Switched Capacitor

Discussion in 'General Electronics Chat' started by legolas11, Apr 25, 2013.

  1. legolas11

    Thread Starter Member

    Feb 26, 2013
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    In the picture attached (Analog Elec. by Razavi) upto time t0 the output voltage should be zero. I am trying to simulate only part a using unity gain Opamp but it gives an high output. Can anyone tell me what am i missing here.

    Thanks in advance
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Show us your simulation circuit and simulation results.
     
  3. legolas11

    Thread Starter Member

    Feb 26, 2013
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    thanks and i have attached
     
  4. crutschow

    Expert

    Mar 14, 2008
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    Your are missing two things in your simulation:

    1. You don't have the power supply grounded. The op amp won't work with a floating supply.

    2. An inverting op amp configuration needs a plus and minus supply (both grounded).

    Note: C1 is redundant in the simulation since the voltage source is ideal with zero ohms AC impedance.
     
  5. WBahn

    Moderator

    Mar 31, 2012
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    Try using your original circuit and increase the amplitude of the signal source from 1mV to 10mV and re-run your simulation. Then interpret the results in light of what crutschow has pointed out.
     
  6. legolas11

    Thread Starter Member

    Feb 26, 2013
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    Hi,
    thanks a lot to both of you,.........
    @crutschow,i have reconnected the supply as explained and it works. But because the output level is in uV range, so as @WBahn suggested, i have increased the vin to 10mv,so with respect to that the output voltage now can be considered ~0.

    Now i have another question, is it possible to make a switched capacitor opamp circuit in discrete format. I understand the switches has to be nmos/pmos. but considering the clocking and synchornization, is not that too complicated for a discrete circuit??
     
  7. #12

    Expert

    Nov 30, 2010
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    Maybe this?
     
  8. WBahn

    Moderator

    Mar 31, 2012
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    I don't follow your schematic. You've got two floating source connections on the right side. Is this is supposed to be an opamp, where are the inputs and where are the outputs?

    Aren't you going to have a problem with both the charge and discharge transistors being turned on at the same time due to the propagation delay through the inverters?
     
  9. #12

    Expert

    Nov 30, 2010
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    Who? Me? I just posted something somebody else posted here. Perhaps it is not a schematic, but a concept drawing, as noted by the complete absence of component values and part numbers.
     
  10. legolas11

    Thread Starter Member

    Feb 26, 2013
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    I was trying to figure out how this makes sense and blaming me for even not understanding a circuit.......
    I think those are inverters and even if its a concept drawing it is very confusing, anyway.
    I think its not possible/ too complicated(to get good result) to make switched cap based circuit in discrete format. I have found an IC from Linear Technology LTC1043 which has kind of building block for switched capacitor support and have internal clock. I will try with that and see how it turns out.

    Thanks
     
  11. #12

    Expert

    Nov 30, 2010
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    In post #6, legolas changed to a different question. I do not understand what he/she is trying to accomplish with a switched capacitor op-amp circuit. The circuit I posted receives power from the left side, charges the capacitors, and then disconnects the power and allows the charge in the capacitors to exit to the right. It demonstrates a method to connect, then disconnect capacitors, with several obvious defects, like the need for a "dead" time zone.

    If the drawing shows you a method you can use, good. If it doesn't, ignore it.
     
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