Transistor scaling has continued to favor digital circuits which benefit from the speed and integration improvements offered by feature shrinking. In contrast, analog design is challenged by the corresponding lower supply voltage and increased parameter variations.

Driven by this trend, a software radio for wireless communication has been envisioned that immediately digitizes the captured signal at the antenna to exploit these inherent benefits of digital circuits. By moving the classic analog signal conditioning to the digital domain, this software radio has the ability to embrace a multitude of communication standards simultaneously with a single chip. The crucial analog building block in such a concept is the analog to digital converter. Although this true software radio is still far from realization, three analog to digital converter designs incorporating partial aspects of this concept are covered in this PhD thesis.

The common denominator in these 3 applications is the use of multirate cascading in ƒ¢ƒ° modulators, which means that the sampling frequency is optimized for each stage inside the converter for enhanced performance. This enables a power reduction, a resolution increase and/or a bandwidth enlargement. Multirate cascading will be demonstrated in the three following architectures: 1) a multimode multirate cascade lowpass ƒ¢ƒ° converter targeting UMTS, Bluetooth and GSM, 2) a downconverted multirate cascade RF bandpass ƒ¢ƒ° converter for the direct digitization of the 80 MHz]wide ISM band at 2.4 GHz and 3) a multirate cascade detuned bandpass DT ƒ¢ƒ° converter for the direct digitization of the 20 MHz]wide FM band at 100 MHz.