A Sensitivity Comparison of Three Transistorized DC Current-Feedback Electrometers
The theoretical equations for transistorized current-feedback dc electrometers have been developed and utilized for the design and evaluation of three electrometers containing (1) a bipolar transistor, (2) a junction field-effect transistor (JFET), and (3) a metal-oxide-semiconductor field-effect transistor (MOSFET) in the input stage. Each electrometer was evaluated in terms of input and output impedance, gain-bandwidth, drift characteristics, and output noise power spectra. For the experimental amplifiers, the measured minimum amplifiable dc input current was approximately 8 × 10-14 amp for the bipolar transistor electrometer, 4 × 10-15 amp for the JFET electrometer, and 5 × 10-16 amp for the MOSFET electrometer. Consultant, Dept. of Elec. Engr., Univ. of Tennessee, Knoxville, Tenn.