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Ultra-compact quasi-true time delay for boosting wireless channel capacity

Nature volume 627, pages 88–94 (2024)Cite this article

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Abstract

Massive-data connectivity has driven the need for efficient, directed communications through beamforming arrays1,2,3,4,5,6,7,8,9,10. Delay elements are critical in any beamforming signal chain. However, these elements impose fundamental limits on size, channel capacity, power efficiency and effective isotropic radiated power11. Although passive phase shifters do not consume DC power, they suffer from narrow bandwidth, poor phase resolution and low power-handling capacity. They introduce a beam squint, in which different frequency components experience different time delays, blurring signals so that they cannot be resolved. This severely limits the data rate of the wireless link, that is, its channel capacity. Although true time delay (TTD) elements12 solve this problem and service a broad bandwidth, they comprise wavelength-scale transmission lines, making them prohibitively area-inefficient for modern semiconductor processes. Here we address this long-standing problem by introducing a quasi-true time delay (Q-TTD) that miniaturizes TTD elements and breaks fundamental channel-capacity limits of these wireless links. We demonstrate this mechanism for a microwave device implemented in a complementary metal–oxide–semiconductor (CMOS) technology. Key to shrinking the footprint is a reflective-type phase-shifting structure with 3D variable TTD reflectors within a sub-wavelength footprint. This achieves ultra-broadband phase tuning by using them to vary the length of the waveguide’s path to ground. They produce a delay-to-area ratio that yields a substantially higher on-chip channel capacity compared with existing state-of-the-art methods. This component, when integrated in arrays, enables high-resolution imaging and low-squint beamforming for wideband communication, on-chip radar and other applications.

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Fig. 1: Introducing the Q-TTD element.
Fig. 2: Mechanism of Q-TTD element with dynamically programmable return path.
Fig. 3: Measured broadband phase shift and time-delay performance for 150 representative Q-TTD states.
Fig. 4: Enhanced resolution and channel capacity through Q-TTD.
Fig. 5: Measured insertion loss, return loss and RF power compression-point characteristics.

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Data availability

The data needed to evaluate the conclusions of this study are in the manuscript and supplementary materials. Source data can be found at https://zenodo.org/records/10234620.

Code availability

The Methods section analyses the channel capacities of arrays composed of phase shifters, TTD elements and the Q-TTD elements, using parameters from the measurements and from refs. 16,22. It also analyses the array factors of the arrays across frequency and their directivity for a target angle. The code to simulate these and reproduce the results in Fig. 4 and Supplementary Fig. 12 is available at Zenodo (https://zenodo.org/records/10234620).

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Acknowledgements

We acknowledge the Cornell NanoScale Facility, a member of the National Nanotechnology Coordinated Infrastructure (NNCI), which is supported by the National Science Foundation (grant NNCI-2025233) and where the work was done in part. The authors thank GlobalFoundries for providing silicon fabrication through the 45RFSOI university programme. B.G. thanks E. Kim, E. Ye and S. Cole for assistance with the experimental calibration.

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Authors and Affiliations

  1. Department of Electrical and Computer Engineering, Cornell University, Ithaca, NY, USA

    Bala Govind, Thomas Tapen & Alyssa Apsel

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  1. Bala Govind
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Contributions

B.G., T.T. and A.A. conceived the concept of the Q-TTD scheme. B.G. performed the circuit simulations and layout design of the delay element and tested the CMOS chip. T.T. designed the coupler. A.A. supervised the experiments and development of theory. All authors analysed the results and contributed to writing the manuscript.

Corresponding author

Correspondence to Bala Govind.

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Competing interests

The authors have filed a US provisional patent (63/588,555) based on this design.

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Nature thanks Khushboo Singh and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.

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This file contains Supplementary Sections 1–4; Supplementary Figures 1–12 and Supplementary Table 1.

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Govind, B., Tapen, T. & Apsel, A. Ultra-compact quasi-true time delay for boosting wireless channel capacity. Nature 627, 88–94 (2024). https://doi.org/10.1038/s41586-024-07075-y

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