01-08-2014, 10:34 AM
Microelectronic Pill
[attachment=66441]
INTRODUCTION
We are familiar with a wide range of sensors in the field of electronics. They are used widely in the various experiments and research activities too. This microelectronic pill is such a sensor with a number of channels and is called as a multichannel sensor. As the name implies this sensor is a pill. That is it is meant to go inside the body and to study the internal conditions. Earlier it was when transistor was invented, that radiometry capsules were first put into use. These capsules made use of simple circuits for studying the gastrointestinal tract. Some of the reasons that prevented their use was their size and their limitation of not to transmit through more than a single channel. They had poor reliability and sensitivity. The lifespan of the sensors were also too short. This paved the way for the implementation of single channel telemetry capsules and they were later developed to overcome the demerits of the large size of laboratory type sensors. The semiconductor technologies also helped in the formation and thus finally the presently seen microelectronic pill was developed. These pills are now used for taking remote biomedical measurements in researches and diagnosis. The sensors make use of the micro technology to serve the purpose. The main intention of using the pill is to perform an internal study and recognize or detect the abnormalities and the diseases in the gastrointestinal tract. In this GI (Gastro Intestinal) tract we cannot use the old endoscope as the access is restricted. A number of parameters can be possibly measured by these pills and they include conductivity, pH temperature and the amount of dissolved oxygen in the gastrointestinal tract.
ABSTRACT
The invention of transistor enabled the first use of radiometry capsules, which used simple circuits for the internal study of the gastro-intestinal (GI) tract. They couldn't be used as they could transmit only from a single channel and also due to the size of the components. They also suffered from poor reliability, low sensitivity and short lifetimes of the devices. This led to the application of single-channel telemetry capsules for the detection of disease and abnormalities in the GI tract where restricted area prevented the use of traditional endoscopy.
They were later modified as they had the disadvantage of using laboratory type sensors such as the glass pH electrodes, resistance thermometers, etc. They were also of very large size. The later modification is similar to the above instrument but is smaller in size due to the application of existing semiconductor fabrication technologies. These technologies led to the formation of "MICROELECTRONIC PILL".
Microelectronic pill is basically a multichannel sensor used for remote biomedical measurements using micro technology. This is used for the real-time measurement parameters such as temperature, pH, conductivity and dissolved oxygen. The sensors are fabricated using electron beam and photolithographic pattern integration and were controlled by an application specific integrated circuit (ASIC).
BLOCK DIAGRAM
The design of the microelectronic pill is in the form of a capsule. The encasing it has is biocompatible. Inside this are multi- channel (four channels) sensors and a control chip. It also comprises of a radio transmitter and two silver oxide cells. The four sensors are mounted on the two silicon chips. In addition to it, there are a control chip, one access channel and a radio transmitter. The four sensors commonly used are a temperature sensor, pH ISFET sensor, a dual electrode conductivity sensor and a three electrode electrochemical oxygen sensor. Among these the temperature sensor, the pH ISFET sensor and the dual electrode conductivity sensor are fabricated on the first chip. The three electrode electrochemical cell oxygen sensor will be on chip 2. The second chip also consists of a NiCr resistance thermometer which is optional
Control Chip
ASIC (Application-Specific Integrated Circuit) is the control chip that connects together the external components of the micro system
Application-Specific Integrated Circuit (ASIC)
An integrated circuit designed to perform a particular function by defining the interconnection of a set of basic circuit building blocks drawn from a library provided by the circuit manufacturer.
ASIC is a novel mixed signal design that contains an analog signal conditioning module operating the sensors, 10-bit ADC & DAC converters & a digital data processing module. An RC relaxation oscillator (OSC) provides the clock signal.
The analog module is based on the AMS (Automated Manifest System), which offer a lot of power saving scheme (sleep mode) & a compact IC design. The temperature circuitry biased the diode at constant current, so that a change in temperature would result in corresponding change in diode voltage. The pH ISFET sensor was biased as a simple source
Radio Transmitter
It’s assembled prior to integration in the capsule using discrete surface mount components on a single-sided PCB. The footprint of the standard transmitter measured 8*5*3mm including the integrated coil (magnetic) antenna. It’s designed to operate at a transmission freq. of 40.01MHz at 20˚C generating a signal of 10kHz band width. A second crystal stabilized transmitter was also used. This unit is similar to the free running STD transmitter, having a transmission frequency limited to 20.08MHz at 20˚C, due to crystal used. Pills incorporating the STD transmitter are Type 1, where as the pills having crystal stabilized unit is Type 2. The transmission range was measured as being 1m & the modulation scheme FSK (Frequency Shift Keying), with a data rate of 1kb/s.
Temperature Channel Performance
The linear sensitivity was measured over a temperature range from 0˚C to 70˚C & found to be 15.4 mV/˚C. This amplified signal response was from the analog circuit, which was later implemented in the ASIC. The sensor (fig a), once integrated in the pill, gave a linearregression of 11.9 bits/˚C , with a resolution limited by the noise band of 0.4˚C (Fig b). The diode was forward biased with a constant current (15 μA) with the n-channel clamped to the ground, while p-channel was floating. Since the bias current supply circuit was clamped to the negative V rail, any change in the supply voltage potential would cause the temporary channel to drift. Thus, it was seen that o/p signal changed by 1.45mV change in supply expressed in mV, corresponding to a drift of – 41.7mV/h in the pill from a supply voltage change of –14.5mV/h.
pH Channel Performance
The linear performance from pH 1 to 13 corresponded to sensitivity of –41.7mV/pH unit at 23˚C. The pH ISFET sensor operated in a constant current mode (15 μA), with drain voltage clamped to positive supply rail & the source voltage floating with the gate potential. The Ag/AgCl reference electrode, representing the potential in which the floating gate was referred to, was connected to ground. The sensor performance, once integrated in the pill (fig b), corresponded to 14.85 bits/pH which give a resolution of 0.07pH/data point. The sensor exhibits a larger responsivity in alkaline solutions. The sensor life time of 20h was limited by Ag/AgCl reference electrode made from electroplated silver. The ph sensor exhibited a signal drift of –6mV/h (0.14pH), of which –2.5mV/h was estimated to be due to the dissolution of AgCl from the reference electrode. The temperature sensitivity of the pH sensor was measured as 16.8mV/˚c. The changing of the pH of the solution at 40˚c from pH 6.8 to 2.3 and 11.6 demonstrated that the two channels were completely independent of each other and there was no signal interference from the temperature channel (fig b).
OTHER APPLICATIONS
The generic nature of microelectronic pill makes it adaptable for use in corrosive environments related to environmental & industrial applications, such as the evaluation of water quality, pollution detection, fermentation process control & inspection of the pipelines. The integration of radiation sensors & the application of indirect imaging technologies such as ultrasound & impedance tomography, will improve the detection of tissue abnormalities & radiation treatment associated with cancer & chronic inflammation
CONCLUSION
We have therefore described about the multichannel sensor, which has been implemented in remote biomedical using micro technology, the microelectronic pills, which is designed to perform real time measurements in the GI tract providing the best in vitro wireless transmitter, multi channel recordings of analytical parameters.
[attachment=66441]
INTRODUCTION
We are familiar with a wide range of sensors in the field of electronics. They are used widely in the various experiments and research activities too. This microelectronic pill is such a sensor with a number of channels and is called as a multichannel sensor. As the name implies this sensor is a pill. That is it is meant to go inside the body and to study the internal conditions. Earlier it was when transistor was invented, that radiometry capsules were first put into use. These capsules made use of simple circuits for studying the gastrointestinal tract. Some of the reasons that prevented their use was their size and their limitation of not to transmit through more than a single channel. They had poor reliability and sensitivity. The lifespan of the sensors were also too short. This paved the way for the implementation of single channel telemetry capsules and they were later developed to overcome the demerits of the large size of laboratory type sensors. The semiconductor technologies also helped in the formation and thus finally the presently seen microelectronic pill was developed. These pills are now used for taking remote biomedical measurements in researches and diagnosis. The sensors make use of the micro technology to serve the purpose. The main intention of using the pill is to perform an internal study and recognize or detect the abnormalities and the diseases in the gastrointestinal tract. In this GI (Gastro Intestinal) tract we cannot use the old endoscope as the access is restricted. A number of parameters can be possibly measured by these pills and they include conductivity, pH temperature and the amount of dissolved oxygen in the gastrointestinal tract.
ABSTRACT
The invention of transistor enabled the first use of radiometry capsules, which used simple circuits for the internal study of the gastro-intestinal (GI) tract. They couldn't be used as they could transmit only from a single channel and also due to the size of the components. They also suffered from poor reliability, low sensitivity and short lifetimes of the devices. This led to the application of single-channel telemetry capsules for the detection of disease and abnormalities in the GI tract where restricted area prevented the use of traditional endoscopy.
They were later modified as they had the disadvantage of using laboratory type sensors such as the glass pH electrodes, resistance thermometers, etc. They were also of very large size. The later modification is similar to the above instrument but is smaller in size due to the application of existing semiconductor fabrication technologies. These technologies led to the formation of "MICROELECTRONIC PILL".
Microelectronic pill is basically a multichannel sensor used for remote biomedical measurements using micro technology. This is used for the real-time measurement parameters such as temperature, pH, conductivity and dissolved oxygen. The sensors are fabricated using electron beam and photolithographic pattern integration and were controlled by an application specific integrated circuit (ASIC).
BLOCK DIAGRAM
The design of the microelectronic pill is in the form of a capsule. The encasing it has is biocompatible. Inside this are multi- channel (four channels) sensors and a control chip. It also comprises of a radio transmitter and two silver oxide cells. The four sensors are mounted on the two silicon chips. In addition to it, there are a control chip, one access channel and a radio transmitter. The four sensors commonly used are a temperature sensor, pH ISFET sensor, a dual electrode conductivity sensor and a three electrode electrochemical oxygen sensor. Among these the temperature sensor, the pH ISFET sensor and the dual electrode conductivity sensor are fabricated on the first chip. The three electrode electrochemical cell oxygen sensor will be on chip 2. The second chip also consists of a NiCr resistance thermometer which is optional
Control Chip
ASIC (Application-Specific Integrated Circuit) is the control chip that connects together the external components of the micro system
Application-Specific Integrated Circuit (ASIC)
An integrated circuit designed to perform a particular function by defining the interconnection of a set of basic circuit building blocks drawn from a library provided by the circuit manufacturer.
ASIC is a novel mixed signal design that contains an analog signal conditioning module operating the sensors, 10-bit ADC & DAC converters & a digital data processing module. An RC relaxation oscillator (OSC) provides the clock signal.
The analog module is based on the AMS (Automated Manifest System), which offer a lot of power saving scheme (sleep mode) & a compact IC design. The temperature circuitry biased the diode at constant current, so that a change in temperature would result in corresponding change in diode voltage. The pH ISFET sensor was biased as a simple source
Radio Transmitter
It’s assembled prior to integration in the capsule using discrete surface mount components on a single-sided PCB. The footprint of the standard transmitter measured 8*5*3mm including the integrated coil (magnetic) antenna. It’s designed to operate at a transmission freq. of 40.01MHz at 20˚C generating a signal of 10kHz band width. A second crystal stabilized transmitter was also used. This unit is similar to the free running STD transmitter, having a transmission frequency limited to 20.08MHz at 20˚C, due to crystal used. Pills incorporating the STD transmitter are Type 1, where as the pills having crystal stabilized unit is Type 2. The transmission range was measured as being 1m & the modulation scheme FSK (Frequency Shift Keying), with a data rate of 1kb/s.
Temperature Channel Performance
The linear sensitivity was measured over a temperature range from 0˚C to 70˚C & found to be 15.4 mV/˚C. This amplified signal response was from the analog circuit, which was later implemented in the ASIC. The sensor (fig a), once integrated in the pill, gave a linearregression of 11.9 bits/˚C , with a resolution limited by the noise band of 0.4˚C (Fig b). The diode was forward biased with a constant current (15 μA) with the n-channel clamped to the ground, while p-channel was floating. Since the bias current supply circuit was clamped to the negative V rail, any change in the supply voltage potential would cause the temporary channel to drift. Thus, it was seen that o/p signal changed by 1.45mV change in supply expressed in mV, corresponding to a drift of – 41.7mV/h in the pill from a supply voltage change of –14.5mV/h.
pH Channel Performance
The linear performance from pH 1 to 13 corresponded to sensitivity of –41.7mV/pH unit at 23˚C. The pH ISFET sensor operated in a constant current mode (15 μA), with drain voltage clamped to positive supply rail & the source voltage floating with the gate potential. The Ag/AgCl reference electrode, representing the potential in which the floating gate was referred to, was connected to ground. The sensor performance, once integrated in the pill (fig b), corresponded to 14.85 bits/pH which give a resolution of 0.07pH/data point. The sensor exhibits a larger responsivity in alkaline solutions. The sensor life time of 20h was limited by Ag/AgCl reference electrode made from electroplated silver. The ph sensor exhibited a signal drift of –6mV/h (0.14pH), of which –2.5mV/h was estimated to be due to the dissolution of AgCl from the reference electrode. The temperature sensitivity of the pH sensor was measured as 16.8mV/˚c. The changing of the pH of the solution at 40˚c from pH 6.8 to 2.3 and 11.6 demonstrated that the two channels were completely independent of each other and there was no signal interference from the temperature channel (fig b).
OTHER APPLICATIONS
The generic nature of microelectronic pill makes it adaptable for use in corrosive environments related to environmental & industrial applications, such as the evaluation of water quality, pollution detection, fermentation process control & inspection of the pipelines. The integration of radiation sensors & the application of indirect imaging technologies such as ultrasound & impedance tomography, will improve the detection of tissue abnormalities & radiation treatment associated with cancer & chronic inflammation
CONCLUSION
We have therefore described about the multichannel sensor, which has been implemented in remote biomedical using micro technology, the microelectronic pills, which is designed to perform real time measurements in the GI tract providing the best in vitro wireless transmitter, multi channel recordings of analytical parameters.