6604425 B1 abstract a method and apparatus for comparing a force to a signal or comparing two signals through mechanical movement of capacitive plates in a transducer the transducer plates are separated by d which in one embodiment is preferably a linear function of a pressure or force f in that embodiment application of a signal i to the plates will cause a voltage representing a correlation between f and i to appear between the plates in another embodiment instead of an external mechanical force or pressure an electrical signal v related to a signal s may drive the transducer plates to achieve a voltage indicating a correlation between s and the signal input i transducers to practice the invention may be microelectromechanical devices fabricated using integrated circuit techniques to permit small size and low cost application_number US 59111300 A description in order to compare two signals according to the present invention a physical capacitive device is required according to a preferred embodiment such a device preferably has capacitive plates which are separated by a distance d which varies as a linear function of an applied force or pressure fig1 a and 1 b show a top and side view respectively of a.