Method and circuit for compensating MOSFET capacitance variations in integrated circuits
AssigneeDialog Semiconductor GmbH
InventorMatthias Eberlein
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Abstract
A method for tracking the MOS oxide thickness by the native threshold voltage of a “native” MOS transistor without channel implantation for the purpose of compensating MOS capacitance variations is achieved. The invention makes use of the fact that in MOS devices the threshold voltage is proportionally correlated to the oxide thickness of said MOS device. Said threshold voltage can therefore be used to build a reference voltage Vx+Vth which accurately tracks the MOS capacitance variations in integrated circuits. Circuits are achieved to create a frequency reference and a capacitance reference using said method Additionally a method is introduced to create a capacitance reference in integrated circuits using said MOSFET capacitors.
Claims4
A method for creating a capacitor reference in integrated circuits comprising:
- providing an RC oscillator circuit, a constant current source, a frequency reference, circuit a phase detector and a capacitor, having switching parts for regulation, to become a reference capacitor;
- generate with said RC oscillator circuit a periodic signal with frequency f1;
- generate with said frequency reference circuit a signal with frequency f2;
- compare said frequency f1 and frequency f2 and regulate the capacitance of the capacitor of said RC oscillator using a closed feedback loop until f1 equals f2;
- calculate the capacitance of the reference capacitor using the equation
- C
- =
- a
- ×
- c
- U
-
-
- r
- ×
- k
- .
- wherein the parameters a, c and k are physical constants or integer numbers and Ur occurs from defining the reference level of the RC oscillator;
- and
- use the calculated capacitance as reference capacitance.
Dependencies are inferred from the claim text.