Flipped gate voltage reference having boxing region and method of using

1. A voltage reference comprising:

a flipped gate transistor, a first terminal and a gate of the flipped gate transistor being connected to a first voltage node, and the flipped gate transistor being connected between an operating voltage node and a second voltage node;

an output node configured to output a reference voltage;

a first transistor, the first transistor having a first leakage current, wherein a gate of the first transistor is connected to the first voltage node, and the first transistor is connected between the operating voltage node and the output node;

a second transistor connected between the output node and the second voltage node, the second transistor having a second leakage current; and

a boxing circuit configured to offset the first leakage current with the second leakage current by providing a voltage level at a drain terminal of the first transistor.

2. The voltage reference of claim 1 , wherein a size of the flipped gate transistor is less than a size of the first transistor.

3. The voltage reference of claim 1 , wherein a size of the first transistor is a first integer multiple of a transistor unit size, and a size of the flipped gate transistor is a second integer multiple of the transistor unit size.

4. The voltage reference of claim 1 , wherein the boxing circuit comprises a negative level-shifter transistor and a positive level-shifter transistor.

5. The voltage reference of claim 1 , wherein the flipped gate transistor is an n-type metal oxide semiconductor (NMOS) transistor, the first transistor is an NMOS transistor and the second transistor is an NMOS transistor.

6. The voltage reference of claim 1 , further comprising:

a first current mirror circuit configured to receive a bias current and to generate a first current and a mirroring current, wherein the flipped gate transistor is configured to receive the first current; and

a second current mirror circuit configured to receive the mirroring current and to generate a second current, wherein the first transistor is configured to receive the second current.

7. The voltage reference of claim 6 , wherein the first current mirror circuit is further configured to provide a first mirrored current to a first portion of the boxing circuit, and the second current mirror circuit is further configured to provide a second mirrored current to a second portion of the boxing circuit.

8. The voltage reference of claim 6 , wherein the first current mirror circuit is configured to receive the bias current from an external current supply.

9. A voltage reference comprising:

a first current mirror circuit configured to receive a first bias current and to generate a first current and a mirroring current;

a second current mirror circuit configured to receive the mirroring current as a second bias current and to generate a second current;

a flipped gate transistor;

a first transistor, a gate of the first transistor connected to the flipped gate transistor, wherein the first transistor has a first leakage current;

an output node configured to output a reference voltage, the output node connected to the first transistor;

a second transistor connected to the output node, the second transistor having a second leakage current; and

a boxing circuit configured to offset the first leakage current with the second leakage current by providing a voltage level at a drain terminal of the first transistor.

10. The voltage reference of claim 9 , wherein the first current mirror circuit is configured to receive the first bias current from an external current supply.

11. The voltage reference of claim 9 , wherein the boxing circuit comprises:

a negative level-shifter transistor configured to receive a first boxing current from the second current mirror circuit; and

a positive level-shifter transistor configured to receive a second boxing current from the first current mirror circuit.

12. The voltage reference of claim 11 , wherein a gate of the negative level-shifter transistor is connected to the flipped gate transistor, a gate of the positive level-shifter transistor is connected to a source terminal of the negative level-shifter transistor, and a source terminal of the positive level-shifter transistor is connected to the first transistor.

13. The voltage reference of claim 9 , further comprising a first bias current generator circuit configured to receive an operating voltage and to generate the first bias current.

14. The voltage reference of claim 9 , wherein the first current mirror circuit is configured to receive the first bias current along a first line, the second current mirror is configured to receive the mirroring current along a second line separate from the first line, and the flipped gate transistor is configured to receive the first current along a third line separate from the first line and the second line.

15. The voltage reference of claim 9 , wherein the first current mirror circuit comprises:

a first mirror transistor configured to receive the first bias current;

a first mirror resistor connected in series with the first mirror transistor;

a second mirror transistor configured to mirror the first bias current and to generate the mirroring current;

a second mirror resistor connected in series with the second mirror transistor;

a third mirror transistor configured to mirror the first bias current and to generate the first current, wherein the flipped gate transistor is configured to receive the first current;

a third mirror resistor connected in series with the third mirror transistor;

a fourth mirror transistor connected to the first transistor and to the boxing circuit; and

a fourth mirror resistor connected in series with the fourth mirror transistor.

16. The voltage reference of claim 15 , wherein a size of the first mirror transistor is different from a size of each of the second mirror transistor, the third mirror transistor, and the fourth mirror transistor.

17. The voltage reference of claim 15 , wherein the second current mirror circuit comprises:

a fifth mirror transistor configured to receive the second bias current;

a fifth mirror resistor connected in series with the fifth mirror transistor;

a sixth mirror transistor connected to the boxing circuit;

a sixth mirror resistor connected in series with the sixth mirror transistor;

a seventh mirror transistor configured to mirror the mirroring current and to generate a second current, wherein the first transistor is configured to receive the second current; and

a seventh mirror resistor connected in series with the seventh mirror transistor.

18. The voltage reference of claim 17 , wherein a size of the fifth mirror transistor is different from a size of the sixth mirror transistor.

19. A method of using a voltage reference, the method comprising:

mirroring a first bias current to generate a first current across a flipped gate transistor and to generate a mirroring current;

receiving the mirroring current as a second bias current;

mirroring the second bias current to generate a second current across a first transistor and to generate a boxing current, wherein the first transistor has a first leakage current;

compensating for the first leakage current using a second transistor, the second transistor having a second leakage current;

boxing a voltage received by the first transistor using the second current and the boxing current, wherein boxing the voltage comprises offsetting the first leakage current with the second leakage current; and

outputting a reference voltage.

20. The method of claim 19 , further comprising receiving the first bias current from an external current source.