Patent ID: 6940294

Claim:
A circuit to use a MOSFET capacitor as a reference capacitor in an integrated circuit comprising: 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 and wherein said frequency reference circuit is comprising: a constant current source; switching means charging and discharging said MOSFET capacitors being activated periodically by the output of comparing means and charging and discharging said MOSFET capacitor; comparing means having an input and an output wherein the input is the voltage of said MOSFET capacitor and a voltage exceeding the threshold voltage of said MOSFET 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 and 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; 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 a capacitor to become a reference capacitor; and said capacitor to become a reference capacitor.