Fast Automatic Frequency Calibrator Using an Adaptive Frequency Search Algorithm
Abstract : A new adaptive frequency search algorithm (A-FSA) is presented for a fast automatic frequency calibrator in wideband phase-locked loops (PLLs). The proposed A-FSA optimizes the number of clock counts for each frequency comparison cycle, depending on the difference between the target frequency and the PLL output frequency, as opposed to a binary frequency search algorithm (B-FSA), where the frequency search time per cycle is fixed. This eliminates unnecessary clocking times during the frequency comparison process, and thus reduces the total PLL lock time. The additional circuitry needed for A-FSA is only a simple counter controller, thus minimizing hardware overhead. To verify the effectiveness of the proposed algorithm, two wideband PLLs are designed and simulated using a 65-nm CMOS technology: one with B-FSA, and the other with A-FSA. The latter achieves a lock time faster than the former by at least a factor of 2, even under worst case conditions.
? It is therefore helpful to compare the performance of this multi-functional system to existing approaches that have been optimized now over many years, but which measure range or displacement/velocity alone.
? The frequency ridges coexist in x over a length equal to the length of the window, even though the two original frequencies do not overlap.
? Besides unifying the mathematics of such filters, researchers in wavelets has discovered certain, discrete, finite-width mother wavelets that are orthogonal to scaled and translated versions of themselves.
? Each ssd surface is a function of all the peaks in a particular region, so no weighting is necessary when combining them.
? To address this problem, this paper proposes a novel AFC technique with ultra-fast calibration time for integer and Fractional-N PLL synthesizer.
? The problem is that fres must be less than half of the frequency spacing fspacing between two adjacent subband tuning curves of VCO, otherwise, the frequency comparison result would not be precise enough to find the optimum sub-band which is closer to target frequency.
? Therefore, reducing Tcal is a palpable design issue in the AFC technique.
? Another veiled design issue is the frequency resolution fres (the frequency-detection resolution of AFC circuit).
• The proposed A-FSA optimizes the number of clock counts for each frequency com-parison cycle, depending on the difference between the target frequency and the PLL output frequency, as opposed to a binary frequency search algorithm (B-FSA), where the frequency search time per cycle is fixed.
• In this paper, an A-FSA is proposed for automatic frequency calibration in wideband PLLs with multibit cap-bank VCOs.
• Therefore, asynchronous work of TOF and FSM is a major breakthrough in the proposed AFC technique.
• However, such a huge time cost is acceptable in the proposed calibration circuit owing to the independence of TOF and FSM.
? The advantage of the A-FSA is that it enables postcorrection of potential frequency search error in the preceding frequency comparisons.
? The most important PLL performance metrics, such as phase noise, clock jitter, and spurious tone suppression, are dominantly determined by the fine frequency tuning part, because the AFC is turned OFF right after the completion of the coarse frequency tuning.
? It is apparent that the efficacy advantage of the proposed A-FSA becomes larger as the number of cap-bank bits increases.
? To demonstrate the efficacy of the proposed A-FSA, two wideband PLLs are designed and simulated using a 65-nm CMOS technology: one with a conventional B-FSA-based AFC (B-AFC) and the other with the proposed A-FSA-based AFC (A-AFC).
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