Hi Derek,
we are using LMK04828 chip on our custom board and generating 256MHz clock and 4MHz SYSREF,we are seeing 25KHz spur on the dac output.
i would like to present my prob in two cases
CASE1 :
we have an eval board which is using LMK chip and DAC with CLKIN0 =10MHz and external VCxO as 160MHz,generating 256MHz clock and
4MHz SYSREF. we are generating DAC output from the board which is very clean and without any spurs. i hav attached the configuration file of it.
CASE2 :
on our custom board with LMK04828 chip and generating 256MHz clock and 4MHz SYSREF,we found two spurs at 25KHz apart from centre
we feel it is generated from the combination of both VCO(2560MH
eval_board_configuration.txt
R0 (INIT) 0x000090 R0 0x000010 R2 0x000200 R3 0x000306 R4 0x0004D0 R5 0x00055B R6 0x000600 R12 0x000C51 R13 0x000D04 R256 0x01006A R257 0x010155 R258 0x010255 R259 0x010301 R260 0x010422 R261 0x010500 R262 0x010670 R263 0x010755 R264 0x01086A R265 0x010955 R266 0x010A55 R267 0x010B00 R268 0x010C22 R269 0x010D00 R270 0x010EF0 R271 0x010F11 R272 0x01106A R273 0x011155 R274 0x011255 R275 0x011301 R276 0x011422 R277 0x011500 R278 0x011670 R279 0x011733 R280 0x01186A R281 0x011955 R282 0x011A55 R283 0x011B01 R284 0x011C22 R285 0x011D00 R286 0x011E72 R287 0x011F01 R288 0x012074 R289 0x012155 R290 0x012255 R291 0x012301 R292 0x012422 R293 0x012500 R294 0x012678 R295 0x012733 R296 0x01286A R297 0x012955 R298 0x012A55 R299 0x012B00 R300 0x012C22 R301 0x012D00 R302 0x012EF0 R303 0x012F00 R304 0x01306A R305 0x013155 R306 0x013255 R307 0x013301 R308 0x013422 R309 0x013500 R310 0x013673 R311 0x013700 R312 0x013800 R313 0x013903 R314 0x013A02 R315 0x013B80 R316 0x013C00 R317 0x013D01 R318 0x013E03 R319 0x013F02 R320 0x014009 R321 0x014100 R322 0x014200 R323 0x014331 R324 0x0144FF R325 0x01457F R326 0x014618 R327 0x01471A R328 0x014806 R329 0x014946 R330 0x014A06 R331 0x014B06 R332 0x014C00 R333 0x014D00 R334 0x014EC0 R335 0x014F7F R336 0x015013 R337 0x015102 R338 0x015200 R339 0x015300 R340 0x015401 R341 0x015500 R342 0x015601 R343 0x015703 R344 0x0158C0 R345 0x015900 R346 0x015A10 R347 0x015BDA R348 0x015C20 R349 0x015D00 R350 0x015E00 R351 0x015F3E R352 0x016000 R353 0x016101 R354 0x016244 R355 0x016300 R356 0x016400 R357 0x0165A0 R369 0x0171AA R370 0x017202 R380 0x017C15 R381 0x017D33 R358 0x016600 R359 0x016700 R360 0x016808 R361 0x016959 R362 0x016A20 R363 0x016B00 R364 0x016C00 R365 0x016D00 R366 0x016E1B R371 0x017300 R386 0x018200 R387 0x018300 R388 0x018400 R389 0x018500 R392 0x018800 R393 0x018900 R394 0x018A00 R395 0x018B00 R8189 0x1FFD00 R8190 0x1FFE00 R8191 0x1FFF53
VCO2560MHz_configuration.txt
R0 (INIT) 0x000090 R0 0x000004 R2 0x000200 R3 0x000306 R4 0x0004D0 R5 0x00055B R6 0x000600 R12 0x000C51 R13 0x000D04 R256 0x01000A R257 0x010155 R258 0x010255 R259 0x010301 R260 0x010422 R261 0x010500 R262 0x010670 R263 0x010755 R264 0x01086A R265 0x010955 R266 0x010A55 R267 0x010BB1 R268 0x010C22 R269 0x010D00 R270 0x010E70 R271 0x010F11 R272 0x01106A R273 0x011155 R274 0x011255 R275 0x0113B1 R276 0x011422 R277 0x011500 R278 0x011670 R279 0x011733 R280 0x01186A R281 0x011955 R282 0x011A55 R283 0x011BB1 R284 0x011C22 R285 0x011D00 R286 0x011E71 R287 0x011F03 R288 0x012072 R289 0x012155 R290 0x012255 R291 0x0123B1 R292 0x012422 R293 0x012500 R294 0x012678 R295 0x012755 R296 0x012808 R297 0x012955 R298 0x012A55 R299 0x012B00 R300 0x012C02 R301 0x012D00 R302 0x012EF9 R303 0x012F00 R304 0x013016 R305 0x013155 R306 0x013255 R307 0x013300 R308 0x013402 R309 0x013500 R310 0x0136F1 R311 0x013700 R312 0x013805 R313 0x013903 R314 0x013A02 R315 0x013B80 R316 0x013C00 R317 0x013D0E R318 0x013E03 R319 0x013F05 R320 0x014009 R321 0x014100 R322 0x014200 R323 0x014321 R324 0x0144FF R325 0x01457F R326 0x014618 R327 0x01470A R328 0x014802 R329 0x014942 R330 0x014A02 R331 0x014B16 R332 0x014C00 R333 0x014D00 R334 0x014EC0 R335 0x014F7F R336 0x015003 R337 0x015102 R338 0x015200 R339 0x015300 R340 0x01540A R341 0x015500 R342 0x0156C5 R343 0x015700 R344 0x015896 R345 0x015900 R346 0x015A64 R347 0x015BD4 R348 0x015C20 R349 0x015D00 R350 0x015E00 R351 0x015F0B R352 0x016000 R353 0x016105 R354 0x016245 R355 0x016300 R356 0x016400 R357 0x01650C R369 0x0171AA R370 0x017202 R380 0x017C15 R381 0x017D33 R358 0x016600 R359 0x016700 R360 0x016820 R361 0x016959 R362 0x016A20 R363 0x016B00 R364 0x016C00 R365 0x016D00 R366 0x016E13 R371 0x017300 R386 0x018200 R387 0x018300 R388 0x018400 R389 0x018500 R392 0x018800 R393 0x018900 R394 0x018A00 R395 0x018B00 R8189 0x1FFD00 R8190 0x1FFE00 R8191 0x1FFF53
VCO3072MHz_configuration.txt
z) and External VCXo(100MHz) used in the design because
R0 (INIT) 0x000090 R0 0x000004 R2 0x000200 R3 0x000306 R4 0x0004D0 R5 0x00055B R6 0x000600 R12 0x000C51 R13 0x000D04 R256 0x01000C R257 0x010155 R258 0x010255 R259 0x010301 R260 0x010422 R261 0x010500 R262 0x010670 R263 0x010755 R264 0x01086C R265 0x010955 R266 0x010A55 R267 0x010BB1 R268 0x010C22 R269 0x010D00 R270 0x010E70 R271 0x010F11 R272 0x01106C R273 0x011155 R274 0x011255 R275 0x0113B1 R276 0x011422 R277 0x011500 R278 0x011670 R279 0x011733 R280 0x01186C R281 0x011955 R282 0x011A55 R283 0x011BB1 R284 0x011C22 R285 0x011D00 R286 0x011E71 R287 0x011F03 R288 0x012072 R289 0x012155 R290 0x012255 R291 0x0123B1 R292 0x012422 R293 0x012500 R294 0x012678 R295 0x012755 R296 0x012808 R297 0x012955 R298 0x012A55 R299 0x012B00 R300 0x012C02 R301 0x012D00 R302 0x012EF9 R303 0x012F00 R304 0x013016 R305 0x013155 R306 0x013255 R307 0x013300 R308 0x013402 R309 0x013500 R310 0x0136F1 R311 0x013700 R312 0x013825 R313 0x013903 R314 0x013A03 R315 0x013B00 R316 0x013C00 R317 0x013D0E R318 0x013E03 R319 0x013F04 R320 0x014009 R321 0x014100 R322 0x014200 R323 0x014321 R324 0x0144FF R325 0x01457F R326 0x014618 R327 0x01470A R328 0x014802 R329 0x014942 R330 0x014A02 R331 0x014B16 R332 0x014C00 R333 0x014D00 R334 0x014EC0 R335 0x014F7F R336 0x015003 R337 0x015102 R338 0x015200 R339 0x015300 R340 0x01540A R341 0x015500 R342 0x0156C5 R343 0x015700 R344 0x015896 R345 0x015900 R346 0x015A64 R347 0x015BD4 R348 0x015C20 R349 0x015D00 R350 0x015E00 R351 0x015F0B R352 0x016000 R353 0x016119 R354 0x016245 R355 0x016300 R356 0x016401 R357 0x016580 R369 0x0171AA R370 0x017202 R380 0x017C15 R381 0x017D33 R358 0x016600 R359 0x016700 R360 0x0168C0 R361 0x016959 R362 0x016A20 R363 0x016B00 R364 0x016C00 R365 0x016D00 R366 0x016E13 R371 0x017300 R386 0x018200 R387 0x018300 R388 0x018400 R389 0x018500 R392 0x018800 R393 0x018900 R394 0x018A00 R395 0x018B00 R8189 0x1FFD00 R8190 0x1FFE00 R8191 0x1FFF53
1. we changed the VCO to 3072 we are not seeing the spur at 25KHz but since the VCO frequency which was selected is at the border of VCO range,we are getting other freq spurs and noise floor also getting increased.
2. we tried to change the external VCxo of 100MHz to 160MHz but in single loop PLL2 mode we still find the 25Khz spurious.
i have attached the configuration file for VCO of 2560MHz and VCO of 3072MHz.
is there any way to reduce the level of these spurs?
Thank You
