ADC-Will this setup work ?

I have been building a data acquisition system to be connected to a pentium 4 system. But the problem is scanning rate of ADC (Analog to Digital) is about 3MHz. But I need a higher rate. Will connecting 2 such ADCs in parallel and scanning them alternatively using my pc give me a better rate like 6MHz (3+3). Also can this be extended ? All opinions are welcome. And, thanks in advance. BZ

Reply to
brazingo
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Hi Bob, I was going to use a USB 2.0 interface to connect this ADC system to my computer - P4 2Ghz. I thought this should work fine given that

6MHz is just a fraction of 2000MHz. I even planned to use assembly programing to get the clock cycles right with an optimum code. I'm not too intent on 6GHz though. Anything around 600Khz to 1MHz scan rate would do fine for me so that I can capture a sine wave of atleast 100Khz with 6 to 10 samples per cycle respectively. I just wanted to push this system to the limit and get 6GHz. I was really surprised by your question. Am I missing something here ?

-BZ

Reply to
brazingo

Ihave heard of this trick being used on high-speed digital scopes. Note that each ADC needs a sample/hold that is at least as fast as the overall desired sample rate would require. I don't think you should try using the PC to provide the interleaved scans at these rates; you'll need a dedicated clock with accurate phases.

Just out of curiosity, how are you going to move the data to the PC at these rates? Or is this for some intermittent application like a scope that can ignore data between trace updates?

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

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Home of DaqGen, the FREEWARE signal generator

Reply to
Bob Masta

I am not sure about your expertise in programming, so please forgive me if this seems condescending. However, in a modern protected mode OS (Windows XP, for example) you have essentially no control over timing issues. The OS can jump in at any time and run some other thread. When you start some operation, Windows may wait several msecs before actually doing anything about it. Some of these issues can be dealt with by Ring 0 drivers, but it would be a big can of worms unless you are already a pro at it.

The normal way A/D systems work under protected mode is to buffer everything. You would collect a block of data to your own memory buffer, then signal Windows that it is full (while you switch to filling another buffer), and Windows will transfer the data whenever it feels like it. You have to insure that the rate of buffer filling doesn't exceed the average transfer rate.

But it sounds like in your case you are making a scope, so you could get by with a single buffer. When the buffer is full (one scope-face sweep), you let Windows have it. The few msec of lag would be no problem, since your eyes don't need display updates all that fast anyway. Note, however, that this supposes you do all the triggering in hardware. If you want to do it in software, you have to pass Windows the entire data stream, which means you need to support sustained throughput. Or at least a big enough block of data that you can be sure it included at least one trigger event plus enough data for display.

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

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Home of DaqGen, the FREEWARE signal generator

Reply to
Bob Masta

it'll give a higher rate (there shouldn't be bus speed problems at that rate), but not neccessarily higher resolution.

maybe have a look into ADCs designed for video capture

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Bye.
   Jasen
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Reply to
Jasen Betts

usb 2.0 is 480M bits per second, so it should work.

Bye. Jasen

Reply to
Jasen Betts

Hi Bob, I confess I'm not a pro at system programming. Just been learning pentium programming limited to only real mode and also restricted to DOS. I thought I could make myself a nice little scope. Guess I overestimated certain things. Thanks for the inputs though. I'll try working with the buffering concept.

Reply to
brazingo

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