# US 8,787,098 B2 · System and method of reference cell testing

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- Number: US 8,787,098 B2
- Document ID: US8787098B2
- Status: Granted
- Kind: B2
- Application number: 13/778,173
- Filed: 2013-02-27
- Published: 2013-07-11
- Granted: 2014-07-22
- Earliest claimed: 2010-08-23
- Assignees: QUALCOMM Incorporated
- Applicants: QUALCOMM Incorporated
- Inventors: Jung Pill Kim; Taehyun Kim; Hari M. Rao
- Web page: https://patentgrep.com/patent/US8787098B2

## CPC

- G11C 7/062: {Differential amplifiers of non-latching type, e.g. comparators, long-tailed pairs}
- G06F 30/00: Computer-aided design [CAD]
- G11C 11/16: using elements in which the storage effect is based on magnetic spin effect
- G11C 29/24: Accessing extra cells, e.g. dummy cells or redundant cells
- G11C: STATIC STORES (semiconductor memory devices H10B)
- G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N)

## Abstract

Systems and methods of testing a reference cell in a memory array are disclosed. In a particular embodiment, a method includes coupling a first reference cell of a first reference cell pair of a memory array to a first input of a first sense amplifier of the memory array. The method also includes providing a reference signal to a second input of the first sense amplifier. The reference signal is associated with a second reference cell pair of the memory array.

## Claims

### Claim 1

A method comprising:
coupling a first reference cell of a first reference cell pair of a memory array to a first input of a first sense amplifier of the memory array; and
providing a reference signal to a second input of the first sense amplifier, wherein the reference signal is associated with a second reference cell pair of the memory array.

### Claim 2 (depends on 1)

The method of claim 1, wherein the first sense amplifier includes comparator circuitry configured to output a comparator output value that is based on a first signal received at the first input of the first sense amplifier and upon a second signal received at the second input of the first sense amplifier.

### Claim 3 (depends on 1)

The method of claim 1, further comprising after coupling the first reference cell to the first input of the first sense amplifier and providing the reference signal to the second input of the first sense amplifier, determining whether the first reference cell is functional by comparing an output of the first sense amplifier to a first threshold.

### Claim 4 (depends on 3)

The method of claim 3, further comprising when the first reference cell is determined to be non-functional, replacing use of the first reference cell in the memory array with use of a redundant reference cell of the memory array.

### Claim 5 (depends on 3)

The method of claim 3, further comprising:
coupling a second reference cell of the first reference cell pair to a first input of a second sense amplifier of the memory array;
providing a second reference signal to a second input of the second sense amplifier; and
substantially simultaneously with determining whether the first reference cell is functional, determining whether the second reference cell is functional by comparing an output of the second sense amplifier to a second threshold.

### Claim 6 (depends on 1)

The method of claim 1, wherein the first reference cell pair comprises a first pair of dedicated reference cells, and wherein the second reference cell pair comprises a second pair of dedicated reference cells.

### Claim 7 (depends on 1)

The method of claim 1, wherein the first reference cell pair comprises a first pair of memory cells coupled to a first dedicated reference word line, and wherein the second reference cell pair comprises a second pair of memory cells coupled to a second dedicated reference word line.

### Claim 8 (depends on 1)

The method of claim 1, further comprising, after coupling the first reference cell to the first input of the first sense amplifier and providing the reference signal to the second input of the first sense amplifier, measuring a first output of the first sense amplifier.

### Claim 9 (depends on 8)

The method of claim 8, further comprising:
decoupling the first reference cell from the first input of the first sense amplifier;
coupling a second reference cell of the first reference cell pair of the memory array to the first input of the first sense amplifier; and measuring a second output of the first sense amplifier.

### Claim 10 (depends on 1)

The method of claim 1, wherein the first input is used as a data input or a reference input during a read operation of a memory cell of the memory array.

### Claim 11 (depends on 1)

The method of claim 1, wherein the second input is used as a reference input during a read operation of a memory cell of the memory array.

### Claim 12 (depends on 1)

The method of claim 1, further comprising activating a switch to selectively couple the first reference cell to the first input.

### Claim 13 (depends on 1)

The method of claim 1, wherein the memory array is a magnetic random access memory (MRAM) array.

### Claim 14 (depends on 1)

The method of claim 1, wherein coupling the first reference cell to the first input of the first sense amplifier and providing the reference signal to the second input of the first sense amplifier are performed at a processor integrated into an electronic device.

### Claim 15

A method of comprising:
a first step for coupling a first reference cell of a first reference cell pair of a memory array to a first input of a first sense amplifier of the memory array; and
a second step for providing a reference signal to a second input of the first sense amplifier, wherein the reference signal is associated with a second reference cell pair of the memory array.

### Claim 16 (depends on 15)

The method of claim 15, further comprising:
a third step for determining whether the first reference cell is functional by comparing an output of the first sense amplifier to a first threshold after coupling the first reference cell to the first input of the first sense amplifier and providing the reference signal to the second input of the first sense amplifier.

### Claim 17 (depends on 16)

The method of claim 16, further comprising:
a fourth step for replacing use of the first reference cell in the memory array with use of a redundant reference cell of the memory array when the first reference cell is determined to be non-functional.

### Claim 18 (depends on 15)

The method of claim 15, wherein the first step and second step are performed by a processor integrated into an electronic device.

### Claim 19

A method comprising:
receiving a data file comprising design information corresponding to a semiconductor device; and
fabricating the semiconductor device according to the design information, wherein the semiconductor device comprises:
a sense amplifier within a memory array, the sense amplifier operable to test a first reference cell of the memory array, the sense amplifier comprising:
a data input to receive a first signal from the first reference cell;
a reference input to receive a second signal from a reference source, wherein the reference source is a second reference cell pair of the memory array; and
comparator circuitry to output a comparator output value that is based on the first signal received at the data input and upon the second signal received at the reference input; and
switching circuitry that is operable to reversibly couple the first reference cell to the data input.

### Claim 20 (depends on 19)

The method of claim 19, wherein the data file includes a GDSII format.

### Claim 21 (depends on 19)

The method of claim 19, wherein the data file includes a GERBER format.