Publications
274 results found
Williams I, Constandinou TG, 2012, An Energy-Efficient, Dynamic Voltage Scaling Neural Stimulator for a Proprioceptive Prosthesis, International Symposium on Circuits and Systems (ISCAS), ISSN: 0271-4302
This paper presents an energy-efficient neuralstimulator capable of providing charge-balanced asymmetric pulses. Power consumption is reduced by implementing a fully-integrated DC-DC converter that uses a reconfigurable switched capacitor topology to provide 4 output voltages for DynamicVoltage Scaling (DVS). DC conversion efficiencies of between 63% and 76% are achieved using integrated capacitances of under 1nF and the DVS approach offers power savings of up to 53.5%compared to the front end of a typical current controlled neural stimulator. Charge balancing is achieved to a low level of accuracy on a single pulse and a much higher accuracy over a series ofpulses. The method used is robust to process and component variation and does not require any initial or ongoing calibration. Monte-Carlo simulations indicate that the charge imbalance willbe less than 0.014% (at 3 sigma ) of charge delivered for a series of pulses. The circuit has been designed in a commercially-available0.18 m HV CMOS technology and requires a die areaof <0.5 sq. mm for a 16 channel implementation.
Paraskevopoulou SE, Constandinou TG, 2012, An Ultra-Low-Power Front-End Neural Interface with Automatic Gain for Uncalibrated Monitoring, International Symposium on Circuits and Systems (ISCAS), ISSN: 0271-4302
This paper presents a dynamic front-end towards achieving unsupervised single-neuron activity monitoring. By implementing at the front-end, an automatic gain control that is optimised for neural signal dynamics, subsequent processing can be achieved without the need for calibration. The system uses three amplification stages (low-noise first stage, variable-gain second stage and high-gain third stage), a tuneable high-pass filter, and a feedback loop to tune the variable gain. The circuit has been implemented in a commercially-available 0.18um CMOS technology with total power consumption between 1.79 and 1.95$uW$ The front-end achieves a variable gain from 52 to 86.4dB with 3kHz bandwidth and a high-pass filter that is tuneable from 100-300Hz. The input referred noise is 9.66uV with a total harmonic distortion of under 1%.
Mirza KB, Luan S, Constandinou TG, 2012, Towards a Fully-Integrated Solution for Capacitor-Based Neural Stimulation, International Symposium on Circuits and Systems (ISCAS), ISSN: 0271-4302
Charge-mode stimulation (ChgMS) is a relatively new method being explored in the field of electrical neural stimulation. One of the key challenges in such a system is to overcome charge sharing between the storage capacitor and the double layer capacitor in the Electrode-Electrolyte-Interface (EEI). In this work, this issue is overcome by using a second-generation negative current conveyor (CCII-) with low current tracking error. The level of charge sharing in the circuit is expressed by a new figure of merit (charge delivery efficiency) introduced in this paper. The proposed system has a maximum power efficiency of 76.6% and a total power consumption of 270uW per electrode for a target charge stimulus of 0.9nC. Crucially, the system achieves a minimum charge delivery efficiency of 98.22%.
Constandinou TG, Hafliger P, 2012, Guest Editorial - Special Issue on Selected Papers From BioCAS 2011, IEEE Transactions on Biomedical Circuits and Systems, Vol: 6, Pages: 401-402, ISSN: 1932-4545
Woods SP, Constandinou TG, 2011, Towards a micropositioning system for targeted drug delivery in wireless capsule endoscopy, Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBS), Publisher: IEEE, Pages: 7372-7375, ISSN: 1557-170X
This paper describes a novel micropositioningmechanism for achieving 1ml of targeted drug delivery within wireless capsule endoscopes. The mechanism allows a needle to be positioned within a 22.5° segment of a cylindrical capsule and be extendible by up to 4mm. The mechanism achieves both these functions using only a single micromotor and occupying a volume of just 200mm³ (including micromotor), this represents only 6.6% of the total available space. Through a detailed stress analysis it has been shown that the proposed mechanismcan be fabricated using FDA approved materials and requires a power budget of under 3.3% of the available capacity. It is envisaged this mechanism would empower a new breed of capsule microrobots for therapy in addition to diagnostics for pathologies such as ulcerative colitis and small intestinal Crohn’s disease.
Liu Y, Georgiou P, Prodromakis T, et al., 2011, An Extended CMOS ISFET Model Incorporating the Physical Design Geometry and the Effects on Performance and Offset Variation, IEEE Transactions on Electron Devices, Vol: 58, Pages: 4414-4422, ISSN: 0018-9383
This paper presents an extended model for theCMOS-based Ion-Sensitive-Field-Effect-Transistor (ISFET), incorporating design parameters associated with the physicalgeometry of the device. This can, for the first time, provide a good match between calculated and measured characteristics bytaking into account the effects of non-idealities such as threshold voltage variation and sensor noise. The model is evaluated through a number of devices with varying design parameters (chemical sensing area and MOSFET dimensions) fabricated ina commercially-available 0.35μm CMOS technology. Threshold voltage, subthreshold slope, chemical sensitivity, drift and noisewere measured and compared to the simulated results. The first and second order effects are analysed in detail and it is shown that the sensors’ performance was in agreement with the proposed model.
Georgiou J, Andreou AG, 2011, Special Issue on Selected Papers From BioCAS 2010, IEEE TRANSACTIONS ON BIOMEDICAL CIRCUITS AND SYSTEMS, Vol: 5, Pages: 401-402, ISSN: 1932-4545
Nikolic K, Serb A, Constandinou TG, 2011, An Optical Modulator in Unmodified, Commercially-Available CMOS Technology, IEEE Photonics Technology Letters, Vol: 23, Pages: 1115-1117, ISSN: 1041-1135
Here we present a method and structures for mid-infrared, free-space optical communication using unmodified, commercially available complementary metal-oxide semiconductor integrated circuits. The modulator is based onthe free carrier absorption in parasitic PN junction structures under reverse bias. Measured results demonstrate the proof-of-concept with speeds of 100bps (1.55um wavelength), but at least two orders of magnitude improvement can be achieved. This technology will enable non-galvanic chip-to-chip and chip-to-package communication as an alternative to wirebonding in applications that benefit from a planar top chip surface, such as chemical sensing lab-on-chip systems as well as general sensorsand mid-infrared communication.
Georgiou P, Prodromakis T, Constandinou TG, et al., 2011, Sensor Array for Measuring Neural Activity
A sensor system comprising a substrate and integrated onto the substrate an array (7) of sensor elements (1), each sensor element comprising one or more inductors (3), one or more electrochemical sensors (4), and one or more optical sensors (2). The system further comprising a controller configured in use to separately address each of the sensor elements (1) to drive the respective inductors and receive outputs of the respective sensors.
Nikolic K, Constandinou TG, Toumazou C, 2011, Method and Apparatus for Optically Outputting Information from a Semiconductor Device
A method of optically outputting information (e.g. digital data) from a semiconductor device, the method comprising: providing a semiconductor device having a semiconducting p-n junction, the p-n junction having a region of reduced free charge carrier density; applying an electrical signal to modulate the extent of the said region, the electrical signal being representative of the information to be outputted; arranging incident light to pass through at least part of the said region, such that the light is at least partially absorbed in dependence upon the modulated extent of the said region, thereby producing intensity-modulated output light; and detecting the intensity of the output light and thereby determining the outputted information. Also provided is an electro-optical assembly, a package module for mounting a semiconductor device on a printed circuit board, and an integrated circuit chip.
Goh ZDC, Georgiou P, Constandinou TG, et al., 2011, A CMOS-based ISFET Chemical Imager with Auto-Calibration Capability, IEEE Sensors Journal, Vol: 11, Pages: 3253-3260, ISSN: 1530-437X
This paper presents a novel auto-calibration technique for eliminating sensor mismatch in CMOS-based chemical imagers. Designed using an 8x8 array comprising of pH sensitive Ion Sensitive Field Effect Transistors (ISFETs), the chemical imager is capable of implementing a gradient based calibration algorithm by biasing programmable-gate (PG) ISFETs at a common operating point when exposed to a solution of homogenous pH. The system was fabricated in a typical 0.35um CMOS technology and demonstrated a fast rate of convergence (500ms per iteration) while a convergence accuracy of 45mV on a gain of 10 (0.5% relative standard error and 2% pixel-to-pixel variation) was achieved. A maximum pH sensitivity of 57mV/pH is also reported.
Serb A, Nikolic K, Constandinou TG, 2011, A CMOS-based light modulator for contactless data transfer: theory and concept, Silicon Photonics VI, Publisher: SPIE, Pages: 794317-794325
A new technique pertaining to the optical contactless chip-to-board communication using a commercially available CMOS technology is under development. The main concept is to use mid-IR light from a small LED which will enter an IC from the underside, impinge upon one or more pn-junctions and be reflected by a metallic sheet so that it falls on an external, discrete photodetector. After propagation through the doped semiconductor, the light undergoes attenuation due to free carrier absorption. By varying the reverse bias across the pn-junction(s), the depletion region widths are changed and therefore modulation of light intensity can be achieved. Through this scheme, data readout can be realized optically, thus alleviating the need for galvanic contacts (most notably wirebonds).
Sole M, Sanni A, Vilches A, et al., 2011, A Bio-Implantable Platform for Inductive Data and Power Transfer with Integrated Battery Charging, IEEE International Symposium on Circuits and Systems (ISCAS), Publisher: IEEE, Pages: 2605-2608
This paper describes a mixed signal subsystem for the inductive transfer of power and data to a fully-implantable medical device. The design includes circuits for the inductive power recovery and energy storage (charging), in addition to data recovery and demodulation. The data link is used to upload (at a data rate of up to 180Kbps) calibration and configuration data to the implanted device and integrates both error detection and correction on the recovered bitstream. The system incorporates an implanted Li-Ion micro-battery with supporting charging hardware to provide an uninterrupted power supply for autonomous deployment. This is to provide continuous operation without the requirement for an externally worn unit and additionally ensures registry (i.e. patient calibration) settings are maintained. The circuit has been implemented in a commercially available 0.35um CMOS technology without requiring high-voltage device options.
Serb A, Nikolic K, Constandinou TG, 2011, Feasibility of an Electro-Optic Link for Bondpad-less CMOS Lab-on-Chips, IEEE Biomedical Circuits and Systems (BioCAS) conference, Publisher: IEEE, Pages: 353-356
This paper explores the feasibility of developing CMOS-based lab-on-chips to analyse the properties of a fluid, without the need for bond wires. Both inductive and electro-optical schemes are suggested as possible solutions. Specifically, this paper details a novel approach in achieving electro-optical modulation in unmodified, commercially-available CMOS technology. By exploiting the plasma dispersion effect, it is shown how mid-infrared light can be modulated using parasitic structures designed in a CMOS integrated circuit. Both the fundamental theory and practical realisation are supported with measured data from an experimental setup.
Paraskevopoulou S, Constandinou TG, 2011, A sub-1μW Neural Spike-Peak Detection and Spike-Count Rate Encoding Circuit, IEEE Biomedical Circuits and Systems (BioCAS) conference, Publisher: IEEE, Pages: 29-32
In this paper we present a circuit for determining neural spike features such as peak occurrence, peak amplitude and spike count rate in continuous-time. The system achieves these functions concurrently and in real-time achieving an accuracy higher than a typical digital solution (constrained by a the sampling time and/or resolution). For an average spike rate of 50$spikes/s$ the system consumes 815nW designed in a commercially-available 0.18μm CMOS technology. The complete circuit core (excluding bondpads) occupies a total area of approximately 0.022mm²
Goh ZDC, Georgiou P, Constandinou TG, et al., 2011, A CMOS-Based Lab-on-Chip Array for Combined Magnetic Manipulation and Opto-Chemical Sensing, IEEE International Symposium on Circuits and Systems (ISCAS), Publisher: IEEE, Pages: 1997-2001
This paper presents a CMOS-based lab-on-chip platform for combined magnetic manipulation and opto-chemical sensing. Within each pixel, a Programmable Gate (PG) ISFET chemical sensor is combined with an active pixel sensor, and is encompassed within an inductive coil. The integrated pixel is tesselated to form an 8×8 array. Fabricated in a commercially available 0.35um CMOS technology, the system can be used for simultaneous optical imaging and pH sensing, and includes auto- calibration mechanisms for eliminating sensor non-idealities. A spatiotemporal magnetic field pattern generator has also been embedded for micro-scale magnetic manipulation. Controlled via a MATLAB based graphical user interface, the system achieves real time data acquisition at 6fps, a pH sensitivity of 57mV/pH and demonstrates magnetic manipulation of micro-beads.
Luan S, Eftekhar A, Murphy O, et al., 2011, Towards an Inductively Coupled Power/Data Link for Bondpad-Less Silicon Chips, IEEE International Symposium on Circuits and Systems (ISCAS), Publisher: IEEE, Pages: 7-10
This paper explores the concept of developing a bondpad-less fullyintegrated inductive link for power/data transfer between a silicon chip and a PCB. A key feature of the implemented system is that it requires no off-chip components. The proposed chip uses a standard 0.35um process and occupies an area of 2.5 x 2.5 mm^2. 9mW power was designed to be obtained on-chip through 900MHz carrier wave. Binary Phase Shift Keying (BPSK) and Load shift keying (LSK) are used for the the PCB-to-chip and chip-to-PCB link respectively for half-duplex communication.
Abshire P, Andreou A, Bermak A, et al., 2011, Confession Session: Learning from Others Mistakes, IEEE International Symposium on Circuits and Systems (ISCAS), Publisher: IEEE, Pages: 1149-1162
People rarely put in their papers the things that didn’t work, the mistakes they made, and how they found out what went wrong. Such confessions can help others learn how to avoid similar mistakes. Twenty-six confessions were collected to form the bulk of this paper. Themes that arise are errors that result from not understanding the limitations of simulation tools in modeling physical reality, chip verification errors that result from lack of clear communication between designers, and projects that are considered in their own isolated environment of technical challenges rather than the broader context of their environment or application.
Hu Y, Liu Y, Constandinou TG, et al., 2011, A 5s-Time-Constant Temperature-Stable Integrator for a Tuneable PID Controller in LOC Applications, IEEE International Symposium on Circuits and Systems (ISCAS), Publisher: IEEE, Pages: 1387-1390
In this paper, we present a novel, ultra-long-time-constant analog integrator circuit as part of an analogue signal processing block. By employing transconductance reduction techniques a time constant of up to 5s is achievable using only a 35pF capacitor. This is achieved by introducing a R-2R current divider network in the feedback loop, additionally allowing the transconductance to be digitally-tuned within a range of 0.2 to 5 seconds to 4-bit resolution. Furthermore, through internal compensation, the clockless integrator achieves a temperature dependance of under 1.2\% over the 0$^oC$ to 100$^oC$ range.
Prodromakis T, Liu Y, Constandinou TG, et al., 2010, Exploiting CMOS Technology to Enhance the Performance of ISFET Sensors, IEEE Electron Device Letters, Vol: 31, Pages: 1053-1055, ISSN: 0741-3106
This paper presents a novel method for fabricating ISFET devices in unmodified CMOS technologies. Conventional CMOS ISFETs utilise the protective passivation coating as the sensing membrane, with the sensed potential being coupled down to the floating MOS gate via a stack of conducting and insulating layers. The proposed structure minimises the use of these layers by exploiting the passivation opening mask, normally intended for bondpad openings. Parasitic effects such as reduced transconductance and trapped charge within the floating gate structure are minimised, resulting in a lower VT and improved chemical transconductance efficiency. Other characteristics including chemical sensitivity, reference leakage current and noise power are at comparable levels with conventional CMOS-based ISFET devices.
Constandinou TG, Hafliger P, 2010, Guest Editorial - Special Issue on Selected Papers from ISCAS 2009, IEEE Transactions on Biomedical Circuits and Systems, Vol: 4, Pages: 137-138, ISSN: 1932-4545
Constandinou TG, Georgiou P, Prodromakis T, et al., 2010, A CMOS-based Lab-on-Chip Array for the Combined Magnetic Stimulation and Opto-Chemical Sensing of Neural Tissue, Berkeley, CA, 2010 12th International Workshop on Cellular Nanoscale Networks and their Applications (CNNA), Publisher: IEEE, Pages: 1-6
This paper presents a novel CMOS-based lab-on-chip platform for non-contact magnetic stimulation and recording of neural tissue. The proposed system is the first of its kind to integrate magnetic-stimulation and opto-chemical sensing in a single pixel, tesselated to form an 8 à 8 array. Fabricated in a commercially-available 0.35 ¿m CMOS technology, the system can be intrinsically used for both optical imaging and pH sensing and includes mechanisms for calibrating out sensor variation and mismatch. In addition to sensory acquisition via an integrated 10-bit ADC, a 64-instruction spatiotemporal pattern generator has been embedded within the array for driving the microscale magnetic neural stimulation. In this application the ISFET-based sensors are used to capacitively-couple neuronal charge in close proximity to the floating gate. Optical imaging hardware has also been embedded to provide topographic detail of the neural tissue.
Garner DM, Bai H, Georgiou P, et al., 2010, A multichannel DNA SoC for rapid point-of-care gene detection, IEEE International Solid-State Circuits Conference (ISSCC), Publisher: IEEE, Pages: 492 -493-492 -493, ISSN: 0193-6530
Eftekhar A, Paraskevopoulou S, Constandinou TG, 2010, Towards Next Generation Neural Interfaces: Optimizing Power, Bandwidth and Data Quality, IEEE Biomedical Circuits and Systems (BioCAS) Conference, Publisher: IEEE, Pages: 122-125
In this paper, we review the state-of-the-art in neural interface recording architectures. Through this we identify schemes which show the trade-off between data information quality (lossiness), computation (i.e. power and area requirements) and the number of channels. These trade-offs are then extended by considering the front-end amplifier bandwidth to also be a variable. We therefore explore the possibility of band-limiting the spectral content of recorded neural signals (to save power) and investigate the effect this has on subsequent processing (spike detection accuracy). We identify the spike detection method most robust to such signals, optimize the threshold levels and modify this to exploit such a strategy.
Constandinou TG, Georgiou J, 2009, A Micropower Tilt Processing Circuit, IEEE Transactions on Biomedical Circuits and Systems, Vol: 3, Pages: 363-369, ISSN: 1932-4545
This paper describes a novel analogue circuit for extracting the tilt angle from the output of a linear MEMS accelerometer. The circuit uses the accelerometer signal together with the gravitational acceleration vector to generate the tilt signal. Using a current-mode representation with MOS devices operating in weak inversion, the appropriate trigonometric function has been realised to compute tilt. Furthermore, implementing a long-time constant filter to extract the mean tilt level provides adaptation to the static tilt level. Specifically, this circuit has been designed as part of an implantable vestibular prosthesis to provide inclination signals for bypassing dysfunctional otolith end-organs. The circuit has been fabricated in AMS 0.35um 2P4M CMOS technology and this paper presents the theory, implementation and measured results.
Constandinou TG, 2009, Biologically Inspired Electronics for Micropower Vision Processing, Publisher: VDM Verlag, ISBN: 978-3639133912
Eftekhar A, Constandinou TG, Abbruzzese D, et al., 2009, A Programmable Neural Interface for Investigating Arbitrary Stimulation Strategies, 14th Annual International FES Society Conference
Constandinou TG, Georgiou J, Toumazou C, 2009, A Neural Implant ASIC for the Restoration of Balance in Individuals with Vestibular Dysfunction, IEEE International Symposium on Circuits and Systems (ISCAS), Publisher: IEEE, Pages: 641-644
Liu Y, Georgiou P, Constandinou TG, et al., 2009, An Auto-Offset-Removal circuit for chemical sensing based on the PG-ISFET, IEEE International Symposium on Circuits and Systems (ISCAS), Publisher: IEEE, Pages: 1165-1168
Constandinou TG, Georgiou J, 2008, A Micropower Tilt Processing Circuit, IEEE Biomedical Circuits and Systems (BioCAS) Conference, Publisher: IEEE, Pages: 197-200
This paper describes a novel analogue circuit for extracting the tilt angle from the output of a standard MEMS accelerometer. The circuit uses the accelerometer signal together with the gravitational acceleration vector to generate the tilt signal. Using a current-mode representation with devices operated in subthreshold, the appropriate trigonometric function has been realised to compute tilt. Furthermore, implementing a long-time constant filter to extract the mean tilt level provides adaptation to the static tilt level. Specifically, this circuit has been designed as part of an implantable vestibular prosthesis to provide inclination signals for bypassing dysfunctional otolith end-organs. The hardware has been implemented in AMS 0.35 mum 2P4M CMOS technology.
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