High voltage tolerant bias circuit with low voltage transistors

1. A voltage bias circuit, comprising:

a self-biased reference circuit disposed between an internal power supply node and a reference node and comprising bias circuits that provide at least one reference value based on a stable bias potential on at least one internal node;

a bias protection circuit coupled between a device power supply node and the reference node, the bias protection circuit comprising

a drive circuit that enables a controllable impedance path between the device power supply node and the internal power supply node according to a potential on at least a first supply bias voltage node,

a limit circuit that enables a first current path between the first supply bias voltage node and the reference node when the first supply bias voltage node exceeds a first predetermined limit with respect to the potential at the reference node, and

a feedback bias circuit that includes a first bias feedback current path coupled between the device power supply node and the reference node that is controlled according to the potential at the one internal node of the self-biased reference circuit; and

a limit supply circuit that provides a current to the limit circuit according to the current provided by the first bias feedback path.

2. The voltage bias circuit of claim 1 , wherein:

the drive circuit comprises at least a first buffer transistor having a source-drain path coupled between the internal power supply node and the device power supply node and a gate coupled to the first supply bias voltage node.

3. The voltage bias circuit of claim 2 , wherein:

the reference node receives a reference voltage; and

the first buffer transistor has a threshold voltage that varies from the reference voltage by no more than about 150 mV.

4. The voltage bias circuit of claim 1 , wherein:

the limit circuit further enables a second current path between a second supply bias voltage node and the reference node when the second supply bias voltage node exceeds a second predetermined limit with respect to the potential at the reference node, the second predetermined limit being different from the first predetermined limit.

5. The voltage bias circuit of claim 4 , wherein:

the drive circuit comprises

a first buffer transistor having a source-drain path coupled between the internal power supply node and the device power supply node and a gate coupled to the first supply bias voltage node, and

a second buffer transistor having a source-drain path in series with the first buffer transistor between the internal power supply node and the device power supply node and a gate coupled to the second supply bias voltage node.

6. The voltage bias circuit of claim 5 , wherein:

the reference node receives a reference voltage; and

the first buffer transistor and second buffer transistors have threshold voltages that vary from the reference voltage by no more than about 150 mV.

7. The voltage bias circuit of claim 1 , wherein:

the limit circuit comprises a first limit path coupled between the supply bias voltage node and the reference node, the first limit path including at least two diode connected transistors arranged in series with one another.

8. The voltage bias circuit of claim 7 , wherein:

the limit circuit further comprises a second limit path arranged in parallel to the first limit path between a second supply bias voltage node and the reference node, the second limit path including at least three diode connected transistors arranged in series with one another.

9. The voltage bias circuit of claim 1 , wherein:

the first bias feedback patch comprises

a first feedback current supply transistor having a source-drain path coupled to the device power supply node, and

at least a first feedback control transistor having a source-drain path coupled in series with the source-drain path of the first feedback current supply transistor, the feedback control transistor having a gate coupled to the one internal node of the self-biased reference circuit.

10. The voltage bias circuit of claim 9 , wherein:

the feedback bias circuit further comprises a second bias feedback current path coupled between the device power supply node and the reference node in parallel with the first bias feedback current path that is controlled according to the potential at the one internal node of the self-biased reference circuit.

11. The voltage bias circuit of claim 10 , wherein:

the second bias feedback path comprises

a plurality of second feedback current supply transistors, each diode connected and having source-drain path coupled in series to the device power supply node, and at least a second feedback control transistor having a source-drain path coupled in series with the source-drain paths of the second feedback current supply transistors, the second feedback control transistor having a gate coupled to the bias node of the self-biased reference circuit.

12. The voltage bias circuit of claim 1 wherein:

the self-biased reference circuit comprises a beta multiplier circuit.

13. The voltage bias circuit of claim 12 , wherein

the self-biased reference circuit further comprises a band gap reference circuit.

14. A method of generating reference voltages with a high voltage power supply and low voltage transistors, comprising:

establishing a first supply bias voltage with at least one series of diode connected transistors coupled to a reference voltage node and a first current supply transistor biased according to a reference bias voltage;

biasing a first supply transistor coupled to a device power supply node according to the first supply bias voltage to generate an internal power supply voltage less than the device power supply voltages, including coupling the supply bias voltage to an n-channel transistor having a threshold voltage of less than 150 mV;

powering a self bias reference circuit with the internal power supply voltage to generate the reference bias voltage at a level between the internal power supply voltage and the reference node;

establishing a second supply bias voltage with at least a second series of diode connected transistors coupled to the reference voltage node and a second current supply transistor biased according to the reference bias voltage; and

biasing a second supply transistor coupled in series with the first supply transistor according to the second supply bias voltage.

15. The method of claim 14 , wherein:

the powering the self-bias reference circuit comprises providing the internal power supply voltage to a beta multiplier circuit.

16. The method of claim 14 , wherein:

the powering the self-bias reference circuit comprises providing the internal power supply voltage to a band-gap reference circuit.

17. A voltage bias circuit, comprising:

a self-biased reference circuit disposed between an internal power supply node and a reference node and comprising bias circuits that provide at least one reference value based on a stable bias potential on at least one internal node; and

a bias protection circuit coupled between a device power supply node and the reference node, the bias protection circuit comprising:

a drive circuit that enables a controllable impedance path between the device power supply node and the internal power supply node according to a potential on at east a first supply bias voltage node, the drive circuit comprising at least a first buffer transistor having a gate coupled to the first supply bias voltage node and a threshold voltage that varies from the reference voltage by no more than about 150 mV,

a limit circuit that enables a fist current path between the first supply bias voltage node and the reference node when the first supply bias voltage node exceeds a first predetermined limit with respect to the potential at the reference node,

a feedback bias circuit that comprises first and second bias feedback current paths both coupled between the device power supply node and the reference node and controlled according to the potential at the one internal node of the self-biased reference circuit, and

a limit supply circuit that provides a current to the limit circuit according to the current provided by the first bias feedback path.

18. The voltage bias circuit of claim 17 , wherein:

the limit circuit further enables a second current path between a second supply bias voltage node and the reference node when a second supply bias voltage node exceeds a second predetermined limit with respect to the potential at the reference node; and

the drive circuit comprises

the first buffer transistor having a source-drain path coupled between the internal power supply node and the device power supply node, and

a second buffer transistor having a source-drain path in series with the first buffer transistor between the internal power supply node and the device power supply node and a gate coupled to the second supply bias voltage node.

19. The voltage bias circuit of claim 18 , wherein:

the second buffer transistor has a threshold voltage that varies from the reference voltage by no more than about 150 mV.