CMOS software-defined radio transceivers: Analog design in digital technology

The introduction of several new cellular and connectivity radio standards has attracted the wireless industry to the concept of softwaredefined radio systems, preferably implemented in advanced nanometer CMOS technology. Several novel circuits and architectures have been investigated to cope with the huge design challenges involved, an overview of which will be given in this article. First, two digitally inspired receiver approaches are presented in detail. Discrete-time radio receivers exploit the paradigm that time is better controllable than voltage in modern CMOS, and are implemented using transistors mainly as switches. RF ADCs digitize the signal as close as possible to the antenna, but still require highspeed analog circuits to achieve the required performance. The second part of the article presents a "traditional" direct-conversion architecture, including also a transmitter, where several new circuits and architectures are used to exploit as much as possible the capabilities of a modern digital CMOS technology.