Direct-conversion bandpass sigma-delta modulator

A bandpass sigma-delta modulation analogue-to-digital (A/D) converter that uses direct conversion to baseband with in phase and quadrature paths within the feedback loop is described. The bandpass input signal is processed with continuous-time circuitry and the I/Q baseband signals are processed with switched-capacitor circuits. Experimental and simulation results indicate that the passband centre frequency can be maximised while suppressing the effects of I/Q mismatches