Voltage comparator circuit and usage thereof

1. A circuit comprising:

a first power supply having a first voltage and a second power supplying having a second voltage, wherein said first and second voltages are different at least in some cycles of said circuit;

a memory element, wherein said first and second power supplies are driven into said memory element;

a voltage comparator having connected thereto said first and second power supplies, wherein said voltage comparator is an analog to digital converter configured to provide digital output indicting of a voltage difference over a predetermined threshold between said first and second power supplies; and

a supply selector element, wherein said supply selector element is configured to disconnect said second power supply from said memory element in response to the digital output of said voltage comparator.

2. The circuit of claim 1 , wherein said memory element is a Static Random-Access Memory (SRAM) element, wherein said first power supply is a cell power supply and said second power supply is a peripheral power supply.

3. The circuit of claim 2 , wherein said memory element comprises an array of bit lines that are used to write to and read from cells of said memory element, wherein said first power supply drives voltage to said cells, wherein said second power supply drives voltage to said bit lines, wherein said supply selector is configured to disconnect said second power supply from said bit lines and connect said bit lines to said first power supply.

4. The circuit of claim 1 , wherein said voltage comparator is a field-effect transistor, having a source terminal, a gate terminal and a drain terminal, wherein said source terminal is driven by the first power supply, wherein said gate terminal is driven by the second power supply, wherein said drain is connected to said supply selector element.

5. The circuit of claim 1 , wherein said field-effect transistor is selected from the group consisting of p-channel field-effect transistor and n-channel field-effect transistor.

6. The circuit of claim 1 , wherein said circuit has a first mode and a second mode, wherein the first mode is a voltage testing mode in which said first and second power supplies are driven into said memory element, wherein in the second mode only the first power supply is driven into said memory element and the second power supply is disconnected from said memory element; wherein said supply selector element is configured to switch from the first mode to the second mode.

7. The circuit of claim 1 , wherein said voltage comparator comprising a first voltage comparator configured to provide a first digital output indicating the first voltage exceeds the second voltage in over the predetermined threshold; and wherein said voltage comparator comprising a second voltage comparator configured to provide a second digital output indicating the second voltage exceeds the first voltage in over the predetermined threshold.

8. The circuit of claim 7 , wherein said first and second digital outputs are summed by stacked field-effect transistors.

9. The circuit of claim 1 , wherein said voltage comparator and said supply selector element consist solely of basic devices.

10. The circuit of claim 1 , wherein said digital output is connected in a feedback loop to said voltage comparator to cause hysteresis.

11. The circuit of claim 10 , wherein the hysteresis is caused by disconnecting one or more pull-down devices thereby increasing impedance resistance of said voltage comparator.