Modeling a IF double sampling bandpass switched capacitor #x03A3;#x0394; ADC with a symmetric noise transfer function for WiMAX/WLAN

摘要

4G technology aims to revolutionize private and professional communication with its ubiquity and high-speed transmission (averaging 100Mbps). WiMAX and WLAN are two of the high speed access technologies to be used in the 4G mobile communication. Apropos to their high bandwidths, oversampling converters, e.g.ΣΔ ADCs, used for these standards would entail high levels of power consumption. Double sampling technique used in ΣΔ ADCs help in reducing the power consumption, since the actual sampling rate is only half the sampling frequency required to achieve a target resolution. But for conventional modulators, with low pass noise transfer functions (NTF), this benefit is hampered by the introduction of folded noise due to the mismatch of sampling capacitances. This paper presents a novel method of designing IF bandpass switched capacitor (SC)ΣΔ modulators with symmetric NTFs. Such a bandpass NTF is formulated with its center frequency at one-fourth the effective sampling frequency. The symmetricity ensures that the folded noise is ‘noise-shaped’ along with the quantization noise. The idea is verified with a discrete time bandpass ΣΔ modulator modeled using Simulink^®, including various nonlinearities, viz. clock jitter, opampnonidealities, and capacitive mismatch effects owing to double sampling and use of a multibitquantizer. Behavioral simulations of the proposed non-ideal model for WiMAX and WLAN, with a bandwith of 10MHz and 11MHz, respectively, achieved a peak resolution greater than 10 bits for each of the standards.