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Circuits à capacités commutées et microsystèmes

Circuits à capacités commutées et microsystèmes. Nicolas Delorme, ndelorme@cea.fr Cyril Condemine, ccondemine@cea.fr Marc Belleville, mbelleville@cea.fr. Outline. Introduction State-of-the-art in capacitance sensing Sensor interfaces at LETI NEMS-induced (r)evolutions Concluding remarks.

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Circuits à capacités commutées et microsystèmes

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  1. Circuits à capacités commutées et microsystèmes Nicolas Delorme, ndelorme@cea.fr Cyril Condemine, ccondemine@cea.fr Marc Belleville, mbelleville@cea.fr

  2. Outline • Introduction • State-of-the-art in capacitance sensing • Sensor interfaces at LETI • NEMS-induced (r)evolutions • Concluding remarks Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  3. Microsystem? Non-volatile memory Antenne antenna Sensors Sensor/actuator Interface ADC/DAC Digital processing RF Power management Security management antenna Antenne Actuators Energy sources • Sensor/Actuator with interface IC • A/D, D/A conversion • Digital processing • Communication • Energy management • Security management …in a small volume! Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  4. Our lab methodology • « Top-down » approach • Analytical models • Linear & non-linear • Control theory tools • Systems engineering • Circuit • Signal & noise • parameters • Building blocks • specifications • IC technology • High-level modelling • Identification • Compensator optimization • (e.g. Matlab) • Feedback • Electrical engineering • Test methodology • Behavioral (VHDL-AMS, Verilog-A) • RTL / Gate-level (VHDL, Verilog) • Transistor-level (Eldo, Spice) • (e.g. ADMS) • Adjustments • Test engineering • Test • equipment • Analog • Digital • Mixed-signal • +MEMS and E source • Testability Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  5. Context 100 W 100 W 100 W • Why low-power? • Handheld, Autonomous sensor nodes… • Environment protection • Available energy sources • Batteries • Energy scavenging 10 W 10 W 10 W Desktop mP Laptop mP 1 W 1 W 1 W GSM GSM 100 mW 100 mW 100 mW MP3 player, Palm 10 mW 10 mW 10 mW Bluetooth Transceiver 1 mW 1 mW 1 mW Miniature FM receiver m m m 100 100 100 W W W Ear implant m m m 10 10 10 W W W RFID tag m m m 1 1 1 W W W Digital wristwatch 100 nW 100 nW 100 nW Crystal oscillator 32 kHz 10 nW 10 nW 10 nW Standby Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  6. Outline • Introduction • State-of-the-art in capacitance sensing • Sensor interfaces at LETI • NEMS-induced (r)evolutions • Concluding remarks Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  7. Review of circuit techniques (1/3) SC=Switched-Capacitor CT=Continuous-TIme • After Wu et. Al., JSSC, May 2004 • Power? Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  8. Review of circuit techniques (2/3) • After Yazdi et. Al. « Precision readout circuits for capacitive microaccelerometers », IEEE 2004 Switched-cap AC bridge Transimpedance amp. Switched-cap+CDS Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  9. Review of circuit techniques (3/3) • Power? • Ease of implementation? • Choice in prospect of co-integration Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  10. Outline • Introduction • State-of-the-art in capacitance sensing • Sensor interfaces at LETI • NEMS-induced (r)evolutions • Concluding remarks Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  11. Our lab approach • Sigma-delta-based • Low bandwidth / high resolution • High performance withmodest analog • Well suited to capacitive MEMS • MEMS embedded in circuit architecture • Lower power • Lower noise Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  12. Open-loop interfaces Test RFID Digital filter Sensor Antenna SD • RFID pressure sensor • 0.6 mm/3.3V CMOS • Full on-chip digital filter (decimator) • Extrapolation to Vdd=1v, 130nm: • 30mW  ~500nW (V210, C6) SD capacitive sensor interface+ADC 12bits @BW=100Hz 2mA @3.3V (RFID) 150mA @3.3V (SD) 10mA @3.3V (Digital) Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  13. Readout SD • Power reduction? After Temes et. Al., ISCAS’98 ref ref Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  14. SD performance w.r.t. opamp BW & SR • 2nd-order SD simulation,sampling T=1.5e-7s (F=6.4MHz) SNDR (dB) Opamp slew rate (x107V/s) Opamp settling time (x10-8 s)  Optimization margins in opamp bias currents Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  15. Interface power optimization SD sampling instants • Time-dependant power & noise control • Made possible by event knowledge Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  16. Interface power optimization • ? • Step further = Passive SD IntegratedR&C Block diagram Continuous-time 2nd-order SD ADC (voltage input) 9bits @ BW=40KHz 15mA @ 3.3V (measured, core) • R • In+ • R • R • CLK • C • C • out • C • C • R • In- • R • R Active area • See also TI, ISSCC’04 (switched-cap) Performance summary Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  17. Interface power optimization Test caps Interface+ADC core • Passive SD applied to capacitive sensor interface Continuous-time 2nd-order SD capacitive sensor interface+ADC Core<Pad opening! 14bits @ BW=100Hz 1mA @ 3.3V (expected) Expected performance summary Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  18. Closed-loop acceleration measurement • Dynamic range: +/-2g & +/-10g • Résolution (SNR+THD) = 15 bits over [0-100Hz] After C. Condemine et. Al., ISSCC’05 Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  19. Readout & actuation SD • Front end: LETI patent Back end after Temes et. Al., ISCAS’98 Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  20. Readout & actuation SD Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  21. Closed-loop controller • 32-bit controller coefficients • Fully programmable • Coefficient design carried out with Laboratoire d’Automatique de Grenoble (LAG) Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  22. Summary • 15-bit SNR @50Hzclosed-loop capacitive accelerometer, 0.35mm CMOS • Better than 16-bit linearity • Extensive use of LP techniques: • Analog current reduction • Analog activity windows • Digital gated clock • Digital level adaptation • All @3.3V, Iana=150mA, Idig=0.65mA • Digital @2.1V, Analog windowed  Power 2 Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  23. Our lab roadmap 2 ( * ) × × D R BW 4kT OM = - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - F - - - - - - - - - Power 10000 1000 (*) ref. Sansen W. Digital output  100   Analog output  10 Commercial circuits  Research circuits 1 LETI Brigati (Pavia)   0.1  Figure of Merit Kulah (Michigan) 0.01  Lang (kaiserslautern) ST/lis3l02a    ST/lis2l02a VTI 0.001   ADXL150   Lemkin (Berkeley) Yazdi (Michigan) 0.0001  ADXL202  ST/lis3l02d 1e-05  ST/lis2l01 1998 1999 2000 2001 2002 2003 2004 1997 1996 2005 2006 Year • Capacitive sensor interface performance Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  24. Outline • Introduction • State-of-the-art in capacitance sensing • Sensor interfaces at LETI • NEMS-induced (r)evolutions • Concluding remarks Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  25. XG « thin SOI » accelerometers (Transparent retiré intentionnellement) Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  26. Application to MIMOSA accelerometer • Use of a LETI-designed SC SD circuit (readout+ADC)(in short: coarse but fast comparison of sensor charge to a reference charge + error reduction by integration) • Top-level Simulink model: Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  27. Simulation setup – Sensor model Vread=0.1V Vread=0V N u m b e r o f t e e t h : n N u m b e r o f t e e t h : n l m L m N u m b e r o f t e e t h : n N u m b e r o f t e e t h : n • 2nd-order differential eq. with: • Feedback non-linearities • Non-linear damping Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  28. Simulation setup – Electronics model • Electronic imperfections: • kT/C noise • OTA noise & non-linearity • Comparator offset Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  29. Simulation setup – existing electronics • Switched-cap Sigma-delta based • Problems to expect: • Low C0 & DC (reliable small caps difficult to integrate) • Low pull-in voltage  Low signal  subject to glitches(only if high mechanical Fc) Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  30. Results • Without Casimir forces • C0=7.2fF, DC=70aF/g • All integrated caps=100fF • Readout voltage=200mV • Input=40g@67Hz • Noise floor=-70dB@BW=100Hz • SNR=33dB@BW=100Hz • THD=-30dB Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  31. Results • Circuit parameter variations around nominal 0.01 vmux_vs_ccfbcm.dat vmux_vs_cfbsd.dat Unrealistic integrated capacitance zone vmux_vs_gmotad.dat vmux_vs_idotad.dat Input-referred noise (Vrms) 0.001 + + + Previous Matlab simulation Higher power 0.0001 1e-16 1e-14 1e-12 1e-10 1e-08 1e-06 0.0001 0.01 1 100 Parameter Value (Ccfbcm (F), Cfbsd (F), gmotad (A/V), idotad (normalized w.r.t. nominal)) Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  32. Capacitive resonant cantilever (1/2) • Cantilever, 40µmx0.8µmx0.6µm • Capacitive detection, Cs=40aF, Cp=0.2fF, Cpa=40fF, Ls=700H, Rs=80MW, DCmax=40aF • Motional current: few nA • After Verd et. Al., IEEE J. MEMS, June 2005 Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  33. Capacitive resonant cantilever (2/2) • Readout circuit: motional current integrated on parasitic capacitance • After Verd et. Al., IEEE J. MEMS, June 2005 Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  34. Concluding remarks • Several approaches possible for capacitance sensing • SD readout well suited to low power with high resolution • Passive approach benefits? • Other than sigma-delta also good LP candidates • Choice between SC and CT depends on Cs0 and Cparasitic • A lot to gain from co-integrated NEMS (low Cs0 and Cparasitic)  AC bridge preferred? • New « active » detection principles would relax noise constraints (higher signal) • Transistor detection • Tunnel effect • … Circuits à capacités commutées et microsystèmes N. Delorme, Club EEA 2005

  35. Thank you for your attention

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