A sixth-order continuous-time quadrature bandpass sigma-delta modulator for UMTS low-IF receivers and a study of the inherent excess loop delay effect

The first continuous-time (CT) quadrature bandpass /spl Sigma//spl Delta/ modulator with a sixth-order architecture is presented. It provides a signal bandwidth of 3.84 MHz (according to the universal mobile telecommunication system (UMTS) standard), centered at a low-IF of 4 MHz, and achieves a simulated peak signal-to-noise-distortion ratio (SNDR) of 78.3 dB and a dynamic range (DR) of 78.6 dB at a clock frequency of 96 MHz. Furthermore, the excess loop delay effect is studied. This effect is one of the main problems in CT /spl Sigma//spl Delta/ modulators. Previously presented papers investigate this effect for CT lowpass and bandpass /spl Sigma//spl Delta/ modulators and for a second-order CT quadrature bandpass /spl Sigma//spl Delta/ modulator. This paper, however, analytically describes and simulates the excess loop delay effect for the high-order CT quadrature bandpass /spl Sigma//spl Delta/ modulator with a sixth-order architecture.