A Loss and Phase Set for Measuring Transistor Parameters and Two-Port Networks Between 5 and 250 mc

In the early stages of development of specific transistor types, compromise performance targets are worked out that are both desirable from a circuit use standpoint and feasible from a fabrication viewpoint. Fairly simple electrical measuring instruments are sufficient to guide the development during this early period. However, past performance has shown that the device designer converges rather rapidly on the agreedupon targets, and device reproducibility quickly reaches a point where * This work was supported in part by Task V of Joint Military Services Contract DA-36-039 sc-64618. S41 840 THE BELL SYSTEM T E C H N I C A L J O U R N A L , MAY l O f i l more precise knowledge of the device characteristics would permit greater sophistication in circuit applications. At this point, accurate measurements must be made of the frequency characteristics of the device and of the circuits in which it is used, in order to sustain further progress in circuitry development. This paper is concerned with an instrument designed to meet such measurement needs in the frequency range from 5 to 250 rac. The first portion of the paper reviews the special problems involved in making accurate broadband measurements on transistors. It is noted that the chief limitation stems from the difficulty of providing a known circuit environment around the unit under test. At high frequencies, this problem is aggravated by selecting excessively large or excessively small termination impedances. For this reason, an impedance level of 50 ohms has been chosen for both source and load in the measurement apparatus that is described.