Method and circuit for compensating MOSFET capacitance variations in integrated circuits
First Claim
1. A method for tracking the MOS oxide thickness by the native threshold voltage Vth of a “
- native”
MOS transistor for the purpose of compensating MOS capacitance variations comprising;
provide a MOS transistor having a native threshold voltage Vth;
sense the native threshold voltage Vth of a native MOS transistor;
build a suitable reference voltage level by adding by a circuit means another constant voltage Vx;
charge a MOS capacitor built out of a native MOS transistor up to the reference level Vref=Vx+Vth; and
measure a capacitance related value in a suitable configuration for oscillators which depends now no more on the oxide thickness.
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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.
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Citations
25 Claims
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1. A method for tracking the MOS oxide thickness by the native threshold voltage Vth of a “
- native”
MOS transistor for the purpose of compensating MOS capacitance variations comprising;
provide a MOS transistor having a native threshold voltage Vth;
sense the native threshold voltage Vth of a native MOS transistor;
build a suitable reference voltage level by adding by a circuit means another constant voltage Vx;
charge a MOS capacitor built out of a native MOS transistor up to the reference level Vref=Vx+Vth; and
measure a capacitance related value in a suitable configuration for oscillators which depends now no more on the oxide thickness. - View Dependent Claims (2, 3, 4, 5, 6, 7)
- native”
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8. A circuit for a frequency reference in an integrated circuit using a MOSFET as a stable capacitor, comprising
a constant current source; -
switching means charging and discharging said MOSFET capacitor being activated periodically by the output of comparing means and charging and discharging said MOSFET capacitance;
comparing means having an input and an output wherein the input is the voltage of said capacitor and a voltage exceeding the threshold voltage of said MOSFET capacitor to influence the frequency and the amplitude of the output of said comparing means and the output is a periodical pulse;
a MOSFET capacitor being charged/discharged periodically by said constant current source and its voltage level being the input to said comparing means and its threshold voltage is used to compensate the variations of its capacitance;
means to provide a voltage exceeding the threshold voltage of said MOSFET to influence the frequency and the amplitude of the output of said comparing means; and
means to transform the periodical pulse into an alternating clock signal to drive said switching means and being the output of said frequency reference circuit. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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15. A circuit to use a MOSFET capacitor as a reference capacitor in an integrated circuit comprising:
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an RC-oscillator circuit having an input and an output wherein the input is a current source and a signal from a phase detector regulating the capacitance of said RC oscillator and the output is a periodical signal;
a frequency reference circuit having an input and an output wherein the input is a current source and the output is a periodical signal;
a phase detector circuit having an input and an output wherein the input are the periodical output signals from said RC oscillator and from said frequency reference and the output is a signal to regulate the capacitance of the RC oscillator and the capacitance of the capacitor to become a reference capacitor; and
said capacitor to become a reference capacitor. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23)
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24. A method for creating a capacitor reference in integrated circuits comprising:
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providing an RC oscillator circuit, a constant current source, a frequency reference, a phase detector and a capacitor 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 until f1 equals f2;
calculate the capacitance of the reference capacitor using an equation; and
use the calculated capacitance as reference capacitance. - View Dependent Claims (25)
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Specification