Gain of phase detector in phase locked loop

Could some electronics guru please clarify this ? The phase detector in a phase locked loop could be purely analog (analog mixer) or mixed signal. We know that the gain of the phase detector is commonly expressed in Volt/Radian. Now suppose I have a mixed signal phase detector with two sinusoidal inputs. Each of the sinusoidal inputs are fed into its own comparator. Comparison is with respect to ground. The outputs of the comparators are fed into an XOR gate. The ouput of the XOR, as per its truth table is high when one input is zero, and zero when both are zero or both are high. Now what would be the gain value, assuming that the amplitude of each comparator can be maximum