A new WiMAX sigma-delta modulator with constant-Q active inductors

This paper presents a new over-sampling sigma delta modulator for WiMAX applications using an active inductor based loop filter and CCO. The loop filter is composed of floating active inductors and offers several key advantages over its MIM capacitor loop filter counterpart including an adjustable bandwidth, an adjustable quality factor, an extremely small silicon area requirement and full compatibility with digitally oriented CMOS processes. The proposed modulator is implemented in UMC's 0.13 mum 1.3 CMOS process. The sigma delta modulator comparator and sampler are driven from a new constant-Q active inductor CCO that provides phase noise below 118 dBc/Hz at 4 GHz operation. The sigma delta modulator exhibits a signal to noise ratio (SNR) of 42 dB and a dynamic range (DR) of 63 dB at a sample rate of 2 G/s with an oversampling ratio (OSR) of 40 making it ideal for base-band sampling in WiMAX transceivers.