Introduction

In this chapter concepts related to connecting test equipment to a device-under-test are explored. Application-specific definitions of device boundaries and measures for signal path and power-ground performance are introduced. Practical measurement system accuracy implications of fixture losses are examined, with the surprising result that sometimes more fixture loss can be beneficial to measurement precision. An introduction to the basic elements of microwave probing and probing applications concludes the discussion.

Device boundaries and measurement reference planes

It is necessary to clearly define the boundary of the target of a measurement (known generally as the Device Under Test, or DUT), to distinguish it from the test system – fixture, probes, or other interconnections. The DUT can take many forms. It could be a functional block in a housing with connectors or waveguides for the inputs and outputs. Or a circuit DUT could be an embeddable semiconductor functional design element with a standard interface point such as a microstripline or other transmission lines. At the other extreme, the DUT could be a circuit component such as a transistor, inductor, capacitor, or resistor with no interface elements other than the constituent electrical contacts. Somewhere in between is the fully distributed circuit element. In all cases, the measurement reference planes define the boundaries of the DUT; see Figure 2.1.

For the purposes of discussion let us broadly and perhaps arbitrarily assign DUTs into three categories: Devices, Transmission Lines, and Circuits.