Chapter 10: Testing of RF, Analogue and Mixed-Signal Circuits for Communications - an Embedded Approach

Mohamed M. Hafed, Gordon W. Roberts

10.1 Introduction

The importance of testing of semiconductor devices in general comes about because of the decidedly imperfect nature of the manufacturing process and its associated tolerances. Given the fine pitch of modern semiconductor devices, even a few particles of dust or debris that fall on a device during fabrication can permanently damage it. As it is impossible to completely eliminate such defects or contaminants from the wafer fabrication and manipulation process, a certain percentage of parts coming out of a fabrication run will always be defective, and a production test phase is required to screen such parts. Apart from debris particles or wafer defects, the variability of the fabrication process itself can also significantly degrade the ‘quality’ of a fabricated device. As device dimensions approach the atomic size [1], even single-atom disturbances can result in significant alteration to the electrical parameters of a device. Low-speed digital design techniques in CMOS are forgiving of electrical parameter variations [2]; however, high-speed digital as well as analogue and RF techniques are sensitive to such variations. Thus, for digital circuits, the problem of production testing is not that of performance measurement or of characterising electrical parameter variation. Instead, it is that of finding structural alterations such as short-circuits or open-circuits due to physical contaminants. When ‘analogue’ performance metrics such as the maximum operating frequency of a microprocessor are required, the test problem changes significantly since a defect-free device can still fail a performance metric. In other words, there exists an uncertainty in the performance of fabricated devices even in the absence of wafer defects or unwanted debris particles, and some direct performance-based test techniques are required [3].

The other main requirement in any production test strategy is speed of test execution and device separation. It is this speed requirement that makes production testing of analogue circuits so challenging. The reason is that analogue circuits are defined by a large set of specifications. As will be seen shortly, attempting to verify all specifications in the production test phase is too prohibitive, so careful planning of which specifications to test is important. In this chapter we describe both techniques for such test selection and optimisation as well as hardware techniques for test-signal delivery. We also describe a recent trend in test integration which promises to reduce many of the burdens of analogue testing. Specifically, we describe the use of embedded mixed-signal test cores, which are integrated circuit ‘macros’ that emulate the functions of fully-fledged automatic test equipment. These embedded test cores are designed to perform DC curve tracing, oscilloscope, timing, and frequency domain measurements using compact and mostly digital integrated electronics. Such scaling of measurement instruments is envisioned to be a natural consequence of semiconductor scaling trends [1] and of performance, cost, and signal handling pressures that are starting to render external test equipment centric techniques more and more impractical.

The scope of the techniques in this chapter is all the analogue and mixed-signal circuitry in a radio IC. This includes the baseband and frontend circuits as well as mixed-mode components such as data converters and clock circuitry.