Abstract:

I reduced the gain of PLLX and PLLY by 6dB and 4 dB, respectively. 
Then, I increased CARM IN2 gain from 20dB to 22dB to set the UGF of ALS_CARM at 2kHz.

Detail:

As reported in klog35127, the bump stracture in the OLTF of ALS_CARM depends on PLL gains.
So, I modified the filter gains to optimize the current ALS_CARM loop for lock acquisition.

To set the UGF of PLL loops at 20kHz, I reduced the gain of PLLX and PLLY by 6dB and 4dB, respectively.
Though I don't measure OLTFs because it cannot be measured remotely, the UGF should be around 20kHz according to the OLTF measurement before (klog35134).

After reducing the PLL gains, ALS_CARM UGF was adjusted to 2kHz, which requires 2dB increase of CARM IN2 gain.
This modification is implemented into the ENGAGE_ALS_CARM state of LSC_LOCK guardian.

Figure 1 shows the OLTF of ALS_CARM before (thin trace) and after (thick trace) the modification.