Patent ID: 8531248

Claim:
An oscillator comprising: a positive power supply node for providing a positive power supply voltage; a constant current source providing a first constant current and coupled to the positive power supply node, wherein the first constant current is independent from a variation in the positive power supply voltage; a capacitor; a charging current source configured to provide a second constant current to charge the capacitor by reducing the voltage across the capacitor independent of variations in the positive power supply node voltage, wherein the second constant current mirrors the first constant current; a constant current source inverter having a third constant current mirroring the first constant current, wherein the constant current source inverter is configured to control the oscillator to a transition state at a constant state transition voltage, and wherein the constant current source inverter comprises a first NMOS transistor, with the third constant current flowing through a source-drain path of the first NMOS transistor; wherein the capacitor is coupled directly between the positive power supply node and a gate of the first NMOS transistor and is configured to, at a predetermined voltage level, turn on the first NMOS transistor and set the constant current source inverter to an on state and generate an oscillating signal with a period independent of variations in the positive power supply node voltage.