Patent ID: 7388446

Claim:
A directly modulated voltage controlled oscillator including a tank circuit comprising: a carrier frequency varactor circuit for generating a carrier frequency determined by a control voltage applied from a control voltage source, said carrier frequency varactor circuit comprising first and second pairs of varactors in a differential arrangement, wherein said first and second pairs of varactors are arranged in parallel between a first pair of nodes connected directly across the tank circuit without coupling capacitors, and wherein a second pair of nodes at respective common connection points of each of said varactors of said first and second pairs of varactors is connected across said control voltage source; a separate modulation varactor circuit for modulating the carrier frequency generated by the carrier frequency varactor circuit in response to a modulation voltage applied from a modulation voltage source, said modulation varactor circuit comprising third and fourth pairs of varactors in a differential arrangement, wherein said third and fourth pairs of varactors are arranged in parallel between a third pair of nodes, and wherein a fourth pair of nodes at respective common connection points of each of said varactors of said third and fourth pairs of varactors is connected across said modulation voltage source; coupling capacitors for connecting respective nodes of said third pair of nodes across said tank circuit and to said respective first pair of nodes; and groups of parallel-connected switched trim capacitors connecting the respective nodes of said third pair of nodes to ground to trim the gain of said modulation varactor circuit.