Patent ID: 6359511
Filing Date: 2002-03-19
Classification: H03F,H03G

Abstract:
A variable gain control circuit comprising:a pair of diode connected transistors comprising a first transistor and a second transistor coupled together in a common mode rejection configuration, wherein said first transistor is capable of receiving an input current signal that is proportional to a first scale factor that has a value between zero and one, and wherein said second transistor is capable of receiving an input current signal that is proportional to a second scale factor that has a value that is equal to one minus said first scale factor; a first differential amplifier comprising a third transistor and a fourth transistor, said first differential amplifier coupled to said pair of diode connected transistors and capable of receiving a first control voltage from said first transistor and capable of receiving a second control voltage from said second transistor; a second differential amplifier coupled in parallel to said first differential amplifier, said second differential amplifier comprising a fifth transistor and a sixth transistor, said second differential amplifier coupled to said pair of diode connected transistors and capable of receiving said first control voltage from said first transistor and capable of receiving said second control voltage from said second transistor; wherein said first differential amplifier is capable of rejecting common mode signals in an input current and providing an output current that is proportional to said first scale factor; and wherein said second differential amplifier is capable of rejecting common mode signals in an input current and providing an output current that is proportional to said second scale factor.