This is the current setup for our PLL-based frequency sensor and this reads out the beatnote of the green light at the vertex serving as a CARM sensor currently.

Here is a measured open loop transfer function of the PLL :

Some parameters and notes:

• UGF is at 60 kHz
• VCO DC response was measured to be 285220 Hz/V by a measurement with the IFR signal generator
• PFD coefficient was found to be 45 deg/V according to my eyeball fitting
• The was a phase lag which can be modeled by a delay of ~ 1.5 usec.
• The in-loop SR560 has
  • gain = 5, pole 300 kHz and another pole at 300 kHz
• The out-of-loop SR560 has
  • gain =10, pole at 100 Hz

These model parameters were used for calibrating  the analog CARM signal described in the previous alog (see alog 6878).The raw data is also attached.