POD capacitors vs. Poly-Poly capacitors

F

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
 
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

"frank" <frank8017@excite.com> wrote in message
news:60bf6cad.0311192012.2bfd9f56@posting.google.com...
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
Click to expand...
 
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