Parallel Continuous-Time $\Delta\Sigma$ ADC for OFDM UWB Receivers

A parallel multibit continuous-time (CT) $\Delta\Sigma$ analog-to-digital converter for an orthogonal-frequency-division-multiplexing (OFDM) ultrawideband receiver intended to operate according to the IEEE 802.15.3a or the ECMA 368 (ISO/IEC 26907) standards has been designed. The overall CT $\Delta\Sigma$ converter consists of two modulators covering two unequal subbands (low-pass (LP) and bandpass (BP) subbands) that are arranged to operate in parallel and whose respective noise transfer functions (NTFs) are designed to match its corresponding frequency band. The composite NTF for the overall converter is defined as the minimum gain value out of these two individual NTFs. The LP and BP subbands were designed by using third- and fourth-order modulators, respectively, based on a 3-bit quantizer and operating at a clock frequency of 1056 MHz. NTF zero locations were optimized according to the criterion that all the in-band composite NTF gain maxima have approximately the same value. Combining OFDM signal characteristics and converter parameters, the effect of the quantization noise on the overall converter performance has been analytically derived. A simulation program has been realized to verify the performance of the converter.