21-01-2013, 01:15 PM
A 0.5-V Biomedical System-on-a-Chip for Intrabody Communication System
[attachment=47868]
Abstract
A low-voltage (0.5 V) and low-power (4.535 mW)
monolithic biomedical system-on-a-chip (SOC) consisting of a receiver,
a transmitter, a microcontrol unit, and an analog-to-digital
converter (ADC), implemented in a 0.18-μm CMOS technology
for intrabody communication is first reported. The SOC can take
command through a human body and activate (or turn on) the
ADC and transmitter inside the SOC. Then, a biomedical signal
is converted to digital format and transmitted to the RF gateway
through a human body. With this transmission methodology and
the proposed SOC circuit, it is much more power efficient than
wireless communication. Moreover, since no antenna is required,
the chip size of the SOC is only 1.5 mm2, excluding the test pads.
INTRODUCTION
THERE IS a well-known dilemma in wireless technology
[1]–[4]. The form factor, mainly determined by the antenna
size, can be small if the operating frequency is high,
which inevitably results in higher power dissipation. On the
other hand, the power dissipation can be low if the operation
frequency is lower, yet the form factor will be larger because of
the need of a large-size antenna. For intrabody communications
(IBCs), which use a human body as the transmission medium,
the tradeoff between the form factor and the power dissipation
is not an issue since no antenna is needed. There are mainly
two types of data transmission methods for IBCs [5], [6].
PROPOSED IBC NETWORK AND THE
IBC BIOMEDICAL SOC
For the optimization of the proposed biomedical SOC for
IBC, the frequency response characteristics of the human-body
channel are investigated as follows. The output of a signal
generator is connected to the forearm by using a Ag/AgCl
electrode. Another electrode, which is attached to the wrist
as a receiver, is connected to a spectrum analyzer. The two
ground electrodes of them are attached to the body as reference
voltage. According to the measurement results in Fig. 2, the
proper frequency band for IBC ranges from 50 to 300 MHz.
The human body behaves as a low-pass filter with a bandwidth
of about 300 MHz and approximately 7-dB transmission
losses. Moreover, for direct digital data transmission without
modulation, large transmitted voltage is necessary. Therefore,
large voltage or power is required. However, this would be
more harmful to human body. Furthermore, according to the
measurement results in [5], the suitable frequency range for
IBC, i.e., the frequency range corresponding to the lowest
path loss, is from 200 to 600 MHz. Hence, in this paper, the
frequency 200 MHz (i.e., the lowest frequency suitable for IBC
based on this work and [5]) is adopted for low-voltage and lowpower
transmission in the human body.
MCU With UART
An MCU is designed to control the proper operation of
command receiving and data transmission. The RS-232 communication
data format is used to communicate with portable
devices conveniently. There are four proprietary commands to
operate the MCU in four system states: Idle, Convert, Transmit,
and Continue. The Idle command asks the MCU to stay idle.
In the Convert state, the MCU sends an active signal to start
the operation of ADC. The ADC will sample the analog signal
only once and convert the sampled analog signal into 8-b digital
data, which are then stored in the data register inside a Universal
Asynchronous Transmitter. The Transmit command requests
the MCU to transmit the data in data register only once by
the on–off-keying transmitter. The Continue command asks the
MCU to measure and transmit the converted data to the portable
device at the wrist end continuously.
MEASUREMENT RESULTS AND DISCUSSION
This fully monolithic IBC SOC is implemented in a standard
0.18-μm CMOS process provided by United Microelectronics
Corporation. Fig. 10 shows the die photo of the SOC. The chip
area is only 1.5 mm2, excluding the test pads. Since the ADC in
the system is operated at 1.8 V, the system cannot be powered
solely by a solar cell. Instead, the ADC of the system is powered
by a molecular battery at 1.8 V, while the other parts of the
system are powered by a power supply at 0.5 V. The receiver
consumes 2.9 mW, i.e., its dc bias current is 5.8 mA. To verify
the feasibility of solar cell powering, the receiver has been
tested with a solar cell under a lamp. The power consumption
of the MCU, ADC, and transmitter is 1, 0.135, and 0.5 mW,
respectively. That is, the power consumption of the IBC SOC is
only 4.535 mW.
CONCLUSION
In this paper, for the first time, a small-size (1.5 mm2) and
low-power-consumption (4.535 mW) IBC biomedical SOC,
which includes a receiver, a transmitter, an MCU, and an ADC,
has been demonstrated. Compared with the traditional batterypowered
receiver which needs more than 1-V supply voltage,
the proposed receiver architecture is more suitable for portable
and wearable applications since it can be driven at an ultralow
voltage of 0.5 V, which, in turn, makes it possible to be powered
solely by a solar cell. The successful results of this work suggest
that the implemented IBC biomedical SOC is very suitable for
applications which require a long-time operation and a very
small form factor, such as human-body health monitoring.
[attachment=47868]
Abstract
A low-voltage (0.5 V) and low-power (4.535 mW)
monolithic biomedical system-on-a-chip (SOC) consisting of a receiver,
a transmitter, a microcontrol unit, and an analog-to-digital
converter (ADC), implemented in a 0.18-μm CMOS technology
for intrabody communication is first reported. The SOC can take
command through a human body and activate (or turn on) the
ADC and transmitter inside the SOC. Then, a biomedical signal
is converted to digital format and transmitted to the RF gateway
through a human body. With this transmission methodology and
the proposed SOC circuit, it is much more power efficient than
wireless communication. Moreover, since no antenna is required,
the chip size of the SOC is only 1.5 mm2, excluding the test pads.
INTRODUCTION
THERE IS a well-known dilemma in wireless technology
[1]–[4]. The form factor, mainly determined by the antenna
size, can be small if the operating frequency is high,
which inevitably results in higher power dissipation. On the
other hand, the power dissipation can be low if the operation
frequency is lower, yet the form factor will be larger because of
the need of a large-size antenna. For intrabody communications
(IBCs), which use a human body as the transmission medium,
the tradeoff between the form factor and the power dissipation
is not an issue since no antenna is needed. There are mainly
two types of data transmission methods for IBCs [5], [6].
PROPOSED IBC NETWORK AND THE
IBC BIOMEDICAL SOC
For the optimization of the proposed biomedical SOC for
IBC, the frequency response characteristics of the human-body
channel are investigated as follows. The output of a signal
generator is connected to the forearm by using a Ag/AgCl
electrode. Another electrode, which is attached to the wrist
as a receiver, is connected to a spectrum analyzer. The two
ground electrodes of them are attached to the body as reference
voltage. According to the measurement results in Fig. 2, the
proper frequency band for IBC ranges from 50 to 300 MHz.
The human body behaves as a low-pass filter with a bandwidth
of about 300 MHz and approximately 7-dB transmission
losses. Moreover, for direct digital data transmission without
modulation, large transmitted voltage is necessary. Therefore,
large voltage or power is required. However, this would be
more harmful to human body. Furthermore, according to the
measurement results in [5], the suitable frequency range for
IBC, i.e., the frequency range corresponding to the lowest
path loss, is from 200 to 600 MHz. Hence, in this paper, the
frequency 200 MHz (i.e., the lowest frequency suitable for IBC
based on this work and [5]) is adopted for low-voltage and lowpower
transmission in the human body.
MCU With UART
An MCU is designed to control the proper operation of
command receiving and data transmission. The RS-232 communication
data format is used to communicate with portable
devices conveniently. There are four proprietary commands to
operate the MCU in four system states: Idle, Convert, Transmit,
and Continue. The Idle command asks the MCU to stay idle.
In the Convert state, the MCU sends an active signal to start
the operation of ADC. The ADC will sample the analog signal
only once and convert the sampled analog signal into 8-b digital
data, which are then stored in the data register inside a Universal
Asynchronous Transmitter. The Transmit command requests
the MCU to transmit the data in data register only once by
the on–off-keying transmitter. The Continue command asks the
MCU to measure and transmit the converted data to the portable
device at the wrist end continuously.
MEASUREMENT RESULTS AND DISCUSSION
This fully monolithic IBC SOC is implemented in a standard
0.18-μm CMOS process provided by United Microelectronics
Corporation. Fig. 10 shows the die photo of the SOC. The chip
area is only 1.5 mm2, excluding the test pads. Since the ADC in
the system is operated at 1.8 V, the system cannot be powered
solely by a solar cell. Instead, the ADC of the system is powered
by a molecular battery at 1.8 V, while the other parts of the
system are powered by a power supply at 0.5 V. The receiver
consumes 2.9 mW, i.e., its dc bias current is 5.8 mA. To verify
the feasibility of solar cell powering, the receiver has been
tested with a solar cell under a lamp. The power consumption
of the MCU, ADC, and transmitter is 1, 0.135, and 0.5 mW,
respectively. That is, the power consumption of the IBC SOC is
only 4.535 mW.
CONCLUSION
In this paper, for the first time, a small-size (1.5 mm2) and
low-power-consumption (4.535 mW) IBC biomedical SOC,
which includes a receiver, a transmitter, an MCU, and an ADC,
has been demonstrated. Compared with the traditional batterypowered
receiver which needs more than 1-V supply voltage,
the proposed receiver architecture is more suitable for portable
and wearable applications since it can be driven at an ultralow
voltage of 0.5 V, which, in turn, makes it possible to be powered
solely by a solar cell. The successful results of this work suggest
that the implemented IBC biomedical SOC is very suitable for
applications which require a long-time operation and a very
small form factor, such as human-body health monitoring.