Multistage operational amplifier with stability control
AssigneeSTMicroelectronics S.r.l.
InventorFrédéric Goutti
Life of this patent
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Abstract
A multistage operational amplifier includes a transconductor input stage, an output stage, and an intermediate stage. A first Miller capacitor is connected between the input and the output of the intermediate stage. A second Miller capacitor is connected between the input of the intermediate stage and an output of the output stage. A current mirror is connected to the output from the intermediate stage to draw a current therefrom.
Claims22
An operational amplifier comprising:
- an input stage comprising differential inputs and an output;
- an output stage;
- at least one intermediate stage connected between said input stage and said output stage and defining a sequence of stages therewith;
- said output stage and each intermediate stage comprising at least one transistor comprising a pair of conduction terminals connected between first and second power supply terminals with one of the conduction terminals defining an output of a respective stage, and a control terminal defining an input of the respective stage;
- a first capacitor connected between the input and the output of said at least one intermediate stage;
- a second capacitor connected between the input of said at least one intermediate stage and an output of a next stage in the sequence of stages;
- a current mirror comprising a driver branch and a slave branch, the slave branch connected to the output of said at least one intermediate stage;
- and
- a third capacitor connected between the driver branch and the output of said output stage.
An operational amplifier comprising:
- an input stage;
- an output stage;
- at least one intermediate stage connected between said input stage and said output stage and defining a sequence of stages therewith;
- said output stage and each intermediate stage connected between first and second power supply terminals, and each respective stage comprising an input and an output;
- a first capacitor connected between the input and the output of said at least one intermediate stage;
- a second capacitor connected between the input of said at least one intermediate stage and an output of a next stage in the sequence of stages;
- a current mirror comprising a first branch and a second branch, the second branch connected to the output of said at least one intermediate stage;
- a third capacitor connected between the first branch and the output of said output stage;
- and
- a ratio of a current being copied from the first branch to the second branch of said current mirror and a value of said third capacitor are chosen such that a current at the output of said at least one intermediate stage is approximately equal to a current conducting through said second capacitor.
A method for increasing the stability of an operational amplifier comprising an input stage, an output stage, and at least one intermediate stage connected between the input stage and the output stage and defining a sequence of stages therewith, the output stage and each intermediate stage connected between first and second power supply terminals, and each respective stage comprising an input and an output, a first capacitor connected between the input and the output of the at least one intermediate stage, and a second capacitor connected between the input of the at least one intermediate stage and an output of a next stage in the sequence of stages, the method comprising:
- removing a current proportional to a current that is output by the second capacitor using a current mirror comprising a first branch and a second branch, the second branch is connected to the output of the at least one intermediate stage, and the first branch is connected to the output of the output stage via a third capacitor connected therebetween.
Dependencies are inferred from the claim text.