Abstract :
A technological development that came out of World War II but attracted little notice at the time is discussed. It is the driven-shield technique for making measuring instruments with high-input impedances, a concept that has proved extremely valuable to the modern semiconductor industry. It was first put to commercial use in Joseph F. Keithley´s phantom repeater as a way to get a signal from extremely small underwater microphones, with capacitances of only a few picofarads, down about 30 cm of shielded cable to an amplifier. The principle of the approach and Keithley´s postwar use of it in commercial instruments are described.<>
Keywords :
audio equipment; military equipment; signal processing equipment; Keithley´s phantom repeater; World War II; amplifier; commercial instruments; driven-shield technique; high-input impedances; measuring instruments; semiconductor industry; underwater microphones; Cable shielding; Capacitance; Cathodes; Circuits; Imaging phantoms; Impedance measurement; Instruments; Repeaters; Time measurement; Voltmeters;
