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Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
automatic fine tuning (AFT) one of the input circuits of a color television receiver specifically designed to maintain the correct oscillator frequency of the tuner for best color reproduction of the picture. The circuit is sometimes called the automatic frequency control. See also automatic frequency control (AFC). automatic focusing on an optical disk, the process in which the distance from the objective focal plane of the disk is continuously monitored and fed back to the disk control system in order to keep the disk constantly in focus. automatic frequency control (AFC) electronic circuitry used to keep the received signal properly placed within the desired IF frequency range. In televisions, the AFC circuitry is also called the AFT or "automatic fine tuning" section. The AFC circuit will generate an error signal if the input frequency to the IF drifts above or below the IF frequency. The error signal is fed back to vary the local oscillator frequency in the tuner section. See also automatic fine tuning (AFT). automatic frequency control (AFC) an automatic feedback control system that is used to
Performance-Linked Phase-Locked Loop Architectures: Recent Developments
Published in Suman Lata Tripathi, Sobhit Saxena, Sushanta Kumar Mohapatra, Advanced VLSI Design and Testability Issues, 2020
Umakanta Nanda, Debiprasad Priyabrata Acharya, Prakash Kumar Rout, Debasish Nayak, Biswajit Jena
Due to the increasing demand for high-frequency multiband and multistandard transceivers in modern communication systems, a wide-band fast locking PLL achieving low phase noise is also highly essential. To improve the locking process, lock range, and lock time and to reduce the total number of comparisons, a code optimization along with a binary search algorithm is used in Ref. [48]. The frequency range is found here to be more than 400 MHz, and the lock time is less than 65 μs when measured in 180-nm technology. To enhance the frequency range, both the discrete and continuous tuning mechanisms are adopted in Ref. [49]. An AFC technique is used where an auxiliary digital loop to select a particular band of VCO is incorporated. This PLL was simulated and implemented on FPGA using Xilinx system generator. The lock-in time achieved here is 1.7 μs. In Ref. [50], the VCO incorporates a 5-bit differential switched capacitor array to build a tuning range from 2 to 3.2 GHz. The calibration time achieved here is less than 6 μs. Another AFC technique implemented in Ref. [51] works in two different modes, namely, frequency calibration mode and store/load mode. In the first mode, a new frequency detector is employed to reduce the lock time to 16 μs, whereas in second mode of operation by loading the calibration results stored after frequency calibration, the AFC makes the VCO come back to the calibrated frequency in about 1 μs. In a 900-MHz PLL [52], an automatic switched-capacitor discrete-tuning loop is deployed to have 20% more tuning range than the conventional one with a calibration time of 2 ms when measured in 0.6-μm technology. However, this method lacks in the calibration time. A better solution is presented in Ref. [53] where both the switched-capacitor bank LC VCO and the AFC technique are used to get a tuning range of 600 MHz, which is as wide as 40% of the highest frequency. However, this technique also suffers from high calibration time of the order of tens of μs.
Fault-tolerant prescribed performance control of active suspension based on approximation-free method
Published in Vehicle System Dynamics, 2022
Yang Wu, Boyuan Li, Haiping Du, Nong Zhang, Bangji Zhang
The time domain responses of the HB cases are very similar to those of the HD cases, and they are omitted here due to space considerations. Figure 10 gives the frequency domain comparison for the HB cases. The AFC cases show better performances in both low- and medium-frequency domain. It is also observed that, the performances of the HB cases are improved than those of the HD cases, which is because the actuation bias has partly compensated the influence of hysteresis. The numerical comparison is presented in Table 3. The overall trend is the same as the previous table, with better ride comfort comes higher tire load variation.
Fractional-N phase-locked loop for split and direct automatic frequency control in A-GPS
Published in International Journal of Electronics, 2018
Chester Sungchung Park, Sungkyung Park
Relative to the output frequency, the measured AFC resolution or accuracy is <5 ppb or on the order of a Hertz, which could be better if the bus width of the AFC control word were wider. This ultra-high resolution is enabled by the use of direct AFC when compared with the existing AFC methods based on tuning the VCO output frequency via switching the capacitors in the array. The resolution of the digital DSM is set by the modulus Q of it and the precision frequency of the master CK, Fdiv, is set by the AFC word F in Figure 2. The equation that relates Fdiv to Q and F is expressed as follows.