Dimitrios N. Loizos

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A robust system architecture to achieve optical coherency free optimization. Several methods that had been proposed in the in multiple-beam free-space laser communication links with adaptive past, such as multi-dithering [4] and sequential perturbations [8], optics is introduced. It is based on deterministic multi-dithering and as well as the recently(More)
A mixed-signal architecture for continuous-time multidimensional model-free optimization is presented. It is based on multi-channel coherent modulation and detection that reliably estimates the objective function’s gradient, with respect to the system parameters, in the presence of time delays. The narrowband nature of the excitation signals reduces the(More)
A architecture for a quadrature sinusoidal oscillator with phase-preserving wide-range linear frequency tunability is discussed. The topology is characterized by low harmonic distortion, as well as controlled and stable amplitude of oscillation that is independent of the oscillation’s frequency and instantaneous frequency changes. The architecture has been(More)
A VLSI implementation of an adaptive controller performing gradient descent optimization of external performance metrics using parallel synchronous detection is presented. Real-time model-free gradient estimation is done by perturbation of the metrics' control parameters with narrow-band deterministic dithers resulting in fast adaptation and robust(More)
Recently, a delay-insensitive architecture for gradient descent adaptive control, based on parallel synchronous detection for model-free gradient estimation was presented [1]. The key to delay insensitivity in the gradient estimation is careful selection of the phase of the local oscillator in the mixer of synchronous detection, amounting to a single(More)
A 3-phase current controlled sinusoidal oscillator, tunable over a wide range of frequencies is presented. The oscillator comprises a ring of 3 cascaded differential Gm C low-pass filter stages, implemented in a fully translinear, NPN-only circuit. Closed-form analytical expressions are derived to quantify both frequency and amplitude tuning, as a function(More)
We demonstrate dynamic power maximization and synchronization of a wireless RF communication link through adaptation of the radiation pattern of a phased array at the transmitter. Adaptation is performed through a multi-dithering, coherent detection gradient descent analog controller chip [1], and compensates for phase variations in the communication link.(More)
We demonstrate the coherent combining of three beams with a phase-locking controller using VLSI multidithering technique. Three …ber-coupled phase shifters are used to compensate phase distortions in the beam propagation path. The highest dither frequency in our system is 70MHz. The achieved closed-loop compensation bandwidth of three beamlets is up to(More)
Effective compensation of phase noise in laser communication calls for fast, real-time, adaptive wavefront control. We present an analog, continuous-time, high-speed VLSI (Very Large Scale Integration) controller implementing multi-dithering perturbative gradient descent optimization of a direct measure of optical performance. The system applies parallel(More)
A fully differential translinear 3-phase sinusoidal oscillator architecture is presented. The architecture is meant for BiCMOS implementation and uses only NPN devices, typically of higher performance than their PNP counterparts in most technologies. The architecture features both frequency and amplitude control and expressions are derived showing the(More)