Compact Low-Voltage and High-Speed CMOS, BiCMOS and Bipolar Operational Amplifiers pp 35-107 | Cite as

# Output Stages

## Abstract

The main function of the output stage is to deliver the output signal to the load. Since high signal levels are likely to occur, the output stage should be able to deal with high voltages and high currents. For a good power efficiency the maximum peak-to-peak output voltage should be nearly equal to the supply voltage and the stage should be biased by a very small quiescent current while being capable of driving much larger output currents. Also, the output stage has to cope with the load connected to the output terminal. The resistive part of the load determines the maximum output current that is needed. Very low resistive loads in the order of 50 ohms require a maximum output current of at least 10 mA and pose large demands upon the construction of the output stage. For example, large output transistors must be used which result in large parasitic capacitances. Consequently, the attainable bandwidth is reduced by the larger capacitances. The capacitive load, on the other hand, determines the minimum current, or quiescent current, that is needed to obtain sufficient phase margin and stability. Finally, distortion is an important overall parameter that is mainly determined by the output stage, because it handles the highest signal levels.

## Keywords

Collector Current Output Stage Bipolar Transistor Minimum Current Voltage Follower## Preview

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