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Paper: A Robust and Fast Algorithm for ALMA Local Oscillator Power Amplifiers Optimization
Volume: 522, Astronomical Data Analysis Software and Systems XXVII
Page: 459
Authors: Siringo, G.
Abstract: I present an algorithm developed for the optimization of the local oscillator power amplifiers of the receivers in use at the Atacama Large Millimeter/submm Array, ALMA. The configuration of ALMA receivers (SIS mixers) is done by applying frequency dependent optimized values of mixer voltage and current extracted from a look-up table. The bias voltage is applied directly to the mixer by the bias voltage controller but the bias current, instead, can only be optimized in an indirect way, by adjusting the power from the local oscillator. The software in charge of the optimization, therefore, has to control the drain voltage of the power amplifiers to make the current response converge within a given tolerance to the target value. This would be a classical root-finding problem if was not for the presence of noise both in the applied power amplifier drain voltage and in the mixer readout current values. The algorithm presented here is a probabilistic variant of the classic bisection algorithm and is able to guarantee fast and reliable convergence even with noisy control and response variables. This new algorithm has been implemented in the ALMA main control software starting from Cycle-5.
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