IEEE Solid-States Circuits Magazine - Summer 2022 - 50

Voltage-mode operation can provide high
efficiency for delivering high power with large
input voltages, while the current mode is
more suitable for low power delivery with a
relatively small input voltage.
presented in [53] to find the optimal
timing scheme for controlling current-mode
operation and maximizing
energy storage for a given period
of time. In [54], a time-interleaved
PMIC with isolated resonator and
quasi-resonant boost converter has
been presented for battery charging
that achieves a high fp of 13.56 MHz
(with a small Rx coil) and continuous
resonance and isolation of the Rx LCtank
(from the load) by utilizing two
separate capacitors in the Rx, which
are interchangeably connected to the
Rx coil.
Voltage regulation in current-mode
power delivery can be achieved with
controlling the switching frequency
[48]. As shown in Figure 10, the number
of cycles for shorting the L2C2tank
can intentionally be increased
to avoid energy transfer to the load
when VL is higher than the required
supply voltage.
Adaptive Voltage/Current-Mode
Power Management
Voltage-mode techniques are optimal
for power delivery to a small RL
(need for a large PDL), particularly
when the Rx coil voltage VR is large
enough (need for a high PCE and low
VCE). On the other hand, currentmode
power delivery is suitable for
powering devices that demand a low
PDL (large RL) with low VR (need for
high VCE) [14]. For most WPT applications
that
involve drastic coils'
Envelope
Detector
VBGR
0.37 VDD
-+VS
Driver
L1
VR
k12
L2
M1
C1
(a)
VL
3.2 V
1.2 V
5 V
3.3 V
VR
C2
Adaptive VCIPM Chip With Self-Regulation Capability
VBGR
Mode Selection
(MS)
CM
Current-Mode
Controller (CMC)
VM
Voltage-Mode
Controller (VMC)
VL VDD = 3.2 V
SW1 SW2
M2
Body-Bias
Gen.
0.37 VDD
M3
CL RL
Current
Gen. (CG)
BGR
VDD
0.37 VDD
distance and orientation changes
and dynamic load variations, neither
voltage mode nor current mode
alone can provide the optimal performance.
The PMIC should be adaptive
to such conditions, which has
led to a reconfigurable voltage/current-mode
inductive power-management
(VCIPM) chip in [48].
The VCIPM chip [block diagram
Current Mode (CM)
4 V
VS was Changed
(b)
FIGURE 11: A block diagram and the measurement results of the VCIPM chip that adaptively
operates either in voltage mode or current mode based on the Rx coil voltage amplitude.
(Source: Adopted from [48].)
50 SUMMER 2022
IEEE SOLID-STATE CIRCUITS MAGAZINE
Voltage Mode (VM)
10 V
VS
50 µs
shown in Figure 11(a)] adaptively
switches between the voltage and
current modes based on VR amplitude
to: 1) maximize the PTE when VR
is larger than the required VL of 3.2 V
by operating as an active voltage
rectifier (M2 switch) with high PCE;
and 2) maximize the VCE for small
VR < 3.3 V by configuring to current
mode and shorting the Rx LC-tank
(through M1 switch) for the optimal
number of cycles to store energy and
then deliver it to the load via a passive
rectifier (M3 diode). As an example,
Figure 11(b) shows the measured
results of the VCIPM chip for adaptive
transition from current-mode
to voltage-mode operation as the Tx
voltage (Vs), and therefore VR, was
increased for generating VL = 3.2 V
from the steady-state VR,peak of 1.2
and 3.3 V [48]. This chip also regulates
VL to 3.2 V by controlling the
reverse current in voltage mode and
adjusting the switching frequency in
current mode, eliminating the need
for a lossy regulator and its associated
off-chip capacitor [48].
The adaptive operation of voltage
and current modes in [48] is
VR
Skin/Air
IEEE Solid-States Circuits Magazine - Summer 2022

Table of Contents for the Digital Edition of IEEE Solid-States Circuits Magazine - Summer 2022
