IEEE Circuits and Systems Magazine - Q3 2022 - 31

detail, the switched resister array, R2, M3 and R3 implement
a programmable current source. M3, R3 and M4 provide
a current mirror with a large current gain factor. M5,
R4, M10 and M11 provide a current mirror with a large gain
factor and two outputs. Moreover, two pulse width modulation
(PWM, provided by the MCU) level shifters (M6-
M9, R5-R8) are exploited to boost the compliance voltage.
The output currents of the current mirror (M10, M11)
drive the H-bridge (M12-M15). One benefit of the H-bridge
is that it is easy to implement the ETI impedance extractor.
For instance, in Fig. 15(a), only one switch (M16) is
used to extract the impedance of the ETI. Controlled by
IMP_CTL, the output signal of the H-bridge (ADC10, which
is either NS+ or NS-) is fed to the MCU to detect the voltage
magnitude of the pulse generator. Knowing the current
magnitude (which is determined by selecting the
switches S0-Sn) and the voltage magnitude of the pulse
generator at a specific moment, the DC impedance of the
tissue can be calculated using Ohm's law. The chargebalancing
network is simply implemented by a switched
discharge resistor (M17 and Rdis) [32], [33], where Rdis
limits the discharging currents through the tissue. The
SRA-PG has the following advantages. First, the current
consumed by the programmable current source is small.
Second, only a few transistors and resistors are used to
generate the stimulus. Third, it can generate a wide current
range, from 10 μA to 12 mA. Fig. 11(b) shows the generated
pulse.
VIII. The Wireless Power Transmitter and Receiver
In the traditional inductive coupling link (ICL), the transmitted
power is sensitive to the (short) distance between the
1,000
200
400
600
800
510152025
10
12
14
16
6
8
2
4
5
10
15
Number of the UTS
Figure 10. The coastline length and slope in the ictal and inter-ictal periods (when k = 3 and d = 2).
THIRD QUARTER 2022
IEEE CIRCUITS AND SYSTEMS MAGAZINE
31
20
25
Inter-Ictal Period (Mean)
Ictal Period (Mean)
Calculated THS
Inter-Ictal Period (Mean)
Ictal Period (Mean)
Calculated THCL
Figure 9. The coastline length and slope as functions of the
UTW in the inter-ictal period.
receiving coil and the transmitting coil. When the distance
between these two coils is reduced, the maximum power
transfer as a function of frequency will split from a peak (at
a single resonance frequency) into two peaks (at both sides
of the previous resonance frequency). This phenomenon is
known as frequency splitting [34]), and thus make the power
transfer at the resonant frequency lower than the
peak power [35]. In order to keep the received power at the
resonant frequency high (i.e., either maximum or close to
the peak power) when shortening the distance, a distancefrequency
adaptive ICL (DFAICL) is proposed.
A. The Transmitter of the DFAICL
In the transmitter of the DFAICL, a high-frequency transistor
(i.e., Q2N2222, TI) is utilized to build a Colpitts
100
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50
1 23 45 67 89 10 11 12
Number of the UTW
1
2
3
4
Slope (µV/ms)
Coastline Length (µV)
Coastline Length, ACL (µV)
Slope, AS (µV/ms)
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