EIA JESD 398:1972 (R2009)

Introduction Transistor capacitances are usually measured on two-terminal capacitance or impedance bridges. When the capacitances are in the low picofarad ranges, this two terminal measurement is not very accurate or reproducible. The stray capacitances to ground are of the same order of magnitude as the quantities being measured and vary with mechanical changes in the surrounding ground planes. Therefore, it is necessary to employ three-terminal capacitance or impedance bridges which have a guard circuit. In these bridges the effects of extraneous capacitance to ground (or guard) are balanced out or otherwise made negligible so that the resulting measurement gives only the terminal-toterminal capacitance. In this manner, accurate, reproducible measurements may be obtained. This method may also be used for larger capacitances where greater accuracy is desired. The purpose of this standard is to define the elements of the transistor terminal capacitances, to specify the terminal connections to the measuring instrument, and to specify a test socket.