Second-order sampling and oversampled A/D- and D/A-converters in digital data transmission

Basic structures for transmitting and receiving any quadrature modulated signal have been developed. As an example, the structures were applied to MSK modulation, and this resulted in working MSK modulator and demodulator structures that were verified by simulations at the functional level. A very simple and compact digital VLSI implementation of a MSK modulator can be built using the structure. The only analog part is the bandpass filter, which is also required in the conventional modulator structure. The use of sigma-delta A/D-convertors makes the demodulator structure very robust. The highest clock frequency (four times the carrier frequency f_c) is needed only for synchronizing purposes, and the parts would be clocked at f_c