| CPC G01N 21/3563 (2013.01) [G01N 21/9501 (2013.01); G01N 2021/3568 (2013.01); G01N 2201/06113 (2013.01)] | 17 Claims |

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1. An electronic circuit comprising:
signal processing electronics comprising:
a filter; and
output electronics; wherein the signal processing electronics is configured to:
receive, by receive circuitry included in the signal processing electronics, an electrical signal from a photodetector, wherein the electrical signal is generated by the photodetector based on a light beam from a location on a material including a signal of interest and one or more modulation frequencies;
discriminate, by the filter, a portion of the electrical signal proportional to at least one characteristic of the signal of interest from other components of the electrical signal using a filter having a filter transfer function including a notch at a notch frequency corresponding to one of the one or more modulation frequencies;
determine, by the filter, a value for the at least one characteristic of the signal of interest from the discriminated portion of the electrical signal; and
output, by the output electronics, the value of the at least one characteristic of the signal of interest, wherein:
the filter operates on samples of the electrical signal having a sample rate period:
the one or more modulation frequencies include a first modulation frequency; and
the first modulation frequency is selected such that a period of the first modulation frequency is an integer number of the sample rate period.
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