In a wireless power transfer system for supplying power to a wireless device, e.g., charging a battery, wireless power transmitter coil voltage is used in place of coil current for communication and power control reference. The transmitter coil voltage waveforms provide phase information, with reference to the pulse width modulation (PWM) waveforms, that can be used to demodulate digital packet communication from a wireless power receiver used to provide a voltage to a device. The DC voltage amplitude of the wireless power transmitter coil is used for controlling the power injected to the wireless power receiver coil, while the phase of the transmitter coil voltage PWM signal is used for demodulation of signal packets from the wireless power receiver to control the transmitter coil voltage and thereby wireless power transfer to the power receiver.