Fractional Sigma-Delta Modulator in SiGe

This paper presents a fourth-order tunable continuous time (CT) bandpass (BP) sigma-delta modulator with fractional delays (fSigmaDelta) fabricated in 0.5 mum/f_T = 47 GHz SiGe technology. The modulator is a fully differential g_m-C based circuit powered from from a 3.3 V supply and occupies 2.3 mm times 2.3 mm. At sampling rates from f_s = 600 MHz to f_s = 1.2 GHz and a single-tone input signal, within a bandwidth of BW = 20 kHz, the modulator demonstrates maximal SNR = 50 dB and maximal dynamic range DR = 47 dB. The center frequency notch of the noise transfer function (NTF) is tunable from 185 MHz to 289 MHz, while the resonator itself can achieve 60 MHz to 295 MHz. This prototype design experimentally confirms validity of the suggested analytical models and design methodology.