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Maybe Trivial question?

MihaKorošec
Intellectual 570 points

Hello!

I've testing TINA and I have maybe trivial question about some signal modification?

 My goal is to cutt-off and ac-couple square signal from function generator with 1hz-1Mhz, 3Vpp, 1,5V offset.

I made simulation:

a)  First AC couple, than cutt-off  with two diodes. Everything works ok.

b)  First cutt-off with two diodes, than AC couple. There is a offset (~-1V) and I don't know why?

Can somebody explain me why insted AC coupled signal in case "b)" , I got ~-1V offset?

  • 0
    TI__Mastermind 26471 points

    Hi,

    You have a signal from 0 to VA ( you are embeding a DC level in it),  InIn second  case  you clamp  the signal to VD first  (only  one diode is working anyways) and then AC couple it later on and in the other case  you AC couple it first ( removing your  DC level) and then clamping the result  to +/-VD.  Deponding on your VD value (and R connected to your source) , you should see what you are calling it "offset" voltage.

    Regards,

     

    Arash

  • 0 in reply to Arash Loloee
    TI__Genius 14455 points

    Hi,

       One possible solution it to try running it for a longer time (probably 2 to 3ms).  The other solution could be to make the initial voltage across the capacitor to be 0V. The problem is VF4 node is at 200mV at t=0. It should be at 800mV at t=0 (the same on VF3). Then you would not see this.

    Regards

    Gerold

  • 0 in reply to Gerold Dhanabalan - Online Design Tools
    Intellectual 570 points

    The right answer is that the Vvf4 get in to the right position after 1 second. So I run simulation for 5seconds and my theory about AC couple and diode clamper works fine.

      Thanks Gerold Dhanabalan!