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The gate-controlled quantum capacitance and the channel resistance play an important role in the performance of graphene field-effect transistors (GFETs). This paper experimentally verifies that the output phase of the graphene field-effect transistor changes under the influence of quantum capacitance and the channel resistance, which are controlled by the gate voltage. This phenomenon is theoretically analyzed, and a model is established to simulate the phase shift. The obtained simulation results of the model are in good agreement with the experimental results. This work reveals the influence of gate voltage variation on the phase characteristics of GFETs and provides a research basis for the application of GFETs in phase shifter and the establishment of the small-signal model.

In this paper, a 4-channel, 100 Gbps inductorless optical receiver analog front-end fabricated in a 55 nm bulk-CMOS technology is presented. Active feedback technique is widely adopted to improve the performance of the optical receiver without the area-occupied inductors. To alleviate the voltage headroom stress of the local feedback loop in traditional regulated cascode transimpedance amplifier, the common gate amplifier is inserted before the traditional common source feedback stage. And the cross-couple active feedback stage provides a negative signal path to extend the bandwidth of the local feedback loop. Multi-stage limiting amplifier with active negative and positive feedback stages are employed to extend bandwidth and acquire high gain simultaneously. The optical receiver was realized as 4-element arrays occupying the area of $800\,\,\mu \text{m}\,\,\times 1800\,\,\mu \text{m}$ , whereas the core area of each channel is just $275\,\,\mu \text{m}\,\,\times 650\,\,\mu \text{m}$ . The measured 3-dB bandwidth reaches 22.8 GHz, sufficient for 25-Gbps operation. For an input voltage of 2.5 mV $_{\text {p-p}}$ , the optical receiver achieves a BER $= 10^{-12}$ at 25-Gbps PRBS7, and 310 mV differential output voltage is delivered. From the supply voltage of 1.2 V, the test chip consumes the power of 226 mW and exhibits the power efficiency of 2.3 mW/Gb/s, when 25-Gbps PRBS31 is supplied.

This paper presents an improved white light-emitting-diode (LED) wireless transmitter for the Joint Illumination and Communication (JIC) System, which consists of two parts: the driver circuit and the pre-emphasis circuit. The main purpose of the driver circuit part is to solve the problem of dissipated power when sweeping the remaining carriers during the signal modulation of the high-efficiency, high-power and high-speed white LED driver. A push-pull structure driver with a current conduction angle less than 180 degrees is proposed, which is analogous to a Class C power amplification driver, thus avoiding the simultaneous existence of voltage and current on the driver circuit when the remaining carriers are swept out, and improves the efficiency of the LED driver. On this basis, the pre-emphasis circuit part adopts the phase shift technology to improve the data transmission rate, and the system efficiency has also been improved. Then, an improved class C push-pull structure white LED driver with phase shift pre-emphasis technology is formed. This novel driver and pre-emphasis technology achieve a system efficiency of 95.73% with a 10 W LED. The test results show that the system communication -3 dB bandwidth expanded from the original 8.3 MHz to 13.67 MHz, and the best-obtained transceiver baud rate is 25 Mbps at a distance of 1.3 m with BER of 1.63 × 10-4. The test result verifies that the LED driver proposed in this paper is currently the highest figure of merit (FoM) for high power JIC systems.

Li3Mg2(Nb1-xWx)O6+x/2 (0 ≤ x ≤ 0.08) ceramics were synthesized by the solid-state reaction route. The effects of W6+ substitution on the phase composition, microstructure and microwave dielectric properties of Li3Mg2NbO6 ceramics were investigated systematically. The XRD results showed that all the samples formed a pure solid solution in the whole doping range. The SEM iamges and relative density revealed the dense structure of Li3Mg2(Nb1-xWx)O6+x/2 ceramics. The relationship between the crystal structure and dielectric properties of Li3Mg2(Nb1-xWx)O6+x/2 ceramics was researched through polarizability, average bond valence, and bond energy. The substitution of W6+ for Nb5+ in Li3Mg2(Nb1-xWx)O6+x/2 ceramics significantly promoted the Q × f values. In addition, the increase of W6+ content improved the thermal stability of the Li3Mg2(Nb1-xWx)O6+x/2 ceramics. The Li3Mg2(Nb0.94W0.06)O6.03 ceramics sintered at 1175 °C for 6h possessed excellent properties: er ~ 15.82, Q × f ~ 124,187 GHz, τf ~ −18.28 ppm/°C.

In this article, a novel method for constructing a pre-equalizer by optimized filter synthesis with vector fitting is proposed to broaden the bandwidth of a visible light communication (VLC) system. By using the proposed method, an active-passive hybrid equalization circuit is constructed, and it is demonstrated that the 3-dB bandwidth of the VLC system with commercially available phosphorescent white LED is extended from 30 MHz to 600 MHz. A 1.35 Gb/s NRZ-OOK VLC transmission over 12 cm free space transmission distance is experimentally realized, achieving a bit error rate (BER) of $\text{8.8} \times \text{10}^{-\text{5}}$ . To the best of the authors knowledge, this is the largest reported 3-dB bandwidth and real-time data rate achieved in the VLC system with a single commercially phosphorescent white LED.

A series of novel Li3+xMg2Nb1-xTixO6 (0.02 ≤ x ≤ 0.08) ceramics with excellent microwave dielectric properties and relatively low sintering temperatures were synthesized via the solid-phase method. The correlations between sintering characteristics and microwave dielectric properties of the novel system were analyzed in detail. By (Li+/Ti4+) ions co-doped Li3Mg2NbO6 ceramics, all compounds possessed a single phase with orthorhombic structure, pertaining to the space group Fddd (70). The change regulation of dielectric constant and Q*f values was similar to density, which ascended to the maximum value first and then declined as the sintering temperature increased. Furthermore, the τf values constantly shifted to 0 ppm/°C with the content of complex ions (Li+/Ti4+) increasing. The best properties of Li3.06Mg2Nb0.94Ti0.06O6 ceramics sintered at 1025 °C were er = 14.34, Q*f = 154,113 GHz, and τf = −2.17 ppm/°C.

This paper proposes a theoretical model of photo-controlled quantum capacitors in double-gated graphene-insulator-graphene (DGGIG) structure for terahertz (THz) frequency and phase modulations. In the model, the current-voltage characteristics of each segment of the DGGIG structure are controlled by different gate voltages. Using the different voltages, the DGGIG structure can be used to either generate plasma oscillation waves or shift phase in the terahertz band. Not only has the DGGIG structure various electrical properties, but also the optical properties are also excellent. Photoexcitation alters carrier concentration in DGGIG channel, and thus causes the change of the quantum capacitors. We propose a photo-controlled quantum capacitor model to quantify this phenomenon. The model shows that the quantum capacitors and photoexcitation have a sublinear dependence. An example of a device based on the model is given to describe the application of photo-controlled quantum capacitors in terahertz frequency and phase modulations. The modelled device shows that photoexcitation can change the frequency and phase of the plasma oscillation waves.

For the further integration of receivers in multi-color visible light communication systems, a novel color photodetector (PD) was designed and fabricated by using a 40 nm standard complementary metal oxide semiconductor (CMOS) process without any process modifications. The PD consists of CMOS photodiode and two-dimensional (2D) polysilicon subwavelength grating above the photodiode. The 2D polysilicon grating is controlled in structural parameters to realize color filtering, based on guided-mode resonance, for the first time in a standard CMOS process. Here three kinds of color PDs were designed to respond to the three primary colors. The measured results demonstrate that the color PDs exhibit wavelength selectivity in the visible range (400-700 nm) and the maximum peaks in the spectral response curves of them are at 660 nm (red), 585 nm (green) and 465 nm (blue), respectively. In addition, the added 2D polysilicon grating almost does not reduce the responsivity of the photodiodes.

The unmanned aerial vehicle (UAV) offers unique advantages of autonomous flight capability and small coefficient of risk, and is increasingly being used in harbor-border inspection to ensure security and orderly operation of harbors. In response to the influence of external factors such as electromagnetic interference in harbor-border inspection, this paper utilizes UAV and visible light communication (VLC) to build an efficient system to track maritime targets near the harbor reliably. In a VLC scenario, a geometrical equation for transmitter positioning is first proposed based on the received signal strength of the optical signal emitted by the target. On this basis, linear iterative positioning (LIP) using first-order Taylor expansion is proposed to realize online beam tracking. Furthermore, quadratic approximative iterative positioning (QAIP), a more precise approximation of the geometrical equation, is proposed based on second-order Taylor expansion. Simulation results show that the proposed algorithms can track targets effectively, and QAIP can achieve higher accuracy with no noise or high signal-to-noise ratio. In addition, compared with the geometrical solution, LIP and QAIP have faster computing speeds and fixed overheads.

In view of the complexity of port ship supervision and the influence of external factors such as electromagnetic interference in harbor-border inspection, an efficient system combining an unmanned aerial vehicle (UAV) and visible light positioning (VLP) is proposed for locating maritime targets. In this system, a rotatable receiver with five photodetectors (PDs) installed obliquely on UAV is designed for expanding the positioning range and allowing a lower flight altitude. On this basis, we propose the Chan–Taylor (CT) method based on time difference of arrival (TDOA) for target positioning. First, the localization problem is reformulated as a weighted least squares (WLS) problem and provides a good initial estimate via the two-step WLS (TWLS) method. Then, based on Taylor expansion of TDOA equations, estimated error is calculated using the initial estimate, which can correct the estimated position of the target iteratively. To offset the error, weighted centroid CT (WCCT) is proposed by endowing different weights based on error difference to estimated results. For further improving accuracy, a restricted-region fingerprinting positioning based on CT (CT-RFP) is proposed. In restricted area determined by CT, a certain number of fingerprints is generated based on received signal strength (RSS) for matching. Simulation results show that CT is significantly improved over the previous methods. Compared with TWLS, the accuracy of CT is improved by 49.71%. For WCCT, the maximum error is reduced from 8.65 to 6.91 cm, which effectively reduces the influence of error. Moreover, CT-RFP can achieve an accuracy within millimeter level via the appropriate number of fingerprints and ensemble runs of CT, even at high noise levels.

The arid area of Northwest China provides a unique terrestrial ecosystem for identifying the response of vegetation activities to natural changes. In order to reveal the influence of climate factors on vegetation, the normalized difference V vegetation index (NDVI), climate data and land use and land cover change (LUCC) map were used to study. The spatial and temporal variation characteristics of NDVI from 2000 to 2015 were analyzed.

A metal-catalyst-free method for the direct growth of patterned graphene on an insulating substrate is reported in this paper. Parylene N is used as the carbon source. The surface molecule layer of...

The data rate for visible light communication (VLC) with commercial phosphorescent white light-emitting diodes (LEDs) is very limited because the $-$ 3 dB modulation-bandwidth of these LEDs is only a few megahertz. To increase the modulation bandwidth, a new, fully integrated driver circuit is proposed in this paper. The integrated circuit chip consists of a pre-emphasis circuit unit, an adjustable remaining carrier-sweep-out circuit, and a power-MOSFET driver. Using this chip, the $-$ 3 dB bandwidth of phosphorescent white LED transmitters can be extended from 3 to 80 MHz. The best obtained transceiver baud rate is 112 Mbit/s for a distance of 1.5 m, and the bit-error-ratio is ${\text{1.04}}\,\times \,10^{-3}$ , which meets the data-rate requirement for IEEE 802.3 100BASE-TX. The LED-driver circuit is manufactured in an UMC ${\text{0.18}}\,{\mu }\text{m}$ CMOS process, and the chip area is ${\text{1052}}\ \times\ {\text{762}}\ {\mu }\text{m}^2$ . This driver chip can be used in VLC systems with the following advantages: low cost, low power-consumption, compatible with standard CMOS technology, and high integration-density.

A high-power, high-efficiency, and high-speed white light-emitting-diode (LED) wireless transmitter is presented in this paper. This transmitter system consists of a gallium nitride field effect transistor (GaN FET) driver with push–pull structure, freewheeling circuit, and remaining carriers sweep-out circuit based on a phosphorescent white LED. A novel push–pull circuit structure with intensity modulation is used to increase the efficiency of the proposed transmitter to 94.2% at 12 Mb/s theoretical baud rate. Generally speaking, LED transmission speed is restricted by the remaining carriers in the junction capacitance. In this paper, we introduce an improved adjustable carrier sweep-out circuit to resolve this problem. High-frequency components in the signal are preemphasized by adding parallel freewheeling diodes between the drain and source of the GaN drivers. Test results show that the power efficiency is 93.17% with −3 dB bandwidth at 8.3 MHz. The results also show that the architecture proposed in this paper allows the baud rate of the transmitter to reach 10 Mb/s with bit error rate below 10 $^{-5}$ , which meets the IEEE 802.11 b requirements at distances farther than 1 m.

In the paper, a mixed-interval multi-pulse position modulation (MI-MPPM) scheme for visible light communication (VLC) system is theoretical proposed and implemented on field programmable gate array (FPGA). It has better bandwidth efficiency than PPM and MPPM. And it has better anti-jamming than MPPM. A real-time VLC link based on phosphorescent white LED is also built to measure the performance of the proposed MI-MPPM scheme. The data rate of 104 Mbps in our VLC system under the distance of 60 cm could be achieved, and bit error rate is 3 . 81 × 1 0 − 5 . As far as we know, it is the highest data rate that can be achieved in continuous real-time VLC system with phosphorescent white LED based on PPM and its derivative modulation. The performance of VLC system under different distances, advantages and the possible application scenarios of MI-MPPM are also discussed.

This paper theoretically explores photocontrolled terahertz amplified modulator in electron plasma wave optically switched resonant tunneling diode (ORTD) gate high-electron mobility transistor. We present a developed distributed circuit model based on the Khmyrova model. Photoexcitation causes ORTD operating state between negative differential conductivity and positive differential conductivity, which power gain of the device can be control by photoexcitation. Numerical and analytical results show that photoexcitation enabling amplified modulator can realize much larger modulation depth (>95%) than what has been reported in photocontrolled modulator. Our results show the potential of this device in several fields of terahertz technology, such as photocontrolled modulator, mixer, and other two port networks.

In this paper, a 25 Gbps inductorless optical receiver analog front-end is presented. The inverter-based modified Cherry-Hooper amplifier is proposed and adopted as main stage of the optical receiver to extend the bandwidth by alleviating Miller capacitance. The optimization of shunt-feedback transimpedance amplifier is implemented by improving the gain bandwidth product of main amplifier. In multi-stage limiting amplifier, the staggered active feedback technique is used to boost the deteriorated bandwidth. Fabricated in a 55 nm CMOS technology, the whole chip occupies an area of 770 μm × 800 μm, and core area is only 100 μm × 400 μm. The measured 3-dB bandwidth reaches 21.7 GHz, sufficient for 25-Gbps operation. For an input voltage of 3 mVp-p, the chip achieves a BER = 10−12 at 25-Gbps PRBS7, and 320 mV differential output voltage is delivered. From the supply voltage of 1.2 V, the test chip consumes the power of 56 mW and exhibits the power efficiency of 2.3 pJ/s.

Optical receivers with potentially high operation bandwidth and low cost have received considerable interest due to rapidly growing data traffic and potential Tb/s optical interconnect requirements. Experimental realization of 65 GHz optical signal detection and 262 GHz intrinsic operation speed reveals the significance role of graphene photodetectors (PDs) in optical interconnect domains. In this work, a novel complementary metal oxide semiconductor post-backend process has been developed for integrating graphene PDs onto silicon integrated circuit chips. A prototype monolithic optoelectronic integrated optical receiver has been successfully demonstrated for the first time. Moreover, this is a firstly reported broadband optical receiver benefiting from natural broadband light absorption features of graphene material. This work is a perfect exhibition of the concept of monolithic optoelectronic integration and will pave way to monolithically integrated graphene optoelectronic devices with silicon ICs for three-dimensional optoelectronic integrated circuit chips.

A metal-catalyst-free method for the direct growth of patterned graphene on an insulating substrate is reported in this paper. Parylene N is used as the carbon source. The surface molecule layer of parylene N is cross-linked by argon plasma bombardment. Under high-temperature annealing, the cross-linking layer of parylene N is graphitized into nanocrystalline graphene, which is a process that transforms organic to inorganic and insulation to conduction, while the parylene N molecules below the cross-linking layer decompose and vaporize at high temperature. Using this technique, the direct growth of a graphene film in a large area and with good uniformity is achieved. The thickness of the graphene is determined by the thickness of the cross-linking layer. Patterned graphene films can be obtained directly by controlling the patterns of the cross-linking region (lithography-free patterning). Graphene-silicon Schottky junction photodetectors are fabricated using the as-grown graphene. The Schottky junction shows good performance. The application of direct-grown graphene in optoelectronics is achieved with a great improvement of the device fabrication efficiency compared with transferred graphene. When illuminated with a 792 nm laser, the responsivity and specific detectivity of the detector measured at room temperature are 275.9 mA/W and 4.93 × 10

Novel medium-permittivity scheelite-structured CaBiVMoO8 ceramics were prepared by a solid-state reaction route. The effects of sintering temperature on the phase composition, microstructure and microwave dielectric properties of CaBiVMoO8 ceramics were investigated systematically. The Rietveld refinements of X-ray data revealed all samples were well crystallized in space group I41/a. All the samples exhibited a closely packed grain morphology and discernable grain boundaries. The relationship between microwave dielectric properties and bulk density of samples at different sintering temperatures was further researched. Besides, the lattice energy was one of the important factors affecting the Q×f values of CaBiVMoO8 ceramics. The temperature coefficient of resonant frequency (τf) could be slightly affected by sintering temperature. The CaBiVMoO8 ceramics were expected to be applied to low temperature co-fired ceramics technology. In this paper, the CaBiVMoO8 ceramics exhibited excellent properties sintered at 850 °C for 4h: er ∼ 40.55, Q×f ∼ 16,670 GHz, τf ∼ +55.90 ppm/°C.

This paper presents the frequency and output power characteristics of oscillators in the graphene tunneling FETs (GTFET) technology. In order to acquire these characteristics, the practical operating conditions of GTFET oscillators are carefully analyzed, and then, the device parameters are simplified to an equivalent circuit and the I/V large signal model is approximated by a compact form. Expressions for the maximum oscillation frequency, maximum output power, and the relationship between frequency and power are given combing the equivalent circuit and the simplified model. In addition, the key device parameters that can be used to improve the performance of a GTFET oscillator are also discussed.