Wireless charging receiver and wireless charging system with reduced audible noise

A wireless charging system comprising a wireless charging receiver configured to

• wirelessly receive electrical power from a wireless charging transmitter,
• modulate an amplitude of an AC signal received through a first capacitor based on the wirelessly received electrical power, and
• transmit the AC signal, of which amplitude is modulated, to the wireless charging transmitter,
• wherein the first capacitor is configured to
• receive the AC signal through a first node,
• receive, from a DC-DC converter, a common voltage, which is not 0, through a second node that is different from the first node, and
• remove noise of an audible frequency band that is included in the AC signal of which amplitude is modulated.

A wireless charging system, comprising:

• a wireless charging transmitter configured to generate charging electrical power;
• and
• a wireless charging receiver configured to wirelessly receive the charging electrical power from the wireless charging transmitter,
• wherein the wireless charging receiver includes
• an inductor inductively coupled to the wireless charging transmitter,
• a rectifier connected to the inductor, the rectifier configured to rectify a signal received from the inductor,
• a DC-DC converter configured to convert a DC signal received from the rectifier,
• a switching block configured to receive a common voltage generated by the DC-DC converter, wherein the switching block includes a first switch,
• a first capacitor configured to receive the common voltage from the switching block at a first terminal of the first capacitor, wherein a second terminal of the first capacitor is connected to the inductor at a first node, and wherein the common voltage is not zero;
• and
• a receive controller configured to operate the first switch to switch a voltage at the first terminal of the first capacitor between a voltage at the first node and the common voltage.