Abstract
A comprehensive analysis of the impact of the finite gain-bandwidth product (GBW) in amplifiers and the excess loop delay on a parallel multibit CT ΔΣ ADC for an orthogonal frequency division multiplexing OFDM ultra-wideband (UWB) receiver has been carried out in this paper. The overall converter consists of two CT ΔΣ modulators covering two sub-bands (each of them implemented by a third and a fourth order CT ΔΣ modulator) that are arranged to operate in parallel. Our study was based on the dependence of the noise transfer function (NTF) poles and zeroes locus in the z-plane on these two nonideal effects for both modulators from a theoretical approach. The corresponding STFs were also analytically evaluated. System-level simulations have been accomplished too. Amplifiers were modeled according to a single-pole transfer function. Using the modified Z-transform method the dependence of the NTF poles and zeroes locus in the z-plane on the finite GBW and on excess loop delay was obtained when the DAC pulse end occurs in the current ("early") or in the following ("late") clock cycle. NTF poles and zeroes loci were evaluated as a function of the two nonideal effects considered separately or combined.
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