Patent ID: 6987391

Claim:
A method of substantially cancelling a repeatable interference signal by synchronous rejection, wherein: a desired signal exists that is a function of a repeatable stimulus signal; and a response signal exists that includes the interference signal plus the desired signal, comprising: defining first and second equal time intervals; wherein: the interference signal has a first interference waveshape during the first time interval and a second interference waveshape during the second time interval; the relationship of the starting time of the second time interval to the starting time of the first time interval is such that the second interference waveshape is expected to be substantially the same as the first interference waveshape; and a repeatable reference signal has a first reference waveshape during the first time interval and a second reference waveshape during the second time interval; adjusting the reference signal during the time between the first and second time intervals so that an uninverted second reference waveshape is the same as the uninverted first reference waveshape; and integrating a product of the response signal times the reference signal over the first and second time intervals to obtain a final result substantially without the interference signal, wherein the second reference waveshape is in an inverted state relative to the state of inversion of the first reference waveshape.