11.4: A Fast-Readout Mismatch-Insensitive Magnetoresistive Biosensor Front-End Achieving Sub-ppm Sensitivity
© 2019 IEEE International Solid-State Circuits Conference 1 of 23
A Fast-Readout Mismatch-Insensitive Magnetoresistive Biosensor Front-End
Achieving Sub-ppm Sensitivity
Xiahan Zhou, Michael Sveiven, Drew A. Hall
University of California, San Diego, La Jolla, CA, USA
11.4: A Fast-Readout Mismatch-Insensitive Magnetoresistive Biosensor Front-End Achieving Sub-ppm Sensitivity
© 2019 IEEE International Solid-State Circuits Conference 2 of 23
Motivation: Point-of-Care (PoC) Devices
NEED: Accurate and fast diagnostic tests
Centralized Laboratory• Bulky instruments• Professional personnel required• Long turnaround time
Point-of-Care Devices• Small and portable• Easy operation• Near instant results
11.4: A Fast-Readout Mismatch-Insensitive Magnetoresistive Biosensor Front-End Achieving Sub-ppm Sensitivity
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Magnetic Immunoassay
Magnetic sensorHuman biological samples intrinsically lack magnetic background high sensitivity
11.4: A Fast-Readout Mismatch-Insensitive Magnetoresistive Biosensor Front-End Achieving Sub-ppm Sensitivity
© 2019 IEEE International Solid-State Circuits Conference 4 of 23
Giant Magnetoresistive (GMR) Sensor
Large baseline-to-signal ratio precludes high sensitivity detection
Problem: Wide dynamic range AFE is required to accommodate large R0/Rsig
11.4: A Fast-Readout Mismatch-Insensitive Magnetoresistive Biosensor Front-End Achieving Sub-ppm Sensitivity
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Conventional MR AFE Architectures
Problem:Sensor mismatch ∆R limits sensitivity
Problem:Fast transient signal requires fast-switching magnetic field and high speed ADC
11.4: A Fast-Readout Mismatch-Insensitive Magnetoresistive Biosensor Front-End Achieving Sub-ppm Sensitivity
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System Architecture
Problems Proposed SolutionsLarge baseline/signal Reference sensorHigh speed ADC required Down-modulator in PGASensor mismatch HFIR in ADC
11.4: A Fast-Readout Mismatch-Insensitive Magnetoresistive Biosensor Front-End Achieving Sub-ppm Sensitivity
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Double Modulation Scheme
Reference sensor rejects MR baseline
11.4: A Fast-Readout Mismatch-Insensitive Magnetoresistive Biosensor Front-End Achieving Sub-ppm Sensitivity
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Analog Front-End
Built-in down modulator relaxes speed requirement on ADC
11.4: A Fast-Readout Mismatch-Insensitive Magnetoresistive Biosensor Front-End Achieving Sub-ppm Sensitivity
© 2019 IEEE International Solid-State Circuits Conference 9 of 23
Sensor Mismatch
Sensor MR mismatch Residual baseline at DCSensor R0 mismatch Interference at fH
Sensor mismatch increases ADC dynamic range requirement
11.4: A Fast-Readout Mismatch-Insensitive Magnetoresistive Biosensor Front-End Achieving Sub-ppm Sensitivity
© 2019 IEEE International Solid-State Circuits Conference 10 of 23
High Frequency Interference Rejection
ADC applies HP feedforward method to realize a fast-settling LPF function
11.4: A Fast-Readout Mismatch-Insensitive Magnetoresistive Biosensor Front-End Achieving Sub-ppm Sensitivity
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High Frequency Interference Rejection
HFIR sampling technique rejects high frequency interference
11.4: A Fast-Readout Mismatch-Insensitive Magnetoresistive Biosensor Front-End Achieving Sub-ppm Sensitivity
© 2019 IEEE International Solid-State Circuits Conference 12 of 23
PGA Implementation
• Switches remain closed after sensor selection for 100µs provide a low impedance path for fast settling
• Switches revert to duty-cycled mode afterwards provide large bias resistance for low noise
11.4: A Fast-Readout Mismatch-Insensitive Magnetoresistive Biosensor Front-End Achieving Sub-ppm Sensitivity
© 2019 IEEE International Solid-State Circuits Conference 13 of 23
Fast Settling Duty-Cycle Resistor (DCR)
Fast settling DCR reduces the settling time by 40×
Measured transient waveforms
11.4: A Fast-Readout Mismatch-Insensitive Magnetoresistive Biosensor Front-End Achieving Sub-ppm Sensitivity
© 2019 IEEE International Solid-State Circuits Conference 14 of 23
Incremental ∆Σ ADC
OSR: 10,000BW: 100 Hz
11.4: A Fast-Readout Mismatch-Insensitive Magnetoresistive Biosensor Front-End Achieving Sub-ppm Sensitivity
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ADC Phase I
C4 samples signal at DCC6 samples OTA offset
11.4: A Fast-Readout Mismatch-Insensitive Magnetoresistive Biosensor Front-End Achieving Sub-ppm Sensitivity
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ADC Phase II
φscr and φchop change at the beginning of Phase II Allow maximum time for settling
11.4: A Fast-Readout Mismatch-Insensitive Magnetoresistive Biosensor Front-End Achieving Sub-ppm Sensitivity
© 2019 IEEE International Solid-State Circuits Conference 17 of 23
Die Photo and Power Breakdown
TSMC 180nm CMOS process
Total power: 1.39 mW
11.4: A Fast-Readout Mismatch-Insensitive Magnetoresistive Biosensor Front-End Achieving Sub-ppm Sensitivity
© 2019 IEEE International Solid-State Circuits Conference 18 of 23
Measurement Results: ADC
HFIR improves ADC DR significantly when sensor mismatch > 2%
11.4: A Fast-Readout Mismatch-Insensitive Magnetoresistive Biosensor Front-End Achieving Sub-ppm Sensitivity
© 2019 IEEE International Solid-State Circuits Conference 19 of 23
Measurement Results: System
The system achieves 0.98ppm (147μΩ) sensitivity with a readout time of 880ms
11.4: A Fast-Readout Mismatch-Insensitive Magnetoresistive Biosensor Front-End Achieving Sub-ppm Sensitivity
© 2019 IEEE International Solid-State Circuits Conference 20 of 23
Measurement Results: BioAssay
11.4: A Fast-Readout Mismatch-Insensitive Magnetoresistive Biosensor Front-End Achieving Sub-ppm Sensitivity
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Summary and Comparison
The chip achieves 22.7× faster readout time, >7.8× lower baseline, and 2.3× lower power than other GMR sensor-based designs
11.4: A Fast-Readout Mismatch-Insensitive Magnetoresistive Biosensor Front-End Achieving Sub-ppm Sensitivity
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Conclusion
• Magnetic sensors are a promising candidate for PoC biosensing; however they suffer form large baseline/signal and sensor mismatch
• To address this we: Used reference sensors to reduce baseline Designed an integrated down-modulator to relax the ADC bandwidth
requirement Proposed a HFIR sampling technique to tolerate sensor mismatch Designed a fast settling duty-cycle resistor to improve readout time
• Result: A design that achieves sub-ppm sensitivity and tolerates 10% sensor mismatch
11.4: A Fast-Readout Mismatch-Insensitive Magnetoresistive Biosensor Front-End Achieving Sub-ppm Sensitivity
© 2019 IEEE International Solid-State Circuits Conference 23 of 23
Acknowledgement
• This work was supported in part by Qualcomm, Inc. and the National Science Foundation under grant No. ECCS-1454608
• The authors would like to thank MagArray, Inc. for providing the GMR sensors
Thank you for your attention