The main purpose of the output stage of an operational amplifier is to deliver a certain amount of signal power into a load with acceptably low levels of signal distortion. In a low-voltage low-power environment, this has to be achieved by efficiently using the supply voltage as well as the supply current. To implement this, the output voltage range must be as large as possible, preferably from rail to rail. To achieve this, the output transistors have to be connected in a common-source configuration. An efficient use of the supply current requires a high ratio between the maximum signal current that can be delivered to a load, and the quiescent current of the output stage. To accomplish this, the output transistors have to be class-AB biased.
KeywordsSupply Voltage Operational Amplifier Output Stage Minimum Current Weak Inversion
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