Class AB output circuit with large swing
AssigneeNational Semiconductor Corporation
InventorDennis M. Monticelli
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Abstract
An output stage is disclosed wherein class AB bias is employed. The stage is quiescently biased by means of current mirrors so that the bias is controlled mainly by ratioed geometric elements. The output transistors are biased by means of unity gain common gate drivers that provide the desired level shifting. The output voltage can be swung from from close to the rail potential of the source of the n channel output transistor to close to the rail potential of the source of the p channel transistor. The circuit can drive relatively large load currents and can be fabricated using either CMOS or conventional bipolar integrated circuits.
Claims12
A complementary metal oxide semiconductor class AB output stage circuit having signal input and output terminals, said circuit comprising:
- positive and negative supply terminals connectable to a source of operating power;
- a p channel output transistor having a source coupled to said positive supply terminal, a drain coupled to said output terminal, and a gate;
- an n channel output transistor having a source coupled to said negative supply terminal, a drain coupled to said output terminal and a gate;
- a p channel common gate bias transistor having its source coupled to said gate of said p channel output transistor, a drain coupled to said gate of said n channel output transistor, and a gate coupled to a source of bias voltage operated at about two p channel transistor thresholds below said positive supply terminal potential;
- an n channel common gate bias transistor having a source coupled to said gate of said n channel output transistor, a drain coupled to said gate of said p channel output transistor and a gate coupled to a source of bias voltage operated at about two n channel transistor thresholds above said negative supply terminal potential;
- a constant current source coupled between said positive supply terminal and said gate of said p channel output transistor;
- a constant current sink coupled between said negative supply terminal and said gate of said n channel output transistor;
- and
- means for applying a signal to said gate of one of said output transistors.
A complementary bipolar transistor class AB output stage having signal input and output terminals, said circuit comprising:
- positive and negative supply terminals connectable to a source of operating power;
- a PNP output transistor having an emitter coupled to said positive supply terminal, a collector coupled to said output terminal, and a base;
- an NPN output transistor having an emitter coupled to said negative supply terminal, a collector coupled to said output terminal, and a base;
- a PNP common base bias transistor having an emitter coupled to said base of said PNP output transistor, a collector coupled to said base of said NPN output transistor, and a base coupled to a source of bias voltage operated at about two V.sub.BE below said positive supply terminal potential;
- an NPN common base bias transistor having an emitter coupled to said base of said NPN output transistor, a collector coupled to said base of said PNP output transistor, and a base coupled to a source of bias voltage operated at about two V.sub.BE above said negative supply terminal potential;
- a constant current source coupled between said positive supply terminal and said base of said PNP output transistor;
- a constant current sink coupled between said negative supply terminal and said base of said NPN output transistor;
- and
- means for applying a signal to said base of one of said output transistors.
Dependencies are inferred from the claim text.