Vco with local feedback for low power supply noise sensitivity

Abstract

The present invention comprises a voltage controlled oscillator (VCO) circuit having high power supply noise rejection. The circuit of the present invention includes an amplifier having positive, negative, and output terminals. A VCO input is coupled to the positive terminal for receiving a control voltage. A replica circuit is coupled to the negative terminal. A replica source follower transistor is coupled to the output terminal and is also coupled to the replica circuit. The replica source follower transistor transmits a replica current from a power supply to the replica circuit and is controlled by the amplifier. The present invention also includes a first and second VCO cell. The first VCO cell and the second VCO cell are both coupled to the replica circuit and to each other and the second VCO cell includes a VCO output for transmitting a VCO output signal. The first and second source follower transistors are respectively coupled to the first and second VCO cells to provide a respective first and second current from the power supply. The output terminal from the amplifier is coupled to control the replica source follower transistor, the first source follower transistor, and the second source follower transistor. The negative terminal of the amplifier receives feedback from the replica circuit such that the replica current, the first current, and the second current are insensitive to noise on the power supply, and such that the output signal is stable regardless of the noise on the power supply.