I'm trying to build a frequency synthesizer using the ADF4002 and I've used ADISimPLL to create a simple PLL loop with a 2-pole active filter. The loop works very well as designed by ADISim. However, when I modify the loop to introduce additional components (mixer, LPF), the loop becomes unstable. That's no surprise given that the loop filter is the unmodified loop filter (and ADISim has no clue about the additional components I've added). I decided to make an attempt at figuring out the transfer function of the ADISim generated loop and work from there. The idea is, I can add my additional components and figure out the phase margin (altering the loop filter to achieve stability). I believe I came close to closed-loop and open-loop form of the TF, but my bode plot doesn't match the graphs in ADISim and I'm struggling to figure out why.
Please see this stackexchange thread where I ask the forum for assitance (https://electronics.stackexchange.com/questions/527738/working-out-the-transfer-function-of-a-pll-loop-given-by-the-analog-devices-adis). You'll find more information there and I'm happy to answer any questions you may ask.
What I'm really looking for is some advice regarding the form of TF equation used by ADISim. In particular, what does gain factor does it use for the charge pump and C1 in the schematic (see SE question). Thanks for your help!