A 72- W 90-dB Wide-Range Potentiostatic CMOS Modulator ...pserra/cnm/2019 - A 72-uW 90-dB Wide-Range Potenti… · 72- W 90-dB Wide-Range Potentiostatic Modulator J. Aymerich Gubern

72- W 90-dB Wide-Range Potentiostatic Modulator

J. Aymerich Gubern

A 72- W 90-dB Wide-Range Potentiostatic CMOS Modulator with Flicker Noise Cancellation

for Smart Electrochemical Sensors

J. Aymerich1, M. Dei1, L. Terés1,2, F. Serra-Graells1,2

1/22

[email protected]

May 2019

1Instituto de Microelectrónica de Barcelona, IMB-CNM(CSIC), Spain2Universitat Autònoma de Barcelona, Spain


J. Aymerich Gubern

Sensors Maket Vision

Sensors/year

Year

56%/year

21%/yea

r

222%/year

Electrochemical sensors are growing exponentially due to potential of miniaturization and mass production

2/22

Several organizations created visionsfor continued growth to trillion(s) sensors

Applications in biosensors, quality control, health care, ...

Expected sensor production growth per year

$15 trillion by 2022

www.eenewsanalog.com

Monolithic or hybrid integrationonto CMOS platforms


J. Aymerich Gubern

3/22

1 Amperometric Electrochemical Sensors

Conclusions

2 Potentiostatic Modulator architecture

3

4

5

Proposed wide-range potentiostat with 1/f noise cancellation

0.18- CMOS Design and Post-Layout simulations


J. Aymerich Gubern

4/22

Amperometric Electrochemical Sensors

Electrochemical time constant:

Measurement independent of the R and C impedances.

Three electrodes:

Interaction with microorganismsInteraction with microorganisms.Selectivity by functionalization.

Reduced speed and life time.Potentiostatic and amperometric operations.

Current associated to the electronsinvolved in a redox process:

Linear model


J. Aymerich Gubern

Classic circuit implementation

A1 establishes the control loop toaccomplish potentiostat operation.

&

Requires multiples OpAmps + ADC.

A2 converts sensor current to voltage for digitization and readout.

Potentiostat

Amperometry

6/22

Large area and power consumption.


J. Aymerich Gubern

7/22


Conclusions


3

4

5




J. Aymerich Gubern

Behaviour similar to low-pass first-ordersingle-bit CT A/D modulator.

Sensor-on-the-loop

Error current converted into voltage and shaped in frequency by the electrochemical sensor itself.

High OSR easly obtained with kHz-rangeclock frequencies.

1st order Potentiostatic

Amperometric read-out through the output by chemical input .

S/H

Feedback DAC

Linear model

8/22


J. Aymerich Gubern

S/H

Feedback DAC

Typical tonal component of 1st order

DAC flicker noise not shaped by loop.Noise floor in the signal band (BW < 1Hz)dominated by flicker noise.

Vpot only applies to the Reference Electrode (R).

Limited potentiostatic range programmability (Vrw):

9/22

1st order Potentiostatic


J. Aymerich Gubern

10/22


Conclusions


3

4

5




J. Aymerich Gubern

From 1st to 2nd order

S/H

Feedback DAC

Quantizer

Second-ordernoise shaper

Feedforward path

From electrochemical only to hybrid/mixed electrochemical/electronic

Tones and pattern noise suppression.

11/22


J. Aymerich Gubern

From 1st to 2nd order

S/H

Feedback DAC

Quantizer

Second-ordernoise shaper

Feedforward path

From electrochemical only to hybrid/mixed electrochemical/electronic

Tones and pattern noise suppression.

Small-signal model

2nd order requires stability compensation

LHP Zero through feedforward path

Feedforward path

11/22


J. Aymerich Gubern

Wide-range potentiostatic 2nd order

Programmable-WE through Gm1: Extend potentiostatic range virtually upto double the supply voltage:

Feedback DAC

12/22


J. Aymerich Gubern

Programmable-WE through Gm1: Extend potentiostatic range virtually upto double the supply voltage:

Small-signal model

High power consumption on Gm1 to push RHP zero to high frequencies:

Loop stability:

Feedback DAC

12/22

Wide-range potentiostatic 2nd order


J. Aymerich Gubern

Differential DAC wide-range potentiostatic 2nd order

Programmable-WE through Gm1:Extend potentiostatic range virtually upto double the supply voltage

Feedback DAC

13/22


J. Aymerich Gubern

Differential DAC wide-range potentiostatic 2nd order

Programmable-WE through Gm1:Extend potentiostatic range virtually upto double the supply voltage

Small-signal model

Loop stability:RHP self-canceledboth Ifsp,n are used in both quantization symbols.

Gm1 only has to cope with Ifsp,n mismatching.

Feedback DAC

13/22


J. Aymerich Gubern

Flicker Noise Cancellation

Ifsp,n noise currents are always bypassed to Gm1 OTA or biphasically integrated into Vrw.

Gm1 OTA switching.

Feedback DAC

14/22


J. Aymerich Gubern



Gm1 OTA switching.

Feedback DAC

qmod = 0 Feedback DAC

14/22


J. Aymerich Gubern



Gm1 OTA switching.

Feedback DAC

qmod = 0 qmod = 1

Feedback DAC

Feedback DAC

14/22


J. Aymerich Gubern



Gm1 OTA switching.

qmod = 0 qmod = 1

Feedback DACFeedback DAC

Feedback DAC

14/22


J. Aymerich Gubern



Gm1 OTA switching.

qmod = 0 qmod = 1

Feedback DAC Feedback DAC

Feedback DAC

14/22


J. Aymerich Gubern


qmod = 0 qmod = 1

Feedback DAC Feedback DAC

Optimum cancellation when qmod has equal probability of 1's and 0's quant. symbols(case of very weak chemical signals).

14/22


J. Aymerich Gubern

15/22


Conclusions


3

4

5




J. Aymerich Gubern

Electrochemical sensor frontend CMOS layout

480μm x 370μm (0.18mm2).

0.18μm 1P6M CMOSX-FAB technology (XH018).

I2C 4-wire bus interface.

1.8-V capless LDO core supply regulator.

On-Chip auxiliary modules.

Current generator.

Vpotp,n programmable sources.

18/22


J. Aymerich Gubern

Post-Layout Simulations

VerilogA: Vrw-Isens DC look-uptable based on a Cyclic Voltammetry.

3-Vpp cyclic voltammetry exampleunder 1.8-V voltage supply.

Third order Butterworthlow-pass filter as digital decimator.2.5-Hz cutt-off freq.

VerilogA.

19/22


J. Aymerich Gubern


Output spectrum comparison w/(a) and w/o(b) flicker cancelation technique.

Weak input signal -65dBFS

(a)

(b)

±100-nA full scale.

Sampling freq. 256Hz

Bandwidth 1Hz

Oversampling ratio 128:

20/22


J. Aymerich Gubern

Performance simulation results

21/22


J. Aymerich Gubern


Conclusions


3

4

5




J. Aymerich Gubern

Conclusions

22/22

Improved dynamic range (90dB) thanks to Feedback DAC flicker noise cancellation mechanism.

Compact architecture (0.18mm2) thanks to the electrode-electrolyte interface used as an integrator stage in the structure.

Wide range (±1.5V) potentiostat programmability with minimalist analog circuits fully integrable in purely digital CMOS technologies.

High resolution with sub kHz-range sampling frequencies (256Hz).


J. Aymerich Gubern

22/22

I2C plug & play (power and comm.)

Applications and benefits

200μm x 200μm pads

First trials of ASIC flip-chip on screen-printed flexible substrates

Wearable for chemical sensing in sweatFood quality and safety


J. Aymerich Gubern

Currently being measured...

Thanks for your attention!


J. Aymerich Gubern

Comparison of CMOS Potentiostatic FRONTENDS


J. Aymerich Gubern

Low-power rail-to-rail CMOS circuits

Wide Vrw programmability imposes wide input/output common-mode rangefor Gm1 and Gm2.

Constant gm over the input common-mode voltage:M3 M4M1 M2M5

1 : 1

M1-M4 in weak inversionSum of tail currents Ibiasp,n constantSum of tail currents Ibiasp,n constant

16/22


J. Aymerich Gubern

Low-power rail-to-rail CMOS circuits

M3 M4

M1 M2

Wide Vrw programmability imposes challenging input common-mode rangefor the quantizer.

Complementary latched comparators:

qoutp,n digitally combined,giving priority to the one stillbeing operational.Zero-static power consumption

17/22


J. Aymerich Gubern


Output spectrum for half full-scale input signal -6dBFS.

Oversampling ratio 128:

±100-nA full scale.

Sampling freq. 256Hz

Bandwidth 1Hz

SNDRmax 70-dB @ ±100nA FS

72-dB @ ±900nA FS


J. Aymerich Gubern

5/22

Amperometric Electrochemical Sensors

Cyclic Voltammetry:

Different detection methods are required:

Most widely used electrochemical technique.

Chronoamperometry:

Wide sweeping potentials

Rapid location of the redox potentials.

0.7

0.0

0.1

0.2

0.3

0.4

0.5

0.6

t [s]

1

[A]

-1-1 10

0

1

-1

0

1

Vrw stepped and Isens monitored as a function of time. [

A]

0

1

0t [s] 1

Documents

A 72- W 90-dB Wide-Range Potentiostatic CMOS Modulator ...pserra/cnm/2019 - A 72-uW 90-dB Wide-Range Potenti… · 72- W 90-dB Wide-Range Potentiostatic Modulator J. Aymerich Gubern