Frequency-Offset Cartesian Feedback Based on Polyphase Difference Amplifiers

The design and calibration of the cross-correlator are crucial issues for interferometric imaging systems. In this paper, an analog complex cross-correlator with output DC offsets and amplitudes calibration capability is proposed for interferometric passive millimeter-wave security sensing applications. By employing digital potentiometers in the low frequency amplification circuits of the correlator, the outputs characteristics of the correlator could be digitally controlled. A measurement system and a corresponding calibration scheme were developed in order to eliminate the output DC offsets and the quadrature amplitude error between the in-phase and the quadrature correlating subunits of the complex correlator. By using vector modulators to provide phase controllable correlated noise signals, the measurement system was capable of obtaining the output correlation circle of the correlator. When injected with −18 dBm correlated noise signals, the calibrated quadrature amplitude error was 0.041 dB and the calibrated DC offsets were under 26 mV, which was only 7.1% of the uncalibrated value. Furthermore, we also described a quadrature errors calibration algorithm in order to estimate the quadrature phase error and in order to improve the output phase accuracy of the correlator. After applying this calibration, we were able to reduce the output phase error of the correlator to 0.3°.

For modern systems working with amplitude modulated signals the high linearity power amplifiers is required. One of methods of linearization allows signify decrease the 3rd order intermediation products is Cartesian feedback. The offset voltages, which arises when integrated system on chip worked, disturbed work of mixers, at result efficient of linearization is decreased. In the article the specialized operational amplifier with four inputs is described, it use as error amplifier, in Cartesian systems for decreasing of output offset voltage. Amplifier was design in process 180 nm CMOS, has unity gain frequency is 10 MHz, gain is 105 dB. Input voltage noise at frequency 10 kHz is 8.5nV√Hz. Consumption current is 4.5 mA.

A dynamic testing system consisting of a totally independent mechanical laboratory has been designed and constructed at the EUCENTRE Foundation. The results of a first experimental trial with the aim of checking the reliability of the system apparatus when stressed by imposing a series of dynamic loading histories on a real-scale two-storey tridimensional frame are presented. Particular care was devoted to equipment and its functioning, reliability of the digital controller, actuator response, and matching between reference input and feedback signal. Furthermore, a brief description regarding the behavior of the tridimensional frame and the experimental results is added.

Amplifier linearization schemes based on modulation feedback (e.g., Cartesian feedback) require a phase correction circuit to stop instability and limit the level of the out-of-band noise floor. It is shown that the optimum phase corrector setting corresponds to the minimum output power condition of the amplifier. A new and very simple method by which the phase correction circuit is adjusted is described. The scheme uses the supply current to the final stage amplifier as a measure of the output power and minimizes this by using a simple direct search algorithm. Phase correction to within 5/spl deg/ of optimum can be obtained after about 50 iterations. The performance is limited by hysteresis in the supply current feedback signal.

Optimal Control of a Pilot Heat-Exchanger

Three‐phase ac choppers feature output voltage amplitude controllability and enable more compact system realizations compared to autotransformers. For the practical realization advantageously standard power transistor with unipolar voltage blocking capability such as MOSFETs can be employed as a naturally resulting offset voltage between the grid and the input‐stage starpoint ensures purely positive power transistor voltages. This offset voltage is, however, not strictly defined and may drift to higher voltage values, resulting in high power transistor voltage stresses and finally a potential overvoltage breakdown. Traditionally, the offset voltage drift is prevented by introducing discharge resistors across the input‐stage capacitors which, however, results in substantial ohmic losses. This paper analyzes the offset voltage formation in ac choppers and proposes a novel clamping modulation scheme which ensures a strictly defined and minimum time‐varying offset voltage without need for discharge resistors. Theoretical analyses and circuit simulations are finally experimentally verified with a 400 V (rms, line‐to‐line) 50 Hz grid connected three‐phase buck‐boost ac chopper with 3 kW rated power.

Attitude control system plays the important role for to maintain the satellite to desired orientation. To control the satellite it is necessary to do the attitude stabilization. Attitude stabilization achieved by Star sensor, sun sensor, Earth sensors. Attitude control is mainly use for antenna pointing accuracy, camera focus to earth surface and solar panel pointing toward sun. Due to tumbling effects, satellite will rotate all the direction in the space. To maintain the orientation of the satellite it is necessary to design the attitude determination and control. Satellite consider as the rigid body. Inertia matrix describes the rigid body dynamics. The orientation of the satellite determine by Euler angle and Quaternion. The Low earth orbiting satellite will have enormous amount of aerodynamic drag stinking the satellite body and gravitational attraction another problem. Because of that satellite dwell, time is reduced. It means satellite more time spending particular part of the earth. The attitude estimation is measures by the orientation of vectors. Attitude estimation means to find the position and orientation of flying object with respect to the fixed reference of reference. Vector remains considered in the frame of reference to compute for find the orientation of the body of the satellite in the inertial reference system. The Earth is an inertial reference frame, and Satellite is a body frame. Attitude sensor used to measure the satellite orientation in the reference frame. This will help in accurately predicting the orbit deviation and a control system to correct if any by providing the satellite momentum means ‘mass in motion’ changes in a body rapidly in Low earth orbit due to centripetal force acting on a satellite. Attitude control system (ACS) need the numerical simulation to find the required torque demand by the help of difference between reference input (Attitude) signal and feedback signal measure by attitude sensor to trim the control surface maintain the actuator required orientation . The results will consist of two parts the first part consisting of the attitude estimation using Euler angle and Quaternion method, second part consist of estimate the control torque from magnetic torquer and error estimation using non-linear filter (Unscented Kalman Filter) with MATLAB simulation. Â

A novel scheme is proposed to reduce the dc drift and stator resistance variation effects in rotor flux based MRAS. In this scheme the voltage model is modified to obtain the compensating voltage from the offset and drift voltages. The low speed performance is improved by implementing the adaptive neuro fuzzy inference system (ANFIS) in adaptive mechanism of MRAS. In this method the reference model is free from dc drift and gives better speed response as voltage and current model rotor flux components are equal. A MATLAB/SIMULINK model of closed loop sensorless indirect vector control induction motor drive at different operating conditions is presented. The results shows faster and better response for ANFIS based model.

A description is given of three prototype transmitters, using digital signal processing in different ways to achieve linear RF amplification. The Cartesian feedback technique, the adaptive predistortion technique, and the LINC (linear amplification with nonlinear components) technique, are all shown to provide a good degree of intermodulation product suppression (>50 dB), with the LINC amplifier approach potentially the most power-efficient (>70%). Both the LINC and predistortion systems can operate in a wideband mode. The Cartesian approach, because of the inherent feedback control system, is limited to a bandwidth of about 10% of the operating frequency. The implementation costs are considerably reduced over conventional analog realizations of such systems for all three techniques. >

This brief presents a fully integrated dc offset cancellation (DCOC) scheme with configurable cut-off frequency and settling time. The proposed digitally assisted real-time DCOC scheme prevents the high gain baseband circuitry from saturation in direct conversion receivers. The proposed DCOC is designed and implemented in a $0.18~\mu \text{m}$ CMOS process. It occupies an area of 0.042 mm2 and consumes a current of 0.58 mA for I and Q paths under 1.8 V supply. The residual output dc offset voltage (DCOV) is less than 5 mV under the maximum baseband gain of 62 dB. The 3-dB high-pass cut-off frequency can be configured from 100 Hz to 1 kHz and settling time varying from 5.7 ms to 0.7 ms when the receiver operates under the maximum baseband gain.

ABSTRACTThe present article describes a low-cost active aerostatic thrust bearing controlled via an Arduino card and with feedback transducers and valves embedded in it. Efforts were made to design a compact thrust bearing with small overall dimensions, robust behavior, and reduced costs. Two embedded electropneumatic digital valves are controlled with pulse width modulation (PWM) logic and used to modify the thrust bearing supply pressure. The feedback signal for the control comes from two embedded backpressure sensors designed and characterized for this purpose. The test benches required for static and dynamic thrust bearing characterization are described; preliminary experimental tests were carried out in open and closed loop configurations. The closed loop configuration of the system, with a proportional integral (PI) control, shows good behavior and the time needed for the thrust bearing to return to the reference gap value after a force perturbation of 40 N is about 0.1 s.

We propose a hysteresis and drift compensation scheme using proportional-integral feedback control for a nanopositioning Pb(ZrTi)O3 (PZT) microstage. A multi-degree of freedom PZT microstage with integrated differential capacitive displacement sensors has been fabricated and tested, demonstrating the feasibility of compensating for hysteresis and creep. The feedback signal to the PZT actuators is fed from differential capacitive sensors of the displacement of the microstage. Experimental results show that the sensitivity of the displacement sensor is approximately 0.53 V µm−1. A maximum resolution of 16 nm is achieved when hysteresis is compensated for, and the minimum detectable variation of capacitance ΔC is 1.25 × 10−3 pF. The hysteresis of the system varies with the proportional gain Kp, integral time constant Ti and reference input frequency. By using feedback control with a proportional and integration (PI) controller, the hysteresis decreases from 30% in open-loop operation to approximately 1% in closed-loop operation at a gain of 20, when the frequency of the sine reference input is 1 Hz and Ti is 20 ms. Efficient compensation of hysteresis is validated by the closed-loop control, especially when the frequency of the reference input is low. Elimination of creep/drift is also verified by the closed-loop control.

Although required for many fundamental immune processes, ranging from self-tolerance to pathogen immunity, interleukin (IL)-2 production is transient, and the mechanisms underlying this brevity remain unclear. These studies reveal that helper T cell IL-2 production is limited by a classic negative feedback loop that functions autonomously or in collaboration with other common γ chain (IL-4 and IL-7) and IL-6/IL-12 family cytokines (IL-12 and IL-27). Consistent with this model for cytokine-dependent regulation, they also demonstrate that the inhibitory effect can be mediated by several signal transducer and activator of transcription (STAT) family transcription factors, namely STAT5, STAT4, and STAT6. Collectively, these findings establish that IL-2 production is limited by a network of autocrine and paracrine signals that are readily available during acute inflammatory responses and, thus, provide a cellular and molecular basis for its transient pattern of expression.

A simulation method that has proven valuable in the design of high-speed regenerative comparators such as those used in pipeline and flash analog-to-digital converters is presented. This method yields an input-referred offset voltage for the comparator while it is operating at speed, including both DC and dynamic effects such as charge injection and capacitive coupling. The speed and efficiency of the method allows the circuit designer to more fully explore the design space, and provides important insights into comparator operation.

5 - CLOSED-LOOP TEMPERATURE CONTROL