Energy Efficient Transceivers Research Articles

A Sub-100-μW 0.1-to-27-Mb/s Pulse-Based Digital Transmitter for the Human Intranet in 28-nm FD-SOI CMOS

Human body communications require energy-efficient transceivers to connect diverse devices on the human body for wellness and medical applications. This article presents a fully digital pulse-based transmitter (TX) for capacitive body-coupled communications (c-BCCs) in 28-nm Fully Depleted Silicon on Insulator (FD-SOI) CMOS. The TX is operating at 450 MHz where surface-wave (SW) propagation is the dominant mechanism of c-BCC, offering a larger bandwidth with a more stable channel. The heavily duty-cycled TX uses a 90-MHz free-running oscillator and edge combiners to generate OOK Gaussian-shaped pulses through a switched-capacitor power amplifier (PA). Wide range forward body biasing (FBB), specific to FD-SOI technology, allows frequency tuning and adaptive efficiency optimization as a function of data rate. The proposed TX consumes 17–76 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> for flexible data rates from 0.1 to 27 Mb/s (170 down to 2.8 pJ/b) with up to 14% system efficiency under 0.5-V supply voltage.

Joint Phase-Time Arrays: A Paradigm for Frequency-Dependent Analog Beamforming in 6G

Hybrid beamforming is an attractive solution to build cost-effective and energy-efficient transceivers for millimeter-wave and terahertz systems. However, conventional hybrid beamforming techniques rely on analog components that generate a frequency flat response such as phase-shifters and switches, which limits the flexibility of the achievable beam patterns. As a novel alternative, this paper proposes a new class of hybrid beamforming called Joint phase-time arrays (JPTA), that additionally use true-time delay elements in the analog beamforming to create frequency-dependent analog beams. Using as an example two important frequency-dependent beam behaviors, the numerous benefits of such flexibility are exemplified. Subsequently, the JPTA beamformer design problem to generate any desired beam behavior is formulated and near-optimal algorithms to the problem are proposed. Simulations show that the proposed algorithms can outperform heuristics solutions for JPTA beamformer update. Furthermore, it is shown that JPTA can achieve the two exemplified beam behaviors with one radio-frequency chain, while conventional hybrid beamforming requires the radio-frequency chains to scale with the number of antennas to achieve similar performance. Finally, a wide range of problems to further tap into the potential of JPTA are also listed as future directions.

47.5 GHz Membrane-III-V-on-Si Directly Modulated Laser for Sub-pJ/bit 100-Gbps Transmission

Near-future upgrades of intra data center networks and high-performance computing systems would require optical interconnects capable of operating at beyond 100 Gbps/lane. In order for this evolution to be achieved in a sustainable way, high-speed yet energy-efficient transceivers are in need. Towards this direction we have previously demonstrated directly-modulated lasers (DMLs) capable of operating at 50 Gbps/lane with sub-pJ/bit efficiencies based on our novel membrane-III-V-on-Si technology. However, there exists an inherent tradeoff between modulation speed and power consumption due to the carrier-photon dynamics in DMLs. In this work, we alleviate this tradeoff by introducing photon–photon resonance dynamics in our energy-efficient membrane DMLs-on-Si design and demonstrate a device with a maximum 3-dB bandwidth of 47.5 GHz. This denotes a bandwidth increase of more than 2x times compared to our previous membrane DMLs-on-Si. Moreover, the DML is capable of delivering 60-GBaud PAM-4 signals under Ethernet’s KP4-FEC threshold (net data rate of 113.42 Gbps) over 2-km of standard single-mode fiber transmission. DC energy-efficiencies of 0.17 pJ/bit at 25 °C and 0.34 pJ/bit at 50 °C have been achieved for the &gt; 100-Gbps signals. Deploying such DMLs in an integrated multichannel transceiver should ensure a smooth evolution towards Terabit-class Ethernet links and on-board optics subsystems.

A High-Speed Moving Average Integrator in Silicon Photonics for TIA-Less Receivers

A high-speed moving average integrator in silicon photonics is demonstrated. The integrator is monolithically fabricated with an optical receiver front-end operating at 1550 nm. The design consists of an optical splitter, an optical low-loss delay line to implement a 400 ps delay between the two received bit streams, two SiGe photodiodes, and a 200 fF capacitor. The proposed moving average structure can perform four-bit integration at 10 Gbps. The resulting signal at the output of the integrator is the moving average of the received bit streams. The moving average integrator is validated through measurements and simulations at 2.5 and 5 Gbps. The proposed structure facilitates the development of next generation cost-effective and energy-efficient optical transceivers by exploiting optical time delay and moving average operation in silicon photonics. This mitigates the need for multiple clock phase generation and trans-impedance amplification on the electronic chip.

Suspended gallium arsenide platform for building large scale photonic integrated circuits: passive devices.

The spectacular success of silicon-based photonic integrated circuits (PICs) in the past decade naturally begs the question of whether similar fabrication procedures can be applied to other material platforms with more desirable optical properties. In this work, we demonstrate the individual passive components (grating couplers, waveguides, multi-mode interferometers and ring resonators) necessary for building large scale integrated circuits in suspended gallium arsenide (GaAs). Implementing PICs in suspended GaAs is a viable route towards achieving optimal system performance in areas with stringent device constraints like energy efficient transceivers for exascale systems, integrated electro-optic comb lasers, integrated quantum photonics, cryogenic photonics and electromechanical guided wave acousto-optics.

Strategies for integration of lasers on silicon

There is a need for closer integration of lasers with silicon electronics in order to realize low-cost, energy-efficient transceivers in high-bandwidth short-reach interconnects for use in data centres, upcoming supercomputer architectures and in fibre-to-the-home applications. As silicon is an inefficient light emitter, it is necessary to integrate a direct bandgap material onto a suitable platform in order to provide the light signal. Powerful photonic integrated circuits can then be realized based on state-of-the-art CMOS wafers or on silicon-on-insulator platforms. We review the different approaches to large-scale integration of light sources with these platforms covering monolithic integration, wafer bonding and epitaxial layer transfer. Transfer printing is demonstrated to be a very effective strategy being scalable and, in conjunction with etched facet reflectors, capable of lithographic alignment in a planar fabrication process. Here, we demonstrate that with a substrate temperature of 60 °C with 100 mA drive current and a voltage of 2.1 V, a 390 µm long laser on a silicon substrate has a total power of >40 mW in continuous wave operation. This technology can also be used to provide the light source for plasmonic transducers required in heat assisted magnetic recording.