A digital constant potential device based on linearity calibration technology

Abstract

The application discloses a digital constant potentiostat based on linearity calibration technology, comprising a quantizer, a control logic module, a current domain digital-to-analog converter, an oscillator and a frequency mixer, which constitutes a digital closed loop circuit with an electrochemical sensor, and realizes constant potential difference between a working electrode and a reference electrode of the electrochemical sensor and sensing current size detection between the working electrode and a counter electrode through negative feedback regulation of the digital closed loop circuit, so that a greater sensing current detection dynamic range is realized under extremely low power consumption, the differential current domain digital-to-analog converter is used to quantitatively transmit the linearity characteristics of the sensing current in the form of frequency while converting the sensing current into a digital code word, so as to realize linearity calibration of the mapping relationship between the detected sensing current size and the output digital control code word, thereby realizing high linearity sensing current detection under extremely low power consumption.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of integrated circuit design, and relates to a digital constant potential device based on linearity calibration technology. BACKGROUND

[0002] Electrochemical sensors can be used for detection of gases, ions and biological compounds, such as carbon monoxide, oxygen, hydrogen sulfide and other gases, cadmium ions, lead ions, mercury ions and other heavy metal ions, glucose, uric acid, cholesterol, dopamine and other biological compounds. Electrochemical sensors are widely used in environmental monitoring and physiological parameter monitoring due to their small size and high sensitivity. Electrochemical sensors use the electrochemical properties of the measured substance to convert the measured chemical quantity into an electrical quantity through a three-electrode electrochemical system.

[0003] A constant potential device is a necessary condition for the operation of an electrochemical sensor. The constant potential device controls the potential difference between the working electrode and the reference electrode in the same electrolytic cell to cause an electrochemical reaction, and at the same time, an electric current loop is established between the working electrode and the counter electrode to measure the sensing current flowing through the working electrode, and the size of the sensing current is proportional to the concentration of the measured substance.

[0004] The size of the current generated by different electrochemical sensors varies greatly. The electrochemical sensor applied to gas detection generates a current in the order of milliamperes (mA), while the electrochemical sensor applied to physiological parameter monitoring generates a current in the order of nanamperes (nA) or even picamperes (pA), so the general constant potential device used with the electrochemical sensor requires a larger sensing current detection dynamic range while maintaining high linearity. In addition, electrochemical sensing is gradually developing in the direction of wireless, and wireless electrochemical sensing systems are beneficial to large-scale long-distance deployment and long-term continuous monitoring, so the general constant potential device used with the electrochemical sensor requires lower power consumption to achieve longer battery life.

[0005] Existing constant potential devices are analog circuit architectures, usually composed of one to two operational amplifiers, and the operational amplifier itself has high power consumption. To simultaneously achieve a large dynamic range covering the order of picamperes to milliamperes and high linearity means greater design difficulty and higher power consumption, which is not suitable for wireless electrochemical sensing systems. SUMMARY

[0006] In order to solve the above technical problems in the prior art, the application provides a digital constant potential device based on linearity calibration technology, and the specific technical scheme is as follows:

[0007] A digital potentiostat based on linearity calibration technology, connected with an electrochemical sensor, the potentiostat comprising a quantizer, a control logic module, a current domain digital-to-analog converter, an oscillator and a frequency mixer; the reference electrode of the electrochemical sensor is connected with the quantizer, and the counter electrode is connected with the current domain digital-to-analog converter; the quantizer monitors the potential change of the reference electrode and converts the potential change into a digital signal, which is then transmitted to the control logic module; the control logic module calculates the control code word of the current domain digital-to-analog converter at the next moment according to the digital signal converted and output by the quantizer and the control code word of the current domain digital-to-analog converter at the last moment, then performs digital signal processing on the control code word by using dynamic element matching technology, and then transmits the processed control code word to the current domain digital-to-analog converter; the current domain digital-to-analog converter converts the digital control code word into an analog sensing current and a complementary current, the branch of the sensing current is connected to the counter electrode of the electrochemical sensor, and the complementary current is transmitted into the oscillator after being summed with the bias current provided by the electrochemical sensing system in which the digital potentiostat is currently located; the oscillator converts the summed current signal into a frequency signal positively correlated with the complementary current, which is transmitted to the frequency mixer, and at the same time, the current domain digital-to-analog converter also transmits the digital control code word at the current moment to the frequency mixer; the frequency mixer outputs a modulation signal whose frequency change is related to the size of the complementary current and whose amplitude change is related to the control code word, and the modulation signal is used as the output signal of the digital potentiostat.

[0008] Preferably, the quantizer uses a dynamic comparator or a static comparator.

[0009] Preferably, the working electrode of the electrochemical sensor is connected to the power supply / ground terminal of the potentiostat according to the positive / negative bias voltage applied by the three-electrode system in which the electrochemical sensor is located.

[0010] Preferably, the current domain digital-to-analog converter is composed of a single-ended current domain digital-to-analog converter unit group and a differential current domain digital-to-analog converter unit group, the single-ended current domain digital-to-analog converter unit group is composed of N single-ended current domain digital-to-analog converter units, the differential current domain digital-to-analog converter unit group is composed of M differential current domain digital-to-analog converter units, N and M are positive integers; each output of a multi-output cascode current mirror contained in the single-ended current domain digital-to-analog converter unit copies the input reference current in proportion, each output terminal of the cascode current mirror contains a switch controlled by the control code word output by the control logic module, and the output currents of the cascode current mirror are summed and then connected to the sensing current branch of the current domain digital-to-analog converter; each differential output of a multi-output differential cascode current mirror contained in the differential current domain digital-to-analog converter unit copies the input reference current in proportion, each differential output terminal of the cascode current mirror contains a pair of complementary switches S and S controlled by the control code word output by the control logic module, and the differential output currents of the cascode current mirror are summed and then connected to the sensing current branch of the current domain digital-to-analog converter. 互补, forming two current branches, and only one switch is turned on at the same time, the current through the switch S in each differential output of the common-source common-gate current mirror is summed and connected to the sensing current branch, and the current through the switch S in each differential output of the common-source common-gate current mirror is summed and connected to the complementary current branch. 互补

[0011] Preferably, the single-ended current domain digital-to-analog converter unit and the differential current domain digital-to-analog converter unit adopt NMOS / PMOS single-ended current domain digital-to-analog converter units and NMOS / PMOS differential current domain digital-to-analog converter units according to the positive / negative bias applied by the three-electrode system, that is, the MOS tube type adopted is N / P type, and the MOS tube type adopted in the input common-source common-gate current mirror in the oscillator is P / N type.

[0012] Preferably, the PMOS single-ended current domain digital-to-analog converter unit comprises a multi-output common-source common-gate current mirror, and the multi-output common-source common-gate current mirror is composed of a reference current input circuit and a multi-output circuit; the reference current input circuit comprises PMOS tubes PM1-PM2, a resistor R1, and a reference current I BP1 connected to the drain of PM2, the gate of PM2 is connected to the drain of PM2, the source of PM2 is connected to the drain and gate of PM1, the source of PM1 is connected to one end of the resistor R1, the other end of the resistor R1 is connected to the power supply of the digital constant potentiometer; each output circuit in the multi-output circuit comprises PMOS tubes PM3-PM4, a resistor R2, a switch S1, one end of the resistor R2 is connected to the power supply of the digital constant potentiometer, the other end is connected to the source of PM3, the gate of PM3 is connected to the gate of PM1, the drain of PM3 is connected to the source of PM4, the gate of PM4 is connected to the gate of PM2, and the drain of PM4 is connected to one end of the switch S1; the substrates of the PMOS tubes PM1-PM4 and the PMOS tube in the switch S1 are all connected to the power supply, and the substrates of the NMOS tubes in the switch S1 are all connected to the ground; the other ends of the switches S1 of all the output circuits in the multi-output common-source common-gate current mirror are connected together.

[0013] Preferably, the PMOS differential current domain digital-to-analog converter unit comprises a multi-output differential common-source common-gate current mirror, and the multi-output differential common-source common-gate current mirror is composed of a differential reference current input circuit, a PMOS tube PM7, a resistor R4, and a multi-output differential circuit; the differential reference current input circuit comprises PMOS tubes PM5-PM6, a resistor R3, and a reference current I BP2 ​The drain of the access PM6 is connected with the gate of the PM6, the source of the PM6 is connected with the drain and the gate of the PM5, the source of the PM5 is connected with one end of the resistor R3, the other end of the resistor R3 is connected with the power supply of the digital constant potential device; each differential output circuit in the multi-channel differential output circuit comprises: a PMOS tube PM8 and a pair of complementary switches S2-S3; one end of the resistor R4 is connected with the power supply of the digital constant potential device, the other end is connected with the source of the PM7, the gate of the PM7 is connected with the gate of the PM5, the drain of the PM7 is connected with the source of the PM8, the gate of the PM8 is connected with the gate of the PM6, the drain of the PM8 is connected with one end of the switch S2 and the switch S3; the substrate of the PMOS tubes PM5-PM8 and the PMOS tubes in the switches S2-S3 are connected with the power supply, the substrate of the NMOS tubes in the switches S2-S3 is connected with the ground; the other end of the switch S2 in all differential output circuits in the common source and common gate current mirror of the multi-channel differential output is connected together, the other end of the switch S3 is connected together.

[0014] Preferably, the oscillator adopts a ring oscillator, and the oscillator converts the current signal after summation into a frequency signal positively correlated with the complementary current, specifically: the current signal after summation is taken as a control current of the ring oscillator, the control current is copied after passing through the common source and common gate current mirror, and then current limiting is performed at the power supply end and the ground end of the ring oscillator, and the frequency of the oscillation signal output by the ring oscillator is positively correlated with the size of the complementary current.

[0015] Preferably, the mixer is composed of a two-input logic AND gate, one input end of the AND gate is connected with the frequency signal from the oscillator, the other input end is connected with the control code word of the current domain digital-to-analog converter at the current moment, the AND gate outputs a digital signal after modulation, as the output signal of the digital constant potential device, the frequency change of the output signal contains the information of the size of the complementary current, and the amplitude change of the output signal contains the information of the control code word of the current domain digital-to-analog converter at the current moment.

[0016] Beneficial effects: (1) the digital negative feedback loop composed of the quantizer, the control logic module, the current domain digital-to-analog converter and the electrochemical sensor is innovatively used to realize the constant potential difference between the working electrode and the reference electrode of the electrochemical sensor and the detection of the sensing current size between the working electrode and the counter electrode, and the operational amplifier used in the existing constant potential device is replaced, so that a greater sensing current detection dynamic range is realized under extremely low power consumption.

[0017] Secondly, the application innovatively uses the differential current domain digital-to-analog converter to quantitatively transmit the linearity characteristics of the sensor current in the form of frequency while converting the sensor current into digital code words, which can be used to realize the linearity calibration of the mapping relationship between the detected sensor current and the output digital code words, thereby realizing the detection of the sensor current with high linearity at extremely low power consumption. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a main component structure schematic diagram of a digital potentiostat based on a linearity calibration technology of the application;

[0019] Figure 2 is a specific component structure schematic diagram of a digital potentiostat applied to a positive bias three-electrode electrochemical system of an embodiment of the application;

[0020] Figure 3 is a specific component structure schematic diagram of a digital potentiostat applied to a negative bias three-electrode electrochemical system of an embodiment of the application;

[0021] Figure 4 is a circuit schematic diagram of a current domain digital-to-analog converter in an embodiment of the application;

[0022] Figure 5 is a specific structure schematic diagram applied to a wireless passive electrochemical sensing system of an embodiment of the application;

[0023] Figure 6 is a specific structure schematic diagram applied to a wireless active electrochemical sensing system of an embodiment of the application. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical scheme and technical effects of the application clearer, the application is further described in detail below with reference to the accompanying drawings.

[0025] As shown in Figure 1 A digital potentiostat based on a linearity calibration technology is connected with an electrochemical sensor, and the digital potentiostat is composed of a quantizer, a control logic, a current domain digital-to-analog converter, an oscillator and a frequency mixer. The quantizer can adopt a dynamic comparator or a static comparator. The reference electrode of the electrochemical sensor is connected with the quantizer, and the counter electrode is connected with the current domain digital-to-analog converter. In addition, in a three-electrode system with negative bias, the working electrode of the electrochemical sensor is connected with the ground of the digital potentiostat; in a three-electrode system with positive bias, the working electrode of the electrochemical sensor is connected with the power supply of the digital potentiostat, and the potential of the working electrode remains unchanged.

[0026] In the normal working of the three-electrode system, the quantizer monitors the potential change of the reference electrode of the electrochemical sensor, and then converts the potential change into a digital signal and transmits it to the control logic module. The control logic module calculates the control code word of the current domain digital-to-analog converter at the next moment according to the digital signal output by the quantizer and the control code word of the current domain digital-to-analog converter at the last moment, and then performs digital signal processing on the control code word by using the dynamic element matching technology. In the case of keeping the output current of the current domain digital-to-analog converter consistent with the control code word before using the dynamic element matching technology, the current domain digital-to-analog converter units that need to be turned on and turned off are randomly allocated. Finally, the processed control code word is transmitted to the current domain digital-to-analog converter.

[0027] The current domain digital-to-analog converter converts the digital control code word into an analog sensing current and a complementary current. The sensing current branch is connected to the counter electrode of the electrochemical sensor, and the complementary current is summed with the bias current provided by the electrochemical sensing system in which the digital potentiostat is currently located and then transmitted to the oscillator. More specifically, the current domain digital-to-analog converter is composed of a single-ended current domain digital-to-analog converter unit group and a differential current domain digital-to-analog converter unit group. The single-ended current domain digital-to-analog converter unit group can be composed of N single-ended current domain digital-to-analog converter units, and the differential current domain digital-to-analog converter unit group can be composed of M differential current domain digital-to-analog converter units, where N and M are positive integers. A single-ended current domain digital-to-analog converter unit can contain a multi-output common-source common-gate current mirror. Each output of the common-source common-gate current mirror copies the reference current input into the single-ended current domain digital-to-analog converter unit according to a certain proportion. Each output of the common-source common-gate current mirror contains a switch controlled by the control code word output by the control logic module. The output currents of each output of the common-source common-gate current mirror are summed and then connected to the sensing current branch of the current domain digital-to-analog converter. A differential current domain digital-to-analog converter unit can contain a multi-output common-source common-gate current mirror. Each differential output of the common-source common-gate current mirror copies the reference current input into the differential current domain digital-to-analog converter unit according to a certain proportion. Each differential output of the common-source common-gate current mirror contains a pair of complementary switches S and S controlled by the control code word output by the control logic module, forming two current branches, and only one switch is turned on at the same time. 互补 The current flowing through the switch S in each differential output of the common-source common-gate current mirror is summed and then connected to the sensing current branch, and the current flowing through the switch S in each differential output of the common-source common-gate current mirror is summed and then connected to the complementary current branch. 互补The current sum of the sensing current and the complementary current is connected to the complementary current branch. Therefore, for each differential current domain D / A converter unit, the sensing current and the complementary current are complementary to each other, and the sum of the current sizes of the two is constant, and the current sizes of the two are inversely proportional. The sensing current branch and the complementary current branch of the current domain D / A converter module are obtained by summing the sensing current branch and the complementary current branch of each unit in the single-ended and differential current domain D / A converter unit group. The sensing current branch is connected to the counter electrode of the electrochemical sensor, and the complementary current flows into the oscillator.

[0028] Because the size of the complementary current varies with the control code word and contains the quantitative mapping relationship between the actual output current size of each current mirror in the differential current domain D / A converter unit group and the control code word, that is, the linearity characteristic of the differential current domain D / A converter, the quantitative mapping relationship can be used to calibrate the linearity of the mapping relationship between the actual size of the real sensing current flowing through the electrochemical sensor and the control code word data in the output signal of the potentiostat.

[0029] The oscillator adopts a current-controlled ring oscillator, which converts the current signal obtained by summing the complementary current output by the current domain D / A converter and the bias current provided by the current electrochemical sensing system into a frequency signal positively correlated with the complementary current and transmits it to the mixer. The conversion process is as follows: the summed current signal is used as the control current of the ring oscillator, which is copied through a common-source common-gate current mirror to limit the current at the power supply end and the ground end of the ring oscillator. The frequency of the oscillation signal output by the ring oscillator is positively correlated with the size of the complementary current. At the same time, the current domain D / A converter also transmits the digital control code word at the current time to the mixer. The control code word and the frequency signal output by the oscillator are mixed in the mixer, and the mixer outputs a modulated signal whose frequency change is related to the size of the complementary current and whose amplitude change is related to the control code word, and the signal is used as the output signal of the digital potentiostat. The mixer is composed of a two-input logical AND gate. One input end of the AND gate is connected to the frequency signal from the oscillator, and the other input end is connected to the control code word at the current time of the current domain D / A converter. The AND gate outputs a modulated digital signal as the output signal of the digital potentiostat. The frequency change of the output signal contains the information of the size of the complementary current, and the amplitude change of the signal contains the information of the control code word of the current domain D / A converter at the current time, that is, the information of the detected sensing current size. In the electrochemical sensing system, the output signal of the potentiostat can be further processed. The information of the size of the complementary current varying with the control code word carried in the frequency of the output signal can be used to calibrate the mapping relationship between the actual size of the detected real sensing current and the control code word carried in the amplitude of the output signal, thereby realizing high-linearity sensing current detection.

[0030] In the digital potentiostat of this invention, a digital closed-loop circuit consisting of an electrochemical sensor, a quantizer, a control logic module, and a current-domain digital-to-analog converter (DAC) monitors the change in the reference electrode potential of the electrochemical sensor to adjust the magnitude of the current in the sensing current branch of the DAC. This adjusts the potential difference between the working electrode and the reference electrode to a pre-set potential difference. Furthermore, the negative feedback adjustment of the digital closed-loop circuit keeps the potential difference constant, thereby controlling the magnitude of the analog sensing current output by the DAC to gradually approach the magnitude of the actual sensing current that should theoretically be generated when the electrochemical sensor undergoes an electrochemical reaction at the pre-set potential difference. Thus, the magnitude of the actual sensing current flowing through the electrochemical sensor is converted into the control code of the DAC, realizing the conversion from analog to digital, thereby achieving the basic function of the digital potentiostat.

[0031] Meanwhile, the magnitude of the complementary current in this digital potentiometer changes with the control code word, containing a quantitative mapping relationship between the actual output current of each current mirror in the differential current domain digital-to-analog converter unit group and the control code word. This quantitative mapping relationship can be used to perform linearity calibration on the mapping relationship between the actual sensing current of the electrochemical sensor and the control code word data in the output signal of the digital potentiometer.

[0032] Example: Figure 2 As shown, when the digital potentiostat based on linearity calibration technology of the present invention is applied to a positively biased three-electrode electrochemical system, the potential difference between the working electrode WE and the reference electrode RE of the electrochemical sensor is positive, which is a necessary condition for the corresponding electrochemical reaction to occur. Therefore, in this embodiment, the working electrode WE of the electrochemical sensor is connected to the power supply of the digital potentiostat, the reference electrode RE is connected to the quantizer, and the counter electrode CE is connected to the sensing current branch I of the current domain digital-to-analog converter. SENS In a positively biased three-electrode electrochemical system, the sensing current flows from the working electrode WE to the counter electrode CE. The current-domain digital-to-analog converter (DAC) section of the digital potentiometer consists of an NMOS single-ended current-domain DAC unit group and an NMOS differential current-domain DAC unit group. The sensing current I corresponding to the NMOS single-ended current-domain DAC unit group... SE-SUM The sensing current I corresponding to the NMOS differential current domain digital-to-analog converter unit group DIF-SUM The sensing current I flowing through the electrochemical sensor is obtained by summing the results. SENS The complementary current I corresponding to the NMOS differential current domain digital-to-analog converter unit group. COMP-SUM Then, the bias current I provided by the electrochemical sensing system BIASThe summation is then fed into the oscillator. In a positively biased three-electrode electrochemical system, the oscillator section uses a PMOS oscillator, which outputs a frequency signal F. SENS The control code D of the current domain digital-to-analog converter SENS After mixing in the mixer, the modulated signal D is obtained. OUT This serves as the output signal of the digital potentiometer.

[0033] like Figure 3 As shown, when the digital potentiostat based on linearity calibration technology of the present invention is applied to a negatively biased three-electrode electrochemical system, the potential difference between the working electrode WE and the reference electrode RE of the electrochemical sensor is negative, which is a necessary condition for the corresponding electrochemical reaction to occur. Therefore, in this embodiment, the working electrode WE of the electrochemical sensor is connected to the ground of the digital potentiostat, the reference electrode RE is connected to the quantizer, and the counter electrode CE is connected to the sensing current branch I of the current domain digital-to-analog converter. SENS In a negatively biased three-electrode electrochemical system, the sensing current flows from the counter electrode CE to the working electrode WE. Therefore, the current-domain digital-to-analog converter (DAC) section of the digital potentiometer consists of a PMOS single-ended current-domain DAC unit group and a PMOS differential current-domain DAC unit group. The sensing current I corresponding to the PMOS single-ended current-domain DAC unit group... SE-SUM The sensing current I corresponding to the PMOS differential current domain digital-to-analog converter unit group DIF-SUM The sensing current I flowing through the electrochemical sensor is obtained by summing the results. SENS The complementary current I corresponding to the PMOS differential current domain digital-to-analog converter unit group. COMP-SUM Then, the bias current I provided by the electrochemical sensing system BIAS The summation is then fed into the oscillator. In the negatively biased three-electrode electrochemical system, the oscillator section uses an NMOS oscillator, which outputs a frequency signal F. SENS The control code D of the current domain digital-to-analog converter SENS After mixing in the mixer, the modulated signal D is obtained. OUT This serves as the output signal of the digital potentiometer.

[0034] like Figure 4 As shown, the PMOS / NMOS single-ended / differential current domain digital-to-analog converter unit is part of the PMOS / NMOS single-ended / differential current domain digital-to-analog converter unit group in the current domain digital-to-analog converter module of the present invention.

[0035] The PMOS single-ended current domain digital-to-analog converter unit comprises a multi-output common-source common-gate current mirror, which is composed of a reference current input circuit and a multi-output circuit. BP1 The drain of the PM2 is connected to the gate and the drain of the PM2, the source of the PM2 is connected to the drain and the gate of the PM1, the source of the PM1 is connected to one end of the resistor R1, and the other end of the resistor R1 is connected to the power supply of the constant potential device. Each output circuit of the common-source common-gate current mirror comprises PMOS tubes PM3-PM4, a resistor R2, and a switch S1. One end of the resistor R2 is connected to the power supply of the constant potential device, and the other end is connected to the source of the PM3. The gate of the PM3 is connected to the gate of the PM1, the drain of the PM3 is connected to the source of the PM4, the gate of the PM4 is connected to the gate of the PM2, and the drain of the PM4 is connected to one end of the switch S1. The substrates of the PMOS tubes PM1-PM4 and the PMOS tube in the switch S1 are connected to the power supply, and the substrates of the NMOS tubes in the switch S1 are connected to the ground. Each output of the common-source common-gate current mirror will output a reference current I BP1 with a certain proportion. The switch S1 is controlled by the control code word given by the control logic module. The other end of the switch S1 of each output of the common-source common-gate current mirror is connected together, and the current flowing through the switch S1 in each output is summed to obtain I DAC-SE . The I Figure 3 of all the PMOS single-ended current domain digital-to-analog converter units in the PMOS single-ended current domain digital-to-analog converter unit group in the PMOS single-ended current domain digital-to-analog converter unit is summed to obtain I DAC-SE . SE-SUM .

[0036] The PMOS differential current domain digital-to-analog converter unit comprises a multi-output common-source common-gate current mirror, which is composed of a differential reference current input circuit, a PMOS tube PM7, a resistor R4, and a multi-output differential circuit. The differential reference current input circuit comprises PMOS tubes PM5-PM6 and a resistor R3. The reference current I BP2The drain of PM6 is connected to the gate and the drain of PM6, the source of PM6 is connected to the drain and the gate of PM5, the source of PM5 is connected to one end of resistor R3, the other end of R3 is connected to the power supply of the constant potential device. Each differential output of the common source common gate current mirror includes: PMOS tube PM8 and switches S2-S3. One end of resistor R4 is connected to the power supply of the constant potential device, the other end is connected to the source of PM7, the gate of PM7 is connected to the gate of PM5, the drain of PM7 is connected to the source of PM8, the gate of PM8 is connected to the gate of PM6, and the drain of PM8 is connected to one end of switches S2 and S3. The substrate of PMOS tubes PM5-PM8 and the PMOS tube in the switch S2-S3 is connected to the power supply, and the substrate of the NMOS tube in the switch S2-S3 is connected to the ground. Each differential output circuit of the common source common gate current mirror will reference current I BP2 Accurately copy in a certain proportion. Switches S2 and S3 are complementary switches controlled by the control code word given by the control logic module, and only one switch is open at the same time. The other end of switch S2 of each differential output circuit in the common source common gate current mirror is connected together, and the other end of switch S3 of each differential output in the common source common gate current mirror is connected together. The current flowing through switch S2 in each differential output is summed to obtain I DAC-DIF The current flowing through switch S3 in each differential output is summed to obtain I DAC-COMP I DAC-DIF and I DAC-COMP The sum of the two currents remains constant, and the current size of the two is complementary. For Figure 3 , the sum of I DAC-DIF output by all PMOS differential current domain digital-to-analog converter units in the PMOS differential current domain digital-to-analog converter unit group in DIF-SUM , the sum of I Figure 3 output by all PMOS differential current domain digital-to-analog converter units in the PMOS differential current domain digital-to-analog converter unit group in DAC-COMP . COMP-SUM .

[0037] The structure of the NMOS single-ended / differential current domain digital-to-analog converter is symmetrical with the PMOS single-ended / differential current domain digital-to-analog converter, and all PMOSs in the common source common gate current mirror except switches are replaced with NMOS. Therefore, it is not described here.

[0038] As Figure 5As shown, a digital potentiostat based on linearity calibration technology of the present invention is applied to a wireless passive electrochemical sensing system. This wireless passive electrochemical sensing system consists of a sensing and transmitting end and a power supply and receiving end. The power supply and receiving end consists of an antenna, a signal source, and a reader module. The signal source transmits radio frequency signals to the sensing and transmitting end via the antenna for wireless power supply. The sensing and transmitting end consists of an antenna, an impedance matching network, a backscatter switch, a rectifier, a power management module, an electrochemical sensor, and the digital potentiostat based on linearity calibration technology of the present invention. The antenna in the sensing and transmitting end receives radio frequency signals from the air. The impedance matching network matches the impedance of the antenna with the impedance of the subsequent modules to achieve minimal energy attenuation. The rectifier converts the AC radio frequency signal into a DC signal that can be used for power supply, powering the power management module. The power management module provides the digital potentiostat with the required supply voltage, bias voltage, and bias current. The digital potentiostat connects to the electrochemical sensor and converts the current signal flowing through the electrochemical sensor into a digital signal applied to the backscatter switch. Backscatter switches alter the antenna's reflection coefficient by changing its impedance, thus enabling backscatter communication. The reader at the power supply and receiver ends receives the backscattered signal via the antenna, and after decoding it, information about the magnitude of the sensing current from the electrochemical sensor at the sensing and transmitting ends can be obtained.

[0039] like Figure 6 As shown, this invention discloses a digital potentiostat based on linearity calibration technology applied to a wireless active electrochemical sensing system. This system comprises a sensing and transmitting end and a receiving end. The sensing and transmitting end consists of an electrochemical sensor, a power supply, a digital potentiostat based on linearity calibration technology, an active transmitter, and an antenna. The power supply module provides power to the digital potentiostat and the active transmitter. The digital potentiostat connects to the electrochemical sensor, converting the current signal flowing through the sensor into a digital signal and transmitting it to the active transmitter. The active transmitter transmits the digital signal outward through the antenna. The reader at the receiving end receives the signal from the sensing and transmitting end through the antenna, decodes it, and obtains information about the magnitude of the sensing current of the electrochemical sensor at the sensing and transmitting end.

[0040] In summary, the application innovatively constructs a digital constant potentiostat based on linearity calibration technology, which discards the operational amplifier in the existing constant potentiostat and uses a current domain digital-to-analog converter to provide a sensing current for an electrochemical sensor. In order to achieve a large dynamic range of sensing current detection from picoampere (pA) to milliamperes (mA) while maintaining high linearity, the operational amplifier in the existing constant potentiostat requires high power consumption, while the power consumption of the current domain digital-to-analog converter used in the application is almost equal to the size of the sensing current, and the remaining modules are digital modules, which have very low power consumption. At the same time, the output signal of the digital constant potentiostat constructed by the application includes complementary current size information embodied in the frequency change of the output signal and control code word information embodied in the amplitude change of the output signal, so that the mapping relationship between the real sensing current size to be detected and the control code word can be calibrated by means of the quantitative mapping relationship between the complementary current size and the control code word, thereby realizing high linearity sensing current detection. Compared with the existing constant potentiostat, the digital constant potentiostat based on linearity calibration technology constructed by the application realizes a larger dynamic range and higher linearity at extremely low power consumption.

[0041] The above is only the preferred embodiment of the application, and does not limit the application in any form. Although the implementation process of the application has been described in detail above, those skilled in the art can still modify the technical solutions recorded in the above examples, or replace some of the technical features. Any modification, equivalent replacement, etc. within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. A digital potentiostat based on linearity calibration technique, connected to an electrochemical sensor, characterized in that, The constant potential device comprises a quantizer, a control logic module, a current domain digital-to-analog converter, an oscillator and a frequency mixer. The reference electrode of the electrochemical sensor is connected to the quantizer, and the counter electrode is connected to the current domain digital-to-analog converter. The quantizer monitors the potential change of the reference electrode and converts the potential change into a digital signal and then transmits the digital signal to the control logic module. The control logic module calculates the control code word of the current domain digital-to-analog converter at the next moment according to the digital signal converted and output by the quantizer and the control code word of the current domain digital-to-analog converter at the last moment, then performs digital signal processing on the control code word by using a dynamic element matching technology, and then transmits the processed control code word to the current domain digital-to-analog converter. The current domain digital-to-analog converter converts the digital control code word into an analog sensing current and a complementary current, the branch of the sensing current is connected to the counter electrode of the electrochemical sensor, and the complementary current is transmitted into the oscillator after being summed with the bias current provided by the electrochemical sensing system in which the digital constant potential device is currently located. Specifically, the current domain digital-to-analog converter is composed of a single-ended current domain digital-to-analog converter unit group and a differential current domain digital-to-analog converter unit group, the single-ended current domain digital-to-analog converter unit group is composed of N single-ended current domain digital-to-analog converter units, the differential current domain digital-to-analog converter unit group is composed of M differential current domain digital-to-analog converter units, N and M are positive integers, each output of a multi-output common-source common-gate current mirror contained in the single-ended current domain digital-to-analog converter unit copies the input reference current in proportion, each output terminal of the common-source common-gate current mirror contains a switch controlled by the control code word output by the control logic module, and the output currents of each output of the common-source common-gate current mirror are summed and then connected to the sensing current branch of the current domain digital-to-analog converter. Each differential output of the multi-differential output common-source common-gate current mirror contained in the differential current domain digital-to-analog converter unit replicates the input reference current in proportion, and each differential output of the common-source common-gate current mirror contains a pair of complementary switches S and S controlled by a control code word output by a control logic module 互补 , forming two current branches, and at the same time, only one switch is turned on, and the current flowing through the switch S in each differential output of the common-source common-gate current mirror is summed and connected to the sensing current branch, and the current flowing through the switch S 互补 in each differential output of the common-source common-gate current mirror is summed and connected to the complementary current branch; The oscillator converts the summed current signal into a frequency signal positively correlated with the complementary current and transmits the frequency signal to the frequency mixer, and the current domain digital-to-analog converter also transmits the digital control code word at the current moment to the frequency mixer. The frequency mixer outputs a modulation signal with a frequency change related to the size of the complementary current and an amplitude change related to the control code word, and the modulation signal serves as the output signal of the digital constant potential device.

2. A digital potentiostat based on linearity calibration technique as claimed in claim 1, wherein, The quantizer adopts a dynamic comparator or a static comparator.

3. A digital potentiostat based on linearity calibration technique as claimed in claim 1, wherein, The working electrode of the electrochemical sensor is connected to the power supply / ground terminal of the constant potential device according to the positive / negative bias voltage applied by the three-electrode system in which the electrochemical sensor is located.

4. A digital potentiostat based on linearity calibration technique as claimed in claim 1, wherein, The single-ended current domain digital-to-analog converter unit and the differential current domain digital-to-analog converter unit specifically adopt NMOS / PMOS single-ended current domain digital-to-analog converter units and NMOS / PMOS differential current domain digital-to-analog converter units according to the positive / negative bias voltage applied by the three-electrode system, that is, the MOS tube type adopted is N / P type, and the MOS tube type adopted in the input common-source common-gate current mirror in the oscillator is P / N type.

5. A digital potentiostat based on linearity calibration technique as claimed in claim 4, wherein, The PMOS single-ended current domain digital-to-analog converter unit contains a multi-output common-source common-gate current mirror, and the multi-output common-source common-gate current mirror is composed of a reference current input circuit and a multi-output circuit. The reference current input circuit comprises PMOS tubes PM1~PM2, a resistor R1, and a reference current I BP1 The drain of the PM2 is connected, the gate of the PM2 is connected with the drain, the source of the PM2 is connected with the drain and the gate of the PM1, the source of the PM1 is connected with one end of the resistor R1, the other end of the resistor R1 is connected with the power supply of the digital constant potential device; each output circuit in the multi-output circuit comprises PMOS tubes PM3~PM4, a resistor R2, a switch S1, one end of the resistor R2 is connected with the power supply of the digital constant potential device, the other end is connected with the source of the PM3, the gate of the PM3 is connected with the gate of the PM1, the drain of the PM3 is connected with the source of the PM4, the gate of the PM4 is connected with the gate of the PM2, the drain of the PM4 is connected with one end of the switch S1; the substrate of the PMOS tubes PM1~PM4 and the PMOS tubes in the switch S1 are connected with the power supply, the substrate of the NMOS tubes in the switch S1 is connected with the ground; the other end of the switch S1 of all the output circuits in the common source and common gate current mirror is connected together.

6. A digital potentiostat based on linearity calibration technique as claimed in claim 4 wherein, The PMOS differential current domain digital-to-analog converter unit comprises a multi-way differential output common-gate current mirror, which is composed of a differential reference current input circuit, a PMOS tube PM7, a resistor R4 and a multi-way differential output circuit. BP2 The drain of the PM6 is connected to the drain of the PM5, the gate of the PM6 is connected to the drain of the PM6, the source of the PM6 is connected to the gate of the PM5, the source of the PM5 is connected to one end of the resistor R3, the other end of the R3 is connected to the power supply of the digital constant potentiometer; each differential output circuit in the multi-way differential output circuit comprises a PMOS tube PM8 and a pair of complementary switches S2-S3; one end of the resistor R4 is connected to the power supply of the digital constant potentiometer, the other end is connected to the source of the PM7, the gate of the PM7 is connected to the gate of the PM5, the drain of the PM7 is connected to the source of the PM8, the gate of the PM8 is connected to the gate of the PM6, the drain of the PM8 is connected to one end of the switch S2 and the switch S3; the substrate of the PMOS tubes PM5-PM8 and the PMOS tubes in the switches S2-S3 is connected to the power supply, the substrate of the NMOS tubes in the switches S2-S3 is connected to the ground; the other end of the switch S2 in all differential output circuits in the multi-way differential output common-gate current mirror is connected together, the other end of the switch S3 is connected together.

7. A digital potentiostat based on linearity calibration technique as claimed in claim 1 wherein, The oscillator adopts a ring oscillator, which converts the summed current signal into a frequency signal positively correlated with the complementary current, specifically: the summed current signal is used as the control current of the ring oscillator, the control current is copied through the common-source common-gate current mirror, and then current limiting is performed at the power supply end and the ground end of the ring oscillator; the frequency of the oscillation signal output by the ring oscillator is positively correlated with the size of the complementary current.

8. A digital potentiostat based on linearity calibration technique as claimed in claim 1 wherein, The frequency signal from the oscillator is connected to one input end of a two-input logic AND gate, and the control code word of the current domain digital-to-analog converter at the current moment is connected to the other input end; the AND gate outputs a modulated digital signal as the output signal of the digital constant potential device, the frequency variation of the output signal contains the information of the size of the complementary current, and the amplitude variation of the output signal contains the information of the control code word of the current domain digital-to-analog converter at the current moment.

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