Other Parts Discussed in Thread: LMX2491
Tool/software:
I am currently working with the LMX2572EVM in order to test out an application that utilizes the automatic ramp feature. I have been successful in using the CalibrateVCO feature when performed with the automatic ramp turned off and the PLL set to the center of my ramp frequency range and then enabling the ramp. The problem is that I am sometimes getting a "bad calibration" with the CalibrateVCO feature that causes the PLL to go out of lock when the ramp is enabled. This is evident by looking at the spectrum on a spectrum analyzer that shows very high sidebands outside of the intended ramp frequency range. I would like to understand why I sometimes get a "bad calibration" and how to avoid it in my application. I usually get the "good calibration" but get the "bad calibration" about 10% of the time.
My center frequency will range from 2410 to 2490MHz with an automatic ramp that is 20MHz wide. I have attached my register values for a "good calibration" as well as a "bad calibration" when set to a center frequency of 2442MHz. My procedure is to turn off the ramp, set the PLL to 2442MHz, click on the CalibrateVCO button, set the PLL to the beginning of the ramp or 2432MHz and then enable the 20MHz automatic ramp. 90% of the time, the output spectrum looks good with most of the energy spanning from 2432 to 2452MHz as desired. However, about 10% of the time, the spectrum has very high sidebands outside of the desired frequency range. In the attached example register files, the "good calibration" R110 is "0178" while it is "0D78" for the "bad calibration". Should Vtune indicate locked during an automatic ramp? There is also a slight difference in R111 which is "010B" for the "good calibration" and "010F" for the "bad calibration" but I don't know if this is enough to cause the bad calibration or why I get a different value sometimes. These are the only differences in the register values between a "good calibration" and a "bad calibration" that I can find. Thanks!
R125 0x7D2288 R124 0x7C0000 R123 0x7B0000 R122 0x7A0000 R121 0x790000 R120 0x780000 R119 0x770000 R118 0x760000 R117 0x750000 R116 0x740000 R115 0x730000 R114 0x727802 R113 0x710000 R112 0x70EE5F R111 0x6F010B R110 0x6E0178 R109 0x6D8D7D R108 0x6C00A1 R107 0x6B8801 R106 0x6A0007 R105 0x690000 R104 0x682710 R103 0x67FD61 R102 0x663FFF R101 0x650010 R100 0x642710 R99 0x63029F R98 0x620000 R97 0x610000 R96 0x600000 R95 0x5F0000 R94 0x5E0000 R93 0x5D0000 R92 0x5C0000 R91 0x5B0000 R90 0x5A0000 R89 0x590000 R88 0x580000 R87 0x570000 R86 0x568F5D R85 0x55FDC2 R84 0x540001 R83 0x538F5D R82 0x5203C2 R81 0x510000 R80 0x500000 R79 0x4F0080 R78 0x4E0001 R77 0x4D0000 R76 0x4C000C R75 0x4B0800 R74 0x4A0000 R73 0x49003F R72 0x480001 R71 0x470081 R70 0x46C350 R69 0x450000 R68 0x4403E8 R67 0x430000 R66 0x4201F4 R65 0x410000 R64 0x401388 R63 0x3F0000 R62 0x3E00AF R61 0x3D00A8 R60 0x3C0000 R59 0x3B0001 R58 0x3A9001 R57 0x390020 R56 0x380000 R55 0x370000 R54 0x360000 R53 0x350000 R52 0x340421 R51 0x330080 R50 0x320080 R49 0x314180 R48 0x3003E0 R47 0x2F0300 R46 0x2E07F0 R45 0x2DC600 R44 0x2C3FA3 R43 0x2BA3D7 R42 0x2A3D70 R41 0x290000 R40 0x280000 R39 0x27FFFF R38 0x26FFFF R37 0x250205 R36 0x240030 R35 0x230004 R34 0x220010 R33 0x211E01 R32 0x2005BF R31 0x1FC3E6 R30 0x1E18A6 R29 0x1D0000 R28 0x1C0488 R27 0x1B0002 R26 0x1A0808 R25 0x190624 R24 0x18071A R23 0x17007C R22 0x160001 R21 0x150409 R20 0x144848 R19 0x1327B7 R18 0x120064 R17 0x110096 R16 0x100080 R15 0x0F060E R14 0x0E1808 R13 0x0D4000 R12 0x0C5001 R11 0x0BB018 R10 0x0A10F8 R9 0x090004 R8 0x082000 R7 0x0740B2 R6 0x06C802 R5 0x0530C8 R4 0x040A43 R3 0x030782 R2 0x020500 R1 0x010808 R0 0x00A118
R125 0x7D2288 R124 0x7C0000 R123 0x7B0000 R122 0x7A0000 R121 0x790000 R120 0x780000 R119 0x770000 R118 0x760000 R117 0x750000 R116 0x740000 R115 0x730000 R114 0x727802 R113 0x710000 R112 0x70EE5F R111 0x6F010F R110 0x6E0D78 R109 0x6D8D7D R108 0x6C00A1 R107 0x6B8801 R106 0x6A0007 R105 0x690000 R104 0x682710 R103 0x67FD61 R102 0x663FFF R101 0x650010 R100 0x642710 R99 0x63029F R98 0x620000 R97 0x610000 R96 0x600000 R95 0x5F0000 R94 0x5E0000 R93 0x5D0000 R92 0x5C0000 R91 0x5B0000 R90 0x5A0000 R89 0x590000 R88 0x580000 R87 0x570000 R86 0x568F5D R85 0x55FDC2 R84 0x540001 R83 0x538F5D R82 0x5203C2 R81 0x510000 R80 0x500000 R79 0x4F0080 R78 0x4E0001 R77 0x4D0000 R76 0x4C000C R75 0x4B0800 R74 0x4A0000 R73 0x49003F R72 0x480001 R71 0x470081 R70 0x46C350 R69 0x450000 R68 0x4403E8 R67 0x430000 R66 0x4201F4 R65 0x410000 R64 0x401388 R63 0x3F0000 R62 0x3E00AF R61 0x3D00A8 R60 0x3C0000 R59 0x3B0001 R58 0x3A9001 R57 0x390020 R56 0x380000 R55 0x370000 R54 0x360000 R53 0x350000 R52 0x340421 R51 0x330080 R50 0x320080 R49 0x314180 R48 0x3003E0 R47 0x2F0300 R46 0x2E07F0 R45 0x2DC600 R44 0x2C3FA3 R43 0x2BA3D7 R42 0x2A3D70 R41 0x290000 R40 0x280000 R39 0x27FFFF R38 0x26FFFF R37 0x250205 R36 0x240030 R35 0x230004 R34 0x220010 R33 0x211E01 R32 0x2005BF R31 0x1FC3E6 R30 0x1E18A6 R29 0x1D0000 R28 0x1C0488 R27 0x1B0002 R26 0x1A0808 R25 0x190624 R24 0x18071A R23 0x17007C R22 0x160001 R21 0x150409 R20 0x144848 R19 0x1327B7 R18 0x120064 R17 0x110096 R16 0x100080 R15 0x0F060E R14 0x0E1808 R13 0x0D4000 R12 0x0C5001 R11 0x0BB018 R10 0x0A10F8 R9 0x090004 R8 0x082000 R7 0x0740B2 R6 0x06C802 R5 0x0530C8 R4 0x040A43 R3 0x030782 R2 0x020500 R1 0x010808 R0 0x00A118
