most implants require a DC power supplier, the induced AC
power needs to be rectified to a DC one. The traditional approach
is to have a bridge diode rectifier followed by a linear
regulator [3]. This approach has two fundamental limitations:
(1) The induced voltage at the receiving coil, vin(AC), must
be significantly higher than twice of the diode’s turn-on
voltage, VON. Otherwise, a significant power loss in the
conversion is expected [1][4]. To mitigate this issue, low
VON diodes are currently in development using either the
active CMOS circuit [1] or the non-standard semiconductor
technology (e.g. Schottky diode [3] or silicon on sapphire
[4]); (2) vin(AC) must be higher than the required DC output
voltage, Vout(DC). To have a high vin, the receiving coil
must be large enough (often in cm range [3]), and often
is separated from the rest of the implant and placed right
under the skin to be close to the transmitting coil [5]. So
far, the receiving coil often is the largest component in a
miniaturized implant [6].
In order to miniaturize a biomedical implant and place
it deep inside of a human body, the power conditioning
circuit must be able to convert a low voltage AC power to
a high voltage DC power efficiently, especially for charging
a battery. To achieve this goal, an innovative feed-forward
controlled AC-to-DC boost converter has been demonstrated
for the first time. In the wireless power transfer using rotating
magnets [2], the induced AC voltage is very slow. Thus, in a
small interval, it can be treated as a DC voltage. The circuit is
able to convert a 500 mV AC power to 5 V DC. The circuitry
architecture and its operating principles are described in
Section II. The circuit implementation is depicted in Section
III. The measurement results and discussions are reported in
Section IV, followed by the conclusions in Section V.