# US 11,906,559 B2 · Enhanced impedance measurement using CTMU > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,906,559 B2 - Document ID: US11906559B2 - Status: Granted - Kind: B2 - Application number: 17/839,964 - Filed: 2022-06-14 - Published: 2022-12-29 - Granted: 2024-02-20 - Earliest claimed: 2021-06-24 - Assignees: Microchip Technology Incorporated - Applicants: Microchip Technology Incorporated - Inventors: Bogdan Bolocan; Ezana Haile; Pat Richards - Web page: https://patentgrep.com/patent/US11906559B2 ## CPC - 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) - G01N 27/223: {for determining moisture content, e.g. humidity (rain detectors on vehicle windows B60S1/0825)} - G01R 27/28: Measuring attenuation, gain, phase shift or derived characteristics of electric four pole networks, i.e. two-port networks; Measuring transient response (in line transmission systems H04B3/46) - G01R 27/32: in circuits having distributed constants {, e.g. having very long conductors or involving high frequencies} - H04B 3/46: Monitoring; Testing - H04B 17/0085: {using test signal generators} - H04B 17/103: {Reflected power, e.g. return loss} - 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) - H04B: TRANSMISSION ## Abstract A method and apparatus for measuring an unknown impedance. The apparatus comprises a first input to receive a first signal generated by a first portion of a sensor circuit, the first portion comprising an unknown impedance and a first known resistance, the unknown impedance to vary based upon a phenomenon to be measured by the sensor circuit. The apparatus also comprises a second input to receive a second signal generated by a second portion of the sensor circuit, the second portion of the sensor circuit comprising a known impedance and a second known resistance. And the apparatus comprises control logic to, based on a difference in time at which each of the first input and the second input reach a reference voltage, determine a measurement of the sensor circuit. ## Claims ### Claim 1 An apparatus, comprising: a first input to receive a first signal generated by a first portion of a sensor circuit, the first portion of the sensor circuit comprising an unknown impedance and a first known resistance, the unknown impedance to vary based upon a phenomenon to be measured by the sensor circuit; a second input to receive a second signal generated by a second portion of the sensor circuit, the second portion of the sensor circuit comprising a known impedance and a second known resistance; and a charge time measurement unit (CTMU) circuit to, based on a difference in time at which each of the first input and the second input reach a reference voltage, determine a measurement of the sensor circuit. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein the CTMU circuit is to, in order to determine the measurement of the sensor circuit based on the difference in time at which each of the first input and the second input reach the reference voltage: apply a current source or sink to a reference capacitor based on a determination that either the first input or the second input has reached the reference voltage; remove the current source or sink from the reference capacitor based on a determination that the other of the first input and the second input has reached the reference voltage; and determine the measurement of the sensor circuit based upon a voltage of the reference capacitor after application then removal of the current source or sink to the reference capacitor. ### Claim 3 (depends on 2) The apparatus of claim 2, wherein the CTMU circuit causes an analog to digital converter to measure the voltage of the reference capacitor in order to determine the measurement of the sensor circuit based on the difference of time at which each of the first input and the second input reach the reference voltage. ### Claim 4 (depends on 2) The apparatus of claim 2, wherein a hold time to determine the voltage of the reference capacitor is independent of the time the current source or sink was applied to the reference capacitor. ### Claim 5 (depends on 1) The apparatus of claim 1, wherein: the unknown impedance is a sensor with a variable capacitance that varies based upon the phenomenon to be measured; the first known resistance is coupled to a common potential; the known impedance is a reference capacitor with a fixed capacitance; and the second known resistance is coupled to the common potential. ### Claim 6 (depends on 5) The apparatus of claim 5, wherein the difference in time at which each of the first input and the second input reach the reference voltage is based upon a difference between the variable capacitance and the fixed capacitance. ### Claim 7 (depends on 1) The apparatus of claim 1, wherein the CTMU circuit is to issue a sensor input voltage to the sensor circuit to cause the first signal and the second signal to change to reach the reference voltage. ### Claim 8 (depends on 1) The apparatus of claim 1, wherein the CTMU circuit is to issue a sensor input voltage to the sensor circuit to cause the sensor circuit to: begin charging or discharging the unknown impedance to generate the first signal; and begin charging or discharging the known impedance to generate the second signal. ### Claim 9 A method for measuring an unknown and variable impedance comprising: receiving a first signal generated by a first portion of a sensor circuit, the first portion of the sensor circuit comprising the unknown and variable impedance and a first known resistance, the unknown and variable impedance to vary based upon a phenomenon to be measured, receiving a second signal generated by a second portion of the sensor circuit, the second portion of the sensor circuit comprising a known impedance and a second known resistance, and determining, based on a difference in time at which each of the first signal and the second signal reach a reference voltage, a measurement of the sensor circuit. ### Claim 10 (depends on 9) The method for measuring an unknown and variable impedance of claim 9 comprising: when either the first signal or the second signal reaches the reference voltage, begin applying a current source or a sink with a known current to a timing capacitor with a known capacitance; and when the other of the first signal or the second signal reaches the reference voltage, terminate application of the current source or sink to the timing capacitor; wherein the step of determining a measurement of the sensor circuit is based on the resultant voltage of the timing capacitor. ### Claim 11 (depends on 10) The method for measuring an unknown and variable impedance of claim 10 comprising: measuring a voltage of the timing capacitor in order to determine the measurement of the sensor circuit. ### Claim 12 (depends on 11) The method for measuring an unknown and variable impedance of claim 11 wherein the hold time for measuring the voltage of the timing capacitor is independent of the time the current source was applied to the timing capacitor. ### Claim 13 (depends on 9) The method for measuring an unknown and variable impedance of claim 9 wherein: the unknown impedance is a humidity sensor with a variable capacitance that varies based upon the humidity of the air around the humidity sensor; the first known resistance is coupled to a common potential; the known impedance is a reference capacitor with a fixed capacitance; and the second known resistance is coupled to the common potential. ### Claim 14 (depends on 13) The method for measuring an unknown and variable impedance of claim 13 wherein the difference in time at which each of the first signal and the second signal reach the reference voltage is based upon a difference between the variable capacitance and the fixed capacitance. ### Claim 15 (depends on 9) The method for measuring an unknown and variable impedance of claim 9, comprising issuing a sensor input voltage to the sensor circuit to cause the first signal and the second signal to change to reach the reference voltage. ### Claim 16 (depends on 15) The method for measuring an unknown and variable impedance of claim 15, wherein the unknown and variable impedance is a sensor with a variable capacitance that varies based upon the phenomenon to be measured, the method comprising: begin charging or discharging the variable capacitor to generate the first signal, the variable capacitor to vary based upon the phenomenon to be measured by the sensor circuit; and begin charging or discharging a sensor reference capacitance to generate the second signal. ### Claim 17 A sensing apparatus to measure a phenomenon, comprising: a voltage input to receive a pulsed input direct current (DC) voltage; a bridge sensor circuit including: a first bridge leg circuit including a variable impedance component, the variable impedance component including an impedance, which varies based upon the phenomenon, coupled at a first output to a first reference resistance connected in series with the variable impedance component, and a second bridge leg circuit including a reference impedance component coupled at a second output to a second reference resistance connected in series with the reference impedance component; a first comparator coupled to the first output and a reference voltage; and a second comparator coupled to the second output and the reference voltage; wherein a combination of an output of the first comparator and an output of the second comparator represent a measurement of the phenomenon. ### Claim 18 (depends on 17) The sensing apparatus of claim 17 to measure a phenomenon, wherein: the variable impedance component is a variable capacitor; the first reference resistance is connected in series between the variable capacitor and ground; the reference impedance component is a reference capacitor; and the second reference resistance is connected in series between the reference capacitor and ground. ### Claim 19 (depends on 17) The sensing apparatus of claim 17 to measure a phenomenon, wherein: the output of the first comparator is coupled to a timing circuit; the output of the second comparator is coupled to the timing circuit; and the timing circuit to measure a time between a first change in one of the two comparator outputs and a second change in the other of the two comparator outputs, wherein the time represents a measurement of the phenomenon. ### Claim 20 (depends on 17) The sensing apparatus of claim 17 to measure a phenomenon, wherein: the output of the first comparator is coupled to a timing circuit; the output of the second comparator is coupled to the timing circuit; and the timing circuit to measure a time between a first change in one of the two comparator outputs and a second change in the other of the two comparator outputs, wherein the time represents a measurement of the phenomenon.