A General Expression for the Electrometer Transfer Impedance

An expression for the electrometer transfer impedance Z21 is derived which describes the high-gain amplifier and the feedback network as general functions of the Laplace operator s. The equation derived is in the form of the general feedback equation, enabling the designer to employ the many tools of feedback analysis, such as root locus, Nyquist or Routh stability criteria, and Bode plots. Previous analyses have been limited to a constant forward transfer function and a feedback network employing a simple pole. Using this general analysis, the electrometer designer can take into consideration the unavoidable poles and zeros which are found in the forward transfer and feedback network. Furthermore, he can use this analysis to synthesize different desirable transform characteristics, thus optimizing electrometer design for a particular application.