Overview of Analog Baseband Filters in Radio Receivers

In this work, the analog baseband low-pass filter is defined as the receiver block between the RF front-end and the analog-to-digital converter (ADC). In a superheterodyne receiver, however, it is placed between the IF stage and the ADC, to be exact. The analog baseband filter is responsible for performing channel-select filtering, either partially with the digital back-end or completely in the analog domain. In addition, the preceding receiver stages may also include passive filters, potentially alleviating the selectivity, and, especially, the stopband linearity requirements of the analog baseband filter. The partitioning of the filtering in a radio receiver depends on the receiver architecture selected, the gain and the linearity of the receiver building blocks employed, and the wireless application that is targeted, including the interferer scenario. The analog baseband filter can be a continuous-time or a discrete-time filter. Continuous-time filters have a speed advantage when compared to their discrete-time counterparts, since no sampling is required [1–3]. Therefore, it is often the case that continuous-time filters are more suitable for wideband applications. Moreover, the following ADC requires anti-aliasing filtering, which can be performed only by continuous-time filters. To accomplish simultaneous channel-select and anti-aliasing filtering and hence to reduce the number of power-consuming and noisy filter stages in a receiver, the employment of continuous-time low-pass filters is a practical choice. This work concentrates on the design and implementation of continuous-time filters and, thus, discrete-time filters are excluded from this book.