What is reference spur?
What is reference spur?
Reference Spur Reduction Techniques for a Phase-Locked Loop This leakage compensation loop senses the leakage current of the loop filter from the up and down pulse widths in the steady state and compensates for the charge loss due to the leakage current.
What is reference spur in PLL?
These spurs are commonly referred to as reference spurs, though reference here does not mean the reference clock frequency. Rather, it refers to fPFD. An LO signal produced by an integer-N PLL has dual sideband spurs at fPFD and its harmonics.
What causes spurs in PLL?
Spurs are generated at the output of conventional PLLs due to nonidealities of the phase-frequency detector and charge pump, and variation in the modulus of the frequency divider. The former two induces reference spurs while the latter causes fractional spurs.
How is PLL frequency calculated?
Therefore, FOUT = (FREF/R) × (BP + A), as in Figure 4. There are many specifications to consider when designing a PLL. The input RF frequency range and the channel spacing determine the value of the R and N counter and the prescaler parameters. The loop bandwidth determines the frequency and phase lock time.
What is cycle slip in PLL?
When the PLL is locked, you expect the number of ref and fbclk cycles to be equal. When one is greater than the other, then you are experiencing cycle slips. If the PLL is initially locked, then cycle slips occur for three reasons: 1) the reference modulates frequency or phase faster than the PLL can respond.
What is integer boundary spur?
Integer boundary spurs appear when the PLL feedback loop fractional divide ratio is programmed to a value very close to an integer. These spurs occur because the harmonics of the PFD frequency mix with the VCO (or its harmonics) and the resultant intermodulation frequency components fall within the loop bandwidth.
Why low pass filter is used in PLL?
A Low Pass Filter (LPF) is used in Phase Locked Loops (PLL) to get rid of the high frequency components in the output of the phase detector. It also removes the high frequency noise. All these features make the LPF a critical part in PLL and helps control the dynamic characteristics of the whole circuit.
Which type of filter is used in PLL?
(b) PLL capture performance PLL with a 5th-order Butterworth filter. In this case, the reference loop gain resulted in a PLL frequency response free of overshoots, without the need of reducing this value.
What is loop filter in PLL?
The loop filter acts to slow the response down. The narrower the loop bandwidth, i.e. the lower the cut-off frequency of the filter, the slower the response of the loop to responding to changes. Conversely if the loop requires a fast response to changes in frequency, then it will need a wide loop bandwidth.