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US 5,128,630 AGranted
High speed fully differential operational amplifier
AssigneeMotorola, Inc.
InventorDejan Mijuskovic
Life of this patent
Estimating the term…
Abstract
An operational amplifier operates with a higher bandwidth by doubling the gate drive to an output stage transistor without increasing the gain of an intermediate stage amplifier. The increased gate drive allows the output stage transistor to be reduced in size while providing the same output drive level to the capacitive load. The smaller output stage transistors reduces its gate capacitance for providing stable operation with the increased bandwidth.
Claims16
An amplifier circuit responsive to a differential input signal for providing first and second differentially related output signals, comprising:
- a differential amplifier responsive to the differential input signal for providing a differential output signal with common mode rejection having first and second inverted components and first and second non-inverted components;
- a first amplifier having inverting and non-inverting inputs and an output, said non-inverting input being coupled for receiving said first non-inverted component of said differential output signal, said inverting input being coupled for receiving said second inverted component of said differential output signal, said first amplifier including,
- (a) a first transistor having a gate, a drain and a source, said gate being coupled for receiving said first non-inverted component of said differential output signal, said drain being coupled to a first power supply conductor, and
- (b) a second transistor having a gate, a drain and a source, said gate being coupled for receiving said second inverted component of said differential output signal said drain being coupled to said source of said first transistor, said source being coupled to a second power supply conductor;
- and
- a second amplifier having inverting and non-inverting inputs and an output, said non-inverting input being coupled for receiving said first inverted component of said differential output signal, said inverting input being coupled for receiving said second non-inverted component of said differential output signal, said outputs of said first and second amplifiers providing the first and second differentially related output signals of the amplifier circuit.
3 more elements
In an amplifier circuit a transconductance stage provides first and second differentially related signals having a predetermined DC offset to an output driver stage for providing a first output signal, comprising:
- a first transistor having a gate, a drain and a source, said gate being coupled for receiving the first differentially related signal, said drain being coupled to a first source of operating potential;
- a second transistor having a gate, a drain and a source, said gate being coupled for receiving the second differentially related signal, said drain being coupled to said source of said first transistor, said source being coupled to a second source of operating potential;
- a third transistor having a gate, a drain and a source, said gate being coupled to said drain of said second transistor, said drain providing the first output signal of the amplifier circuit, said source being coupled to said second source of operating potential;
- and
- means for providing third and fourth differentially related signals to the output driver stage for producing a second output signal of the amplifier circuit.
2 more elements
In an amplifier circuit a transconductance stage responsive to a differential input signal for providing first and second non-inverted components of a differential output signal and first and second inverted components of the differential output signal to an output stage, the transconductance stage comprising:
- a current mirror circuit having an input and first and second outputs, the differential input signal being applied at said first and second outputs of said current mirror circuit;
- current supply means having first and second outputs for providing first and second currents of predetermined magnitude;
- a first transistor having a gate, a drain and a source, said gate being coupled to said first output of said current supply means, said drain being coupled to a first source of operating potential, said source being coupled to said input of said current mirror circuit;
- a second transistor having a gate, a drain and a source, said gate being coupled to said second output of said current supply means, said drain being coupled to said first source of operating potential, said source being coupled to said input of said current mirror circuit;
- first level-shifting means coupled between said first output of said current mirror circuit and said gate of said first transistor for providing the first and second non-inverted components of the differential output signal;
- and
- second level-shifting means coupled between said second output of said current mirror circuit and said gate of said second transistor for providing the first and second inverted components of the differential output signal.
4 more elements
A method of increasing the bandwidth of an amplifier circuit, comprising the steps of:
- applying a differential input signal to a first differential amplifier for providing inverted and non-inverted output signals of the amplifier circuit at first and second outputs;
- splitting said inverted output signal of said first differential amplifier into first and second inverted components having a predetermined DC offset;
- splitting said non-inverted output signal of said first differential amplifier into first and second non-inverted components having said predetermined DC offset;
- combining said first inverted component with said second non-inverted component for providing a non-inverted output signal of the amplifier circuit having twice the magnitude as said non-inverted output signal of said first differential amplifier;
- and
- combining said first non-inverted component with said second inverted component for providing a inverted output signal of the amplifier circuit having twice the magnitude as said inverted output signal of said first differential amplifier;
- and
- feeding back said non-inverted output signal and said inverted output signal of the amplifier circuit through a second differential amplifier for controlling bases of first and second transistors, said first and second transistors having drains coupled to a first power supply conductor and having sources coupled to said first and second outputs of the amplifier circuit respectively for maintaining balanced operation for said non-inverted output signal and said inverted output signal.
5 more elements
Dependencies are inferred from the claim text.