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Sallen key

Discussion in 'General Electronics Discussion' started by luke67, Jul 26, 2012.

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  1. luke67

    luke67

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    Mar 18, 2012
    Hi people ! I am projecting a PCB for analog signals ; they have to be filtered by a sallen key. I used a quadopamp. What do you think about the positiion of R,C and distance between wires ?? Wire size is ok ? (0.8 for supply and 0.25 for signals ) Have you any idea to reduce noise or this disposition is ok ? THank you !
     

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    Last edited: Jul 26, 2012
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    11,013
    2,506
    Nov 17, 2011
    The placement looks o.k. at first sight. All components near the OpAmps.
    Since your PCB is double-sided anyway, you may want to consider flooding the bottom plane (blue) with copper and connect this plane to GND. This will minimize the impedance of GND and thus help to avoid crosstalk.

    Harald
     
  3. luke67

    luke67

    46
    0
    Mar 18, 2012
    what do you think about decoupling capacitors ? Should they be located nearer to the op-amp pin or are they ok ? Many thanks !
     
  4. luke67

    luke67

    46
    0
    Mar 18, 2012
    the supply of the second and third row will pass on the bottom side in order to not cross top-signal wires. Is this a problem considering that the ground plane is at the bottom side of the PCB?
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    11,013
    2,506
    Nov 17, 2011
    If the caps like C30, C39 etc are the decoupling caps, then the placement is already near the OpAmp pins. If you find a wy to move them nearer (possibly mounted on the bottom) you could improve a bit.
    As to the power supply: If you put the Vcc traces on bottom you will open a gap in the GND plane thus reducing its effectivity. It would be better to keep the GND plane as closed as possible and use wire jumpers on top instead.

    Harald
     
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