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Zhang J.,National University of Singapore | Lian Y.,National University of Singapore | Yao L.,Kunming Institute of Physics | Shi B.,Institute for Infocomm Research
IEEE Journal of Solid-State Circuits | Year: 2011

The design of a low-voltage low-power fourth-order single-bit continuous-time Delta-Sigma modulator is presented in this paper for audio applications. The modulator employs an input-feedforward topology in order to reduce internal signal swings, thus relaxes the linearity and slew rate requirements on amplifiers leading to low-voltage operation and low-power consumption. The energy efficiency is further improved by embedding the summation of feedforward paths into the quantizer. For low-voltage operation, a gain-enhanced fully-differential amplifier and a body-driven rail-to-rail input CMFB circuit are developed. The modulator, implemented in a 0.13-μm standard CMOS technology with a core area of 0.11 mm2, achieves an 82-dB dynamic range (DR), and a 79.1-dB peak signal-to-noise and distortion ratio (SNDR) over a 20-kHz signal bandwidth. The power consumption of the modulator is 28.6 μW under a 0.6-V supply voltage. The achieved performance make it one of the best among state-of-the-art sub-1-V modulators in terms of two widely used figures of merit. © 2011 IEEE.


Yang Z.,National University of Singapore | Yao L.,Kunming Institute of Physics | Lian Y.,National University of Singapore
IEEE Journal of Solid-State Circuits | Year: 2012

This paper presents a 0.5-V 1.5-bit double-sampled δσ modulator for audio applications. Unlike existing double-sampled designs, the proposed double-sampled δσ modulator employs an input-feedforward topology to reduce internal signal swings, thereby relaxing design requirements for the low-voltage building blocks and reducing distortion. Moreover, in order to avoid instability and noise shaping degradation, the proposed architecture restores the noise transfer function (NTF) of the double-sampled modulator to its single-sampled equivalent with the help of compensation loops. In the circuit implementation, the proposed fully-differential amplifier adopts an inverter output stage and a common-mode feedback (CMFB) circuit with a global feedback loop in order to reduce power consumption. A resistor-string-reference switch matrix based on a direct summation quantizer is used to simplify the analog compensation loop. The chip prototype has been fabricated in a 0.13-μm CMOS technology with a core area of 0.57 mm . The measured results show that when operating from a 0.5-V supply and clocked at 1.25 MHz, the modulator achieves a peak signal-to-noise and distortion ratio (SNDR) of 81.7 dB, a peak signal-to-noise ratio (SNR) of 82.4 dB and a dynamic range (DR) of 85.0 dB while consuming 35.2 μW for a 20-kHz signal bandwidth. © 2012 IEEE.


Yao L.,Kunming Institute of Physics
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

Photo current integration is the key to improve the performance of a thermal imaging system. By integrating the photo current in the capacitance, the signal-to-noise ratio of the system is greatly improved. Theoretically, the maximum integration time of a thermal imaging system is the frame time of the system. However, due to the low well capacity of the readout integrated circuit, the integration time of the photo current is often shorter than the frame time of the system. To increase the well capacity of the readout circuit is one of the main research topics in thermal imaging system. The super-framing technique can overcome the restriction by reading-out the detector signal in a rate higher than the frame rate and then integrating the signal outside the IRFPA. As the signal integration is carried out outside the pixel, the integration time is no longer restricted. The key of the super-framing technique is the transmission of the signal in high readout rate. The digital readout circuit by integrating the analog-to-digital converter (ADC) array on the readout circuit chip becomes more and more popular with the development of CMOS technologies. Since the digital signal can be transferred outside the chip in a GS/s rate without any concern on noise and distortion, the super-framing technique based on digital readout circuit is advantageous over the analog solution. © 2014 SPIE.


Tang L.,Hong Kong Polytechnic University | Tang L.,Kunming Institute of Physics | Ji R.,Kunming Institute of Physics | Li X.,Yunnan Normal University | And 8 more authors.
ACS Nano | Year: 2014

Material that can emit broad spectral wavelengths covering deep ultraviolet, visible, and near-infrared is highly desirable. It can lead to important applications such as broadband modulators, photodetectors, solar cells, bioimaging, and fiber communications. However, there is currently no material that meets such desirable requirement. Here, we report the layered structure of nitrogen-doped graphene quantum dots (N-GQDs) which possess broadband emission ranging from 300 to >1000 nm. The broadband emission is attributed to the layered structure of the N-GQDs that contains a large conjugated system and provides extensive delocalized π electrons. In addition, a broadband photodetector with responsivity as high as 325 V/W is demonstrated by coating N-GQDs onto interdigital gold electrodes. The unusual negative photocurrent is observed which is attributed to the trapping sites induced by the self-passivated surface states in the N-GQDs. © 2014 American Chemical Society.


Tang L.,Hong Kong Polytechnic University | Tang L.,Kunming Institute of Physics | Ji R.,Kunming Institute of Physics | Li X.,Yunnan Normal University | And 2 more authors.
Journal of Materials Chemistry C | Year: 2013

The doping of carbon-based materials is of great importance due to its ability to modulate their optical, electrical and optoelectronic properties. Nitrogen-doped graphene quantum dots (N-GQDs) have received significant attention due to their superior electrocatalytic activity, optical properties and biocompatibility. The energy-level structure of N-GQDs remains unknown, which hinders the development of N-GQDs for various applications. Here, we report a one-pot synthesis method to prepare large-quantity N-GQDs at room temperature and atmospheric pressure under a prolonged reaction time. Using this approach, we can effectively dope N into the N-GQDs. As revealed by electron energy loss spectroscopy, N-doping introduces a new energy level into the electronic structure, which is responsible for tuning the optical properties of the N-GQDs. © 2013 The Royal Society of Chemistry.

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