Agilent Measurement Journal - Issue 5 - 2008 - (Page 47)

Referring back to Equations 3 and 4, any noise from the input source and CP-based PFD is low-pass ﬁltered. The noise due to static phase offsets, contributed by the CP leakage current, can be kept low using good PFD and CP design techniques. The noise from the LF is shaped by a bandpass transfer function whereas the noise contribution from the VCO is high-pass ﬁltered. Using these tools, characterization and simulation of the PLL closed-loop phase noise can be accomplished using a ﬁve-step process: 1. Characterize the VCO/divide-by-N chain 2. Model the VCO/divide-by-N chain 3. Characterize the CP and PFD 4. Model the CP and PFD 5. Create the PLL functionality model A closer look at these ﬁve steps will further illustrate what is possible with these tools. Exploring analysis capabilities and methodologies Tools such as RFDE and ADS provide an accurate, well-deﬁned methodology for predicting ﬁrst-order phase-noise performance in PLLs. These tools in particular provide ﬁve important noisesimulation capabilities: • Linear noise analysis: S-parameter and small-signal AC (noise voltage). • Budget noise analysis: System-level design at the block diagram level. • Nonlinear noise analysis: Harmonic balance (HB) mixer noise ﬁgure, HB phase noise and noise voltage. • Transient nonlinear noise analysis: Noise generated by noise sources, nonlinear devices and passive devices (jitter). • Circuit envelope noise analysis: A Monte Carlo technique to simulate noise. Steps 1 and 2: Characterize and model the VCO/divide-by-N chain A transistor-level VCO/divide-by-N chain can be simulated using the HB oscillator and noise analysis. The phase-noise modulator component from the ADS/RFDE model library can then be used to emulate VCO/divide-by-N phase noise. Figure 3 compares phase noise results from a model and an HB simulation. Steps 3 and 4: Characterize and model the CP and PFD Characterization of the transistor-level CP and PFD is done using a two-step simulation. First, transient analysis is performed to ﬁnd PFD/CP sensitivity (e.g., CP current versus input phase difference at the PFD). Next is transient nonlinear noise analysis, which is performed with time-domain noise off and on. CP noise current is then calculated by taking the difference between currents with noise on and off. Jitter can be calculated using the transient nonlinear noise and the sensitivity calculation of the PFD/CP. Jitter can then be used for a current-noise source or for the PFD/CP model. 2pN Kp K vco wc 1 Qout QLF N P (s) 1 Qout QPFD Qout Qi P (s) 2 P (s) 3 Qout QVCO ( t1 ) w 2 c log w Figure 2. Noise contributions from individual blocks affect closedloop PLL phase-noise performance Figure 3. Overlaid phase noise plots from a model (blue) and an HB simulation (red) show close agreement Agilent Measurement Journal 47

Table of Contents Feed for the Digital Edition of Agilent Measurement Journal - Issue 5 - 2008

Agilent Measurement Journal Issue 5 Finding a New Path when Assumptions Break Down Contents Testing MIPI D-PHY Protocols Oscilloscope Firmware Update DNA Replication Joining the LTE/SAE Trial Initiative Testing Proteins Praise for DC Power Analyzer Scripting Features for AMDS Testing Hybrid PCBA Systems Improving the Gene Expression System Workflow Turning a “Good Enough” Test Strategy into One That’s Reliable, Repeatable and Traceable Understanding the Effects of Limited-Bandwidth Channels on Digital Data Signals Introducing the 3GPP LTE Downlink Validating the 26 Validating the Physical and Protocol Layers in DDR Memory Interfaces Understanding Total Jitter Measurements of Low Probabilities Using Behavioral-Model Simulation to Accurately Predict First-Order PLL Performance Creating Synchronous High-Frequency Sampling across Multiple Digitizers Overcoming the Challenges of Testing FlexRay Networks Understanding Operating Life and Repeatability of Electromechanical Switches and their Effect on Total Cost of Ownership Implementing Micro and Nano LC/MS Techniques for High Sensitivity Lipidomics Analysis

Agilent Measurement Journal - Issue 5 - 2008

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