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March 2010 [Components] Analyze Phase Noise In A Sampled PLL (Part 3) Some have suggested that PLL noise degrades with frequency because the charge pumps are powered on for longer periods compared to the sampling period and therefore allow more noise to be transferred to the loop filter. In fact, the noise follows exactly what would be expected from FM theory and sampling theory. From FM theory, the noise is expected to increase by 6 dB for every doubling of frequency (20logfs). However, from sampling theory, the noise ... February 2010 [Test & Measurement] Analyze Phase Noise In A Sampled PLL (Part 2) Phase noise in sampled phase-locked loops (PLLs) can impact the performance of a wide range of commercial and military systems, including communications networks based on phase modulation. As shown last month in the first installment of this three-part series, modeling approaches may differ depending upon whether a PLL is a continuous-time or sampled system, with nonlinear approaches needed for th latter. In this second article installment, it may be... January 2010 [Test & Measurement] Analyze Phase Noise In A Sampled PLL, Part 1 Phase locked loops (PLLs) have been used for years to stabilize signal sources such as oscillators. In the past, loop bandwidths tended to be small compared to the sampling frequency, but with modern communications systems, requirements for faster switching times mean that this is no longer the case. Narrow-bandwidth PLLs can be effectively modeled and simulated by means of linear analysis, but these same approaches fall short for ... |
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