In most biomedical implant designs, the rectifier block is
either a hybrid diode bridge [8], [10], which increases the
number of off-chip components and the size of the implant or
an inefficient half-wave rectifier using the substrate diode [7].
Using a full-wave bridge rectifier [3] on the other hand,
significantly reduces the implant size and also helps the
regulator to achieve better AC-DC conversion efficiency (as
compared to a half-wave rectifier). Implementing an on onchip
full-wave rectifier in the CMOS technology also leads to
the added value of being fast enough to operate in the MHz range due to eliminating off-chip interconnect and parasitic
components. Using high W/L diode-connected MOS
transistors with dynamic voltage controlled separated N-well
regions helps keeping all parasitic components off at all times
and eliminate the body effect. Therefore, the rectifier does not
dissipate excessive power through substrate leakage current or
show a high dropout voltage. It also significantly reduces the
risk of latchup.
Circuit schematic of the CMOS full-wave bridge rectifier used
in this work is shown in Fig. 2 [3]. MP1 and MP2 are the diode
connected pMOS transistors, which separated N-well
potentials follows coil and Vout, whichever is at a higher
potential, through M3~6 auxiliary transistors. Mn1 and Mn2 help
Q1 and Q2 vertical parasitic PNP transistors to return current
from grounded substrate to the coil.