Part Number: LMX2594
Other Parts Discussed in Thread: LMX2485E
Hi TI Team,
I am using the LMX2594 in my application and need to generate output frequencies from 100 MHz to 200 MHz.
Setup details:
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RF reference frequency: 28 MHz
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Tested PFD frequencies: 1 MHz, 14 MHz, and 28 MHz
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Loop filter: 3rd-order (designed using TICS Pro)
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Spectrum analyzer spans used: 200 MHz, 6 MHz, and 2 MHz
When generating integer (round) frequencies such as 133 MHz or 177 MHz, I do not observe significant spurious signals — performance is within acceptable range.
However, when generating fractional frequencies such as 166.875 MHz or 170.250 MHz, I observe noticeable spurious tones. I tested different PFD frequencies (1 MHz, 14 MHz, and 28 MHz), but the spurs remain present, and in some cases, they are worse.
I also tried different charge pump current settings (3 mA, 6 mA, 9 mA, and 15 mA). While the spur frequencies and their amplitudes change slightly with different charge pump currents, the spurious levels are still above my requirement.
My target specification is to achieve spurious levels below –100 dBc across the 100–200 MHz band.
For your reference, I have attached a Google Drive link containing:
https://drive.google.com/drive/folders/14GEU2mRZY-xm8Jh4dQUUJeYvelwwkS1D?usp=sharing
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Spectrum analyzer results
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Loop filter design details
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TICS Pro configuration files
[Insert Google Drive Link Here]
Could you please advise what parameters I should further optimize (loop bandwidth, PFD frequency, charge pump current, fractional denominator settings, output divider configuration, etc.) to reduce the spurs below –100 dBc in this band?
Thank you for your support.
