POD capacitors vs. Poly-Poly capacitors

Discussion in 'Cadence' started by frank, Nov 20, 2003.

  1. frank

    frank Guest

    Hello,

    What are the drawbacks to using poly-on-diffusion capacitors instead
    of poly-poly capacitors ? If pod capacitors are more capacitive than
    pp capacitors, why are pp caps used ? Are pp caps better ? Is their
    lineraity coefficients significantly better than the pod's ? Obviously
    the pod cap diffusion node's voltage cannot drop below VSS (or rise
    above VDD, if the substrate is N-type), but assuming this node's
    voltage stays within the [VSS,VDD] range would there be a significant
    difference if pp caps were used? Are the pod caps more resistive than
    pp caps? less reliable maybe?

    -Frank
     
    frank, Nov 20, 2003
    #1
  2. frank

    Hristo Brachkov Guest

    First of all, MOS cap is voltage dependent and the Q-factor would be
    probably lower compared to poly-poly capacitor. The other thing is that the
    parasitic capacitance WELL-SUBSTRATE is significant for the MOS capacitor.
    So in case the second node of the capacitor is not connected to VSS it is
    not good idea to use MOS capacitor.

    BR,
    Hristo
     
    Hristo Brachkov, Nov 20, 2003
    #2
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