MODELING OF SILICON CONDENSER MICROPHONES

Several models concerning the sensitivity of capacitive pressure senso rs have been presented in the past. Modelling of condenser microphones , which can be considered to be a special type of capacitive pressure sensor, usually requires a more complicated analysis of the sensitivit y, because they have a strong electric field in the air gap. It is fou nd that the mechanical sensitivity of condenser microphones with a cir cular diaphragm, either with a large initial tension or without any in itial tension, increases with increasing bias voltage (and the corresp onding static deflection), whereas the mechanical sensitivity of other capacitive pressure sensors does not depend on the static deflection. It is also found that the mechanical sensitivity increases with incre asing input capacitance of a preamplifier. In addition, the open-circu it electrical sensitivity and, consequently, the total sensitivity too , also increases with increasing bias voltage (or static deflection). However, the maximum allowable sound pressure at which the diaphragm c ollapses, an effect that has to be taken into account, decreases with increasing static deflection in most cases, ultimately resulting in an optimum value for the bias voltage. The model for microphones with a circular highly tensioned diaphragm has been verified successfully for two microphone types.