This looks like part , and only a small part, of a PLL model. I'm not sure it can do anything as it is except produce whatever frequency the VCO wants to offer, without any control over it.
VCTRL normally tunes the VCO (Voltage Controlled Oscillator being a clue there!) and the difference between it and a reference oscillator is the PD.
It may be this design is intended to deliberately add a DC offset to the VCO signal to somehow skew the PD signal but without the remainder of the diagram we will never know.
Brian.