A Bit-Interleaved Sigma-Delta-Over-Fiber Fronthaul Network for Frequency-Synchronous Distributed Antenna Systems

Cell-free massive multiple-input multiple-output (MIMO) has attracted wide attention as wireless spectral efficiency has become a 6G key performance indicator. The distributed scheme improves the spectral efficiency and user fairness, but the fronthaul network must evolve to enable it. This work demonstrates a fronthaul network for distributed antenna systems enabled by the bit-interleaved sigma-delta-over-fiber (BISDoF) concept: multiple sigma-delta modulated baseband signals are time-interleaved into one non-return-to-zero (NRZ) signal, which is converted to the optical domain by a commercial QSFP and transmitted over fiber. The BISDoF concept improves the optical bit-rate efficiency while keeping the remote unit complexity sufficiently low. The implementation successfully deals with an essential challenge—precise frequency synchronization of different remote units. Moreover, owing to the straightforward data paths, all transceivers inherently transmit or receive with fixed timing offsets which can be easily calibrated. The error vector magnitudes of both the downlink and uplink data paths are less than 2.8% (–31 dB) when transmitting 40.96 MHz-bandwidth OFDM signals (256-QAM) centered around 3.6 GHz. (Optical path: 100 m multi-mode fibers; wireless path: electrical back-to-back.) Without providing an extra reference clock, the two remote units were observed to have the same carrier frequency; the standard deviation of the relative jitter was 9.43 ps.

New 2 2 Sigma Delta Modulators for Different Applications

This work presents the design of a new 2-2 programmable sigma delta modulator architecture, for different applications, this transformation design of the ΣΔ modulator low-pass, band-pass and high-pass or vice versa with loopbacks addition, which improved the linearity of the converter and reduced the quantization noise. In this work, the MASH structure enables the implementation of stable and high-order modulator. This makes low voltage and low power applications ideal. The simulation result for sigma delta modulator for biomedical applications exhibit a signal to noise ratio is 95 dB @ 250Hz bandwidth and a 75dB @ 200KHz ,85dB @1MHz for pass band modulator. The SNR is about 70dB for 5MHz bandwidth and for high pass application. This tool will allow a development contribution and characterize a system optimization set from the start while remaining at a high level of design that is suitable for electronic systems and models VHDL-AMS, RF, Biomedical.

A high-precision interface for tunneling magnetoresistance sensors with 0.15 nT/√Hz resolution

The tunneling magnetoresistance (TMR) with high-resolution digital output is widely used in military and civil fields. In this work we proposed a low-noise read-out circuit and a four-order fully differential sigma-delta modulator for TMR sensors. In the read-out circuit, we used symmetrical cascade for good matching. We used correlated double sampling (CDS) technique to improve the conversion accuracy of the modulator. In switched capacitor circuits we used time-division multiplexing to suppress charge injection and clock feedthrough. The high-precision application specific integrated circuit (ASIC) chip was fabricated by a 0.35 [Formula: see text]m CMOS process from Shanghai Huahong foundry. The TMR sensor was placed in an environment of three-layer magnetic shielding for test. The active area of the ASIC is only about [Formula: see text]. At a sampling frequency of 20 kHz, the TMR magnetometer consumes 77 mW from a single 5 V supply; the sigma-delta modulator for TMR can achieve an average noise floor of −141 dBV. The magnetometer works at a full scale (FS) of [Formula: see text], it can achieve a nonlinearity of 0.2% FS and a resolution of 0.15 nT/Hz[Formula: see text] over a signal bandwidth.