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US 5,471,174 AGranted
Amplifier having an output stage with bias current cancellation
AssigneeMotorola, Inc.
InventorsThomas D. Petty, Troy L. Stockstad, Robert L. Vyne
Life of this patent
Estimating the term…
Abstract
An amplifier circuit (10) receives a differential input signal and provides an amplified differential signal. A converter circuit (14) is responsive to the amplified differential signal and provides a single-ended signal. An output stage (16) is responsive to the single-ended signal for providing an output signal of the amplifier circuit. The output stage provides bias cancellation for the single-ended signal by injecting a current equal to the bias requirement of the input transistors (20, 38). The bias cancellation maintains a high input impedance and high gain and output drive for the output stage.
Claims17
A circuit, comprising:
- a first transistor having a base, a collector and an emitter, said base being coupled to an input of the circuit, said emitter being coupled to a first power supply conductor;
- a first current mirror circuit having an input coupled to said collector of said first transistor;
- a second current mirror circuit having an input and an output, said output being coupled to a first output of said first current mirror circuit and to said input of the circuit, said input being coupled to a second output of said first current mirror circuit;
- and
- a second transistor having a base, a collector and an emitter, said base being coupled to said input of the circuit, said emitter being coupled to said first power supply conductor, said collector providing an output signal of the circuit.
2 more elements
An amplifier output stage, comprising:
- a first transistor having a base, a collector and an emitter, said base being coupled to an input of the amplifier output stage, said emitter being coupled to a first power supply conductor;
- a first current mirror circuit having an output coupled to said collector of said first transistor;
- a second transistor having a base, a collector and an emitter, said collector being coupled to an input of said first current mirror circuit, said emitter being coupled to said first power supply conductor;
- a third transistor having a base, a collector and an emitter, said base being coupled to said collector of said first transistor, said emitter being coupled to a second power supply conductor, said collector being coupled to said base of said second transistor at a first node;
- a fourth transistor having a base, a collector and an emitter, said base being coupled to said first node, said emitter being coupled to said first power supply conductor;
- a second current mirror circuit having an input coupled to said collector of said fourth transistor;
- and
- a third current mirror circuit having an input coupled to a first output of said second current mirror circuit and having an output coupled to a second output of said second current mirror circuit and to said input of the amplifier output stage.
5 more elements
An amplifier circuit, comprising:
- a differential input stage having first and second inputs coupled for receiving a differential input signal and having first and second outputs for providing an amplified differential signal;
- a converter circuit having first and second inputs coupled for receiving said amplified differential signal and having an output for providing a single-ended signal;
- and
- an output stage having an input coupled for receiving said single-ended signal and having an output for providing an output signal of the amplifier circuit, said output stage including,
- (a) a first transistor having a base, a collector and an emitter, said base being coupled to said input of said output stage, said emitter being coupled to a first power supply conductor,
- (b) a first current mirror circuit having an input coupled to said collector of said first transistor,
- (c) a second current mirror circuit having an input and an output, said output being coupled to a first output of said first current mirror circuit and to said input of said output stage, said input being coupled to a second output of said first current mirror circuit, and
- (d) a second transistor having a base, a collector and an emitter, said base being coupled to said input of said output stage, said emitter being coupled to said first power supply conductor, said collector providing the output signal of the amplifier circuit.
5 more elements
An amplifier circuit, comprising:
- a differential input stage having first and second inputs coupled for receiving a differential input signal and having first and second outputs for providing an amplified differential signal;
- a converter circuit having first and second inputs coupled for receiving said amplified differential signal and having an output for providing a single-ended signal;
- and
- an output stage having an input coupled for receiving said single-ended signal and having an output for providing an output signal of the amplifier circuit, said output stage including,
- (a) a first transistor having a base, a collector and an emitter, said base being coupled to said input of said output stage, said emitter being coupled to a first power supply conductor,
- (b) a first current mirror circuit having an input and having an output coupled to said collector of said first transistor,
- (c) a second transistor having a base, a collector and an emitter, said collector being coupled to said input of said first current mirror circuit, said emitter being coupled to said first power supply conductor,
- (d) a third transistor having a base, a collector and an emitter, said based being coupled to said collector of said first transistor, said emitter being coupled to a second power supply conductor, said collector being coupled to said base of said second transistor at a first node,
- (e) a fourth transistor having a base, a collector and an emitter, said base being coupled to said first node, said emitter being coupled to said first power supply conductor,
- (f) a second current mirror circuit having an input coupled to said collector of said fourth transistor, and
- (g) a third current mirror circuit having an input coupled to a first output of said second current mirror circuit and having an output coupled to a second output of said second current mirror circuit and to said input of said output stage.
8 more elements
Dependencies are inferred from the claim text.