Wireless charging, more generally referred to as wireless power transfer or wireless energy transmission, is on its way to becoming mainstream. Wireless charging eliminates the “battery anxiety” of the users of electronic devices by providing a convenient and automatic way of charging. In the near future wireless charging will not only enable consumers to charge their phones wherever they go but will also enable drones, robots and cars to automatically dock to charging stations.

Wireless Power Diagram Load
(Magnetic Resonance)
Frequency range 80-300 kHz 6.78 MHz / 13.56 MHz
Max transfer range 5mm 200mm+
Multi-device charging No Yes, at different power levels
Spatial freedom Low High
Power range Low & limited, 30W max Broad & versatile, 20W to 20kW+
Efficiency Limited to 80% High: up to 95%

Comparison of Wireless Charging Technologies (Source: GaN Systems)

The Need for Standards

In order for wireless charging to gain wide market adoption, standards are needed to ensure safety and compatibility. There are currently two major standards for wireless charging:

  • Qi – Inductive technology
  • Magnetic Resonance Technology – Led by AirFuel and Witricity

Standard Wireless Power Technologies:
Inductive vs. Resonant

Just what do we mean by “inductive” and “resonant” technologies? Here are the main differences between the two.

Inductive technology, which is a closely coupled solution, is the type of compliance used by Qi. This technology transfers power using low-frequency resonant tanks (100-205kHz) over very short distances (mostly anything under 10mm).

In 2009, the first standard for Qi had a 5W power requirement (“Low Power”). In 2015, that was increased to 15W capability (“Medium Power”). This year, Qi is hoping for over 100W (“High Power”). Those are currently in testing and should be rolled out later this year.

The other wireless power technology, resonant, is considered a loosely coupled solution. Primarily championed by the AirFuel Alliance, this technology uses a high-frequency resonant tank (6.78MHz) to transmit power over long distances (multitudes of feet). Resonant technology offers the ability to charge multiple devices at the same time, with a capability of up to 22W for upcoming systems. There are also up to 20kW magnetic resonance techonogies enabled by companies such as WiTricity in the USA.

Challenges of today’s technology

Developing wireless charging product that offers great user experience has its challenges. Take the recent news from Apple announcing the cancellation of its AirPower wireless charging product, which had been in the works for more than eighteen months. The product was canceled due to the complexity of offering spatial freedom while charging multiple devices at the same time. Clearily the current Qi inductive technology adapted by major cellphone companies are not enough to cover the following challenges

  • Spatial freedom in X-Y-Z directions

  • Efficiency

  • Rapid charging

  • The ability to simultaneously charge multiple devices at various power levels

  • A scalable and interoperable global infrastructure

Benefits of using GaN in Wireless Charging

  • Enable high efficiency transmitter and receiver at high frequency (6.78 Mhz), ideal for resonant technology
  • Lower system BOM cost

  • Reduce system size and weight

  • Reduce surface heat due to loss


For more GaN Systems products and technical resources: