Granted Patent B2

US 7,514,706 · App. 11/549,964 · Granted Apr 7, 2009

Abstract

Claims (30)

1. A method of operating a programmable variable resistance cell voltage reference, said method comprising:

forcing a programming current into a programmable variable resistance cell for a predetermined period of time, wherein the programming current instigates a change of resistance in the programmable variable resistance cell;

causing the programming current in the programmable variable resistance cell to produce a reduced current and to stop programming after said predetermined programming period; and

buffering the resulting voltage across the programmable variable resistance cell with a voltage amplifier,

wherein the resulting voltage across the programmable variable resistance cell is the difference between the potentials of the first terminal and the second terminal of said programmable variable resistance cell.

2. The method as recited in claim 1 , wherein said programmable variable resistance cell includes a first terminal and a second terminal, wherein one of said first and second terminals of said programmable variable resistance cell is common to other programmable variable resistance cells in a system and is held at a predetermined low impedance voltage potential.

3. The method as recited in claim 1 , further comprising:

disabling said reduced current in said programmable variable resistance cell; and

forcing a reverse bias across the programmable variable resistance cell to disable said programmable variable resistance cell voltage reference and increase the resistance of said programmable variable resistance cell.

4. The method as recited in claim 1 , further comprising referencing an output from the step of buffering the resulting voltage across the programmable variable resistance cell from one terminal of the programmable variable resistance cell to the lowest potential of the system.

5. The method as recited in claim 1 , wherein the programmable variable resistance cell limits a voltage across the first terminal and the second terminal to a threshold voltage for programming said programmable variable resistance cell when said programming current is forced into said programmable variable resistance cell.

6. The method as recited in claim 1 , wherein a ratio of said programming current and said reduced current is proportional to a ratio of a threshold voltage for programming and a resulting bias across the programmable variable resistance cell.

7. A voltage reference, comprising:

a programmable variable resistance cell, having an anode and a cathode, wherein a reduction in resistance in said programmable variable resistance cell occurs when a voltage threshold for programming is developed across the anode and the cathode, and an increase in resistance occurs when voltage threshold for erase is developed from the cathode to the anode;

a first low impedance voltage source coupled to the anode;

a second low impedance voltage source, of lower value than the first low impedance voltage source, coupled to the cathode via a first switch;

a first current source coupled to the cathode via a second switch;

a second current source coupled to the cathode via a third switch; and

an amplifier coupled to the cathode to perform voltage buffering,

wherein the amplifier is coupled to said anode and said cathode to output a difference in potentials across said programmable variable resistance cell.

8. The voltage reference as recited in claim 7 , wherein said first and second current sources are implemented with transistors.

9. A voltage reference, comprising:

a programmable variable resistance cell having an anode and a cathode, wherein a reduction in resistance in said programmable variable resistance cell occurs when a voltage threshold for programming is developed across the device from the anode to the cathode, and an increase in resistance occurs when a voltage threshold for erase is developed from the cathode to the anode;

a first low impedance voltage source coupled to the cathode;

a second low impedance voltage source of lower value than the first low impedance voltage source coupled to the anode via a first switch;

first current source coupled to the anode via a second switch; and

a second current source coupled to the anode via a third switch,

wherein the amplifier is coupled to said anode and said cathode to output the difference in potentials across the programmable variable resistance cell.

10. The voltage reference of claim 9 , further comprising an amplifier coupled to the anode to perform voltage buffering.

11. The voltage reference as recited in claim 9 , wherein said first and second current sources are implemented with transistors.

Assignments (10)