Alias Rejection Research Articles

Novel droop-compensated comb decimation filter with improved alias rejections

This paper presents a novel two-stage comb decimator with the improved magnitude characteristic. Simple multiplierless corrector filters, which are designed using the frequency sampling and IFIR methods, are introduced. The proposed filters compensate the comb passband droop in the wideband passband region and increase the attenuations in the folding bands. Using the multirate identity the filters may be moved to a lower rate. The filter design depends only on the number of the cascaded comb filters and do not depend on the decimation factor M.

On Continuous-Time $\Delta\Sigma$ Modulators With Return-to-Open DACs

We examine the alias rejection of continuous-time ΔΣ modulators (CTDSMs) with return-to-open (RTO) feedback digital-to-analog converters (DACs). We show that using an RTO DAC can compromise the alias rejection of the CTDSM around odd multiples of the sampling rate. The intuition and theory behind this curious phenomenon are given. A circuit technique that mitigates this problem is proposed, and its efficacy is verified with simulations.

Alias Rejection of Continuous-Time $\Delta\Sigma$ Modulators With Switched-Capacitor Feedback DACs

Continuous-time ΔΣ modulators (CTDSMs) with switched-capacitor (SC) feedback digital-to-analog converters (DACs) are relatively less sensitive to clock jitter when compared to converters that use non-return-to-zero feedback DACs. However, as we show in this paper, using an SC DAC can seriously compromise the alias rejection of the modulator, thereby nullifying one of the principal advantages of continuous-time operation. We give an intuitive understanding, as well as an analytical basis, for computing the signal transfer function of CTDSMs with SC DACs. We propose power-efficient circuit techniques to improve alias rejection in such modulators and give experimental results that illustrate some of our ideas.

Passive second-order anti-aliasing filter for RF sampling based receivers

A second-order FIR anti-aliasing filter for RF sampling receivers is presented. The principle and circuit implementation are detailed for a GSM 900 receiver. The achieved alias rejection is sufficient to meet the specifications without any RF preselect filters.

X‐f choice: Reconstruction of undersampled dynamic MRI by data‐driven alias rejection applied to contrast‐enhanced angiography

A technique for reconstructing dynamic undersampled MRI data, termed "x-f choice," was developed and applied to dynamic contrast-enhanced MR angiography (DCE-MRA). Regular undersampling in k-t space (a hybrid of k-space and time) creates aliasing in the conjugate x-f space that must be resolved. When regions in the object containing fast dynamic change are sparse, as in DCE-MRA, signal overlap caused by aliasing is often much less than the undersample factor would imply. x-f Choice reconstruction identifies overlapping signals using a model of the full non-aliased x-f space that is automatically generated from the undersampled data, and applies parallel imaging (PI) to separate them. No extra reference scans are required to generate either the model or the coil sensitivity maps. At each location in the reconstructed images, g-factor noise amplification is compared with predicted reconstruction errors to obtain an optimized solution. Acceleration factors greater than the number of receiver coils are possible, but are limited by the sparseness of the dynamic content and the signal-to-noise ratio (SNR) (in DCE-MRA the latter is dominant). Temporal fidelity was validated for up to a factor 10 speed-up using retrospectively undersampled data from a six-coil array. The method was tested on volunteers using fivefold prospective undersampling.