High-Frequency Amplifiers

As the operating frequency of communication channels for both video and wireless increases, there is an ever-increasing demand for high-frequency (HF) amplifiers. Furthermore, the quest for single-chip integration has led to a whole new generation of amplifiers predominantly geared toward CMOS VLSI. In this chapter, we will focus on the design of high-frequency amplifiers for potential applications in the front-end of video, optical, and RF systems. Figure 17.1 shows, for example, the architecture of a typical mobile phone transceiver front-end. With channel frequencies approaching the 2 GHz range, coupled with demands for reduced chip size and power consumption, there is an increasing quest for VLSI at microwave frequencies. The shrinking feature size of CMOS has facilitated the design of complex analog circuits and systems in the 1-2 GHz range, where more traditional low-frequency lumped circuit techniques are now becoming feasible. Since the amplifier is the core component in such systems,

there has been an abundance of circuit design methodologies for high-speed, low-voltage, low-noise, and low-distortion operation. This chapter will present various amplifier designs that aim to satisfy these demanding requirements.

In particular, we will review, and in some cases present new ideas for power amps, LNAs, and transconductance cells, which form core building blocks for systems such as Figure 17.1. Section 17.2 begins by reviewing the concept of current feedback, and shows how this concept can be employed in the development of low-voltage, high-speed, constant-bandwidth CMOS amplifiers. The next two sections of the chapter focus on amplifiers for wireless receiver applications, investigating performance requirements and design strategies for optical receiver amplifiers (Section 17.3) and HF low-noise amplifiers (LNAs) (Section 17.4). Section 17.5 considers the design of amplifiers for the transmitter side, and in particular the design and feasibility of Class E power amps are discussed. Finally, Section 17.6 reviews a very recent low-distortion amplifier design strategy termed ‘‘log-domain,’’ which has shown enormous potential for HF, low-distortion tunable filters.