Green Energy Micro-System Group

The orthogonal frequency division multiplexing (OFDM), which is the key technology for 5G wireless commutations, suffers from the high peak-to-average power (PAPR) ratio [1]. To maintain sufficient linearity under a high PAPR, the RF power amplifier (PA) has to use a large power back-off, which degrades the efficiency significantly. This linearity and efficiency tradeoff problem is widely recognized as one of the key challenges for 5G wireless systems. Supply-modulated RF PA [2] is one of the most promising techniques to resolve this challenge, but critically relies on a wide bandwidth high efficiency supply modulator. Both linear regulator and switching regulator fail to meet these two requirements simultaneously. The hybrid supply modulator (HSM), which combines a linear regulator and a switching regulator in parallel, is a very promising solution to achieve both high linearity and high efficiency. We have proposed several novel HSM architectures [3],[4].

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References

[1] T. Jiang and Y. Wu, “An overview: Peak-to-average power ratio reduction techniques for OFDM signals,” IEEE Trans. Broadcast., vol. 54, no. 2, pp. 257–268, Feb. 2008.
[2] B. Kim, J. Kim, D. Kim, J. Son, Y. Cho, and B. Park, “Push the envelope: Design concepts for envelope-tracking power amplifiers,” IEEE Microw. Mag., vol. 14, no. 3, pp. 68–81, Mar. 2013.
[3] M. Tan and W.-H. Ki, “An efficiency-enhanced hybrid supply modulator with single-capacitor current-integration control,” IEEE J. Solid-State Circuits (JSSC), vol. 51, no. 2, pp. 533–542, Feb. 2016.
[4] M. Tan and W.-H. Ki, “ A 100MHz hybrid supply modulator with ripple-current-based PWM control ,” IEEE J. Solid-State Circuits (JSSC), vol. 52, no. 2, pp. 569–578, Feb. 2017.

Electronic-photonic integration is one of the most promising research directions in the post-Moore era [1]. It is going to bring revolutionary changes to areas such as sensing, communication, and precision measurement. The high thermal-optic coefficient of the substrate presents a major challenge to the robustness and the integration density of integrated photonics. Due to both random and systematic process variations, it is difficult to resolve this challenge by improving the fabrication process alone [2]. Recent study shows that the robustness of integrated photonics can be ensured by using electronic-photonic hybrid feedback thermal control [3].

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References

[1] Zhicheng Wang, Yu Yu, Xi Xiao, Miaofeng Li, Xuecheng Zou, Dingshan Gao, M Tan*, “A time-division-multiplexing scheme for simultaneous wavelength locking of multiple silicon micro-rings”, in Proc. IEEE Int. Symp. Circuits Systems (ISCAS), Florence, Italy, May, 2018
[2] Sun, C., et al. "Single-chip microprocessor that communicates directly using light." Nature 528.7583(2015):534.
[3] Krishnamoorthy, A. V, et al. "Exploiting CMOS manufacturing to reduce tuning requirements for resonant optical devices." IEEE Photonics Journal 3.3(2011):567-579.
[4] S. Agarwal, et al. "Wavelength locking of a Si ring modulator using an integrated drop-port OMA monitoring circuit," in IEEE Journal of Solid-State Circuits, vol. 51, no. 10, pp. 2328-2344, Oct. 2016.

We have proposed a number structures for two-stage [1],[2] and three-stage amplifiers [3]. Furthermore, we have established a generic model [4] that links the compensation techniques used in two-stage amplifiers to the structures of three-stage amplifiers. Our previous results provide a solid foundation for further investigation of amplifiers and other basic IC building blocks.

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References

[1] M. Tan and W.-H. Ki, “Current-mirror Miller compensation: An improved frequency compensation technique for two-stage amplifiers,” in International Symposium on VLSI Design, Automation, and Test (VLSI-DAT), Hsinchu, Taiwan, pp. 312-315, Apr. 2013.
[2] M. Tan and W.-H. Ki, “Split-output miller-compensated two-stage amplifiers,” in IEEE International Conference of Electron Devices and Solid-state Circuits (EDSSC), Hong Kong, China, Jun. 2013.
[3] M. Tan and W.-H. Ki, “A cascode Miller-compensated three-stage amplifier with local impedance attenuation for optimized complex-pole control,” IEEE J. Solid-State Circuits (JSSC), vol. 50, no. 2, pp. 440–449, Feb. 2015.
[4] M. Tan and W.-H. Ki, “A generic model for constructing three-stage amplifiers,” in IEEE International Symposium on Circuits and Systems (ISCAS), Montreal, Canada, May 2016.