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Fast modulation based on analog signal: FPGA worth it?

palle93

Hello everyone,

 

I'm currently planning a setup where (among other things) a galvanometer mirror helps a laser scan a certain area. For different mirror positions the laser should be on and for others off. You could imagine a shutter controlling the beam here.

 

I would like to open and close this shutter (acousto-optic modulator) really fast. Really fast in this case means 2 MHz. However, the shutter should not be modulated periodically, e.g. with constant frequency. The shutter shall open, when an analog input signal Uin is above a certain threshold U1 and close again above another threshold U2.

Furthermore, the voltages U1 and U2 are provided digitally as 16 bit numbers. Both are not static, however. They will change in the worst case with a frequency of 1 MHz.

An added bonus would be, if the actual level of Uout does not have to be binary but could also be modulated with 1 MHz.

 

I tried to sketch a schematic for this and attached it to this posting.

 

I thought about solving this problem using an FPGA with really fast ADCs and DACs on a Mezzanine Card, which is connected via FMC to the FPGA board. This would fulfill my specifications, however I get the constant feeling that I'm overshooting my specifications here. Is a FPGA really suited for this application or am I overlooking an obvious implementation with a cheaper system?

 

Thank you!

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  • Pascal,

     

    Where I think that Michael's approach makes sense, I think I would turn the problem around and do it more in the analog domain.  I would use a pair of voltage comparitors to generate the shutter signals.  You could use a pair of DACs to set the thresholds for the high and low values of the window.  Computationally, this would greatly reduce the complexity of your design.

     

    Good luck!

    Gene

  • in reply to genebren

    Hey Gene,

     

    we also thought about working more in the analog domain. The problem I saw with that solution was the sheer amount of data, which the voltage comparator has to process. In extreme cases only the U1 and U2 data from the computer can be up to 1 TB.

     

    For the setup 2 galvanometer mirrors will be used. So the shutter signal should only be open if both mirrors are in the given range. Wouldn't the design of such an analogue processing unit be pretty complex?

     

    However, I understand your argument regarding the computationally complexity. I will once again think about the analog solution.

     

    Thank you very much for your help!

     

    Pascal

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  • in reply to genebren

    Hey Gene,

     

    we also thought about working more in the analog domain. The problem I saw with that solution was the sheer amount of data, which the voltage comparator has to process. In extreme cases only the U1 and U2 data from the computer can be up to 1 TB.

     

    For the setup 2 galvanometer mirrors will be used. So the shutter signal should only be open if both mirrors are in the given range. Wouldn't the design of such an analogue processing unit be pretty complex?

     

    However, I understand your argument regarding the computationally complexity. I will once again think about the analog solution.

     

    Thank you very much for your help!

     

    Pascal

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