Inductive powering ASICs

Wireless powering of medical implants at ICsense

Wireless powering (or WPT – Wireless Power Transfer) is becoming increasingly popular in miniaturised medical applications. Electromagnetic power transfer uses a contactless link between 2 coils to transfer electrical energy. Implants using this type of power transfer can include a rechargeable or a primary battery or have no internal power source at all. In the latter case, only activity-on-demand (such as measurements, stimulation, …) can take place. ICsense has designed several custom ASICs exploiting the use of WPT in accordance with ISO13485 medical standards.

Benefits of using a wireless power link ?

Choosing the type of implant powering depends on several aspects and is very dependent on the use cases envisaged. The benefits of using wireless power transfer for implants include:

Avoidance of (chemical) based batteries inside the body
No connecting wires
No need for surgical procedure to replace batteries
Reliable source of power
Re-use of power link for bi-directional data transfer

Types of wireless powering

Near-field powering (typically in the kHz to MHz frequency range): Power transfer is using either the magnetic component of the EM (Electro-Magnetic) wave and is then mostly referred to as inductive coupling using coils. When using the electric field, transfer is done through metal electrodes referred to as capacitive coupling. ICsense has implemented several wireless power transfer ASICs for Implantable Neural Stimulators, RFID tags, Cochlear hearing aids, 13.56MHz NFC based tags for wearable patches, etc.

Far-field powering: this technique is mostly popular in beam forming applications and uses electromagnetic radiation or lasers. In the medical implant domain it is not frequently used. The typically high frequencies (GHz to THz range) are blocked by the human body which is composed of >60% of water (1).

Integrated Data communication

*Wireless implant powering using a coil coupled antenna pair for battery-less operation*

In many inductively powered implant systems, the data rates are limited and the power coil set serves equally as data channel. Transmitting data towards the implant can be done by means of several modulation structures:

FSK – Frequency Shift Keying
PSK – Phase Shift Keying
ASK – Amplitude Shift Keying

FSK switches between 2 carrier frequencies to modulate the data. PSK introduces phase shifts on the carrier wave. These types can only be used for forward communication (external unit towards implant) when the external power amplifier is wide-banded. In that case the coil’s Q-factor should also be decreased as it would otherwise work as a narrow bandpass filter. For moderate data rates, ASK is widely used and the modulation depth is ranges from 100% (ON-OFF keying) to lower values in cases where the power link must remain during data transfer.

The data communication from implant to external controller is typically done using LSK – Load Shift Keying. By changing the internal load at implant side, the equivalent impedance at primary side changes and changes can be captured by the external reader. LSK is the most commonly used passive telemetry technique allowing power and data transfer at the same time.

Why choose ICsense for wireless powering ?

ICsense is ISO13485 certified for medical ASIC developments. Since 2004, the mixed-signal ASICs of ICsense are used in implantable class III medical devices, ultra-low-power devices with enhanced battery life, hearing aid devices and wearables/portables for world-class medical device manufacturers. Through its systematic and certified development process, ICsense can ensure the quality, safety and long-term reliability for medical ASICs. Why choose ICsense ?

In-house proven topologies for highest efficiency and low-power (uW) implant operation
Over 15 years of expertise in wireless powering and power management architectures in kHz to Mhz ranges
ISO13485 certified for medical IC designs (implants + external)
Largest design team in Europe for on-time project delivery