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. Mixed-signal IC test and measurement has grown into a highly specialized field of electrical engineering. It has become harder to hire and train new engineers to become skilled mixed-signal test engineers. 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. This book was written in response ot the shortage of basic course material for mixed-signa test and measurement. The book assumes a solid background in analog and digital circuits as well as a working knowledge of computers and computer programming. A background in digital signal processing and statistical analysis is also helpful, though not absolutely necessary. This material is desinged to be useful as both a university textbook and as a reference manual for the beginning professional test engineer. The prerequisite for this book is a junior level course in linear continuous-time and discrete-time systems, as well as exposure ot elementary probability and statistical concepts. Chapter 1 presents an introduction to the context in which mixed-singal testing is performed and why it is necessary. Chapter 2 examines the process by which test programs are generated, from device data sheet to test plan to test code. Test program structure and functionality are also discussed in Chapter 2. Chapter 3 introduces basic DC measurement definitions, including continuity, leakage, offset, gain, DC power supply rejection ratio, and many other types of fundamental DC measurements. Chapter 4 covers the basics of absolute accuracy, resolution, software calibration, standards traceability, and measurement repeatability. In addition, basic data analysis is presented in Chapter 4. A more thorough treatment of data analysis and statistical analysis is delayed until Chapter 15. Chapter 5 takes a closer look at the architecture of a generic mixed-signal ATE tester. The generic tester includes instruments such as DC sources, meters, waveform digitizers, arbitrary waveform generators, and digital pattern generators with source and capture functionality. Chapter 6 presents an introduction to both ADC and DAC sampling theory. DAC sampling theory is applicable to both DAC circuits in the device under test and to the arbitrary waveform generators in a mixed-signal tester. ADC sampling theory is applicable to both ADC circuits in the device under test and to waveform digitizers in a mixed-signal tester. Coherent multi-tone sample sets are also introduced as an introduction to DSP based testing. Chapter 7 further develops sampling theory concepts and DSP-based testing methodologies, which are at the core of many mixed-signal test and measurement techniques. FFT fundamentals, windowing, frequency domain filtering, and other DSP-based testing fundamentals are covered in Chapter 6 and 7. Chapter 8 shows how basic AC channel tests can be performed economicaly using DSP-based testing. This chapter covers only non-sampled channels, consisting of combinations of op-amps, analog filters, PGAs and other continuous-time circuits. Chapter 9 explores many of these same tests as they are applied to sampled channels, which include DACs, ADCs, sample and hold (S/H) amplifiers, etc. Chapter 10 explains how the basic accuracy of ATE test equipment can be extended using specialized software routines. This subject is not necessarily taught in formal ATE tester classes, yet it is critical in the accurate measurement of many DUT performance parameters. Testing of DACs is covered in Chapter 11. Several kinds of DACs are studied, including traditional binary-weighted, resistive ladder, pulse with modulation (PWM), and sigma delta architectures. Traditional measurements like INL, DNL and absolute error are discussed. Chapter 12 builds upon the concepts in Chapter 11 to show how ADCs are commonly tested. Again, several different kinds of ADC's are studied, including binary-weighted, dual-slope, flash, semi-flash, and sigma-delta architectures. The weaknesses of each design are expalined, as well as the common methodologies used to probe their weaknesses. Chapter 13 explores the gray art of mixed-signal DIB design. Topics of interest include component selection, power and ground layout, crosstalk, shielding, transmission lines, and tester loading. Chapter 13 also illustrates several common DIB circuits and their use in mixed-signal testing. Chapter 14 gives a brief introduction to some of the techniques for analog and mixed-signal design for test. There are fewer structured approaches for mixed-signal DfT than for purely digital DfT. The more common ad-hoc methods are explained, as well as some of the industry standards such as IEEE Std. 1149.1 and 1149.4. A brief review of statistical analysis and Gaussian distributions is presented in Chapter 15. This chapter also shows how measurement results can be analyzed and viewed using a variety of software tools and display formats. Datalogs, shmoo plots, and histograms are discussed. Also, statistical process control (SPC) is explained, including a discussion of process control metrics such as Cp and Cpk. Chapter 16 examines the economis of production testing, The economics of testing are affected by many factors such as equipment purchase price, test floor overhead costs, test time, dual-head testing, multi-site testing, and time to market. A test engineer's debugging skills heavily impacts time to market. Chapter 16 examines the test debugging process to attempt to set down some general guidelines for debugging mixed-signal test programs. Finally, emerging trends that affect test economics and test development time are presented in Chapter 16. Some or all these trends will shape the future course of mixed-siganl test and measurement.