An introduction to mixed-signal ic test and measurement

Integrated circuits incorporating both digital and analog functions have become increasingly prevalent in the semiconductor industry. Complex digital circuits are now commonly combined with analog circuits as part of the continuing drive toward higher levels of electronic system integration. For example, complex microprocessors are frequently combined with highperformance
analog and mixed-signal circuits to form so-called "system-on-a-chip" devices. An example of this is a single chip modem combining a digital signal processor with precision analog-to-digital and digital-to-analog functions on a single silicon die. Such devices offer the semiconductor customer significant savings in manufacturing costs due to the resulting reduction of chip-to-chip interconnections.
Mixed-signal IC test and measurement has grown into a highly specialized field of electrical engineering. However, test engineering is still a relatively unknown profession compared with IC design engineering. It has become harder to hire and train new engineers to become skilled mixed-signal test engineers. It may take one to two years for a mixed-signal test engineer to develop enough knowledge and experience to develop adequate test solutions. The slow learning
curve for mixed-signal test engineers is largely due to the shortage of written materials and university-level courses on the subject of mixed-signal testing. While many- books have been devoted to the subject of digital test and testability, the same cannot be said for analog and mixed-signal automated test and measurement.
Training for mixed-signal test engineers has historically started with a sink-or-swim training course covering the use of the test equipment itself, with little or no training on the basics of mixed-signal test and measurement. This equipment-centric approach to training is analogous to teaching a student how to drive by simply explaining the mechanics of the automobile itself (pull this knob, push that pedal, etc.). It would be unwise to assign such an inadequately trained
student to drive from L.A. to Pittsburgh without a roadmap and without a working knowledge of trivialities such as stop lights and police sirens. Similarly, a new test engineer is often assigned to develop tests for a complex circuit without training in basic test definitions and common test techniques.
The test engineer is also exp~cted to contribute to the defmition of testability circuits that are incorporated into the design of the device to be tested. Again, there is little fonnal reference material or training on the subject of basic mixed-signal design for test (Dff). As a result, new test engineers often overlook basic deficiencies in the circuit architecture that prevent the device from being tested thoroughly and economically.