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
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Installation
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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.
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Main form
Figure 1. STWPLLSim: main form and project flow
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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.
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Main form
2.2
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) b) c) d) e) f) Device choice (STW81101, STW81102, STW81103) Output frequency [MHz] Frequency step [kHz] Output stage (direct output, divider by 2, divider by 4) VCO and phase detector frequencies are calculated from the inserted data. A table helps to choose the correct output stage depending on the desired output frequency and the selected device.
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Main form Figure 2. Main settings
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Main form
2. 3.
Prescaler: select the prescaler (either 16/17 or 19/20). Reference clock (see the screenshot in Figure 3): a) b) Reference frequency Fitting parameters for phase noise performance Reference clock settings
Figure 3.
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Main form
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Charge pump current [mA] (see the screenshot in Figure 4): Charge pump current settings
Figure 4.
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VCO (see the screenshot in Figure 5): a) b) c) The VCO frequency set in the main settings form is shown. A typical VCO gain is set depending on the VCO frequency. This value can be changed by the user. A default or a user measure file can be loaded for the noise calculation.
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Main form
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Main form 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
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- Suggested (and default) phase margin = 48 (best trade-off between phase noise and settling time performance) c) 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)
Figure 6.
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Waveform viewers
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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. 2. 3. Loop filter PLL open loop PLL closed loop Transfer function waveform viewer
Figure 7.
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Waveform viewers
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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: 2. 3. 4. 5. reference clock phase detector loop filter VCO RF output divider
Save the overall phase noise to a text file. Load user measure/simulated data from a text file. Calculate the integrated phase noise by inserting the integration range limits and pressing Enter. "K" and "M" are valid unit prefixes for the frequency. 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
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Waveform viewers
3.3
Transient response
The step time response is plotted and the following parameters can be set: 1. 2. 3. 4. 5. Time unit (s or ms) Time window: if the specified time window value is lower than the settling time, a warning message is shown. Points Settling time (frequency error, in ppm, with respect to the Fout final value) 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
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Report generation and documentation
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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
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Revision history
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Revision history
Table 1.
Date 19-Jul-2007 20-Jul-2007
Document revision history
Revision 1 2 Initial release. Corrected the numbering in Figure 2: Main settings. Changes
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