Patent ID: 7800446

Claim:
A gain control circuit, comprising: a first transistor having a collector, a base and an emitter, the collector of the first transistor operable to generate an output current; a second transistor having a collector, a base and an emitter, the second transistor forming a differential pair with the first transistor, the emitter of the first transistor coupled to the emitter of the second transistor; a current-controlled voltage source coupled to the base of the first transistor; a third transistor having a collector, a base and an emitter, the third transistor matched to the second transistor, the emitter of the third transistor coupled to the current-controlled voltage source; a current mirror coupled to the collector of the second transistor and to the collector of the third transistor; an input current source coupled to the emitter of the first transistor; and the gain control circuit operable to receive a primary control signal at the base of the second transistor and the base of the third transistor and to generate a secondary control signal at the base of the first transistor and the base of the second transistor.