# US 4,400,809 A · Arbitrary drive for magnetic field waveform control > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,400,809 A - Document ID: US4400809A - Status: Granted - Kind: A - Application number: 06/239,280 - Filed: 1981-03-02 - Granted: 1983-08-23 - Earliest claimed: 1981-03-02 - Assignees: Texas Instruments Incorporated - Inventors: Robert J. Whitinger - Web page: https://patentgrep.com/patent/US4400809A ## CPC - G01R 31/2834: {Automated test systems [ATE]; using microprocessors or computers (G01R31/317 takes precedence; ATE for detection of defective computer hardware G06F11/2736)} - G11C 19/085: {Generating magnetic fields therefor, e.g. uniform magnetic field for magnetic domain stabilisation} - G11C 29/003: {in serial memories} - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) - G11C: STATIC STORES (semiconductor memory devices H10B) ## Abstract Disclosed is a method and apparatus for digital implementation and closed loop feedback of magnetic field waveforms utilizing three channels of a four channel incrementally programmable voltage source to drive field coils in each of three spatial axes, respectively. A fourth channel is utilized for signal conditioning of an output signal from a magnetic bubble memory undergoing test by injecting inverted noise to maximize the signal-to-noise ratio. ## Claims ### Claim 1 An apparatus for controlling magnetic fields in one or more spatial axes comprising: (a) means for inducing magnetic fields in one or more spatial axes; (b) means for controlling said induced magnetic fields utilizing a set of programmed increments in digital format; (c) means for sensing said induced magnetic fields; and (d) means connected to said means for controlling and to said means for sensing said induced magnetic fields for modifying said induced magnetic fields in a closed loop feedback system such that said sensed magnetic fields are made to more closely resemble said set of programmed increments. ### Claim 2 (depends on 1) An apparatus as in claim 1 wherein said means for controlling the induced magnetic fields is comprised of a programmable digital computer system utilizing three channels of a multiple channel network to control the magnetic field of each of the three spatial axes independently of the others. ### Claim 3 (depends on 2) An apparatus as in claim 2 wherein said means for controlling said induced magnetic field includes: (a) means for sampling each field coil current; (b) means for comparing said current to a programmed set of waveform values; and (c) means for modifying said sampled current to more closely resemble said programmed set of waveform values. ### Claim 4 (depends on 2) An apparatus as in claim 2 wherein said means for controlling said induced magnetic field is comprised of a software programmable analog-to-digital converter interconnected between a field coil current sensing device and said programmable digital computer system. ### Claim 5 A method for controlling magnetic fields in one or more spatial axes comprised of the steps of: (a) programming a desired current waveform into a digital computer; (b) converting said current waveform into an analog voltage waveform; (c) amplifying said analog voltage waveform and applying it across a field coil, said coil developing an induced magnetic field corresponding to the resultant analog current waveform; (d) sampling said analog current waveform incrementally; (e) comparing said samples with said programmed current waveform; and (f) adjusting said analog voltage waveform with respect to said comparing step for the purpose of causing said sampled waveform to more nearly approximate said programmed waveform. ### Claim 6 (depends on 5) A method as in claim 5 including the step of operating a signal conditioning feedback circuit, said circuit operable to provide incremental sampling of an output signal from a magnetic bubble memory device undergoing test, for the purpose of detecting noise therein, and adding said noise in an inverted form to said signal. ### Claim 7 (depends on 6) A method as in claim 6 wherein the step of operating a signal conditioning feedback circuit is included the steps of: (a) sampling a signal from a magnetic bubble memory device undergoing test and detecting noise therein; (b) inverting said detected noise in an incremental format; and (c) adding said inverted noise to said signal at an adjustable rate for the purpose of increasing the signal to noise ratio in said signal. ### Claim 8 (depends on 5) A method as in claim 5 wherein said step of converting a programmed waveform into an analog voltage waveform is comprised of utilizing three channels of a multiple channel digital computer system to incrementally control the magnetic field of each of three spatial axes independently of the others. ### Claim 9 (depends on 8) A method as in claim 8 wherein the step of converting a programmed waveform includes the steps of: (a) sampling each field coil current; (b) comparing said current to the programmed current waveform value; and (c) modifying said sampled current to more closely resemble said programmed current waveform value. ### Claim 10 (depends on 8) A method as in claim 8 wherein the step of converting a programmed waveform includes the step of utilizing a software programmable analog-to-digital converter interconnected between a field coil current sensing device and said programmable digital computer system. ### Claim 11 A magnetic bubble memory testing method comprising the steps of: (a) programming a desired waveform into a multichannel digital computer; (b) converting signals from said computer into analog waveforms; (c) amplifying said analog waveforms; (d) converting said analog waveforms into magnetic fields; (e) sensing said magnetic fields and providing feedback to said digital computer; (f) improving an output signal from a magnetic bubble memory undergoing test utilizing one channel of said multichannel digital computer; and (g) controlling the timing of the above steps with respect to the various channels and functions. ### Claim 12 (depends on 11) A method as in claim 11 further including the step of switching programmed current waveforms in one or more channels independently of the other channels. ### Claim 13 A magnetic bubble memory testing apparatus comprising: (a) a multichannel digital computer; (b) means for converting a series of digital signals into analog waveforms; (c) means for amplifying said analog waveforms; (d) means for converting said waveforms into magnetic fields; (e) means for sensing said magnetic fields and providing feedback to said digital computer; (f) a magnetic bubble memory undergoing test in magnetic communication with said magnetic fields to produce an output signal; (g) means for improving said output signal from said magnetic bubble memory utilizing one channel of said multichannel digital computer; and (h) means for interconnection and timing control of said apparatus. ### Claim 14 (depends on 13) Apparatus as in claim 13 further including means connected to said means for converting to provide a selected one of a plurality of series of digital signals thereto.