arm7 core with fast monolithic 12-bit ADC

If clz and division are important then you might want to consider Cortex-M3 instead, for example the LM3S628 (8x 1MHz adc, 50MHz, 32KB flash,

Wilco

NXP have Cortex cores at 1MHz / 12 bits, and Atmel AT91SAM3 seems to have slipped - I think that was 12 bits/ 1MSPS too . Documents suggesting Q3/Q4 08 SAM3 samples, have not been correct, and their newest ARM family guide, skips the SAM3 entirely

XMega is a little short on ADC speed ?.

If you already have an ADC chip, why not morph slightly, and make that a TI Picolo : $3 for 12 bit ADC 325ns conversion, high precision timers, (and a free DSP), and then any-old-arm can do the rest. ?

-jg

Actually, division is less important. I've got those operations down to a bare minimum and can tolerate some execution time. I'm still hoping for something more than 1MHz on a monolithic ADC, which will put a small kink into the idea of moving away from an outboard ADC. I'm a bit unhappy at 1Mhz. It might be livable, but the extra bit of speed would be worth going after. If you don't know of one, then I guess there may be nothing staring me in the face that I've missed on a quick search this morning. But don't get me wrong. I'm not opposed to an M3. I'm just waffling about the ADC speed.

Jon

Yes, I'm kind of thinking so, too.

Yes, I had only this morning before posting noted the ADuC7022 from Analog.

I think I saw an LPC175x series with 12-bit. But no information on when it will be sampling. Apparently, not now anyway. On the XMEGA with 2MHz 12-bit pipelined ADC, Digikey told me yesterday that it was at least sometime April before they'd see any there to ship. Maybe longer. Which just may... may... be okay.

Thanks.

Well, supposedly I saw an ATxmega16A4 (up to 128A4) variety with 2MHz and 12bit, nicely pipelined for my needs. So in one-off conversions, it is too slow. But free-running it looks good and would suit the application (well, I haven't checked through the specifications in any detail, so there might be something there that would kill the idea.)

I hadn't even thought to look at that one. It kind of defeats the idea using two big chips -- I'm looking to reduce the chip and supplier count, not increase it. But if there is, say, 12-14 I/Os there and if I can set up RS232 on it then I might not need anything else. The 64kb flash and 12kb ram seems okay. This application used to run on an ADSP21xx, so I'm perfectly comfortable with DSPs for this. I just didn't like my earlier experiences with the TI C30/C40 clan. If this is another roll of one of those cores, I'm not going to be happy unless they've learned a lot more about their own chips, enough that they can explain an observed cycle count running out of cache. They couldn't tell me why a 7 cycle count loop in cache took

Thanks for the thought. I'll take a closer look.

Jon

I'm seeing towards $4. But then I won't really know until an order is placed. Can you say anything about the tool chains you've experienced for this device? Cost, support reponsiveness, etc. Alternative development tools you looked at but didn't actually wind up trying out?

Jon

Not on this family yet, but I did like the look of the Peripheral mix, so it is on our radar for future use... . Very fast ADC, and high resolution timers.

TI are pushing some low-cost stuff Experimenter Kit w/ControlCARD I see in stock at Newark for ~$82, Piccolo controlSTICK is a USB stick, for $40.50

so that would be an easy way to quickly try the latest tools ?.

-jg

Yeah. I'm impressed.

I suppose so. I'm a little disappointed looking at Eclipse development tool costs for active development (not trial stuff.) That's kind of off my radar range, if I decide to go that way. Which means I need to dig a little deeper about tools. But yes, the device appears attractive to me and I definitely appreciate the pointer. I think I'd heard the name dropped here once or twice, but never took notice before. But my head is turned now. So I'll put a little effort into looking further.

Jon

is

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Be vary, that F28xx (including the picolo family) internal ADC does not deliver the promised 12 bits. Event the TI acknowledge this and state thet the ENOB is around 10 bits (that was for the first members of the family the F2812). For more info on this take a look at comp.dsp and comp.arch.embedded archives and TI forum

The TI improves the ADC module each generation, but I can not tell you how the picolo series ADC behaves

Regards, Mitja

This doesn't surprise me that much. It's hard for me to imagine getting 12 bits on something monolithic with a micro. I mentioned in my original post (perhaps you didn't see it) that 10.5 bits would be enough. I use integration, so if the noise is essentially gaussian I may be able to deal with this, satisfactorily. If not, could be an issue. I'll read up and thanks for the pointers!

Jon

Gaussian noise is the least likely issue they have. Most if not all of the 12 bit ADCs I have seen on MCUs are in reality more like 10 bits, INL is just that bad (DNL is 12-bittish, they have no missing codes after all). Please keep us posted if you find a true 12bit/1MSPS ADC on MCU, this would be something worth seeing.

Dimiter

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I took a quick look. The gain error is +- 10 bits. But in this application, the algorithms are intentionally designed to perform compuations that remove gain as a factor. So long as the signal is in the conversion window, the gain is pretty much irrelevant (cancels out as a factor in the equations); so long as it doesn't vary over time during the snapshot, I'm fine. And I'm not looking at sine waves.

I don't find a specification of internal noise -- magnitude, shape, etc. Nothing. There is some talk in the manual about SINAD and ENOB, but no data on input referred noise at various source voltages or S-N or distortion (the SINAD figure.) I've been using converters with about 11.3 ENOB in the past (about 70dB SINAD), but could live with

Do you know of any discussions that attempt to bound this figure for the Piccolo 2802x?

Jon

You can also take a look at ST's STM32 family. It it CM3 with very interesting mix of peripherals. It also has multichannel 12-bit ADC @ 1MHz. (No 1.5MHz or more sampling rate tough, for what you are looking for.)

~ Ale?

I see a specification on the data sheet (one of the very few things they actually talk about regarding the ADC) of DNL +- 1 bit, INL +- 2 bits. Did you look at the datasheet? (Not that it should be believed, but I'm just wondering where you came up with the "12-bittish" for this device.)

If I'm lucky enough to find something interesting, I will. The XMEGA specification is entirely TBD. So there is absolutely no information on it, btw.

Jon

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There are actually few ADC that give you the same number of effective bits as resolution. Any noise at all causes a loss of effective bits and every part has noise, even separate ADC chips. It is just a question of how many bit survive the journey through the chip. 10 ENoB is not at all bad for a low cost 12 bit ADC, especially in an MCU. If you need much better than that, you are unlikely to find it without using a higher bit resolution device. But as others have said, uncorrelated noise can be averaged out... *if* it is uncorrelated. It is common for the noise to be related to the clock. After all, the same master clock is driving the MCU and the ADC.

Rick

The ADUC7k family has a 12 bit, 1MHz ADC (as you probably know). It seems pretty good for an "embedded" ADC. As one might expect from an ADC manufacturer. It does in fact work at 2MHz if you set the clock divider bits appropriately, but to what extent that violates the spec I don't know. (I tried it just for fun once, and seemed to work fine!).

No, this is just my general experience with ADCs speaking. I have looked through a fair number of MCU ADCs, and I do not remember having seen one like the one you describe, that's all.

If they specify INL as +/- 2 *bits*, not LSBs, this might be reason to raise some suspicion. It may mean the 2 lowest bits are meaningless, which will match my observation on MCU ADCs lately. IIRC I saw one - I think on some Microchip part I was reviewing for someone - which was true 12 bit or sort of, but was much much slower (double integrating IIRC).

I have been spoilt by ADI when it comes to ADCs, I guess, but I know only their standalone ones (their specs are really trustworthy).

Dimiter

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I never imagined differently. Resolution is almost a waste to care about. The only thing it does is provide a __suggestion__ about the care they took in designing it.

I know.

I know that isn't bad. In fact, as I mentioned earlier, my expectations are only for about 10.5 bits ENOB, 65dB SINAD. I'm not expecting the impossible here. Just something that isn't garbage.

Which, obviously, would mean "slower" when talking about monolithic designs with the microcontroller. It's the combination of speed and ENOB that I'm looking for in a monolithic design and frankly I think it isn't entirely out of the ballpark. It's a doable, not unreasoned goal I'm looking for.

Obviously. Gaussian distribution (integral of Poisson) is the assumption that goes into the very idea.

Of course. Correlated noise violates the assumption.

Indeed.

I know.

I might expect this kind of lecture had I asked for something crazy. I didn't. Perhaps someone else learned something, though.

Jon

Sorry, I screwed up. They specified it in LSBs. Any fault there is mine.

Yes, me too. It's what I've been using in the past, btw.

Jon

Now there is an interesting suggestion!! (Yes, I knew about it.) I may even have one or two of their devices sitting in a nicely packaged (sealed) box to try out. In any case, I didn't know that was possible so I'll go take a look at the datasheet to see for myself. It might be worth some playing.

These are some of the kinds of detailed suggestions to examine that I was hoping for to help me expand the possibilities -- difficult to find in a google survey and yet worth thinking about as a shot in the dark.

Thanks, Jon