Thomas Jacob Koickal

Combined smart chemFET/resistive sensor array

Here we describe a novel CMOS compatible gas sensor array based on a combined resistive/chemFET sensor cell. We have fabricated an array of 70 sensors with integrated drive, gain and baseline removal circuitry using an AMS 0.6 /spl mu/m CMOS process. The sensing materials are carbon black/polymer composite (CB) thin films, which have been previously reported to have good vapour-sensing properties. Different CB films have been deposited onto the sensor array and have been shown to respond differently to volatile organic compounds. This combined sensing element both reduces silicon area and, more importantly, measures different physical properties of the same gas sensitive material improving discrimination and giving more insight into the sensing mechanism.

A Bio-Realistic Analog CMOS Cochlea Filter With High Tunability and Ultra-Steep Roll-Off

This paper presents the design and experimental results of a cochlea filter in analog very large scale integration (VLSI) which highly resembles physiologically measured response of the mammalian cochlea. The filter consists of three specialized sub-filter stages which respectively provide passive response in low frequencies, actively tunable response in mid-band frequencies and ultra-steep roll-off at transition frequencies from pass-band to stop-band. The sub-filters are implemented in balanced ladder topology using floating active inductors. Measured results from the fabricated chip show that wide range of mid-band tuning including gain tuning of over 20dB, Q factor tuning from 2 to 19 as well as the bio-realistic center frequency shift are achieved by adjusting only one circuit parameter. Besides, the filter has an ultra-steep roll-off reaching over 300 dB/dec. By changing biasing currents, the filter can be configured to operate with center frequencies from 31 Hz to 8 kHz. The filter is 9th order, consumes 59.5 ~ 90.0 μW power and occupies 0.9 mm2 chip area. A parallel bank of the proposed filter can be used as the front-end in hearing prosthesis devices, speech processors as well as other bio-inspired auditory systems owing to its bio-realistic behavior, low power consumption and small size.

An Asynchronous Spike Event Coding Scheme for Programmable Analog Arrays

This paper presents a spike event coding scheme for the communication of analog signals in programmable analog arrays. In the scheme presented here no events are transmitted when the signals are constant leading to low power dissipation and traffic reduction in analog arrays. The design process and the implementation of the scheme in a programmable array context are explained. The validation of the presented scheme is performed using a speech signal. Finally, we demonstrate how the event coded scheme can perform summation of analog signals without additional hardware.

Low frequency tantalum electromechanical systems for biomimetical applications

The integration of p-channel metal-oxide-semiconductor transistors and tantalum bridge structures for the fabrication of resonant gate transistors (RGTs) that operate in the audible frequency range has been developed. Resonant gate transistors with channel length of 15 μm and clamped-clamped tantalum bridges of 0.5 mm to 1.6 mm in length have been fabricated. The measured first modal frequency of the bridges has been found to be higher than the expected theoretical value. From the experimental and theoretical analysis of the first three modes, the stress in the bridges has been extracted and found to be tensile with values of 3 MPa – 10 MPa. Finite element simulation has validated the extracted stress and the mode shapes of the tantalum bridges. The modulation of conductance in the channel region between the source and drain by the tantalum bridge of the RGT has been demonstrated. The threshold voltage and transconductance of the fabricated p-channel RGT have been measured to be −37 V and 6.84 μS, respect...

Microelectromechanical systems for biomimetical applications

An etch release process capable of releasing long resonant gate transistor bridges from a sacrificial layer has been studied as a step towards developing a system to mimic the cochlear mechanism inside the human ear. The developed etch release process involves the use of a gentle etch tool that is capable of a clean and damage-free etch release. The influence of temperature and oxygen/nitrogen gas flow rates on the undercut etch rates and the profiles of photoresist and polyimide sacrificial layers have been investigated. An array of aluminum bridges of length 0.278–1.618 mm, which cover the frequencies from 1 to 33.86 kHz, has been designed and released from a sacrificial layer. The resonating beams have been measured.

Silicon-based Neuromorphic Implementation of the Olfactory Pathway

Here we describe the component subsystems which comprise the first silicon-based olfactory system, each implemented in analog VLSI/MEMS. These include a biologically constrained neuronal model, chemical micro-sensor array and associated interface circuitry. We present a spiking olfactory bulb model, a reduced 70 element broadly-tuned chemosensor array (25 different chemsensor tunings), alongside details of their silicon implementation. Our results show that the olfactory bulb model is capable of pattern classification and that the odour delivery, uptake and sensor circuitry, as well as the fundamental units of the neuromorphic model (spike-driven synapse and spiking soma), are all functional. Work will continue towards completing a fully-integrated and scalable silicon implementation of the olfactory system

Design of a spike event coded RGT microphone for neuromorphic auditory systems

This paper presents the design of a spike event coded resonant gate transistor microphone system for neuromorphic auditory applications. The microphone system employs an array of resonant gate transistors (RGT) to transduce acoustic input directly into bandpass filtered analog outputs. The bandpass filtered analog outputs are encoded as spike time events by a spike event coder and are then transmitted asynchronously by using the Address Event Representation (AER) protocol. The microphone system is designed to receive external inputs in the spike time domain to actively control the RGT response, a feature not present in other MEMS microphone systems implemented so far. System level simulations showing the response of the RGT sensor model and its spike event coded response are presented.

Smart Interface Circuit to Ameliorate Loss of Measurement Range in Chemical Microsensor Arrays

A programmable analog sensor interface integrated with an array of heterogeneous chemical FET/resistive sensors is presented. The sensory interface primarily addresses the problem of loss of measurement range due to large variations in baseline signals among sensors in the array. A circuit is proposed to cancel the baseline signals in the sensor array leading to improved measurement resolution. An integrated sensory array and interface electronics chip is fabricated and tested to perform odour analysis

A Power-Efficient Capacitive Read-Out Circuit With Parasitic-Cancellation for MEMS Cochlea Sensors

This paper proposes a solution for signal read-out in the MEMS cochlea sensors that have very small sensing capacitance and do not have differential sensing structures. The key challenge in such sensors is the significant signal degradation caused by the parasitic capacitance at the MEMS-CMOS interface. Therefore, a novel capacitive read-out circuit with parasitic-cancellation mechanism is developed; the equivalent input capacitance of the circuit is negative and can be adjusted to cancel the parasitic capacitance. Chip results prove that the use of parasitic-cancellation is able to increase the sensor sensitivity by 35 dB without consuming any extra power. In general, the circuit follows a low-degradation low-amplification approach which is more power-efficient than the traditional high-degradation high-amplification approach; it employs parasitic-cancellation to reduce the signal degradation and therefore a lower gain is required in the amplification stage. Besides, the chopper-stabilization technique is employed to effectively reduce the low-frequency circuit noise and DC offsets. As a result of these design considerations, the prototype chip demonstrates the capability of converting a 7.5 fF capacitance change of a 1-Volt-biased 0.5 pF capacitive sensor pair into a 0.745 V signal-conditioned output at the cost of only 165.2 μW power consumption.

An asynchronous spike event coding scheme for programmable analog arrays

This paper presents a spike time event coding scheme for transmission of analog signals between configurable analog blocks (CABs) in a programmable analog array. The analog signals from CABs are encoded as spike time instants dependent upon input signal activity and are transmitted asynchronously by employing the address event representation protocol (AER), a widely used communication protocol in neuromorphic systems. Power dissipation is dependent upon input signal activity and no spike events are generated when the input signal is constant. Computation is intrinsic to the spike event coding scheme and is performed without additional hardware. The ability of the communication scheme to perform computation will enhance the computation power of the programmable analog array. The design methodology and analog circuit design of the scheme are presented. Test results from prototype chips implemented using a 3.3-V, 0.35-μm CMOS technology are presented.