Differential amplifier

Résumé

A differential amplifier is a type of electronic amplifier that amplifies the difference between two input voltages but suppresses any voltage common to the two inputs. It is an analog circuit with two inputs V_\text{in}^- and V_\text{in}^+ and one output V_\text{out}, in which the output is ideally proportional to the difference between the two voltages: : V_\text{out} = A(V_\text{in}^+ - V_\text{in}^-), where A is the gain of the amplifier. Single amplifiers are usually implemented by either adding the appropriate feedback resistors to a standard op-amp, or with a dedicated integrated circuit containing internal feedback resistors. It is also a common sub-component of larger integrated circuits handling analog signals. Theory The output of an ideal differential amplifier is given by : V_\text{out} = A_\text{d}(V_\text{in}^+ - V_\text{in}^-), where V_\text{in}^+ and V_\te

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https://en.wikipedia.org/wiki/Differential_amplifier

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Direct measurement of the spectral dependence of Lamb coupling constant in a dual frequency quantum well-based VECSEL

Andrei Caliman, Elyahou Kapon, Alexandru Mereuta, Salvatore Pes

Spectral dependence of Lamb coupling constant C is experimentally investigated in an InGaAlAs Quantum Wells active medium. An Optically-Pumped Vertical-External-Cavity Surface-Emitting Laser is designed to sustain the oscillation of two orthogonally polarized modes sharing the same active region while separated in the rest of the cavity. This laser design enables to tune independently the two wavelengths and, at the same time, to apply differential losses in order to extract without any extrapolation the actual coupling constant. C is found to be almost constant and equal to 0.84 +/- 0.02 for frequency differences between the two eigenmodes ranging from 45 GHz up to 1.35 THz. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

OPTICAL SOC AMER2019

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On the INS and GPS Data Processing for Airborne Gravity Applications

Telmo Cunha, Phillip Tomé

Airborne gravimetric and altimetric measurements depend heavily on the determination of the instantaneous position and attitude of the aircraft. Here, a methodology to process raw inertial data together with GPS data collected from at least two antennas/receivers in the aircraft is presented. This methodology is primarily aimed at the attitude determination, but has potential to be applied in precise position determination as well. The main idea behind the methodology is to process GPS carrier phase measurements in differential mode between a pair of aircraft antennas to obtain precise heading angles. These, together with doppler velocity readings and approximate position estimates, serves to maintain stability of the attitude angles obtained from filtering raw inertial measurements. On the other hand, the availability of precise attitude estimates from the inertial sensors allows keeping phase integer ambiguities fixed through cycle slips and satellite configuration changes. As a side effect, it is also possible to evaluate the quality of each phase measurement in order to exclude readings corrupted by noise or multipath effect. This is important for absolute position determination where the aircraft GPS measurements are processed against a reference station, namely when long baselines are used. The integration of displacement estimates computed from inertial data is potentially helpful to solve and keep integer phase ambiguities between the aircraft and the reference station. This methodology is being employed to process data from the Azores campaign of the AGMASCO project.

1998

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Many airborne applications, such as altimetry or photogrammetry without ground control points, strongly rely on the precise evaluation of the aircraft’s attitude. This paper presents an approach to the attitude determination problem, where a system combining Litton’s LN-200 Inertial Measurement Unit (IMU) with differential GPS (DGPS) is described. The methodology is based on the integrated processing of raw inertial measurements and GPS data collected from at least two receivers on board the aircraft and one, or possibly more, reference stations. It is well known that GPS and inertial navigation systems have complementary operational characteristics that can be exploited in an integrated system for continuous tracking of the aircraft’s navigational parameters (attitude, velocity and position). The incorporation of DGPS observations of one of the aircraft’s GPS antennas, specifically absolute position and doppler velocity readings, improves the overall system accuracy, including the estimates of roll and pitch angles that result from filtered raw inertial measurements, since it enables the continuous alignment of the strapdown analytical platform. By processing carrier phase measurements in differential mode between a pair of the aircraft’s GPS antennas (without information from any reference station), good attitude observations, especially true heading, are obtained. This is critical to align the low cost inertial platform in heading, since azimuth errors are weakly coupled with velocity or position errors. In fact, by this method alignment is achieved in motion and very quickly. The inertial system also provides high rate (DGPS filtered) position and velocity estimates that can be valuable during GPS signal outages and in DGPS ambiguity fixing procedures that occur whenever a new satellite becomes visible or cycle slips are detected. The estimated accuracy is 0.01º (1s) for roll and pitch and 0.1º (1s) for heading. Should the reference station data be absent and stand-alone doppler and position estimates be used instead, some degradation of the roll and pitch accuracy are to be expected. Besides a description of the relevant theory, this paper also includes post-processing results from one of a series of flights that took place in the Azorean area during a gravimetric and altimetric survey. The present methodology was successfully employed to process all data from this campaign.

1999

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1999