Magnetic sensor array having an analog frequency-division multiplexed output

• US 20050258821A1
• Filed: 05/11/2005
• Published: 11/24/2005
• Est. Priority Date: 05/12/2004
• Status: Active Grant

• Current Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford Management Co.)
• Original Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford Management Co.)
• Inventors: Han, Shu-Jen, Wang, Shan X.
• Granted Patent: US 7,939,338 B2
• Time in Patent Office: Days
• US Class Current: 324/200
• CPC Class Codes: B82Y 25/00 Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
• CPC Class Codes: G01N 33/5438 Electrodes
• CPC Class Codes: G01R 33/09 Magnetoresistive devices
• CPC Class Codes: G01R 33/093 using multilayer structures, e.g. giant magnetoresistance sensors thin magnetic films H01F10/00
• CPC Class Codes: G01R 33/12 Measuring magnetic properties of articles or specimens of solids or fluids involving magnetic resonance G01R33/20
• CPC Class Codes: G01R 33/1269 of molecules labeled with magnetic beads magnetic particles for bio assay G01N33/54326
• CPC Class Codes: Y10T 436/13 Tracers or tags

Abstract

A magnetic sensor array including magnetoresistive sensor elements having outputs combined by frequency division multiplexing (FDM) is provided. Each sensor element provides an input to a mixer which provides a distinct frequency shift. Preferably, time division multiplexing is also used to combine sensor element outputs. Each sensor element is typically in proximity to a corresponding sample. The sensor elements are preferably subarrays having row and column addressable sensor element pixels. This arrangement provides multiple sensor pixels for each sample under test. Multiplexing of sensor element outputs advantageously reduces readout time. A modulated external magnetic field is preferably applied during operation, to reduce the effect of 1/f noise on the sensor element signals. The effect of electromagnetic interference (EMI) induced by the magnetic field on sensor element signals is advantageously reduced by the mixing required for FDM.

Claims

1. A sensor for sensing a magnetically tagged sample, the sensor comprising:

a) two or more sensor subassemblies, each sensor subassembly including;

i) a magnetoresistive (MR) sensor element providing a sensor element signal responsive to the sample; and

ii) a mixer receiving the sensor element signal and providing a frequency shifted sensor element signal;

wherein each of the mixers provides a distinct frequency shift; and

b) an output summing junction providing a combined output signal proportional to a sum of the frequency shifted sensor element signals.

2. The sensor of claim 1, wherein said sample comprises a biological sample selected from the group consisting of oligomer samples, DNA samples, RNA samples, proteins, peptides, antibodies, antigens, lipids, and viruses.

3. The sensor of claim 1, wherein said sample comprises a chemical sample selected from the group consisting of polymers, toxins, pharmaceutical compounds, biohazardous compounds and explosive compounds.

4. The sensor of claim 1, wherein said sensor is fabricated in part with BiCMOS technology.

5. The sensor of claim 1,

wherein each of said MR sensor elements includes an MR device, an output transistor and a sensor transistor,

wherein the sensor transistor is connected to the MR device,

wherein the output transistor has a source-follower relation to the sensor transistor and provides said sensor element signal.

6. The sensor of claim 5, wherein each of said MR sensor elements does not include any transistors other than said output transistor and said sensor transistor.

7. The sensor of claim 1, wherein each of said MR sensor elements comprises a voltage controlled current source providing current to an MR device.

8. The sensor of claim 1, wherein each of said MR sensor elements comprises a subarray of MR sensor element pixels addressable by a row decoder and a column decoder.

9. The sensor of claim 1, wherein each of said mixers comprises a double-balanced, passive CMOS mixer.

10. The sensor of claim 1, wherein each of said subassemblies further includes an amplifier receiving said frequency shifted sensor element signal and providing an amplified sensor element signal to said summing junction.

11. The sensor of claim 1, wherein each of said subassemblies further includes a reference MR sensor element providing a reference signal received by said mixer, and wherein each of said mixers provides an output responsive to a difference of its two inputs.

12. The sensor of claim 1, further comprising a signal processor receiving said combined output signal.

13. The sensor of claim 12, wherein phase-sensitive detection of said frequency shifted sensor element signals within said combined output signal is performed by said signal processor.

14. The sensor of claim 1, wherein each of said sensor subassemblies further comprises a molecular probe coating on said magnetoresistive sensor element.

15. The sensor of claim 14, wherein each of said molecular probe coatings binds to the same molecular species.

16. The sensor of claim 14, wherein said molecular probe coatings bind to two or more different molecular species.

17. The sensor of claim 14, wherein said molecular probe coatings are only present on active areas of said magnetoresistive sensor elements.

18. A sensor array comprising:

two or more of the sensors of claim 1;

a multiplexer receiving each of said combined output signals and providing a multiplexer output signal;

wherein the multiplexer output signal is related to said combined output signals by time-division multiplexing.

19. The sensor of claim 18, wherein each of said MR sensor elements comprises a subarray of MR sensor element pixels addressable by a row decoder and a column decoder.

20. A method for sensing a magnetically tagged sample, the method comprising:

a) providing two or more sensor subassemblies, each sensor subassembly including;

i) a magnetoresistive (MR) sensor element providing a sensor element signal responsive to the sample; and

ii) a mixer receiving the sensor element signal and providing a frequency shifted sensor element signal;

wherein each of the mixers provides a distinct frequency shift; and

b) providing a combined output signal proportional to a sum of the frequency shifted sensor element signals.

21. The method of claim 20, further comprising applying an external magnetic field to said magnetically tagged sample.

22. The method of claim 20, wherein said external magnetic field is modulated at a modulation frequency f_B, whereby each of said sensor element signals is modulated at f_B.

23. The method of claim 20, wherein said MR sensor elements are driven by an electrical signal modulated at a modulation frequency f_A, whereby each of said sensor element signals is modulated at f_A.