Portability of electronic systems has become a key driver of advanced semiconductor technologies. A new class of wireless, portable consumer electronics has been enabled by advances in IC manufacturing and innovations in design. The capabilities of these new electronic products include completely integrated functionality, embedded signal processing, high-speed data processing, and high bandwidth communication channels. However, as system performance has improved through integration and architecture, power dissipation has tended to increase as well, resulting a shortened lifetimes of practical battery sources. With current product trends toward mobile portable electronic systems, it is clear that it will be necessary to decouple, or at least decrease the constant of proportionality between power dissipation and performance/functionality. Low-power technologies that are capable of providing leading edge performance and integration are of critical importance in developing new portable electronic information systems for all applications.
Circuit technology employed for the portable electronic information systems was analog and now has been switched to mixed-signal. Integrating both digital and analog on a single chip has significantly improved performance and reduced board size and cost. The current trend shows that high-speed and lower power data converter, analog-to-digital converters (ADCs) and digital-to-analog converters (DACs), are embedded on a complex mixed-signal ASIC containing mostly digital blocks for DSP (digital signal processing) and control. Typically, silicon area in a mixed-signal IC contains 10% analog circuits and 90% digital circuits. Therefore, the overall system cost can be reduced significantly if the analog portion can be fabricated using the same low cost digital CMOS process and share the same supply-voltage. In addition, system cost can be further reduced by enhancing testability of the analog portion. More specifically, manufacturers have recently found the costs associated with high-volume production of mixed-signal ICs are strongly affected by the cost of testing, where analog testing cost dominates. Because the analog components are used to process/interface analog signals, their accessibility is drastically low.
Traditionally, the analog interface portion of a mixed-signal circuit employs the switched-capacitor (SC) technique which requires high quality linear capacitors. Recently, a class of analog circuits wherein current rather than voltage is the primary signal medium has received considerable attention. A number of high-performance and low-cost circuits have been designed and fabricated using switched-current (SI) techniques. With SI technique, both analog and digital portions of mixed-signal circuits can use the same supply-voltage and be fabricated using the low-cost digital CMOS process. In addition, the circuits using the SI technique are easily testable. However, why haven’t the SI technique become an industrial standard yet? A simple answer is that the accuracy, linearity, and noise problems are still not resolved completely and satisfactorily. To make it become an acceptable industrial standard, it is necessary to develop sound design methodology and synthesis process for generating high performance analog circuits.