Multi-level output cascode power stage

1. A power stage to generate an output voltage at one of a high reference voltage, an intermediate reference voltage and a low reference voltage, comprising:

a first switch stage connecting the output terminal to the high reference voltage, comprising a pair of transistors connected in series along their source-to-drain paths, a first transistor coupled to the output terminal and having its gate biased at the intermediate voltage, a second transistor having a gate that receives a first stage control signal that varies between the high reference voltage and the intermediate reference voltage,

a second switch stage connecting the output terminal to the intermediate reference voltage, having a gate that receives a second stage control signal that varies among the high reference voltage, intermediate reference voltage and low reference voltage;

a third switch stage connecting the output terminal to the low reference voltage, having a pair of transistors connected in series along their source-to-drain paths, a first transistor coupled to the output terminal and having its gate biased at the intermediate voltage, a second transistor having a gate that receives a third stage control signal that varies between the intermediate reference voltage and the low reference voltage wherein the third switch stage provides a protective mode when at least one of the pair transistors is off.

2. The power stage of claim 1 , wherein the transistors have a breakdown voltage that is lower than a difference between the high reference voltage and the low reference voltage.

3. A power stage to generate an output voltage at one of a first reference voltage, an second reference voltage and a third reference voltage, comprising:

a first switch stage connecting the output terminal to the first reference voltage, comprising a pair of transistors connected in series along their source-to-drain paths, a first transistor coupled to the output terminal and having its gate biased at the second voltage, a second transistor having a gate that receives a first stage control signal that varies between the first reference voltage and the second reference voltage,

a second switch stage connecting the output terminal to the second reference voltage, having a gate that receives a second stage control signal that varies among the first reference voltage, second reference voltage and third reference voltage;

a third switch stage connecting the output terminal to the third reference voltage, having a pair of transistors connected in series along their source-to-drain paths, a first transistor coupled to the output terminal and having its gate biased at the second voltage, a second transistor having a gate that receives a third stage control signal that varies between the second reference voltage and the third reference voltage, wherein the third switch stage provides a protective mode when at least one of the pair transistors is off.

4. The power stage of claim 1 , wherein the transistors have a breakdown voltage that is lower than a difference between the first reference voltage and the third reference voltage.

5. An amplifier system, comprising:

a power stage having inputs for at least two supply voltages and an output voltage node for coupling to a load, the power stage including:

a first plurality of transistors, at least one of the first plurality of transistors being disposed between an intermediate voltage node and the output voltage node, and at least two of the first plurality of transistors being connected in series and disposed between a high voltage node and the output voltage node;

a second plurality of transistors being connected in a cascode configuration and disposed between the output voltage node and a low voltage node, wherein the cascode configuration provides a protective mode when at least one of the transistors of the second plurality is off; and

a driver to generate control signals to the power stage that causes the power stage to vary an output voltage applied to the load from among the at least three voltage levels.

6. The amplifier system of claim 5 , wherein the first plurality of transistors includes PMOS transistors.

7. The amplifier system of claim 5 , wherein the second plurality of transistors includes NMOS transistors.

8. The amplifier system of claim 5 , wherein the output node is adapted to output high, intermediate, and low voltage levels.

9. The amplifier system of claim 5 , further comprising a backgate controller to generate control signals to at least one of the first plurality of transistors.

10. A method, comprising:

generating an output voltage to a load, by a power stage having inputs for at least two supply voltages, the power stage including:

a first plurality of transistors, at least one of the first plurality of transistors being disposed between an intermediate voltage node and an output voltage node, and at least two of the first plurality of transistors being connected in series and disposed between a high voltage node and the output voltage node;

a second plurality of transistors being connected in a cascode configuration and disposed between the output voltage node and a low voltage node, wherein the cascode configuration provides a protective mode when at least one of the transistors of the second plurality is off; and

generating control signals to the power stage, by a controller, to cause the power stage to vary the output voltage applied to the load from among more three voltage levels.

11. The method of claim 10 , wherein the first plurality of transistors includes PMOS transistors.

12. The method of claim 10 , wherein the second plurality of transistors includes NMOS transistors.

13. The method of claim 10 , wherein the output node is adapted to output high, intermediate, and low voltage levels.

14. The method of claim 10 , further comprising generating backgate control signals to at least one of the first plurality of transistors.

15. A multi-level output power stage, comprising:

inputs for at least two supply voltages;

an output voltage node for coupling to a load;

a first plurality of transistors, at least one of the first plurality of transistors being disposed between an intermediate voltage node and the output voltage node, and at least two of the first plurality of transistors being connected in series and disposed between a high voltage node and the output voltage node; and

a second plurality of transistors being connected in a cascode configuration and disposed between the output voltage node and a low voltage node, wherein the cascode configuration provides a protective mode when at least one of the transistors of the second plurality is off.

16. The multi-level output cascade power stage of claim 15 , further comprising a driver to generate control signals to the power stage that causes the power stage to vary an output voltage applied to the load from among the at least three voltage levels.

17. The multi-level output cascade power stage of claim 15 , wherein the first plurality of transistors includes PMOS transistors.

18. The multi-level output cascade power stage of claim 15 , wherein the second plurality of transistors includes NMOS transistors.

19. The multi-level output cascade power stage of claim 15 , wherein the output node is adapted to output high, intermediate, and low voltage levels.

20. The multi-level output cascade power stage of claim 15 , further comprising a backgate controller to generate control signals to at least one of the first plurality of transistors.