 Good models for telecommunication frontends: Architectures and their behavioral properties Having considered models, modeling and analysis from a global perspective, the main topic of this book can be phrased as: the construction of good models for telecom- munication systems and their building blocks. As was outlined in section 2.1.2, the construction of good models requires us to incorporate all relevant prior knowledge and experience. This section summarizes this knowledge. It presents a brief review of common frontend architectures, their building blocks and their behavioral properties. It attempts to answer the question: what has experience taught us on the behavior of telecommunication frontends and their building blocks? 2.2.1 Frontend architectures and their building blocks Fig. 2.5 depicts two commonly used receiver frontend architectures. The heterodyne receiver on top provides good performance in terms of channel selectivity and sensitiv- ity, but typically requires surface-acoustic wave (SAW) bandpass filters in combination with additional IF circuitry. The low-IF architecture on the bottom requires less parts, but exhibits inherent problems such as self-mixing, 1/f noise and sensitivity. Self- mixing comes from the local oscillator (LO) signal making its way to the input of the mixer. This generates a DC component at the mixer output, possibly saturating the filters and gain amplifiers that follow. In [Crol97] a more rigorous overview of receiver (and transmitter) architectures is presented. 2.2.2 Properties of frontend building block behavior Observing both architectures, it is seen that their functioning relies on similar building blocks: low-noise amplifiers (LNAs), automatic gain control (AGC), filters, mixers, analog-to-digital converters (ADCs) and local oscillator (LO) signals. The latter are typically derived from a reference signal using a voltage-controlled oscillator (VCO) embedded in a phase-locked loop (PLL). Modeling an entire receiver frontend therefore requires us to have models for 