Electrochemical cell characterisation

1 . Circuitry for determining an impedance of an electrochemical cell comprising at least one first electrode and a second electrode, the circuitry comprising:

drive circuitry configured to apply a stimulus to the electrochemical cell, the stimulus having a stimulation frequency and a stimulation amplitude; and

measurement circuitry configured to:

sample an output of the electrochemical cell at a sampling frequency to generate an output signal;

determine an output amplitude of output signal at one or more alias frequencies, the one or more alias frequency based on the stimulation frequency and the sampling frequency; and

determine the impedance of the electrochemical cell at the stimulation frequency based on the output amplitude at the one or more alias frequencies and the stimulation amplitude; and

control circuitry configured to:

control the sampling frequency and the stimulation frequency such that a Nyquist rate of the sampling frequency is less than stimulation frequency.

2 . Circuitry of claim 1 , wherein the drive circuitry comprises:

a digital-to-analog converter (DAC) configured to convert a digital input signal into the stimulus at a conversion frequency; and

apply the stimulus at the second electrode of the electrochemical cell.

3 . Circuitry of claim 2 , wherein the measurement circuitry comprises:

an analog-to-digital converter (ADC) configured to sample the output of the electrochemical cell at the at least one first electrode.

4 . Circuitry of claim 3 , wherein DAC and the ADC are synchronised.

5 . Circuitry of claim 4 , wherein:

the DAC is clocked by a first clock signal at the conversion frequency;

the ADC is clocked by a second clock signal at the sampling frequency; and

a first frequency of the first clock signal is an integer multiple of a second frequency of the second clock signal.

6 . Circuitry of claim 1 , wherein the stimulus comprises a square wave.

7 . Circuitry of claim 2 , wherein the control circuitry is configured to control the sampling frequency based on the digital input signal or the stimulus, or wherein the control circuitry is configured to control the digital input signal or the stimulus based on the sampling frequency.

8 . Circuitry of claim 1 , wherein the control circuitry is configured to control the stimulation frequency and the sampling frequency so as to reduce aliasing of one or more harmonic components of a digital output signal onto a fundamental component of the digital output signal.

9 . Circuitry of claim 8 , wherein the control circuitry is configured to vary the stimulation frequency and sampling frequency over time to reduce aliasing of the one or more harmonic components of the digital output signal onto the fundamental component of the digital output signal.

10 . Circuitry of claim 1 , wherein the control circuitry is configured to control the stimulation frequency and the sampling frequency to maintain a greatest common denominator of the stimulation frequency of an analog measurement stimulus and the sampling rate at approximately 1.

11 . Circuitry of claim 1 , wherein the control circuitry is configured to control the stimulation frequency and the sampling frequency to be approximately co-prime.

12 . Circuitry of claim 1 , wherein the control circuitry is configured to vary the stimulation frequency over a first range of frequencies below the Nyquist rate of the sampling frequency, wherein the measurement circuitry is configured to determine the output amplitude of the output signal at one or more frequencies unaffected by aliasing.

13 . Circuitry of claim 1 , wherein the control circuitry is configured to vary the stimulation frequency and the sampling frequency over time to minimize an impact of harmonic aliasing at a predefined aliasing frequency.

14 . Circuitry of claim 1 , wherein the at least one first electrode is a working electrode, and wherein the second electrode is a counter electrode.

15 . Circuitry of claim 1 , wherein the at least one first electrode comprises an anode and the second electrode comprises a cathode.

16 . A system comprising:

the circuitry of claim 1 ; and

the electrochemical cell.

17 . An electronic device, comprising the circuitry of claim 1 .

18 . The electronic device of claim 17 , wherein the device comprises one of an analyte monitor, a continuous glucose monitor, a battery, a battery monitor, a mobile computing device, a laptop computer, a tablet computer, a games console, a remote control device, a home automation controller or a domestic appliance, a toy, a robot, an audio player, a video player, or a mobile telephone, and a smartphone.

19 . A method of determining an impedance of an electrochemical cell comprising at least one first electrode and a second electrode, the method comprising:

applying a stimulus to the electrochemical cell, the stimulus having a stimulation frequency and a stimulation amplitude;

sampling an output of the electrochemical cell at a sampling frequency and generate an output signal, a Nyquist rate of the sampling frequency being less than the stimulation frequency;

determining an output amplitude of output signal at one or more alias frequencies, the one or more alias frequency based on the stimulation frequency and the sampling frequency; and

determining the impedance of the electrochemical cell at the stimulation frequency based on the output amplitude at the one or more alias frequencies and the stimulation amplitude.