Low-power potentiostat 2 nd Order CT ADC for ECS 1/26 Design of a Low-Power Potentiostatic Second-Order CT Delta-Sigma ADC for Electrochemical Sensors Joan Aymerich Gubern joan.aymerich@imb-cnm.csic.es Integrated Circuits and Systems (ICAS) Instituto de Microelectrónica de Barcelona, IMB-CNM(CSIC) June 2017 J. Aymerich Gubern PRIME 2017
Low-power potentiostat 2 nd Order CT ADC for ECS 2/26 Trillion-Sensor Vision Several organizations created visions for continued growth to trillion(s) sensors $15 trillion by 2022 Electrochemical sensors are growing r a e y / Sensors/year % 6 exponentially due to potential of 5 miniaturization and mass production 21%/year Monolithic or hybrid integration 222%/year onto CMOS platforms Applications in biosensors, quality control, ... Year Expected sensor production growth per year www.tsensorssummit.org J. Aymerich Gubern PRIME 2017
Low-power potentiostat 2 nd Order CT ADC for ECS 3/26 1 Amperometric Electrochemical Sensors 2 Potentiostatic Modulator architecture Proposed architecture 3 4 Design methodology and trade-o ff s 5 Conclusions J. Aymerich Gubern PRIME 2017
Low-power potentiostat 2 nd Order CT ADC for ECS 4/26 1 Amperometric Electrochemical Sensors 2 Potentiostatic Modulator architecture Proposed architecture 3 4 Design methodology and trade-o ff s 5 Conclusions J. Aymerich Gubern PRIME 2017
Low-power potentiostat 2 nd Order CT ADC for ECS 5/26 Amperometric Electrochemical Sensors Interaction with microorganisms Interaction with microorganisms Selectivity by functionalization Reduced speed and life time Potentiostatic and amperometric operations Three electrodes: Electrochemical time constant: Measurement independent of the R and C impedances. Rct = charge-transfer resistance Cdl = double-layer capacitance J. Aymerich Gubern PRIME 2017
Low-power potentiostat 2 nd Order CT ADC for ECS 6/26 Classic circuit implementation Potentiostat A 1 establishes the control loop to accomplish potentiostat operation & Amperometry A 2 converts sensor current to voltage for digitization and readout Requires multiples OpAmps + ADC Large area and power consumption J. Aymerich Gubern PRIME 2017
Low-power potentiostat 2 nd Order CT ADC for ECS 7/26 1 Amperometric Electrochemical Sensors 2 Potentiostatic Modulator architecture Proposed architecture 3 Design methodology and trade-o ff s 4 5 Conclusions J. Aymerich Gubern PRIME 2017
Low-power potentiostat 2 nd Order CT ADC for ECS 8/26 Potentiostatic Behaviour similar to low-pass fi rst-order single-bit CT A/D modulator Error current converted into voltage and shaped in frequency by the electrochemical sensor itself High oversampling ratios ( OSR>100 ) can be easly obtained with kHz-range clock frequencies f S Amperometric read-out through the modulation of output bit stream by chemical input J. Aymerich Gubern PRIME 2017
Low-power potentiostat 2 nd Order CT ADC for ECS 9/26 Potentiostatic Behaviour similar to low-pass fi rst-order single-bit CT A/D modulator Error current converted into voltage and shaped in frequency by the electrochemical sensor itself High oversampling ratios ( OSR>100 ) Electrochemical can be easly obtained with kHz-range sensor clock frequencies f S Amperometric read-out through the modulation of output bit stream by chemical input Monolithic CMOS integration Inexpensive 2.5 in-house CMOS technology (CNM25) developed by ICAS group at IMB-CNM(CSIC) Potentiostatic J. Aymerich Gubern PRIME 2017
Low-power potentiostat 2 nd Order CT ADC for ECS 10/26 Potentiostatic Quantizer Typical tonal component of 1 st order Typical tonal component of Quantization error and input signal correlation Electrochemical sensor Potentiostat operation not well-de fi ned Potentiostatic error in fl uenced by the input signal J. Aymerich Gubern PRIME 2017
Low-power potentiostat 2 nd Order CT ADC for ECS 11/26 1 Amperometric Electrochemical Sensors 2 Potentiostatic Modulator architecture Proposed architecture 3 4 Design methodology and trade-o ff s 5 Conclusions J. Aymerich Gubern PRIME 2017
Low-power potentiostat 2 nd Order CT ADC for ECS 12/26 Proposed amperometric potentiostatic M Incremental work: Addition of electronic integration Higher resolution: 2 nd order noise shaping Idle tones attenuation Potentiostatic operation well-de fi ned Electronic integrator forces New design trade-o ff s! Stability compensation is required A zero must be added in the loop fi lter to compensate the phase shift J. Aymerich Gubern PRIME 2017
Low-power potentiostat 2 nd Order CT ADC for ECS 13/26 Stability compensation Distributed FeedBack Topology High frequency path Loop Filter Zero frequency location J. Aymerich Gubern PRIME 2017
Low-power potentiostat 2 nd Order CT ADC for ECS 14/26 8/15 Stability compensation Distributed FeedBack Topology Loop fi lter gain [dB] Loop Filter (s) Frequency [Hz] Loop Filter Zero frequency location f Z depends on sensor time constant f Z Leading to instability!! J. Aymerich Gubern PRIME 2017
Low-power potentiostat 2 nd Order CT ADC for ECS 15/26 8/15 Stability compensation Distributed FeedBack Topology Loop fi lter gain [dB] Loop Filter (s) Frequency [Hz] Loop Filter Zero frequency location 0.025 0.02 Distributed feedback 1 st Order 0.015 0.01 0.005 f Z depends on sensor time constant 0 f Z Leading to unstability!! -0.005 -0.01 Potentiostatic voltage strongly -0.015 in fl uenced by the sensor input signal -0.02 -0.025 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 DC Input [Full Scale] J. Aymerich Gubern PRIME 2017
Low-power potentiostat 2 nd Order CT ADC for ECS 16/26 Stability compensation 1 5 Feed-Forward Topology Loop gain [dB] High frequency path - 3 - 2 - 1 0 1 2 3 4 5 10 10 10 10 10 10 10 10 Frequency [Hz] Loop Filter Zero frequency location Variations in the sensor time constant do not compromise the stability of the system! J. Aymerich Gubern PRIME 2017
Low-power potentiostat 2 nd Order CT ADC for ECS 17/26 Stability compensation 1 5 Feed-Forward Topology Loop gain [dB] Loop Filter (s) - 3 - 2 - 1 0 1 2 3 4 5 10 10 10 10 10 10 10 10 Frequency [Hz] Loop Filter Zero frequency location 0.025 0.02 Distributed feedback Feedforward 0.015 1 st order 0.01 Variations in the sensor time constant 0.005 do not compromise the stability of the system! 0 -0.005 -0.01 Electronic integrator forces its input -0.015 to have DC zero component . -0.02 -0.025 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 DC Input [Full Scale] J. Aymerich Gubern PRIME 2017
Low-power potentiostat 2 nd Order CT ADC for ECS 18/26 1 Amperometric Electrochemical Sensors 2 Potentiostatic Modulator architecture 3 Proposed architecture 4 Design methodology and trade-o ff s 5 Conclusions J. Aymerich Gubern PRIME 2017
Low-power potentiostat 2 nd Order CT ADC for ECS 19/26 Small-Signal Stability Analysis 0.6 (a) Linear model (b) 0.4 (a)(b)(c) (c) Real axis poles location / fs 0.2 Quantizer Gain 0 -0.2 DAC Linear model -0.4 Stability region as a function of f Z /f S 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 Root locus analysis: Closed-loop poles moves as quantizer gain changes Stability condition: J. Aymerich Gubern PRIME 2017
Low-power potentiostat 2 nd Order CT ADC for ECS 20/26 Small-Signal Stability Analysis 0.6 (a) Linear model (b) 0.4 (c) (a)(b)(c) Real axis poles location / fs 0.2 Quantizer Gain 0 -0.2 DAC Linear model -0.4 Stability region as a function of f Z /f S 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 Root locus analysis: Closed-loop poles moves as quantizer gain changes Stability condition: Power Spectrum as function of zero location (More 1 st order behaviour) Less safety stability margin Better noise shaping J. Aymerich Gubern PRIME 2017
Low-power potentiostat 2 nd Order CT ADC for ECS 21/26 Potentiostat Voltage Ripple Voltage ripple may be required to be kept below certain minimum Feedback current DAC (I FS ) charges/discharges Cdl T S is the only degree of freedom to minimize ripple ( C dl and I FS are fi xed by the application) J. Aymerich Gubern PRIME 2017
Low-power potentiostat 2 nd Order CT ADC for ECS 22/26 SQNR vs input signal Top-level simulation J. Aymerich Gubern PRIME 2017
Low-power potentiostat 2 nd Order CT ADC for ECS 23/26 Low-power circuit implementation Flexible and modular to be mapped into di ff erent CMOS technologies Electronic integrator: Gm 1 -C 1 Feed-Forward path Latch comparator for 1-bit quantization D-type fl ip- fl op for S/H Feedback current DAC Power consumption mainly determined by current DAC FS, allowing chemical reaction take place J. Aymerich Gubern PRIME 2017
Low-power potentiostat 2 nd Order CT ADC for ECS 24/26 Simulation Results CMOS technology Performance simulation results Power consumption mainly determined by current DAC FS Rest of circuit blocks Cyclic Voltammetry Method for studying electrochemical reactions Triangular waveform is applied to the R eference-electrode, while the sensor current is measured simultaneously. VerilogA model Ferrocyanide Cyclic Voltammetry J. Aymerich Gubern PRIME 2017
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