Near zero quiescent current circuit for selecting a maximum supply voltage

1. A circuit, comprising:

a comparator powered by a first voltage, wherein the comparator compares the first voltage and a second voltage, wherein the first voltage is presented on an inverting terminal and the second voltage on a non-inverting terminal of the comparator;

a pull-up resistor having a first terminal and a second terminal configured to receive the first voltage across the first terminal and the second terminal, the second terminal being the output of the comparator;

a first inverter powered by the first voltage, wherein the first inverter inverts the output of the comparator;

a pull-down resistor having first terminal connected to the output of the first inverter and second terminal connected to ground;

a first P-MOSFET having gate terminal connected to the first terminal of the pull-down resistor, source terminal connected to the second voltage and drain and bulk terminals connected to an output node;

a second inverter having an input terminal connected to the gate of the first P-MOSFET and an output terminal, wherein the second inverter is powered by maximum of one of the first voltage and the second voltage;

a second P-MOSFET having gate terminal connected to the output terminal of the second inverter, source terminal connected to the first voltage and drain and bulk terminals connected to the output node; and

a third P-MOSFET having gate terminal connected to the gate terminal of the first P-MOSFET, source terminal connected to the gate terminal of the second P-MOSFET and drain and bulk terminals connected to the output node.

2. The circuit as claimed in claim 1 , wherein the maximum of one of the first voltage and the second voltage is selected by a back-to-back PMOS voltage selector.

3. The circuit as claimed in claim 1 , wherein the first inverter is a CMOS-based inverter.

4. A circuit for selecting a maximum supply voltage between a first voltage and a second voltage, the circuit comprising:

a comparator for

receiving a first voltage and a second voltage, from a first voltage source and a second voltage source, respectively; and

generating a difference signal by comparing the first voltage and the second voltage, wherein the difference signal at the output of the comparator is 0V when the first voltage is greater than the second voltage, and wherein the difference signal at the output of the comparator is pulled up to the first voltage when the second voltage is greater than the first voltage;

a first biasing circuit for generating a first bias signal based on the difference signal;

a second biasing circuit for generating a second bias signal based on the difference signal; and

a first power switch and a second power switch, wherein the first power switch supplies the first voltage at an output node and the second power switch supplies the second voltage at the output node, wherein the first power switch and the second power switch are selectively configured using the first bias signal and the second bias signal respectively, for providing maximum supply voltage as an output voltage at an output node.

5. The circuit as claimed in claim 4 , wherein the first power switch is a P-MOSFET.

6. The circuit as claimed in claim 4 , wherein the second power switch is a P-MOSFET.

7. The circuit as claimed in claim 4 , wherein the first bias signal switches ON the first power switch and the second bias signal switches OFF the second power switch when the first voltage is greater than the second voltage.

8. The circuit as claimed in claim 4 , wherein the first bias signal switches OFF the first switch and the second bias signal switches ON the second power switch when the second voltage is greater than the first voltage.

9. The circuit as claimed in claim 4 , wherein the first bias signal switches OFF the first switch and the second bias signal switches ON the second power switch when difference between the first voltage and the second voltage is less than the threshold voltage of a MOSFET.

10. A method for selecting a maximum supply voltage between a first voltage and a second voltage, the method comprising:

receiving a first voltage and a second voltage, from a first voltage source and a second voltage source, respectively;

generating a difference signal by comparing the first voltage and the second voltage, wherein the difference signal at the output of the comparator is 0V when the first voltage is greater than the second voltage, and wherein the difference signal at the output of the comparator is pulled up to the first voltage when the second voltage is greater than the first voltage; and

generating a first bias signal and a second bias signal based on the difference signal, wherein the first bias signal and the second bias signal are used to selectively configure one of a first power switch and a second power switch for providing maximum supply voltage as an output voltage at an output node, wherein the first power switch supplies the first voltage at the output node and the second power switch supplies the second voltage at the output node.

11. The method as claimed in claim 10 , wherein the first bias signal switches ON the first power switch and the second bias signal switches OFF the second power switch when the first voltage is greater than the second voltage.

12. The method as claimed in claim 10 , wherein the first bias signal switches OFF the first switch and the second bias signal switches ON the second power switch when the second voltage is greater than the first voltage.

13. The method as claimed in claim 10 , wherein the first bias signal switches OFF the first switch and the second bias signal switches ON the second power switch when difference between the first voltage and the second voltage is less than the threshold voltage.