how to calculate the transfer function of hmc3716 and the active loop filter


When I was deriving the transfer function of PLL, I found that HMC3716 is different from traditional phase detector with charge bump. In traditional phase detector with charge bump, we use Kp = Icp / (2π)  to present the gain of phase detector and charge bump. Then the current from charge bump flows to loop filter, we can get the tune voltage through the formula V(s) = Kp * Z(s). Z(s) is the transfer function of loop filter derived from Z(s) = V(s) / I(s), which is resistive. But when using HMC3716 and active loop filter, the unit of Kp is V/rad and the former is A/rad. So when I calculate the tune voltage, do I need to change the formula Z(s) = V(s) / I(s) to Z(s) = Vo(s) / Vi(s)?