Ultra low power tracked low voltage reference source

• US 20030057931A1
• Filed: 08/28/2002
• Published: 03/27/2003
• Est. Priority Date: 08/30/2001
• Status: Active Grant

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Micron Technology, Inc.
• Inventors: Di Iorio, Ercole
• Granted Patent: US 6,713,996 B2
• Time in Patent Office: Days
• US Class Current: 323/313
• CPC Class Codes: G11C 16/30 Power supply circuits
• CPC Class Codes: G11C 5/147 Voltage reference generators, voltage or current regulators; Internally lowered supply levels; Compensation for voltage drops G11C5/141 takes precedence

Abstract

A reference voltage source for an integrated circuit includes a first voltage reference that is adjustable, a second voltage reference, a differential sensing device to compare a voltage provided by the first voltage reference to a voltage provided by the second voltage reference, a controller to provide a trim control signal to the first voltage reference in response to an output of the differential sensing device for adjusting the first voltage reference and to provide a signal to power down the second voltage reference after the first voltage reference has been adjusted.

Claims

1. A reference voltage source for an integrated circuit comprising:

a first voltage reference that is adjustable;

a second voltage reference;

a differential sensing device to compare a voltage provided by the first voltage reference to a voltage provided by the second voltage reference;

a controller to provide a trim control signal to the first voltage reference in response to an output of the differential sensing device for adjusting the first voltage reference and to provide a signal to power down the second voltage reference after the first voltage reference has been adjusted.

2. The reference voltage source for an integrated circuit of claim 1 wherein the first voltage reference is adjusted periodically.

3. The reference voltage source for an integrated circuit of claim 1 wherein the second voltage reference is reactivated to enable readjustment of the first voltage reference.

4. The reference voltage source for an integrated circuit of claim 3 wherein the second voltage reference is reactivated periodically.

5. The reference voltage source for an integrated circuit of claim 1 wherein the controller provides a digital trim control signal.

6. The reference voltage source for an integrated circuit of claim 1 wherein the controller functions in response to a clock and activates in response to a signal that switches at a frequency that is much lower than the frequency of the clock.

7. The reference voltage source for an integrated circuit of claim 1 wherein the first voltage source comprises a plurality of series connected resistors tapped by a plurality of switches selectively engaged in response to the trim signal from the controller.

8. The reference voltage source for an integrated circuit of claim 7 wherein the plurality of switches are selectively engaged in response to the trim signal from the controller by a decoder.

9. The reference voltage source for an integrated circuit of claim 1 wherein the first voltage source comprises a resistor ladder coupled to a current source, in which the resistors are selectively shunted by switches in response to the trim control signal.

10. The reference voltage source for an integrated circuit of claim 1 wherein the first voltage reference requires less current to operate than the second voltage reference.

11. The reference voltage source for an integrated circuit of claim 1 wherein the second voltage reference has higher precision than the first voltage reference.

12. The reference voltage source for an integrated circuit of claim 1, wherein the controller provides signals for deactivating the second voltage reference in response to a signal from the differential sensing device.

13. The reference voltage source for an integrated circuit of claim 12 wherein the controller deactivates the second voltage reference source after the first voltage source has reached a predetermined level.

14. The reference voltage source for an integrated circuit of claim 13 wherein the controller reactivates the second voltage reference source after a predetermined time.

15. The reference voltage source for an integrated circuit of claim 1 wherein the integrated circuit is a flash memory.

16. A method of generating a stable reference voltage for an integrated circuit comprising:

providing a first reference voltage from a first reference voltage source;

providing a second reference voltage from a second reference voltage source;

comparing the first reference voltage to the second reference voltage;

adjusting the first reference voltage in response to a difference between the first and second reference voltages; and

deactivating the second voltage reference source after a predetermined time.

17. The method of providing a reference voltage for an integrated circuit of claim 16, further comprising reactivating the second voltage reference source after a predetermined time so that the first reference voltage source can be readjusted.

18. The method of providing a reference voltage for an integrated circuit of claim 16, further comprising powering down circuit components comprising the second voltage reference source after the first reference voltage has been adjusted.

19. The method of providing a reference voltage for an integrated circuit of claim 18, wherein the duty cycle of operation of the powered down components is much shorter than the duty cycle of operation of the first voltage reference source.

20. A method of providing a reference voltage for a low power memory circuit comprising

providing a voltage reference;

adjusting a trimmable voltage reference source by comparing it to the voltage reference;

deactivating the voltage reference after the trimmable voltage reference source has been adjusted; and

using the trimmable voltage reference as a reference voltage in the low power memory circuit.

21. The method of providing a reference voltage for a memory circuit of claim 20 further comprising reactivating the voltage reference after a predetermined period so that the trimmable voltage reference source can be readjusted.

22. The method of providing a reference voltage for a memory circuit of claim 21 wherein the predetermined period is set by an astable circuit.

23. A system comprising:

a processor; and

a memory coupled to the processor, comprising;

a first voltage reference that is adjustable;

a second voltage reference;

a differential sensing device to compare a voltage provided by the first voltage reference to a voltage provided by the second voltage reference;

a controller to provide a trim control signal to the first voltage reference in response to an output of the differential sensing device for adjusting the first voltage reference and to provide a signal to power down the second voltage reference after the first voltage reference has been adjusted.

24. A reference voltage source for an integrated circuit comprising:

a first voltage reference that is adjustable;

a second voltage reference;

a differential sensing device to compare a voltage provided by the first voltage reference to a voltage provided by the second voltage reference;

a controller that provides a trim control signal to the first voltage reference and which sequences through states comprising;

a state to provide signals enabling circuit elements comprising the differential sensing device and second voltage reference;

a state to permit changes in the value of the digital trim control signal in response to signal comprising a signal from the second voltage source indicating that it has reached a predetermined output level, a signal from the first voltage reference that it is ready to be adjusted and a signal from the differential sensing device that a change is appropriate; and

a state to power down circuit components comprising the second voltage reference after the first voltage reference has been adjusted.

25. A memory circuit comprising:

a first voltage reference that is adjustable;

a second voltage reference;

a differential sensing device to compare a voltage provided by the first voltage reference to a voltage provided by the second voltage reference;

a controller to provide control signals to circuit elements comprising the first voltage reference, the second voltage reference, and the differential sensing device and which transitions through states comprising;

a state to enable circuit elements comprising the differential sensing device and second voltage reference;

a state to permit changes in the value of the first voltage reference in response to a signal from the differential sensing device;

a state to power down circuit elements comprising the second voltage reference after the first voltage reference has been adjusted.

26. A memory circuit comprising a first voltage reference that is periodically calibrated to a second voltage reference by a control circuit that periodically powers down the second voltage reference.

27. A memory circuit comprising:

a trimmable voltage reference;

a voltage reference that is set to a predetermined value;

a comparator to compare a voltage provided by the trimmable voltage reference to a voltage provided by the voltage reference that is set to a predetermined value;

a controller to provide a trim control signal to the trimmable voltage reference in response to an output of the comparator for adjusting the first voltage reference and to provide a signal to power down the a voltage reference that is set to a predetermined value after the first voltage reference has been adjusted.

28. A memory circuit, comprising:

a low current Vref generator to provide a trimmable Vref voltage;

a low voltage reference to provide a predetermined reference voltage;

a comparator to compare the Vref voltage to the predetermined reference voltage and to signal whether the value of the Vref signal is greater than or less than the value of the predetermined reference voltage;

a controller to provide a trim signal to the low current Vref generator in response to a signal from the comparator and to transition an enable signal to the low voltage reference after the trim signal has been provided.