On-chip inductor using active magnetic energy recovery

A monolithic active inductor circuit, comprising:

• an input terminal which receives an RF input signal,
• a primary coil which carries a first current, said first current having an AC component which varies with said input signal,
• a capacitor connected between said input terminal and said primary coil which phase shifts said input signal by approximately 90° prior to its being applied to said primary coil,
• a secondary coil which carries a second current and is located in close proximity to said primary coil such that a magnetic field induced by a current in said secondary coil is coupled to said primary coil, and
• an on-chip current source comprising a transistor which conducts said second current in response to a drive signal comprising said RF input signal and a DC tuning voltage, said second current having an AC component which varies with and is 180° out-of-phase with said input signal,
• a DC voltage source which provides said DC tuning voltage, and
• a choke connected between said DC voltage source and said RF input signal to isolate said input signal from said DC tuning voltage,
• said active inductor circuit arranged such that the magnetic field induced by said second current compensates for energy that would otherwise be dissipated by said primary coil,
• said primary coil, said secondary coil, and said current source integrated together on a common substrate.

A bandpass filter, comprising:

• a plurality of capacitors, and
• a plurality of inductors, said capacitors and inductors interconnected to form a bandpass filter, each of said inductors comprising a monolithic active inductor circuit which comprises:
• an input terminal which receives an RF input signal,
• a primary coil which carries a first current, said first current having an AC component which varies with said input signal,
• a secondary coil located in close proximity to said primary coil such that a magnetic field induced by a current in said secondary coil is coupled to said primary coil, and
• a current source which provides a second current in said secondary coil, said second current having an AC component which varies with said input signal, said active inductor circuit arranged such that there is a phase difference of approximately 90° between the AC components of said first and second currents and such that the magnetic field induced by said second current compensates for energy that would otherwise be dissipated by said primary coil,
• said primary coil, said secondary coil, and said current source integrated together on a common substrate.