1 Wireless power for mobile phones - System overview Nov 25, 2012 V1.1

System overview Rx Tx Embedded in mobile device After market case/dongle connected through the power connector Add-on connected through dedicated WLC pins Embedded in furniture/car/infrastructure After market mat 2

Resonance circuit & power driver Power Source TX Coil RX Coil Control Unit Demodulator Matching circuit & Rectifier Control Unit Modulator DC/DC Communication Power 3 Block diagram

4 Tx-Rx coils

Electric current flowing in a wire gives rise to a magnetic field around it. Alternating the current will alternate the magnetic field Shaping the wire as a loop will band that field in a “lung” shape. 5 Tx-Rx coils – Magnetic induction basics Figures:

Figure 1: Figure 2: transformer/ Figure 3: transformer/ 6 Tx-Rx coils – Magnetic induction basics Wireless power system is an air core transformer between planar coils one on top of the other. Energy coupling means that an energy source has a mean of transferring its energy to a second object. Transformers may use iron core to deliver the magnetic flux

Single coil– Most common design Pros – chip and easy solution / Cons – difficult alignment Fig1: Large Tx coil – Common in loosely coupled systems Pros – easy alignment / Cons – difficult design and tune Array of small Tx coil – One or more coils provide power simultaneously Pros – easy alignment / Cons – Cost of coils and drivers 3 coil array – Only one coil provides power at a time Pros – easy alignment / Cons – Cost of coils and drivers 7 Tx-Rx coils – Coil designs

8 Resonance circuit and power driver

Power driverResonance circuit Figure 1: HIGH EFFICIENCY LOOSELY COUPLED WIRELESS POWER TRANSFER SYSTEM VIA MAGNETIC INDUCTION By ZHEN NING LOW Resonant circuit - Determines the self resonance frequency of the Tx, Mainly influenced by the coil and the resonance capacitors. Power driver - pushes the current to the resonance circuit in different frequencies around the self resonance 9 Resonance circuit and power driver

Figure 1: 10 Resonance circuit The overall impedance the driver “sees” when modeled as a series RLC circuit At the resonance frequency the capacitive and inductive impedance equals The driver then sees resistive only minimum overall impedance and the power delivery to the Rx is maximal The resonance curve changes with each different :  Rx design (EE & ME)  Phone material  Misalignment from the center  Variation during manufacturing  Load drawn Frequency Amplitude

Frequency control – the driver changes the frequency along the resonance curve  Control becomes difficult when Q is high & at resonance control is unstable  Frequency range shall be dynamic due to curve changes  Passing to the second side of the peak may reverse the control rules Frequency Amplitude Other methods of control: Voltage control – increasing the input voltage will increase the current through the coil and the transmitted power Pulse width control – increasing the on time of the signal will increase the transmitted power 11 Driving the power

12 Data modulation

Power driver Modulator Demodulator Matching circuit & Rectifier load modulation - Rx modulates the operational frequency by short circuiting the coil to a secondary load The secondary load changes both the load of the Tx and the resonance curve The demodulator sense the change in voltage, current or phase between them on the operational frequency 13 Data modulation

Example of voltage change at the Tx Example of phase change at the Tx Signals in reality may vary a lot from the simulation presented…. 14 Data modulation

15 Questions? Comments? Remarks? Thanks, Rotem Shraga ( ; ) Figure: It’s called wireless power, it’s the future