of ADC.

That should move ADI to the top, with TI close behind. [SiLabs have a 16bit 1MSPS device, but that's 8 bit CPU]

Atmel tend to be at the generic end, and their ADC specs rarely give worst case promises on anything - just typicals. They are also very new to offering 12 bit ADCs on any uC.

You are also more likely to get better results from a faster ADC averaged, that a slower ADC over-clocked

With TI's high precision PWMs you could self-test the ADCs for transfer quality fairly easily.

-jg

I get the impression that they took a pretty good ADC (+ good DACs), and managed to get a mediocre ARM onto the same die.

Whereas the other manufacturers have higher performance ARMs, with better peripherals - except for their mediocre ADCs.

Yes, if the extra bits aren't fixed at 0 or 1. The point you are making assumes a nice Gaussian around the 10 bits in the extra 2. Which is very useful, for obvious reasons.

What I'm pushing for is that this is monolithic, that the core is ARM7 or compatible, and that the speed is better than 1.5MHz in delivering the rest. 10.5 ENOB is acceptable, though of course I'd like to push that, too.

Yes, I said more than 1MHz (though I could [and may] settle for 1MHz.) Past experience in the application space is 1.5MHz at 11.3 ENOB, which I know is more than enough to get the job done. That would be a perfect fit, but I don't expect it monolithically.

Let me put it this way. The only case I know well is Poisson events. These do, when summing, integrate into Gaussian curves. Gaussian distributions around a mean provide predictable results when averaged. If there is another distribution that you feel can achieve predictable results, that is not Gaussian in nature, I'd have to examine it using mathematics to see. So far as I'm aware, in practical experience, it's Gaussian or else you get distortions that are difficult to remove. But I'm open to suggestions that I can analyze that aren't Gaussian, are found in these circumstances, and can be used without distorting the result (in uncorrectable ways.) My experience is admittedly limited in many ways and I'm sure that there are many ideas out there that I haven't thought about before.

Yeah. I needed less advice on theory and more on what's out there or what might be finessed into working for what I want to get.

In this case, I am not looking for flat out speed of the ARM7. I've had to write every line of this application on entirely integer processors in assembly code and I pretty much know exactly where the time sinks are and what to do about them. I was already aware of the ADI parts, though I haven't used them before, and have one or two parts here, in fact. (Requested samples just sitting here on the possibility.) The idea of running the converter faster was just suggested and that makes the part more interesting for a time. So I'll look into it.

Okay. I may take a look over there. I seem to recall a spurt of activity here about that site (from you), now that you bring my attention to it again. That may be a big help, at least in eliminating things to look at, if not finding ones to spend time on.

Jon

Agreed.

Yes. Thanks for reminding me about the 8051 Cygnal core. I may look at that. Problem will be in the analog section leading up, though, if I try 16 bits. Best to catch noise in the first stage input, though, and it is a good idea to consider a redesign on that side given a good ADC on a cpu. I think I could live with the 8051, by the way. Have to think more closely about it, but it's possible.

Thanks for that.

Okay.

I think this is an excellent point to consider in the context of overclocking the ADI ARM's ADC.

Hmm. I hadn't considered that idea here. Thanks for bringing my attention to it.

Jon

die designs that are good for CPU's are not good for quiet fast accurate A/D's, that's why most A/D's in micro are not even speced out

I wouldn't design a product with an internal micro A/D unless I had a complete spec or I was using it for a simple low res monitor system (

Just a quick note on overclocking. Overclocking a flash is not uncommon because of the difference of the accuracy of the converter and the bandwidth of the chip input. But most MCUs use successive approximation and that can get you into real trouble if you overclock it. I am not an expert on these devices, but from what I understand about them if you don't give enough settling time on each bit, you can get an answer that is way off. I guess you could just stop the converter before it has converted all the bits, but that would require access to the converter at a low level.

I guess I am saying that if you want to overclock a successive approximation converter, be sure to test this thoroughly before you put that in your plan.

Rick

If the bits were fixed, then they wouldn't really be part of the resolution, eh? Actually, the point I am making is that I am pretty sure you ***can't*** assume a Gaussian curve, but I don't think that is needed. It only has to be uncorrelated so that it averages out. Gaussian is symmetrical, so it will average out, but other shapes will average out as well.

I thought you said it needed to be an ARM7. I see in another post you are also considering the Cygnal parts.

Ok, at this point I think you just need to look at the parts out there.

I think at this point you may be over analyzing the issue. You don't need to characterize the noise mathematically. You just need to characterize the operation of the device. So grab an eval board and collect some data. Then run it through your signal analysis software on the PC and, voila, a value for ENOB!

I hear you. Often people don't analyze things this carefully. They either grab a part and live with the results or they pick a part that gives them some margin of safety (in this case that would be two parts, an ADC and an MCU). So you are not likely to get any more useful info without analyzing some parts.

Good luck! and let us know what you find...

Rick

That seems to be the wisdom of the day. I am looking into experimenting with both, as well as one or two other options.

Jon

That's a pretty good summary. I've done some work with the ADI ADuC7026 part and while the analog I/O is good (4 parallel DACs!), the ARM processor is hamstrung:

• No DMA - all I/O must be programmed through the CPU

• No VIC - Only IRQ/FIQ available and vectoring must be done in firmware

• Program flash is only 16-bits wide - must use Thumb mode for zero wait state code access

• SPI interface is limited to ~3MHz clock rate, 8-bits only.

On the upside this part has a parallel external memory bus that comes in hand for some kinds of interfacing, and it's pretty easy to develop for. Just don't expect screaming fast performance. I ended up porting the application intended for the ADuC7026 to a Microchip dsPIC with a quad SPI DAC and saw about a 2x improvement in throughput.

Eric

Interesting. Thanks.

Jon

or

at

but does that really matter?

Another (future) data point from Atmel - they have a family brochure showing the AVR32uC3C as having Dual 1.5MSPS 12 bit ADCs and 12 bit DACs and tagged as 'future' in status,

Arrow do show a part code AT32UC3C0128-ALUT, so maybe not too 'future'.?

That is the CAN/USB variant

-jg

Thanks. Although 'future' at Atmel has unique meaning to me (not in a good way), I do at least enjoy seeing some promises on the subject. The more the better. More likely one will get through the vaporware stage.

Jon

:)

back in October 2008, Ulf said this "Ulf Samuelsson wrote: The AT32UC3C will have a 1,5 MSpl 12 bit ADC, CAN, SPI (but not Ethernet), but it wont be sampling until early next year.

and it is now early 2009.... Ulf ?? :)

-jg

What's your problem? - it's still true :)