A Compact Inductively Coupled Connector for Mobile DevicesWenxu Zhao, Peter Gadfort, Evan Erickson, Paul D. Franzon

North Carolina State University

IntroductionA nested inductive connector, consisting of a single power channel and one or more data channels, is proposed as replacement for legacy conductive connectors in mobile devices. As an example, a prototype of the proposed connector was designed as a replacement for a standard TRS headphone jack found on many mobile devices.

Motivation

AcknowledgementsThe authors would like to thank Dr. John Wilson for his valuable suggestions on

power supply design and implementation.

Prototype Design

Results & ConclusionLosses in an inductively coupled channel can generally be minimized by increasing the diameter of

the inductor, increasing the number of turns in the inductor. By increasing the number of turns, and consequently the diameter of the inductor, the frequency at which peak coupling occurs decreases and the peak increases.

Low profile: as thin as a PCB Breaks away to avoid stress damage Waterproof

Magnet PowerInductor

Digital DataInductors

Magnet

Connector Design

Forward transfer coefficients (S21) for the proposed

connector’s power inductor as turns are varied

Forward transfer coefficients (S21) for the proposed

connector’s data inductor as turns are varied

Effect of increasing the gap between the two mating connectors on the power channel

Effect of increasing the gap between the two mating connectors on the data channel

Designed and fabricated in IBM 0.13um CMOS technology Input digital stereo audio sampled at 44.1 kHz with 16 bits resolution Processing of audio data: Sending sampled digital audio data across the high-pass inductive data channel Recovery of the data on the receiver side Converting the digital data to power amplified analog audio signal with Class-D PA to

output 12mW on each 32Ω load The power recovered from the power transformer is converted from AC to DC power

using a two-stage differential-drive CMOS rectifier, producing a stable 1.2 V supply

ANSYS HFSS model of the prototype connector with a 2-turn power inductor and a 3-turn data inductor

100um Metal Width 500um Diameter via 3mm by 3mm dimension

400

Time (µs)

-1.00

3002001000

-0.50

0

0.50

1.00

Vo

ltag

e (V

)

80

Frequency (kHz)6040200

0.00

0.25

0.50

0.75

1.00

Mag

nitu

de

5 kHZ, 0.8514

15 kHZ, 0.0295

35 kHZ, 0.1275

45 kHZ, 0.2447

Technology IBM 0.13 μm CMOS

Area 1 mm x 1 mm

PowerDissipation

TX 3 mW

RX 1 mW

Deserializer 200 μW

Alignment 100 μW

Clock Recovery 400 μW

PWM Generator 400 μW

Output Buffer (include load) 50 mW

Max Data Rate 2 Gbps

PWM Output for a 5 kHz tone Frequency spectrum for the 5 kHz output

Inductive headphone driver performance metrics

Tip

Ring Sleeve

TipRing

Sleeve

Requires significant space Easily bent when stressed Not waterproof

Legacy TRS Connector Proposed Connector

Space is at a premium in modern mobile devices as manufactures strive to make the thinner, lighter devices with the longest battery lives possible. By transitioning from legacy connectors, TRS audio jacks, to a low-profile inductively coupled connector for the transmission of both power and high-speed data, space inside the mobile device can be conserved while providing an orientation independent, waterproof design that can breakaway when stressed.

Another parameter that has significant impact on the connector is the gap between the two mating connectors. In order to maintain a waterproof design, the two connectors would be coated in a thin layer of plastic. As seen in the figures, the separation distance of the connectors has a large impact on the peak in the forward transfer coefficient, but does not shift its frequency. Thus, a connector with embedded circuitry would not have to be redesigned for a specific spacing.

Isolation of the power and data channels Isolation between a pair of data coils in the proposed connector

When adding additional channels, sufficient isolation between the channels is required, a connector composed of a pair of 2-turn data coils within a 2-turn power coil was simulated while varying data-to-data spacing.

To study the effect of crosstalk between the power and the data channel, the spacing between a 2-turn power inductor and a 2-turn data inductor was varied from 0.5 mm to 1.25 mm.

The complete design was simulated using a single tone of 5 kHz, which is sampled at 44.1 kHz with a resolution of 16-bits. The transient simulation results, as presented on the left, shows the PWM output voltage across the 32load, while figure on the right shows the corresponding frequency spectrum.

The 5 kHz tone is recovered, however distortion at the harmonics of the input frequency is present, but can be mitigated by implementing an algorithm based PWM generation process instead of uniform sampling and implementing a feedback loop in the power amplifier