Abstract-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 proposed stochastic parallel gradient descent gradient descent flows and accounts for phase delays in the dither signal, during propagation in the atmosphere, as well as saturation of the optical [5] [10]), however the one proposed communications has always been one of their major advantages over here features several properties that make it attractive for use in conventional RF communications, as it provides a larger modulation modem laser communications. First, it is meant for implementation bandwidth and therefore higher data rates, and less interference in a VLSI circuit, combining low-power consumption, compact size, between optical systems. The reason that laser communications have faster computation, higher perturbation frequencies and control of not expanded as expected, so far, has been the difficulty to compen-multiple channels. Second, it compensates for possible phase shifts sate for atmospheric turbulence. Turbulence causes random optical of the dither signal in the case of long-distance communications. inhomogeneities in the atmosphere that result in beam spreading, Finally, it accounts for saturation of the phase controllers when the beam wander and scintillation (intensity fluctuation), and therefore multi-dither algorithm dictates continuous increase or decrease in the distort the transmitted data [1].controlling phase. Over the last few decades, significant work has been done in the field of adaptive optics in order to alleviate or at least mitigate wave-II. THE MULTI-DITHER ALGORITHM front distortion and therefore enhance the use of laser communicationThe purpose of the multi-dither algorithm is to maximize the value systems. The techniques that have been so far proposed can be divided of a performance metric of the optical system, usually the waveinto two main categories [2]: wave-front conjugation and model-free front's intensity. This is done by calculating the gradient of the optimization. Wave-front conjugation requires the reconstruction of metric and then, using the gradient descent method, find its maximum the wave-front at the receiver and provides information for both phase value. First, a brief overview of the gradient descent method is given (2) of strong intensity modulation used in several laser communication dt dt schemes, the wave-front can be difficultly reproduced, imposing indicating that J(u(t)) is a strictly decreasing function of time unless constraints in the use of the wave-front conjugation technique [5]. u has reached an equilibrium point of (1). The factors discussed above, as well as the emergence of highAssuming that J does not have saddle points, (2) implies that the bandwidth phase controllers (e.g. [7]...

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 G m -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 of two current biases. Experimental results from a 0.5 lm SiGe BiCMOS chip demonstrate 7 decades of tuning range, from 80 Hz to 800 MHz, as well as low harmonic distortion. Power consumption scales with oscillation frequency, measuring 2 lW/MHz The circuit serves a range of applications including agile communications, analog built-in self-test, stochastic adaptive control, spectroscopy, and bioinstrumentation.

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 performance. A fully translinear design has been employed for the architecture, making the controller operation scalable within a very wide range of frequencies and control bandwidths, and, therefore customizable for a variety of systems and applications. Experimental results from a SiGe BiCMOS implementation are provided demonstrating the broadband and high-speed performance of the controller.

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