Patent ID: 8519799

Claim:
A voltage controlled oscillator generating an oscillation signal according to a first control signal, comprising: a control signal adjuster, receiving the first control signal and generating a second control signal according to the first control signal, wherein the second control signal generated to be higher than a voltage level of the first control signal when the voltage level of the first control signal is lower than a transistor threshold voltage; and a plurality of delay cells, ring-connected and controlled by the first and the second control signals to generate the oscillation signal, wherein each delay cell comprises: a first set of current generation transistors, wherein each transistor provides a control terminal to receive the first control signal; and a second set of current generation transistors, wherein each transistor provides a control terminal to receive the second control signal, wherein when the voltage level of the first control signal is too low to turn on the first set of current generation transistors, the second control signal turns on the second set of current generation transistors.