I can now digitize one signal at 100MHz using my A/D card, capture in the Digilent Xilinx FPGA board, and upload to a PC via the USB port. I'm using Octave to upload and display the data, making a sort of oscilloscope. So I decided it's time to create a sourceforge open-source project.
It's http://mhz100q.sourceforge.net . Code is all in Subversion. It's all there, but I still need to create some build instructions and other documentation.
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10 comments:
Hi Joe,
What is the input range on your A/D frontend? I see you have a 2x gain in your single ended to double buffer, but I'm not sure how your Vcc=Vcm+0.3 limits or improves the range. ?
Hi zbaker,
Yes, the single-ended to differential amplifier has a gain of 2, and the A/D has a range from -0.512 to +0.512 volts, so the input signal has a range of about 0.5 volts: -0.23 is a 0x00 output and 0.33 is 0xff. It's not quite centered on zero due to the feedback circuit.
The equation should be Vcm=Vcc*0.3. The 0.3 factor comes from the A/D converter spec sheet: its input signals are supposed to be biased around 0.3*Vcc, or about 0.9 volts with a 3 volt supply. Vcm is the voltage on the common mode input pin of the amplifier; it's used to bias the amplifier outputs so they are centered on 0.9 volts and keep the A/D happy.
Hope that helps.
Joe
Hi Joe, thanks for the response.
I downloaded your MHz100Q A/D board (w/4 channels)from the SVN. I see lots of question marks and unconnected signals in kicad 2012-01-19 BZR 3256. Not sure why? I wanted to convert it manually to Eagle 6.4 which I am better acquainted with. I could send you a screenshot of what I see that makes it hard to decipher theconnection.s
Abu,
I need to verify those files; I was still learning about kicad when I posted them. Not sure if all the essential parts are online. Check back in a day or so.
Joe
Okay thanks...Abu Saliha means Father of Saliha, my real name is Salman Sheikh. I am an EE at NASA but only in the digital domain (fpgas). I might try to learn kicad...I thought it was the syms library file. I included it in a directory with .net file but still get ? marks..
Salman,
I think you're right; custom symbols that I created aren't saved in the *.sch file.
I just uploaded mhz100q_syms.lib. which should have them. If you add that to your library list (Preferences->Library in the schematic editor) things should look ok.
Also, I uploaded an updated version of the design to a new directory (pcb/mhz100q_b) Same basic 4-channel design, but cleaned up the layout.
Sourceforge is doing a major update; I'm going to update the project page info after that is over.
Let me know how it works out.
Joe
Is it possible to send me a pdf screenshot of your ADC 4-channel board?
what coilcraft part are you using?
It's a coilcraft P7LP-306L . That's the 30MHz 7-pole lowpass, with a stopband somewhere around 50MHz.
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