Browsing by Author "Aggrawal, Himanshu"

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    Design & Applications of Silicon-Based Picosecond Pulse Systems
    (2018-04-19) Aggrawal, Himanshu; Babakhani, Aydin
    Terahertz waves, which occupy the band from 0.1 mm to 1 mm, are unique in the spectrum because of their potential applications in secure communications, automotive radar, spectroscopy and medical imaging. Despite the interest in using terahertz waves, we currently lack the underlying hardware platform to build upon. Currently, the only way to sample a picosecond signal is via photoconductive detection with a femtosecond laser and a PCA (photo-conductive antenna). Such systems require an expensive laser, sensitive optical alignment, and a mechanical delay line to scan the sampling time, thus limiting the beneficiaries to a limited number of research laboratories and universities. My research investigates and builds next generation of THz receivers and samplers with few picosecond sampling window based on the integrated circuit technology. The goal is to implement laser-free, fully electronic samplers to sub-sample Terahertz signal.
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    High-speed Track and Hold Amplifiers in CMOS for Enabling Pulse-based Direct Modulation, Secure Communication and Precision Localization
    (2015-08-06) Aggrawal, Himanshu; Babakhani, Aydin; Cavallaro, Joseph; Mittleman, Daniel
    Last few decades have seen a puissant desire for fast communication links that has shaped the evolution of high-speed circuits and silicon- based technology. This desire accompanied with a large consumer market has fueled the development of ever-shrinking, faster technology nodes. These advanced nodes open doors for designers to develop new ways of transferring data with unprecedented speed and accuracy. There are a number of challenges in building high-speed, secure communication links, one being the lack of availability of fast Analog to Digital Converters (ADCs), which form the front end of a receiver. Even in advanced technology nodes, the leakage in the transmission gate due to parasitic source-drain capacitance provides an alternate path for signals to pass, thus lowering the performance of the ADCs at high frequencies. Second, the current communication schemes use beam-forming or Direct Antenna Modulation (DAM) to narrow the information beam and point it in the direction of communication. Such techniques still have a wide information beam compared pulse-based directional modulation, as discussed in this thesis. In this dissertation, we address the issue of parasitic leakages in the transmission gate of a fast sampler by introducing active cancellation. A track-and-hold amplifier with active cancellation is designed and fabricated in 45nm CMOS SOI technology, which can operate at 40GSample/second real-time. In addition to this, we also study a pulse-based directional modulation scheme which can be used for secure communication, imaging and localization. Two coherent pulse generators with pulse width less than 200ps were used to attain an information beamwidth of less than 1 degree and localize objects with millimeter accuracy.
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    Impulse sampler architecture and active clock cancellation architecture
    (2019-02-12) Aggrawal, Himanshu; Babakhani, Aydin; Rice University; United States Patent and Trademark Office
    A novel nonlinear impulse sampler is presented that provides a clock sharpening circuit, sampling stage, and post-sampling block. The clock sharpening circuit sharpens the incoming clock while acting as a buffer, and the sharpened clock is fed to the input of the sampling stage. The impulse sampling stage has two main transistors, where one transistor generates the impulse and the other transistor samples the input signal. Post-sampling block processes the sampled signal and acts as a sample and hold circuit. The architecture uses an ultrafast transmission-line based inductive peaking technique to turn on a high-speed sampling bipolar transistor for a few picoseconds. It is shown that the sampler can detect impulses as short as 100 psec or less.
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    Systems and methods for active cancellation for improving isolation of transmission gates in high-frequency analog to digital converters
    (2016-01-26) Aggrawal, Himanshu; Babakhani, Aydin; Rice University; United States Patent and Trademark Office
    An active cancellation system may provide a first and second transmission gates that are fed with an input signal and a complimentary signal, respectively. The first transmission gate may be switched on/off, and a second transmission gate may remain off at all times. When switched off, the first transmission gate may provide a leakage signal resulting from leakage in current, especially at high input frequencies, which is detrimental to performance. The complimentary signal fed to the second transmission gate is out of phase with the input signal, but identical in amplitude. Thus, second transmission gate may output a signal that can cancel out the leakage signal from the first transmission gate.