I have a HMC829LP6GE rev A evaluation board. I have removed R24 and mount R23 to use external source 100MHz.
I cannot the PLL to lock. Attached is the register settings. What could be wrong?
To get the Lock Detect indicator to work program Reg07h = C4Dh. This is required for the 100MHz comparison frequency. However, the PLL should show a locked signal on a spectrum analyzer even with a wrong value in Reg07h. All the other register values look correct. Which output are you connected to (RF_N or RF_P)? By default only the RF_N output is enabled (RF_P is disabled). To enable both outputs (Differential mode), another write to Reg05h is required (Reg05h= 2818h and make sure it is inserted before the Reg05h = 0 command).
Attached is a commented register file for this configuration.
Thanks for your help. The Lock Detect indicator is working now.
Attached is the phase noise measurement @RFout of HMC829.
Are these the reference sidebands? Is there any way to improve it?
The spectral plot looks oddly distorted. This is not normal behavior.
Did you re-work the evaluation board to allow the use of the external reference? R36 & R20 need to be installed and jumpers JP3 & JP4 must be removed to remove power from the on-board 50MHz VCXO. See the evaluation board schematic attached.
On another note, when operating with 100MHz comparison frequency, during a lock activity (frequency change) the CP Offset current (Reg09h) should be disabled until lock is complete, then re-enable the CP Offset current. Also, the CP offset current should be increased (vs. the setting for 50MHz comparison) to provide the best spectral performance.
I had re-attached the phase noise plot. The previous plot has some smoothing feature enabled, resulting in the distortion.
How do I disable the CP Offset current? is it by setting reg09H=0 and reg09H=0?
When lock is completed, enable the CP Offset current by setting reg09H=1 and reg09H=1?
The PLL is operating in interger mode, is the enabling/disabling of the CP Offset current still required?
1. The spurs appeared when I connected to external source but they don't appear when i connect to on-board source. Is there anything wrong with the settings?
2. how to enable/disable CP Offset current? using reg09H and reg09H?
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