# US 2018/0321302 A1 · Impedance characteristic circuit for electrochemical sensor > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2018/0321302 A1 - Document ID: US20180321302A1 - Status: Published application - Kind: A1 - Application number: 15/586,869 - Filed: 2017-05-04 - Published: 2018-11-08 - Earliest claimed: 2017-05-04 - Assignees: Analog Devices Global - Applicants: Analog Devices Global - Inventors: GuangYang Qu; Junbiao Ding; Tony Yincai Liu; Shurong Gu; Yimiao Zhao; Hanqing Wang; Leicheng Chen - Web page: https://patentgrep.com/patent/US20180321302A1 ## CPC - G01R 31/2829: {Testing of circuits in sensor or actuator systems (testing of apparatus for measuring electric or magnetic variables G01R35/00; testing of indicating or recording apparatus G01D; in airbag systems B60R21/0173; checking gas analysers G01N33/007; monitoring or fail-safe circuits for electromagnets H01F7/1844)} - G01R 15/16: using capacitive devices - G01N 27/416: Systems (G01N27/27 takes precedence) - G01N 27/4163: {checking the operation of, or calibrating, the measuring apparatus (G01N27/3274, G01N27/4175 and G01N33/0006 take precedence)} - G01N 27/4175: {Calibrating or checking the analyser} - G01R 27/02: Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant (by measuring phase angle only G01R25/00) - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) ## Abstract A electrochemical or other sensor interface circuit architecture can deliver substantial DC offset bias to an electrochemical or other sensor separately or independently from delivering a time-varying AC excitation signal, which can then be provided with higher resolution, which, in turn, can allow better resolution of the measured response signal providing the impedance characteristic of sensor condition. For example, a differential time-varying AC excitation signal for the sensor condition characteristic can be delivered separately and independently from a differential stable (e.g., DC or other) bias signal, such as by using separate digital-to-analog converters (DACs), so that providing the more stable signal does not limit the resolution and accuracy of the time-varying signal, such as by using up the dynamic range of a single DAC. ## Claims ### Claim 1 An impedance characteristic sensor interface circuit for independently delivering a differential stable bias signal component and a differential time-varying AC excitation signal component for testing an impedance of an electrochemical sensor having a sensor input node, first and second differential sensor feedback nodes, and a sensor output node, the sensor interface circuit including: an impedance excitation amplifier circuit, including: a first differential pair of inputs, coupled to receive the differential time-varying AC excitation signal component for communication onto first and second amplifier input nodes during a sensor impedance testing mode; a second differential pair of inputs, coupled to receive the differential stable bias signal component for communication onto the first and second amplifier input nodes; and a third differential pair of inputs, coupled to receive a feedback signal from the differential sensor feedback nodes for communication onto the first and second amplifier inputs nodes; and a sensor response amplifier circuit, coupled to the sensor for receiving a response signal to the differential time-varying AC excitation signal component, during the sensor impedance testing mode, for communication to a sensor response signal output node. ### Claim 2 (depends on 1) The sensor interface circuit of claim 1, comprising a first digital-to-analog converter (DAC) circuit, to convert a first digital input signal into a first analog signal for providing the differential time-varying AC excitation signal component. ### Claim 3 (depends on 2) The sensor interface circuit of claim 2, comprising a second DAC circuit, to convert a second digital input signal into a second analog signal for providing the differential stable bias signal component. ### Claim 4 (depends on 3) The sensor interface circuit of claim 3, wherein the second DAC circuit is also used to provide the differential stable bias signal component during an operating mode of the sensor during which the differential time-varying AC excitation signal component is not applied. ### Claim 5 (depends on 3) The sensor interface circuit of claim 3 wherein the second DAC circuit includes outputs to which shunt capacitors are respectively coupled. ### Claim 6 (depends on 2) The sensor interface circuit of claim 2, comprising an attenuating amplifier circuit to attenuate an output signal of the first DAC for providing the differential time-varying AC excitation signal component onto the first and second amplifier input nodes. ### Claim 7 (depends on 1) The sensor interface circuit of claim 1, comprising a load resistor to couple the sensor to at least one of (1) a transimpedance amplifier input of the sensor response amplifier circuit or (2) at least one of the differential sensor feedback nodes. ### Claim 8 (depends on 1) The sensor interface circuit of claim 1, wherein the differential time-varying AC excitation signal component is frequency-varying during the sensor impedance testing mode. ### Claim 9 (depends on 1) The sensor interface circuit of claim 1, wherein the differential stable bias signal component is temperature compensated. ### Claim 10 A method of determining usability of an electrochemical sensor by determining an impedance associated with the electrochemical sensor, the method including: delivering a differential time-varying AC excitation signal component to first and second amplifier input nodes for driving an excitation signal into the sensor during a sensor impedance test; separately delivering a differential stable bias signal component to the first and second amplifier input nodes for biasing the first and second amplifier input nodes while driving the excitation signal into the sensor during the sensor impedance test; communicating a differential feedback signal from the sensor to the first and second amplifier input nodes while driving the excitation signal into the sensor; and measuring a response from the sensor while driving the excitation signal into the sensor during the sensor impedance test. ### Claim 11 (depends on 10) The method of claim 10, comprising: converting a first digital input signal into a first analog signal for providing the differential time-varying AC excitation signal component during the sensor impedance test; and converting a second digital input signal into a second analog signal for providing the differential stable bias signal component during the sensor impedance test. ### Claim 12 (depends on 11) The method of claim 11, further comprising also using the second analog signal for providing the differential stable bias signal component during an operating mode of the sensor during which the differential time-varying AC signal component is not applied. ### Claim 13 (depends on 11) The method of claim 11, comprising attenuating the first analog signal for providing the differential time-varying AC excitation signal component during the sensor impedance test. ### Claim 14 (depends on 11) The method of claim 11, comprising converting a current from the sensor in response to the differential time-varying AC excitation signal component into a voltage to provide an indication of a sensor characteristic related to usability of the sensor. ### Claim 15 (depends on 11) The method of claim 11, comprising varying a frequency of the differential time-varying AC signal component during the sensor impedance test. ### Claim 16 (depends on 11) The method of claim 11, comprising temperature compensating the differential stable bias signal component. ### Claim 17 (depends on 11) The method of claim 11, comprising providing at least one of a proportional-to-absolute-temperature (PTAT) or complementary-to-absolute-temperature (CTAT) signal to generate the differential stable bias signal component. ### Claim 18 An impedance characteristic sensor interface circuit for independently delivering a differential stable bias signal component and a differential time-varying AC excitation signal component for testing an impedance of an electrochemical sensor, the sensor interface circuit including: an impedance excitation amplifier circuit, including: a first digital-to-analog converter (DAC) circuit, to convert a first digital input signal into a first analog signal for providing the differential time-varying AC excitation signal component during a sensor impedance testing mode; a second DAC circuit, to convert a second digital input signal into a second analog signal for providing the differential stable bias signal component during the sensor impedance testing mode; and a sensor response amplifier circuit, coupled to the sensor for receiving a response signal to the differential time-varying AC excitation signal component, during the sensor impedance testing mode. ### Claim 19 (depends on 18) The sensor interface circuit of claim 18, comprising: a first differential pair of inputs, coupled to receive the differential time-varying AC excitation signal component for communication onto first and second amplifier input nodes during a sensor impedance testing mode; a second differential pair of inputs, coupled to receive the differential stable bias signal component for communication onto the first and second amplifier input nodes; and a third differential pair of inputs, coupled to receive a feedback signal from the differential sensor feedback nodes for communication onto the first and second amplifier inputs nodes. ### Claim 20 (depends on 19) The sensor interface circuit of claim 19, in combination with an electrochemical sensor including a reference electrode, a working or sensing electrode, and a counter or auxiliary electrode, wherein: the counter or auxiliary electrode is coupled to the sensor interface circuit to receive the differential time-varying AC excitation signal component superimposed on the differential stable bias signal component during the sensor impedance testing mode; the reference electrode is coupled to one of the differential sensor feedback nodes of the sensor interface circuit; and the sensing electrode is coupled to the other of the differential sensor feedback nodes of the sensor interface circuit and to the sensor response amplifier circuit. ### Claim 21 (depends on 18) The sensor interface circuit of claim 18, wherein the same second DAC circuit is configured to convert the second digital input signal into the second analog signal for providing the differential stable bias signal component during a gas sensing operating mode of the sensor during which the differential time-varying AC excitation signal component is not applied.