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Inspired by the mechanism of visual attentional selection, a color feature selection unit consisting of photoreceptors and an attentional selection circuit (ASC) is presented. The detection and wavelength recognition of trichromatic light are accomplished by the photoreceptors with RGB filters. The ASC, fabricated in a standard CMOS technology, activates the competition among photoreceptors to select the principal color-component feature defined as the attentional focus. The number of focuses and resolution can be changed with a top-down stimulus. Electrical test results show that the ASC can select and interpret the most important color-component feature. In optical tests, the ASC chip-based unit can extract the principal color-component of single-color and dual-color light in real-time to complete color recognition. The percentage ratio between the intensity of stray light relative to the light with maximum intensity is up to 93.58%. And the maximum achievable recognition frame rate is 1 kHz, which is more than one order of magnitude higher than the frequency of the biological vision systems. Besides, the unit's outputs can be transformed into binary codes as labels for color recognition, and the color recognition process does not require the participation of ADC, CPU, and memory, consequently avoiding the von Neumann bottleneck.

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.

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.

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.

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.

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 1.04 × 10-3, which meets the data-rate requirement for IEEE 802.3 100BASE-TX. The LED-driver circuit is manufactured in an UMC 0.18μm CMOS process, and the chip area is 1052 × 762 μm2. This driver chip can be used in VLC systems with the following advantages: low cost, low powerconsumption, 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.

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.