Current and voltage sensing in ACT 'block NDS' transversal filters

Fixed ACT (acoustic charge transport) transversal filters look like apodized SAW transducers, but because they capacitively sense charge packets directly below the surface, the individual lines can be smeared together into two plates separated by a wavy boundary. In the conventional voltage sense approach, the shape of the gap is made to be the desired impulse response, and each side is loaded by an RC network. In the current sense approach described, the shape of the gap is the integral of the desired impulse response and the current, which must oscillate from one nondestructive sense (NDS) plate to the other, is taken to be the output. Unlike voltage sensing, current sensing does not have a DC pedestal in its impulse response to create an undesired passband at low frequencies.<
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