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Analog to digital converters are the interface between the analog world and the digital domain where information is extracted, processed and interpreted. The performance of all electrical devices depends on this interface. As the electronic devices are evolving to more complex designs, requirements on A/D converters are becoming more stringent consequently. This thesis is focused on the design of high performance analog to digital converters for broadband wireless applications. The complete design flow for such converters is done starting with the system design for two future generations of mobile systems: convergence of WiMAX/WLAN and 3G/WLAN. Based on the requirements for A/D in the 3G/WLAN, two different designs based on single-loop and MASH architectures are done in TSMC 0.18um technology using 1.8 V supply. As the submicron technologies are unable to provide high performance analog designs without sacrificing power consumption, high performance analog to digital converters need some type of calibration to achieve their required speed and accuracy. In this thesis, different adaptive calibration techniques for sigma delta modulators are studied. Most of the previous work is limited to the MASH architectures. A new adaptive technique is proposed that can be used for any sigma delta converter. The proposed method is a fully-digital solution and does not add any complexity to the analog circuitry. Adaptive compensation of analog imperfections can be also applied to other types of analog to digital converters. Pipeline ADCs, for example, are the competitors of sigma delta converters in wireless applications. This thesis also presents a new adaptive technique for nonlinear calibration of pipeline ADCs.