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IN the fall of 1970, I undertook some consulting work for TRW and was asked by them to help develop the design details for a novel low-cost infrared ground mapping system. Originally, I was concerned with the optical design and with analysis of the expected performance, i.e., the relationship between signal-to-noise ratio, ground coverage rate, and resolution. After a while, with these matters under control, I was asked by TRW to become involved in solving a problem that had arisen in the design of the sensor's focal plane. It is in working on this matter that I developed the concept for realization on an integrated circuit chip of what is now referred to as a switched-capacitor filter, which concept I reported in my 1972 paper . I believe that this was the first published paper developing the switched-capacitor filter concept and noting its high degree of compatibility with silicon circuitry.