Transconductance reduction using multiple collector pnp transistors in an operational amplifier

Claim 2

An integrated circuit operational amplifier comprising: a transconductance stage including a differential input stage and a differential to single-ended converter stage, said differential input stage including a first constant current source and also including first, second, third and fourth transistors, said first and second transistors having, respectively, an emitter electrode, a base electrode, and first and second collector electrodes, said third and fourth transistors having, respectively, an emitter electrode, a base electrode, and collector electrode, said first and second transistors being split collector lateral PNP transistors, said third and fourth transistors being substrate PNP transistors, said constant current source being coupled to a first power supply conductor, and also being connected to both of said emitters of said first and second transistors, said third transistor having its base electrode coupled to a first input terminal its collector electrode coupled to a second power supply conductor, and its emitter electrode coupled to said first collector electrode and said first base electrode of said first transistor, said fourth transistor having its base electrode coupled to a second input terminal, its collector electrode coupled to said second power supply conductor, and its emitter electrode coupled to said first collector electrode and said base electrode of said second transistor, said differential to single-ended converter including a fifth transistor and a diode, said fifth transistor being an NPN transistor having an emitter electrode, a base electrode, and a collector electrode, said collector electrode of said fifth transistor being coupled to said second collector electrode of said second transistor, said emitter electrode of said fifth transistor being coupled to said second power supply conductor, said base electrode of said fifth transistor being coupled to an anode of said diode and also to said second collector electrode of said first transistor, a cathode of Said diode being coupled to said second power supply conductor; and a transimpedance stage coupled between said collector of said fifth transistor and an output terminal, whereby the transconductance of said transconductance stage is reduced, permitting reduction in value of a feedback compensation capacitor in said transimpedance stage.

Claim 3

The integrated circuit operational amplifier as recited in claim 1 wherein said feedback compensation capacitor is coupled between said collector of said fifth transistor and an output stage of said transimpedance stage.

Claim 4

The integrated circuit operational amplifier as recited in claim 1 wherein said transimpedance stage comprises: second and third constant current soruces; and sixth, seventh, eighth, ninth, tenth, eleventh, twelfth and thirteenth transistors each having, respectively, an emitter electrode, a base electrode, and a collector electrode, said sixth, seventh, and thirteenth transistors being PNP transistors and said eighth, ninth, tenth, eleventh, and twelfth transistors being NPN transistors, said base electrode of said sixth transistor being coupled to said collector electrode of said fifth transistor, said sixth transistor having its collector electrode connected to said second power supply conductor and its emitter electrode connected to said collector electrode of said seventh transistor and also to said base electrode of said eighth transistor, said seventh transistor having its emitter coupled to said second constant current source and said collector of said eighth transistor and its base connected to a voltage reference node, said second constant current source also being coupled to said first power supply conductor, said emitter of said eighth transistor being coupled to said base electrode of said ninth transistor, said ninth transistor having its emitter electrode coupled to said second power supply conductor and its collector electrode coupled to said base electrode of said thirteenth transistor and also to said collector electrode of said tenth transistor and also to said base electrode of said eleventh transistor and also to said third constant current source, said third constant current source also being coupled to said first power supply conductor, said eleventh transistor having its collector electrode coupled to said first power supply conductor and its emitter electrode coupled to said base electrode of said twelfth transistor, said twelfth transistor having its collector electrode coupled to said first power supply conductor and its emitter electrode coupled to said base electrode of said tenth transistor, said tenth transistor having its emitter electrode coupled to said emitter electrode of said thirteenth transistor, said thirteenth transistor having its collector electrode coupled to said second power supply conductor, a first resistor being coupled between said emitter of said thirteenth transistor and said emitter of said twelfth transistor, said emitter of said thirteenth transistor being coupled to said output terminal, said feedback compensation capacitor being coupled between said base of said thirteenth transistor and said base of said sixth transistor.