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Optical Wireless Receiver Design
Published in Roberto Ramirez-Iniguez, Sevia M. Idrus, Ziran Sun, Optical Wireless Communications, 2008
Roberto Ramirez-Iniguez, Sevia M. Idrus, Ziran Sun
An LA is an amplifier with no special provisions to avoid clipping or limiting the output signal. An AGC amplifier consists of a variable-gain amplifier and an automatic gain control mechanism that keeps the output swing constant over a wide range of input swings. Here, where the LA would start to distort for large input signals, the AGC reduces its gain and manages to stay in the linear regime. This is shown in Figure 7.17, where the idealized DC transfer function of an LA and AGC amplifier is illustrated. The DC transfer function of an AGC amplifier depends on the input signal. Nevertheless, for very large signals, the AGC amplifier cannot reduce its gain any further and limiting eventually occurs. The system designer must make sure that the input dynamic range of the AGC amplifier is sufficiently wide to avoid this situation.
Tracking Radars
Published in Habibur Rahman, Fundamental Principles of Radar, 2019
A typical conical-scan pulsed radar system may be represented by the block diagram in Figure 10.9. As shown in the schematic diagram of the tracker, the AM signal out of the range gate is demodulated by the azimuth and elevation reference signals to produce the two angle error signals. These angle errors drive the angle servos, which in turn control the position of the antenna, and drive it to minimize the error (a null tracker). Since the conical-scan system utilizes amplitude changes to sense position, amplitude fluctuations at or near the conical-scan frequency will adversely affect the operation of the conical-scan radar system by inducing tracking errors. Three major causes of amplitude fluctuations include the inverse-fourth-power relationship between the echo signal and range, conical-scan modulation, and amplitude fluctuations in the target cross section. The function of the AGC is to maintain a constant level of the receiver output and to smooth amplitude fluctuations as much as possible without disturbing the extraction of the desired error signal. The d-c level of the receiver output must be maintained constant by preventing saturation caused by large signals. Thus the AGC that is required to normalize the pulse amplitude must be carefully designed. The required dynamic range of the AGC depends on the variation in range over which the targets are tracked, and should be in the order of 90 dB or more. Two/three stages of IF amplifiers are normally used to stabilize the dynamic range of the system. An alternative AGC filter design would maintain the AGC loop gain up to frequencies much higher than the conical-scan frequency resulting in the measurement of range in the normal manner. In such a case the error signal can be extracted from the AGC voltage.
A
Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
automatic tracking such as a subroutine. Automatic allocations are usually made upon entry to a subroutine. automatic black-level control electronic circuitry used to maintain the black levels of the video signal at a predetermined level. The black level reference is either derived from the image or from the back porch of the horizontal blanking interval. automatic chroma control (ACC) ACC is used to correct the level of the input chroma signal. Typically, the ACC circuitry makes corrections to the chroma, based on the relative degeneration of the color burst reference signal, since this signal will have been subjected to the same degradation. automatic circuit recloser See recloser. maintain active power balance by means of the speed governor system. In an interconnected system, scheduled power interchanges are maintained by means of controlling area generations. automatic gain control (AGC) a method to control the power of the received signal in order to be able to use the full dynamic range of the receiver and to prevent receiver saturation. automatic generation control (AGC) phrase describing the computer-based process by which electric utilities control individual generating stations to maintain system frequency and net interchange of power on a highly interconnected transmission grid. Automatic generation control (AGC) systems monitor grid frequency, actual and scheduled power flows, and individual plant output to maintain balance between actual and scheduled power production, both within transmission control areas and at individual generating stations. Control is generally accomplished by adjusting the speed control (or droop) characteristics of individual generating units. Control actions are determined by planned production schedules and power exchange agreements among participating utilities. automatic level control (ALC ) a feedback system where an RF signal from a source is sampled, detected, and sent to a voltage controlled attenuator to maintain a constant amplitude output over a specified band of frequencies. automatic repeat request (ARQ) an error control scheme for channels with feedback. The transmitted data is encoded for error detection and a detected error results in a retransmission request. automatic tracking on an optical disk, the process in which the position of the disk head relative to the disk surface is constantly monitored and fed back to the disk control system in order to keep the read/write beam constantly on track.
An MDPSK homodyne receiver with adaptive phase-diversity
Published in Journal of Modern Optics, 2020
Changqing Cao, Zengyan Wu, Wenrui Zhang, Xiaodong Zeng, Xu Yan, Zhejun Feng, Yutao Liu, Bo Wang
This section discusses the procedure for compensating for the asymmetry of and . We assumed that amplifier in Figure 1 has a constant gain , and that is a variable gain amplifier. The AGC system comprises two envelope detectors and a differential amplifier , which outputs an error signal u to control the gain of amplifier . The AGC system does not drive the gain back to the value . Instead, the purpose of the error signal is to drive the total amplitude difference back to the correct value of zero such that . When is greater than , u is positive; hence, increases such that equals , and vice versa. The AGC system can accurately eliminate the overall amplitude asymmetry attributed to the asymmetry of the optical paths and the electrical circuits of the two branches.
A New Resistorless and Electronic Tunable Third-Order Quadrature Oscillator with Current and Voltage Outputs
Published in IETE Technical Review, 2018
Hua-Pin Chen, Yuh-Shyan Hwang, Yi-Tsen Ku
Considering (7) and (8), the gmF2 can control the oscillation condition, and the gain, kAGC, or the gmF1 can control the oscillation frequency. The AGC technique stabilizes the output level and ensures the overall THD of the resulting signals. Thus, an additional auxiliary amplitude control circuit and technique can be used to reduce the THD of the resulting output signal through an external device [12–17,43].