Biomedical Engineering Reference
In-Depth Information
RF-DC
This module converts the 13.56MHz current induced in the coil to 7 V DC
power. The arrangement of RF-DC circuits is a voltage-double-rectifier with a
voltage feedback control. The reason to use these circuits is based on the fact
that an MOS transistor has lower pass-resistance when the applied gate voltage
is high.
Power-up Reset
It outputs a high voltage only after the Vdd reaches a certain level and is
stabilized. The power-up reset is not only for digital circuits to initialize, but also
to enable the analog modules as a global start-up signal. Many analog circuits
may lock the Vdd at zero with lack of proper start-up.
DC-DC
It further filters Vdd and outputs a 3.3 V power. Since most circuits do not
require high voltage, this lower voltage saves 80% power and provides a very
clean power source. The DC-DC module has two separated outputs for analog
and digital to reduce the noise. One or two 3.3 V wires are optional outputs of
WIBI.
Transceiver
For transmitting, it shorts the implanted coil to switch its load; for receiving,
it retrieves the envelope of the waveform induced in the coil, and detects
it using a threshold. The main design issue is how to avoid any mistrans-
mitting pulse, since during the transmitting a significant power loss will
happen.
Digital PLL(DPLL)
It is one of the essential functions of the WIBI system. It provides a clock signal
synchronized to the base station. The DPLL uses a novel algorithm that enables
large pull-in range with high accuracy based on a simple phase detection method.
It can tolerate high circuit mismatch and high noise. Since the working frequency
of this new DPLL is equal to its output frequency, the power consumption is
very low.
Digital Circuits of WIBI
The digital modules handle the encoding and decoding of the bidirectional
communication and control the data flow. They also monitor the working
condition of the implantable device and feedback these in formations to the base
station. There are five modules: two-wire data bus, decoder, encoder, data buffer,
and controller.
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