Continuous time delta-sigma modulator with an embedded passive low pass filter

This paper presents a methodology to improve filtering in continuous time delta-sigma modulators (CTDSMs). A first order passive low pass filter is incorporated into the delta-sigma loop with a small modification of the existing active RC integrator configuration. The delay associated with the filter is compensated without any additional active components such as opamps. The proposed scheme provides an additional first order filtering to CTDSMs, resulting in an increased immunity to out-of-band blockers. Also, it relaxes the design complexity of the preceding filters. Detailed Cadence and Matlab simulations are provided to prove the operation of the proposed scheme.