# US 11,112,481 B2 · Differential circuit calibration apparatus and method > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,112,481 B2 - Document ID: US11112481B2 - Status: Granted - Kind: B2 - Application number: 16/418,710 - Filed: 2019-05-21 - Published: 2019-11-28 - Granted: 2021-09-07 - Earliest claimed: 2018-05-24 - Assignees: Cirrus Logic, Inc. - Applicants: Cirrus Logic International Semiconductor Ltd. - Inventors: Sarang Vadnerkar; Vinod Jayakumar - Web page: https://patentgrep.com/patent/US11112481B2 ## CPC - G01R 35/005: {Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references (G01R33/0035, G01R35/002 take precedence)} - G01R 19/10: Measuring sum, difference or ratio - H03F 3/45475: {using IC blocks as the active amplifying circuit} - H03G 3/20: Automatic control ({H03G3/005 takes precedence;} combined with volume compression or expansion H03G7/00) - H03K 5/24: the characteristic being amplitude - H03M 1/00: Analogue/digital conversion; Digital/analogue conversion (conversion of analogue values to or from differential modulation H03M3/00) - H03M 1/1057: {by trimming, i.e. by individually adjusting at least part of the quantisation value generators or stages to their nominal values} - H03M 1/765: {using a single level of switches which are controlled by unary decoded digital signals} - H02M 3/07: using capacitors charged and discharged alternately by semiconductor devices with control electrode {, e.g. charge pumps} - H03F 3/217: Class D power amplifiers; Switching amplifiers - H03F 2200/03: the amplifier being designed for audio applications - H03F 2203/45048: Calibrating and standardising a dif amp - H03F 2203/45512: the FBC comprising one or more capacitors, not being switched capacitors, and being coupled between the LC and the IC - H03G 1/0088: {using discontinuously variable devices, e.g. switch-operated} - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) - H03F: AMPLIFIERS - H03G: CONTROL OF AMPLIFICATION - H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M) - H03M: CODING; DECODING; CODE CONVERSION IN GENERAL (using fluidic means F15C4/00; optical analogue/digital converters G02F7/00; coding, decoding or code conversion, specially adapted for particular applications, see the relevant subclasses, e.g. G01D, G01R, G06F, G06T, G09G, G10L, G11B, G11C, H04B, H04L, H04M, H04N; ciphering or deciphering for cryptography or other purposes involving the need for secrecy G09C) - H02M: APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF (transformers H01F; dynamo-electric converters H02K47/00; controlling transformers, reactors or choke coils, control or regulation of electric motors, generators or dynamo-electric converters H02P) ## Abstract An apparatus for calibrating a differential circuit that includes a differential integrator having an input, a gain, and an output connected to a comparator. The differential integrator output is chargeable to a threshold prior to an integration period. The differential integrator integrates the input during the integration period such that the differential integrator output goes toward zero from the threshold. The comparator detects the output of the differential integrator reaching zero. The apparatus includes a closed-loop gain trim circuit to perform a coarse calibration to adjust and set the gain of the differential integrator and a reference generator that generates the threshold to which the differential integrator output is pre-charged. The reference generator is trimmable during a fine calibration to adjust and set the threshold to correct for residual gain error in the differential circuit remaining after the coarse calibration is performed. ## Claims ### Claim 1 An apparatus for calibrating a differential circuit that includes a differential integrator having an input, a gain, and an output connected to a comparator, wherein the differential integrator output is chargeable to a threshold prior to an integration period, wherein the differential integrator integrates the input during the integration period such that the differential integrator output goes toward zero from the threshold, wherein the comparator detects the output of the differential integrator reaching zero, the apparatus comprising: a closed-loop gain trim circuit to perform a coarse calibration to adjust and set the gain of the differential integrator; a reference generator that generates the threshold to which the differential integrator output is pre-charged; and wherein the reference generator is trimmable during a fine calibration to adjust and set the threshold to correct for residual gain error in the differential circuit remaining after the coarse calibration is performed. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein the input of the differential integrator senses a current drawn from a voltage source/supply; and wherein the differential circuit is operable to detect the over-threshold condition of an average current drawn from the voltage source/supply if the comparator detects the output of the differential integrator reaches zero. ### Claim 3 (depends on 2) The apparatus of claim 2, wherein after the coarse calibration and fine calibration are performed, the differential circuit is configured to detect the over-threshold condition of the average current drawn from the voltage source/supply with a range of error less than 0.3%. ### Claim 4 (depends on 2) The apparatus of claim 2, wherein the input of the differential integrator senses the current drawn from the voltage source/supply across a sense resistor; wherein a resistance value of the sense resistor is configurable to a plurality of different values; and wherein the threshold generated by the reference generator is scalable to a plurality of different values corresponding to the plurality of different configurable resistance values of the sense resistor. ### Claim 5 (depends on 1) The apparatus of claim 1, wherein the fine calibration is performed by sourcing a known current value to the differential circuit for a known value of the integration period and adjusting the threshold in an iterative manner until successive transitions of the output of the comparator are detected. ### Claim 6 (depends on 1) The apparatus of claim 1, wherein the reference generator comprises a trimmable digital-to-analog converter (DAC). ### Claim 7 (depends on 6) The apparatus of claim 6, wherein the fine calibration applies a successive approximation register (SAR) algorithm to the trimmable DAC. ### Claim 8 (depends on 6) The apparatus of claim 6, wherein the reference generator is programmable to a plurality of different values of the threshold; and wherein the coarse calibration and fine calibration are performed at a single programmed value of the plurality of different values of the threshold. ### Claim 9 (depends on 8) The apparatus of claim 8, wherein resistive elements of the DAC are accurately sized to achieve a range of error less than 0.3% for detection of an over-threshold condition for each of the plurality of different values of the threshold after performance of the coarse calibration and fine calibration at the single value. ### Claim 10 (depends on 1) The apparatus of claim 1, wherein the coarse calibration comprises adjusting and setting a capacitance of an integrating capacitor of the differential integrator or an integrating resistor of the differential integrator. ### Claim 11 (depends on 1) The apparatus of claim 1, wherein single-ended outputs of the differential integrator concurrently cross a common mode reference when the output of the differential integrator reaches the zero value; wherein the reference generator converts the common mode reference to the threshold; and wherein the reference generator is trimmable during the fine calibration to adjust and set the threshold by adjusting and setting the common mode reference. ### Claim 12 (depends on 1) The apparatus of claim 1, wherein the reference generator is adjustable to support a plurality of different values of the integration period. ### Claim 13 A method for calibrating a differential circuit that includes a differential integrator having an input, a gain, and an output connected to a comparator, wherein the differential integrator output is chargeable to a threshold prior to an integration period, wherein the differential integrator integrates the input during the integration period such that the differential integrator output goes toward zero from the threshold, wherein the comparator detects the output of the differential integrator reaching zero, the method comprising: performing, in a closed-loop manner, a coarse calibration to adjust and set the gain of the differential integrator; and performing a fine calibration of a trimmable reference generator that generates the threshold to which the differential integrator output is pre-charged by adjusting and setting the threshold to correct for residual gain error in the differential circuit remaining after the coarse calibration is performed. ### Claim 14 (depends on 13) The method of claim 13, wherein the input of the differential integrator senses a current drawn from a voltage source/supply; and wherein the differential circuit is operable to detect the over-threshold condition of an average current drawn from the voltage source/supply if the comparator detects the output of the differential integrator reaches zero. ### Claim 15 (depends on 14) The method of claim 14, wherein after the coarse calibration and fine calibration are performed, the differential circuit is configured to detect the over-threshold condition of the average current drawn from the voltage source/supply with a range of error less than 0.3%. ### Claim 16 (depends on 14) The method of claim 14, wherein the input of the differential integrator senses the current drawn from the voltage source/supply across a sense resistor; wherein a resistance value of the sense resistor is configurable to a plurality of different values; and wherein the threshold generated by the reference generator is scalable to a plurality of different values corresponding to the plurality of different configurable resistance values of the sense resistor. ### Claim 17 (depends on 13) The method of claim 13, wherein said performing the fine calibration comprises sourcing a known current value to the differential circuit for a known value of the integration period and adjusting the threshold in an iterative manner until successive transitions of the output of the comparator are detected. ### Claim 18 (depends on 13) The method of claim 13, wherein the reference generator comprises a trimmable digital-to-analog converter (DAC). ### Claim 19 (depends on 18) The method of claim 18, wherein said performing the fine calibration comprises applying a successive approximation register (SAR) algorithm to the trimmable DAC. ### Claim 20 (depends on 18) The method of claim 18, wherein the reference generator is programmable to a plurality of different values of the threshold; and wherein said performing the coarse calibration and the fine calibration are performed at a single programmed value of the plurality of different values of the threshold. ### Claim 21 (depends on 20) The method of claim 20, wherein resistive elements of the DAC are accurately sized to achieve a range of error less than 0.3% for detection of an over-threshold condition for each of the plurality of different values of the threshold after performance of the coarse calibration and fine calibration at the single value. ### Claim 22 (depends on 13) The method of claim 13, wherein said performing the coarse calibration comprises adjusting and setting a capacitance of an integrating capacitor of the differential integrator or an integrating resistor of the differential integrator. ### Claim 23 (depends on 13) The method of claim 13, wherein single-ended outputs of the differential integrator concurrently cross a common mode reference when the output of the differential integrator reaches the zero value; wherein the reference generator converts the common mode reference to the threshold; and wherein said performing a fine calibration by adjusting and setting the threshold comprises adjusting and setting the threshold by adjusting and setting the common mode reference. ### Claim 24 (depends on 13) The method of claim 13, wherein the reference generator is adjustable to support a plurality of different values of the integration period. ### Claim 25 A non-transitory computer-readable medium having instructions stored thereon that are capable of causing or configuring an apparatus for calibrating a differential circuit that includes a differential integrator having an input, a gain, and an output connected to a comparator, wherein the differential integrator output is chargeable to a threshold prior to an integration period, wherein the differential integrator integrates the input during the integration period such that the differential integrator output goes toward zero from the threshold, wherein the comparator detects the output of the differential integrator reaching zero, wherein the instructions cause or configure the apparatus to perform operations comprising: performing, in a closed-loop manner, a coarse calibration to adjust and set the gain of the differential integrator; and performing a fine calibration of a trimmable reference generator that generates the threshold to which the differential integrator output is pre-charged by adjusting and setting the threshold to correct for residual gain error in the differential circuit remaining after the coarse calibration is performed.