Reminiscences on the invention of the switched-capacitor network

ABOUT mid year, 1965, I was asked if I had any experience with filters where the center frequency could be changed without changing the network components. At a later time, I realized that the reference was to lead-lag carrier servo compensation networks using TV-path filter techniques. Not being aware of such methods, but fascinated by the thought, I asked how the networks were structured. The verbal, incomplete, reply was, “They look like they have ‘switches and capacitors.’“ That inadequate description of the N-path filter and my complete lack of knowledge coupled with youthful curiosity led to what I thought must be a means for realizing a network where the singularities could vary without changing the element values.