Consider a PLL circuit with voltage supply VDD =12 V, The phase difference between the input square wave and the VCO output waveform is , find the output waveform of the XOR phase detector and the DC voltage VDC of the output waveform. When the PLL is in the lock-in state, and the DC voltage to the VCO is Vin = 4 V. What is the phase difference between the input square wave and the VCO output waveform