A Compact Measurement Technique for Detector Capacitance of Charge Amplifiers

A detector connected to a charge amplifier adds parasitic input capacitance that alters the amplifier's gain. The detector capacitance therefore must be characterized so as to properly account for its effect. This paper presents a novel, compact technique to measure the detector capacitance by exploiting the circuit elements within the charge amplifier itself. Reconfiguring the charge amplifier with programmable switches, a capacitor divider network emerges to measure the detector capacitance without the need for any accurate timing references and complex controls. Experimental results of the proposed charge amplifier fabricated in a 180-nm CMOS technology demonstrate the ability to measure the detector capacitance to within 3% of its actual value. An actual charge measurement is also presented.