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Wireless charging standards: Can they all coexist?

09 Apr 2015  | Pavan Pudipeddi

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The system design in the Power Transmitting Unit (PTU) consists of a Source DC supply, a resonator, matching unit, a power conversion unit, and a signalling and control unit. The Power Receiving Unit (PRU) consists of a resonator, rectifier, power conversion unit, signalling, and control unit. The system architecture featuring PTU and PRUs is of star topology, with bidirectional signalling between PTU and PRU.


Figure 1: This is the typical transmitter coil structure of A4WP technology.6


Features

 • Loosely coupled magnetic resonance based technology
 • Communication is out-of-band Bluetooth Low Energy at frequency range of 2.4GHz ISM
 • The power transmission frequency is 6.78MHz
 • Received power of 3.5 and 6.5W suited for smartphone kind of applications, expected to increase up to 50W to include wide variety of consumer devices
 • Promises greater Z distance vs current inductive alternatives
 • More than 100 industry backers including Samsung, Dell, Fujitsu, LG, Sharp, Cannon, Panasonic, HTC, Lenovo, and Qualcomm

Pros

 • Maximum spatial freedom at potentially lower cost vs inductive alternative
 • Allows multi device charging
 • Extension into higher power and wearables a major selling point

Cons

 • Early stages for establishing a certification and test houses
 • Communication cost is high because of separate signalling circuitry
 • Increased electromagnetic interference/High radiated emissions
 • Low efficiency levels due to loosely-coupled coil structures
 • Limited accessory play as extra communication band adds cost
 • 
 • 

Factors that affect convergence
It has been mentioned widely that the standards have to converge for the market to take off. Does it really make sense to combine inductive and resonance technology?

At an ecosystem level, larger component vendors who are not married to a particular technology can drive the ecosystem to cater to all technologies. The support for Qi and PMA technologies inbuilt in Samsung Galaxy S6 is going to further drive the demand for wireless charging transmitters, considering Samsung holds one of the largest market share in the smartphone arena. Also, introduction of more than 15 products from Ikea supporting the Qi standard will go a long way in bringing wireless power into everyday homes giving a significant edge to the wireless power consortium.

At the end of the day we are looking at enormous volumes—2.26 billion units of mobile phone and tablets projected to be shipped in 2015, according to Gartner3—to hit the market. As we brainstorm the possibilities, it is essential to understand the challenges involved from a receiver and transmitter perspective.


Figure 2: This comparison shows the difference between inductive and resonant wireless power transfer.7


From a convergence/collaboration standpoint, there are three types of design possibilities for transmitters and receivers. They are:

Multi-mode: MI-MI (WPC-PMA) – Pure Inductive mode that is compatible with Qi and PMA standards

Multi-mode: MI-MR (WPC-A4WP / PMA-A4WP) – Compatibility with combination of Magnetic Induction (Qi/PMA) and Magnetic Resonance (A4WP) standards

Tri mode: (WPC-PMA-A4WP) – Compatible to all three wireless charging standards


Receiver side
Single mode chips are available for the receiver from TI, Freescale, IDT, Broadcom, and others. According to TI, more than 80% of Qi complaint wireless charging systems are using TI's solutions.8 The Samsung Galaxy S4 has a TI receiver chip for wireless charging.7

Purely inductive multi-mode, where Qi and PMA are the standards supported, presents less of a challenge due to similarity of technology. However to develop a system that is optimised between Qi and PMA, in one of the cases there is going to be slightly lower efficiency. IDT announced their industry-first dual mode receiver in 2013 that supports Qi and PMA standards.9 Other companies that have cracked the puzzle are TI and Triune systems.

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