The read-out characteristics of an integrated charge amplifier for potentially broad-field applications

Presents an improved integrable charge amplifier circuit which is utilized to measure a small capacitance. Applications of the basic charge amplifier are primarily in the sensor area to read-out the capacitance of a micromechanical sensor. The amplifier was implemented in a bipolar full-custom design, and its response with the sensing capacitance was measured. Measurements have shown that the performance of the basic charge amplifier was affected with a non-linearity, which increased with drive frequency. A careful study of the origin of this undesired effect is required to optimize the amplifier characteristics. This effort implies a complete description of the charge amplifier in terms of small-signal modeling and biasing, which leads to the formulation of circuit performance as a function of circuit components and drive frequency. This analysis has identified the common-mode rejection as the prime cause of the nonlinearity and has resulted in an improved circuit, which can be used in many measuring applications