Processing circuits of weak capacitance signal for spherical scattering electrical-field probing sensor

A spherical scattering electrical-field probe (SSEP) with noncontact, 3D isotropy and approximate point probing characteristics has been proposed for high-precision measurement of micro and small structures with large aspect ratio. Development of signal processing circuits for detection of weak cpacitantive signal on sub-picofarad level is the key to realize nanometer resolution. In this paper, a set of signal processing circuits based on operational capacitance measurement principle is proposed, and characteristics of the circuits are theorically analyzed and optimized. Experimental results indicates that resolution of 1 nm and nonlinearity of 6 nm are achieved with the proposed signal processing circuits for a SSEP with φ2.5 mm probing ball.