Part Number: LMX2595EVM
Testing the LMX2595 EVM and the output power at 8 GHz without doubler enabled is good, around 3.62 dBm with 50 Ohm Resistor pull-up, and around 6.92 dBm with Inductor pull-up. However, when I enable the doubler to get 16 GHz the power decreases dramatically to -30.3 dBm with 50 Ohm Resistor pull-up, and around -26 dBm with Inductor pull-up. Per the datasheet P.63 Output power graph Fig-58, the Output power at 16 GHz should be around -1 dBm. Changing DBLR_IBIAS_CTRL1 does not improve output power, and twiddling the OUTA_PWR register in TICS Pro has little effect as well. The initial output inductor and capacitors were not designed for 16 GHz and the Output power results were 5 - 7 dB worse then the numbers I measured above after re-tuning the output to a 1nH inductor resonant at 16 GHz and 0.3pF capacitor resonant at 16 GHz.. I already designed this part into a product and the board is in fabrication so I'm panicking about the output power. Any suggestions to improve output power are appreciated.
Just wanted to make sure that you have set R45[12:11], OUTA_MUX to 0x2 and R27, VCO2X_EN=1?
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In reply to Noel Fung:
Hi Noel, thanks for your quick reply. The register R45 is set to 0x2DD0D4, and register R27 is set to 0x1B0002. It seems I had missed checking the VCO2X_EN and after clicking it I got an immediate power boost to around -18 dBm. Much better results but still far from the datasheet values. Can you think of anything else that would boost the power? Have you measured other LMX2595 EVM boards and checked the output power, and do they match the datasheet? FYI, I checked my cable loss and its around -1.5 dB and DC voltage set to 3.3V with current drawing 430 mA currently.
In reply to Rob Monroe:
Can I have your TICS Pro register setting?
Is reference clock frequency = 100MHz?
Hi Noel, i'm using the on-board 100 MHz VCO for the REF. The registers are below:
Output power is not max. with OUTA_PWR=63. See datasheet Figure 26 for details. Try make this register equal to around 31.
R25 should be changed to 0x190C2B. (0x0C2B = 3115)
Hopefully these changes fix your problem.
Noel, those register settings are a success! I measure 5.3 dBm output power at 16 GHz. The only hardware modification I made is installing Coilcraft 0402HP-1N0X, 1nH Inductor pull-ups to 3.3V at the outputs (resonant at 16 GHz) and 3.3V bypass capacitor and output series capacitors Murata GRM1555C2AR40BA01D (Cap, 0.4 pF,100V, COG, 0402) resonant at 16 GHz. No other modifications were made aside from the register settings you suggested. The phase noise I measure is similar but slightly worse than the datasheet P.16 Fig-10. I measure -100.5 dBc/Hz @ 10 KHz, -101.8 dBc/Hz @ 100 KHz and -119.5 dBc/Hz @ 1 MHz. Thanks for your suggestions and support!
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