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US 5,327,100 AGranted
Negative slew rate enhancement circuit for an operational amplifier
AssigneeMotorola, Inc.
InventorsTroy L. Stockstad, Renwin J. Yee, Thomas D. Petty
Life of this patent
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Abstract
An operational amplifier enhances its negative slew rate by providing more base current to a bottom PNP output drive transistor. A large signal applied at the inverting input of the operational amplifier unbalances the differential input stage and provides maximum current through a current mirror circuit to the base of the PNP output transistor. A transistor is biased on by sufficient current flow through the current mirror circuit to draw even more base current from the base of the PNP output transistor and thereby enhance its negative slew rate.
Claims19
An operational amplifier, comprising:
- a differential input stage responsive to first and second input signals for developing first and second voltages at first and second nodes;
- a first transistor having a base, an emitter and a collector, said emitter being coupled to an output of the operational amplifier, said collector being coupled to a first power supply conductor, said base being coupled to said second node;
- and
- circuit means having first and second conduction paths coupled to said first and second nodes respectively, said second conduction path being further coupled to said base of said first transistor for providing a drive signal to said base of said first transistor upon sensing a predetermined level of said first and second voltages.
1 more element
An operational amplifier, comprising:
- a differential input stage responsive to first and second input signals for developing first and second voltages at first and second nodes;
- a first transistor having a base, an emitter and a collector, said emitter being coupled to an output of the operational amplifier, said collector being coupled to a first power supply conductor, said base being coupled for receiving said second voltage;
- a current mirror circuit having a first conduction path coupled to said first node for receiving an input current and having a second conduction path coupled to said base of said first transistor for sinking an output current, said second conduction path of said current mirror circuit developing a voltage in response to said output current;
- and
- a second transistor having a base, an emitter and a collector, said base receiving said voltage from said second conduction path of said current mirror circuit, said collector being coupled to said base of said first transistor, said emitter being coupled to said first power supply conductor.
2 more elements
An operational amplifier, comprising:
- a differential input stage responsive to first and second input signals for developing first and second voltages at first and second nodes;
- a first transistor having a base, an emitter and a collector, said emitter being coupled to an output of the operational amplifier, said collector being coupled to a first power supply conductor;
- a second transistor having a base, an emitter and a collector, said collector being coupled to said first node;
- a first resistor coupled between said emitter of said second transistor and said first power supply conductor;
- a third transistor having a base, an emitter and a collector, said base and collector being coupled to said base of said second transistor;
- a fourth transistor having a base, an emitter and a collector, said base being coupled to said collector of said second transistor, said collector being coupled to said base of said first transistor, said emitter being coupled to said collector of said third transistor;
- a third resistor coupled between said emitter of said third transistor and said first power supply conductor;
- a fifth transistor having a base, an emitter and a collector, said base being coupled to said emitter of said third transistor, said collector being coupled to said base of said first transistor;
- and
- a third resistor coupled between said emitter of said fifth transistor and said first power supply conductor.
7 more elements
Dependencies are inferred from the claim text.