Patent ID: 7777581

Claim:
A voltage controlled oscillator (VCO) including: a plurality N of amplifier stages, each amplifier stage comprising a differential output, a differential primary input, and a differential feedback input, and at least one of the amplifier stages including a differential tuning input, wherein: (a) each differential output is connected to the differential primary input of a different stage so as to form a ring of stages; (b) the differential feedback input of each stage is connected to the differential output of an immediately following stage in the ring; and (c) said at least one of the amplifier stages comprises: (i) a primary amplifier terminating the differential primary input and including a primary controllable gain function block and a first current source; (ii) a secondary amplifier terminating the differential feedback input and including a secondary controllable gain function block and a second current source; (iii) a common amplifier load section for combining the outputs of the primary amplifier and the secondary amplifier; and (iv) a tuning circuit terminating the differential tuning input and connected to the first and second current sources for adjusting gains of the primary and secondary amplifiers respectively; (v) the tuning circuit comprising a third current source and means for directing a fraction of the current from the third current source to one of the first and second current sources, and directing the remaining fraction of the current from the third current source to the other one of the first and second current sources, to control relative gains of the primary and secondary amplifiers, thereby controlling an oscillating frequency of the ring.