This chapter describes tunable circuits in CMOS and BiCMOS technologies. First, active and passive basic components are briefly described: MOS and bipolar transistors, and passive components like MOM capacitors, and transmission lines. Slow-wave transmission lines are described and compared to their microstrip lines counterparts, in terms of electrical performance and footprint. Next, tunable components are introduced,varactors and switches, anddigital tunable capacitors. Then, tunable transmission lines are described. Some examples of tunable inductances are also highlighted. Finally, two families of tunable circuits are addressed, phase shifter and VCOs, respectively. Both circuits are used in many systems for beam-forming/steering concerning phase shifters, and transceivers concerning VCOs, respectively. Many design examples are given. Topologies based on the use of lumped components (varactors and inductances) are compared to those based on distributed components (tunable transmission lines). In the middle, hybrid approaches mixing lumped and distributed components can lead to very efficient solutions, both in terms of electrical performance and footprint.

Several RF MEMS circuits were developed in the late 90s and early 2000s, showing low insertion loss, high linearity with low intermodulation and high power handling. Despite their superior behavior in many aspects, switching and tuning at microwave frequencies is mainly done by FET transistors, varactor diodes or MOS varactors, since their performance is acceptable and encapsulation costs are reduced. However, as the frequency increases into the millimeter wave range, their quality factor is considerably reduced and MEMS switches and varactors becomes a relevant option. In this chapter, the effect of the parasitics in the performance of the MEMS switch at millimeter wave frequencies is analyzed. Guidelines for the millimeter wave switch are presented. A literature review of the narrow-band and broadband switches , as well as phase shifters is also presented. The electromechanical behavior of RF MEMS switches and varactors has been covered extensively in the literature and will not be covered in this chapter.

The chapter introduces the Microwave Liquid Crystal Technology which features unique properties for reconfigurable systems for mm-wave communications. After an intrioduction of the material's properties, different implementations of components and systems are compared and discussed such as phase shifters, tunable filters and steerable antenna systems. These LC-based components are implemented for wide frequency range from about 10 GHz up to THz. Characterization, modelling and simulation are key for the design of such components,. Therefore, suited methodology is presented. Additionally, anliterature review on available realizations and technologies is given.

A complex quadrature charge-sharing (CS) technique is utilized to implement a discrete-time band-pass filter with a programmable bandwidth of 20–100 MHz. The BPF is a natural part of a cellular superheterodyne receiver and completely determines the receiver frequency selectivity. It operates at the full sampling rate (4×) (described in Chapter 2 of up to 5.2 GHz corresponding to the 1.2 GHz RF input frequency, thus making it free from any aliasing or replicas in its transfer function. Furthermore, the advantages of CS-BPFover other band-pass filters, such as N-path, active-RC, Gm-C, and biquad are described. A mathematical noise analysis of the CS-BPF and the comparison of simulations and calculations are presented. The entire 65 nm CMOS receiver, which does not include a front-end LNTA for test reasons, achieves a total gain of 35 dB, IRN of 1.5 nV/?Hz, out-of-band IIP3 of +10 dBm. It consumes 24 mA at 1.2 V power supply.

In this chapter, we describe four realized examples of discrete-time receivers that are largely based on the architecture and circuitryintroduced in previous chapters. Starting with a commercial DT receiver designed for GSM single-chip radios, which introduces the novel low-pass IIR filter, we then continue with three highly reconfigurable superheterodyne receivers that employ the complex IQ charge-sharing band-pass filter (BPF) for image rejection.

One of the main building blocks in a receiver is a low-pass filter (LPF) used at the baseband. This block is responsible for selecting the desired channel. In zero-IF receivers, this block is placed directly after the RF downconversion mixer. In a high-IF receiver,the LPF is required after a second downconversion from the IF to baseband. In addition to wireless communication applications, integrated LPFs are the key building blocks in various other types of applications, such as hard disk drive readchannels,videosignalprocessing,smoothingfilteringinaDAC,andantialiasingfilteringbeforea sampling system. The noise of these filters is one of the key system-level concerns. This noise can be usually traded off with the total filter capacitance and, consequently, total power and area. Therefore, for a given system-level noise budget, a filter with a lower noise coefficient reduces the area and power consumption. On the other hand, the linearity of the filter should be high enough to maintain the fidelity of the wanted signal.

We start the book with the basics. In this chapter, we first present the motivation and fundamentals of discrete-time (DT) radio-frequency (RF) signal processing, and an overview of zero/low intermediate-frequency (IF) and superheterodyne receiver architec-tures. Then, different sampling schemes present in the state-of-the-art zero-IF DT receivers are studied using a simplified DT receiver. At the end, a 4×-sampling concept is introduced for use in DT high-IF receivers.