Sinusoidal RF DACs for undersampled LC bandpass ∑Δ modulabrs

In this paper, we present a systematic technique to design bandpass LC Sigma Delta modulators with sinusoidal feedback DACs. The output resistance of the DAC degrades the quality factor of the LC resonator and the DAC output capacitance modifies its resonance frequency. It is shown that the DAC output resistance should be taken into account while designing the Q enhancement circuit of the integrated LC resonator. The resonance frequency is adjusted by modifiying the parallel capacitor of the LC resonator. Using the proposed method, different sinusoidal 3.256 GHz DACs are designed in a CMOS 0.13 mum process. Simulation results are presented to compare their performances in the context of an undersampled LC SigmaDelta modulator.