The radio frequencies used in communication standards are currently higher than 1 GHz, while they carry a signal bandwidth narrower than 5 MHz. In order to recover such signals, the carrier is usually removed by at least one set of mixers and lowpass filters, and then an ADC is used for digitization. This method can be improved if the ADC could digitize the RF signal directly with the same power consumption. The improvement is due to removing the analog components and having a programmable system. The goal of this book is to introduce undersampling Delta-Sigma modulators as a promising method for implementation of multi-standard receivers. It investigates different approaches to eliminate analog building blocks in such receivers by using the undersampling Delta-Sigma modulators. This book proposes architectural and circuit-level techniques to achieve this goal. It also validates the proposed concepts and architecture with analytical models, circuit simulation, chip layouts and prototype integrated circuits.