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Part Number: LMK61E07
I've noticed that the phase noise of the LMK61E07 is not as good as it was when I2C operations taken place.
I've tried periodically sending commands to change the LMK61E07 frequency or sending command just to read the product ID, or sending non-I2C PRN data to the I2C ports on the chip.
All the above three significantly worsen the phase noise of the LMK61E07 at the sideband related to the I2C port's communication.
Please see the following figure attached.
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Hi, please check the attachment for what we've seen in our EVM when we do continuous write on I2C bus. As Shawn recommends, please share the schematics for us to review. Thanks a lot.
LMK61xx I2Cwrite phase noise.pptx
In reply to Madhu Balasubramanian:
I've been using silicon labs evaluation board, Si5xxUC-EVB.
The microcontroller has been disabled.
Three wires, SDA, SCL and GND are connected from Xilinx KC705.
Is that just because the evm is from a wrong company...?
There doesn't seem to have significant defects and I've added quite a few decouple caps as well.
Thanks a lot.
In reply to Weida Zhang:
We didn't use reflow. It was hand soldered.
Do you mean this may due to mechanical stretching/tension?
We can certainly buy another eval board and chip to do a proper reflow if the soldering is likely the cause to the fault.
Thanks for your feedback!
I suspect this could be due to mechanical tension from the solder profile exceeding recommended reflow temperatures. Please do try machine solder with right profile and let us know the results.
We have bought the LMK61E2EVM and tested it.
It appears the default frequency is as the datasheet specified, however, when set to a different frequency (125MHz is the frequency we wanted to use it) the performance is much worse.
Please see the attached figure.
I tried to alter the internal PLL setting, however, the Ko (VCO gain) seems not mentioned anywhere.
Also, I found that when the EVM is powered with ext 5V, and let the on board LDO reg to provide the 3.3V, the noise is much worse than using an external 3.3V to power the chip directly.
In reply to Alan O:
Please find the updated result attached. I've tried to upload the TCS file, however the website avoids me from doing so. The registers values are provided following.
R0 0x0010R1 0x010BR2 0x0233R8 0x08B0R9 0x0901R16 0x1000R17 0x1180R21 0x1502R22 0x1600R23 0x172AR25 0x1900R26 0x1A34R27 0x1B20R28 0x1C00R29 0x1D01R30 0x1E3FR31 0x1FFFR32 0x20FFR33 0x2103R34 0x2224R35 0x2327R36 0x2424R37 0x2502R38 0x2600R39 0x2707R47 0x2F00R48 0x3000R49 0x3110R50 0x3200R51 0x3300R52 0x3400R53 0x3500R56 0x3800R72 0x4802
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