Low-power potentiostat 2 nd Order CT ADC for ECS 1/26 A CMOS Potentiostatic Delta-Sigma for Electrochemical Sensors Joan Aymerich, Michele Dei, Lluís Teres and Francisco Serra-Graells joan.aymerich@imb-cnm.csic.es Integrated Circuits and Systems (ICAS) Instituto de Microelectrónica de Barcelona, IMB-CNM(CSIC) July 2018 J. Aymerich Gubern PRIME 2018
Low-power potentiostat 2 nd Order CT ADC for ECS 2/26 Sensors Market Vision Several organizations created visions for continued growth to trillion(s) sensors $15 trillion by 2022 Electrochemical sensors are growing 56%/year exponentially due to potential of Sensors/year 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 2018
Low-power potentiostat 2 nd Order CT ADC for ECS 3/26 1 Amperometric Electrochemical Sensors 2 Potentiostatic Modulator architecture Low-Power Circuit Implementation 3 4 0.18- CMOS Design Example 5 Conclusions J. Aymerich Gubern PRIME 2018
Low-power potentiostat 2 nd Order CT ADC for ECS 4/26 1 Amperometric Electrochemical Sensors 2 Potentiostatic Modulator architecture Low-Power Circuit Implementation 3 4 0.18- CMOS Design Example 5 Conclusions J. Aymerich Gubern PRIME 2018
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: Measurement independent of the R and C impedances. Current associated to the electrons involved in a redox process Electrochemical time constant: J. Aymerich Gubern PRIME 2018
Low-power potentiostat 2 nd Order CT ADC for ECS 5/26 Amperometric Electrochemical Sensors Di ff erent detection methods are required 1 1 0.7 0.6 0.5 Cyclic Voltammetry (CV) Oxidation 0.4 0.3 [A] 0.2 0.1 Sensor performance, 0.0 t [s] 0 0 rapid location of redox potentials, ... Sweeping electrode potential and measuring resulting current Reduction Potentiostat must sink/source current -1 -1 -1 0 1 1 1 2mM Chronoamperometry (CA) [A] 0.6mM 0.5mM 0.3mM 0.4mM fi xed and monitored as a 0.1mM 0.2mM function of time while concentration is swept 0 0 1 t [s] J. Aymerich Gubern PRIME 2018
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 2018
Low-power potentiostat 2 nd Order CT ADC for ECS 7/26 1 Amperometric Electrochemical Sensors 2 Potentiostatic Modulator architecture Low-Power Circuit Implementation 3 4 0.18- CMOS Design Example 5 Conclusions J. Aymerich Gubern PRIME 2018
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 2018
Low-power potentiostat 2 nd Order CT ADC for ECS 9/26 9/26 From electrochemical only to hybrid/mixed EC/electronic Electronic time constant Allows precise potentiostatic operation Tones and pattern noise suppression Feed-Forward through Stabilize the loop [5] J. Aymerich, M. Dei, L. Terés and F. Serra-Graells, ”Design of a Low-Power Potentiostatic Second-Order CT Delta-Sigma ADC for Electrochemical Sensors, ” 2017 13th Conference on Ph.D. Research in Microelectronics and Electronics (PRIME) J. Aymerich Gubern PRIME 2018
Low-power potentiostat 2 nd Order CT ADC for ECS 10/26 Improved architecture Direct path from Vr to input the single-bit quantizer Area and power consumption Low-power CMOS circuits Large fl exibility on the selection of potentiostatic voltage Wide common-mode voltage range J. Aymerich Gubern PRIME 2018
Low-power potentiostat 2 nd Order CT ADC for ECS 11/26 1 Amperometric Electrochemical Sensors 2 Potentiostatic Modulator architecture Low-Power Circuit Implementation 3 4 0.18- CMOS Design Example 5 Conclusions J. Aymerich Gubern PRIME 2018
12/26 Low-power potentiostat 2 nd Order CT ADC for ECS Improved architecture Direct path from Vr to input the single-bit quantizer Area and power consumption Low-power CMOS circuits Large fl exibility on the selection of potentiostatic voltage . Single-bit quantizer : Wide input common-mode voltage range Transconductance : Wide input/output common-mode voltage range J. Aymerich Gubern PRIME 2018
Low-power potentiostat 2 nd Order CT ADC for ECS 13/26 Single-bit quantizer Rail-to-rail complementary latch comparator High-input impedance Zero-static power consumption NMOS-input latch Combinational logic allows to merge both NMOS-PMOS-input comparators PMOS-input latch Comb. logic J. Aymerich Gubern PRIME 2018
Low-power potentiostat 2 nd Order CT ADC for ECS 14/26 Single-bit quantizer Rail-to-rail complementary latch comparator High-input impedance Zero-static power consumption Combinational logic allows to merge both NMOS-PMOS-input comparators PMOS OFF: Input common-mode > (Vdd-VTHp) Outp nodes remain at the negative rail regardless J. Aymerich Gubern PRIME 2018
Low-power potentiostat 2 nd Order CT ADC for ECS 15/26 Single-bit quantizer Rail-to-rail complementary latch comparator High-input impedance Zero-static power consumption Combinational logic allows to merge both NMOS-PMOS-input comparators PMOS OFF: Input common-mode > (Vdd-VTHp) Outp nodes remain at the negative rail regardless NMOS OFF: Input common-mode < (VTHn) Outn nodes remain at the positive rail regardless J. Aymerich Gubern PRIME 2018
Low-power potentiostat 2 nd Order CT ADC for ECS 16/26 From 1st order to 2nd order Improved architecture Direct path from Vr to input the single-bit quantizer Area and power consumption Low-power CMOS circuits Large fl exibility on the selection of potentiostatic voltage . Single-bit quantizer : Wide input common-mode voltage range Transconductance : Wide input/output common-mode voltage range J. Aymerich Gubern PRIME 2018
Low-power potentiostat 2 nd Order CT ADC for ECS 17/26 Gm-C Integrator Constant gm over the input common-mode voltage Avoid variations in the electronic integrator time constant M1 - M4 operated in weak inversion Sum of the tail currents constant Wide output swing Overdrive voltage J. Aymerich Gubern PRIME 2018
Low-power potentiostat 2 nd Order CT ADC for ECS 17/26 1 Amperometric Electrochemical Sensors 2 Potentiostatic Modulator architecture Low-Power Circuit Implementation 3 4 0.18- CMOS Design Example 5 Conclusions J. Aymerich Gubern PRIME 2018
Low-power potentiostat 2 nd Order CT ADC for ECS 18/26 Low-power 0.18- CMOS Design Gm-C integrator occupy most of the area to minimize o ff set , i.e potentiostatic error (Vr - Vpot) slow integrator time constant (sampling frequency @ 1kHz) Large Feedback DAC To minimize low-frequency noise . (DAC noise added directly to the input, it is not shaped by the delta-sigma loop- fi lter) Ongoing run XFAB-XH018 J. Aymerich Gubern PRIME 2018
Low-power potentiostat 2 nd Order CT ADC for ECS 19/26 Post-Layout Simulations Output spectrum comparison w/ and w/o electronic transient 40dB/dec 70-dB dynamic range for 1.25uA current full scale. (280pA RMS, noise) Higher resolution is achievable enlarging the area of the feedback DAC J. Aymerich Gubern PRIME 2018
Low-power potentiostat 2 nd Order CT ADC for ECS 20/26 23/26 Post-Layout Simulations 1.8 0.7 Cyclic Voltammetry 0.6 Vpot-Vref [V] 0.5 0.4 0.3 0.2 0.1 Triangular waveform is applied to the 0.0 reference electrode while the sensor t [s] 0.9 current is measured simultaneously VerilogA model : Vrw-Isens DC look-up tables based on two experimental measurements of ferricyanide CVs 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 V p o t - V r e f [ V ] Ferricyanide Cyclic Voltammetry J. Aymerich Gubern PRIME 2018
Low-power potentiostat 2 nd Order CT ADC for ECS 21/26 Simulation Results Performance simulation results Power consumption mainly determined by feedback current DAC Rest of circuit blocks J. Aymerich Gubern PRIME 2018
Low-power potentiostat 2 nd Order CT ADC for ECS 22/26 1 Amperometric Electrochemical Sensors 2 Potentiostatic Modulator architecture Low-Power Circuit Implementation 3 4 0.18- CMOS Design Example 5 Conclusions J. Aymerich Gubern PRIME 2018
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