Phase noise reduction in voltage controlled oscillators

A method of operating a voltage controlled oscillator (VCO) comprising an LC tank circuit and an oscillator core, the method comprising:

• using the LC tank circuit for generating an oscillator output signal at an oscillator frequency (fo);
• operating the oscillator core to provide regenerative feedback to the tank circuit to help maintain the oscillator output stable;
• connecting the VCO to a voltage source;
• connecting the VCO to a current source;
• operating a low-impedance, noise by-pass circuit in parallel with the LC tank circuit and the oscillator core, at a frequency approximately twice the oscillator frequency to at least partially immunize the oscillator core from external noise and to reduce noise contribution from the oscillator core, the low-impedance, noise by-pass circuit including a variable capacitor and a variable inductance transmission line;
• and
• applying a voltage control to the variable capacitor and a digital control to the variable inductance transmission line, and using the voltage control and the digital control in tandem to adjust the frequency at which the noise by-pass circuit resonates to adjust a performance of the VCO.

A design structure comprising machine readable instructions tangibly embodied in a machine readable hardware medium for design, manufacturing, or testing a semiconductor device, the design structure, when executed in the machine, generating a representation of a semiconductor substrate including a voltage controlled oscillator (VCO) comprising:

• an LC tank circuit for generating an oscillator output signal at an oscillator frequency (fo);
• an oscillator core including first and second cross-coupled semiconductor devices connected to the tank circuit to provide regenerative feedback to the tank circuit to help maintain the oscillator output stable;
• a supply node connected to the tank circuit for connecting the VCO to a voltage source;
• a tail node connected to the oscillator core for connecting the VCO to a current source;
• a noise by-pass circuit having a first end connected to the supply node and a second end connected to the tail node and forming a low-impedance by-pass circuit connecting the supply node and the tail node, in parallel with the LC tank circuit and the oscillator core, at a frequency approximately twice the oscillator frequency to at least partially immunize the oscillator core from external noise and to reduce noise contribution from the cross-coupled semiconductor devices, and including a variable capacitor and a variable inductance transmission line;
• and
• a frequency control including a voltage control applied to the variable capacitor and a digital control applied to the variable inductance transmission line, the voltage control and the digital control being used in tandem to adjust the frequency at which the noise by-pass circuit resonates to adjust a performance of the VCO.