AN2455 Application note STWPLLSim phase noise and settling time simulator for STW8110x Application and scope The STWPLLSim tool helps the end user to design the optimal loop filter for the STW81101x synthesizers. It provides a very accurate estimation of the overall phase noise and settling time performances, allowing the user to interactively compare measurements with simulated performance. July 2007 Rev 2 1/14 www.st.com Installation 1 AN2455 Installation The STWPLLSim software is written in Java and designed to run on Windows 2000/XP. To perform time domain simulations, STWPLLSim requires the MATLAB Component Runtime (MCR) Libraries (Copyright 1984-2005, The MathWorks, Inc. See http://www.mathworks.com/access/helpdesk/help/toolbox/compiler/index.html?/access/help desk/help/toolbox/compiler/f12-999353.html). Run SETUP.bat to install STWPLLSim. 2 Main form Figure 1. 1 3 STWPLLSim: main form and project flow 4 5 6 2 2.1 Creating and managing projects New and Open buttons allow the user to create a new project or to open an existing one. The project can be saved by pressing the Save / Save As buttons. 2/14 AN2455 2.2 Main form Project flow These are the steps to follow in using STWPLLSim, as shown in Figure 1: 1. Main settings (see the screenshot in Figure 2): a) Device choice (STW81101, STW81102, STW81103) b) Output frequency [MHz] c) Frequency step [kHz] d) Output stage (direct output, divider by 2, divider by 4) e) VCO and phase detector frequencies are calculated from the inserted data. f) A table helps to choose the correct output stage depending on the desired output frequency and the selected device. 3/14 Main form AN2455 Figure 2. Main settings 1a 1b 1c 1d 1e 1f 4/14 AN2455 Main form 2. Prescaler: select the prescaler (either 16/17 or 19/20). 3. Reference clock (see the screenshot in Figure 3): a) Reference frequency b) Fitting parameters for phase noise performance Figure 3. Reference clock settings 3a 3b 5/14 Main form AN2455 4. Charge pump current [mA] (see the screenshot in Figure 4): Figure 4. Charge pump current settings 4 5. 6/14 VCO (see the screenshot in Figure 5): a) The VCO frequency set in the main settings form is shown. b) A typical VCO gain is set depending on the VCO frequency. This value can be changed by the user. c) A default or a user measure file can be loaded for the noise calculation. AN2455 Main form Figure 5. VCO settings 5a 5b 5c 7/14 Main form AN2455 6. Loop filter (see the screenshot in Figure 6): a) Loop filter network: - 2nd order - 3rd order b) PLL specifications: - Suggested loop BW ≤Fcomp/10 - Suggested (and default) phase margin = 48° (best trade-off between phase noise and settling time performance) c) Figure 6. Suggested or user defined values for resistances and capacitances can be used. Valid unit prefixes are "K" for resistances and "n" and "p" for capacitances. Loop filter settings forms (2nd and 3rd order) 6a 6b 6c 8/14 AN2455 3 Waveform viewers Waveform viewers Waveform viewers are available for transfer functions, phase noise and transient response. 3.1 Transfer functions The magnitude and phase of the following transfer functions can be plotted: 1. Loop filter 2. PLL open loop 3. PLL closed loop Figure 7. Transfer function waveform viewer 1 2 3 9/14 Waveform viewers AN2455 After selecting the waveforms to plot, press the Plot Selected Curves button. You can modify the frequency range from the main form by clicking the Freq Range button. 3.2 Phase noise The following functions are available in the phase noise waveform viewer: 1. Plot the overall phase noise and the following contributions: – reference clock – phase detector – loop filter – VCO – RF output divider 2. Save the overall phase noise to a text file. 3. Load user measure/simulated data from a text file. 4. Calculate the integrated phase noise by inserting the integration range limits and pressing Enter. “K” and “M” are valid unit prefixes for the frequency. 5. Calculate phase noise values for five fixed frequencies and for one user frequency. You can modify the frequency range from the main form by clicking the Freq Range button. Figure 8. Phase noise waveform viewer 3 1 2 4 5 10/14 AN2455 3.3 Waveform viewers Transient response The step time response is plotted and the following parameters can be set: 1. Time unit (μs or ms) 2. Time window: if the specified time window value is lower than the settling time, a warning message is shown. 3. Points 4. Settling time (frequency error, in ppm, with respect to the Fout final value) 5. Zoom on settling region (default: on) The VCO calibration time is calculated according to the Fcomp value and taken into account in the settling time value. Figure 9. Transient response waveform viewer 1 2 3 4 5 11/14 Report generation and documentation 4 AN2455 Report generation and documentation A report containing the synthesizer specification, the bill of materials and the design parameters can be generated by the tool. The documentation form contains datasheets and application notes. Figure 10. Design data report and documentation form 12/14 AN2455 5 Revision history Revision history Table 1. Document revision history Date Revision Changes 19-Jul-2007 1 Initial release. 20-Jul-2007 2 Corrected the numbering in Figure 2: Main settings. 13/14 AN2455 Please Read Carefully: Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. All ST products are sold pursuant to ST’s terms and conditions of sale. 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