Design of a CMOS Potentiostat Circuit for Electrochemical Detector Arrays

High-throughput electrode arrays are required for advancing devices for testing the effect of drugs on cellular function. In this paper, we present design criteria for a potentiostat circuit that is capable of measuring transient amperometric oxidation currents at the surface of an electrode with submillisecond time resolution and picoampere current resolution. The potentiostat is a regulated cascode stage in which a high-gain amplifier maintains the electrode voltage through a negative feedback loop. The potentiostat uses a new shared amplifier structure in which all of the amplifiers in a given row of detectors share a common half circuit permitting us to use fewer transistors per detector. We also present measurements from a test chip that was fabricated in a 0.5-mum, 5-V CMOS process through MOSIS. Each detector occupied a layout area of 35 mumtimes15 mum and contained eight transistors and a 50-fF integrating capacitor. The rms current noise at 2-kHz bandwidth is ap110 fA. The maximum charge storage capacity at 2 kHz is 1.26times10⁶ electrons     

A physical compact model of DG MOSFET for mixed-signal circuit applications- part I: model description

To use double-gate (DG) MOSFET for mixed-signal circuit applications, especially for circuits in which the two gates are independently driven, such as in the case of dynamic-threshold and fixed-potential-plane operations, physical compact models that are valid for all modes of operations are necessary for accurate design and analysis. Employing physically rigorous current-voltage (I-V) relationship in subthreshold and above-threshold regions as asymptotic cases, we have constructed a model that joins the two operating regions by using carrier-screening functions. We have included consistently source/drain series resistance, low drain-field mobility, and small-geometry effects of drain-induced barrier lowering (DIBL), MOS interface mobility, velocity saturation and channel-length modulation (CLM) with validation from two-dimensional (2-D) distributed simulation. All model parameters can be extracted from large-signal I-V characteristics in dc conditions with given geometrical data. Parameter extraction methods and verification from simulation are presented in Part II.     

A floating-gate MOS learning array with locally computed weightupdates

We have demonstrated on-chip learning in an array of floating-gate MOS synapse transistors. The array comprises one synapse transistor at each node, and normalization circuitry at the row boundaries. The array computes the inner product of a column input vector and a stored weight matrix. The weights are stored as floating-gate charge; they are nonvolatile, but can increase when we apply a row-learn signal. The input and learn signals are digital pulses; column input pulses that are coincident with row-learn pulses cause weight increases at selected synapses. The normalization circuitry forces row synapses to compete for floating-gate charge, bounding the weight values. The array simultaneously exhibits fast computation and slow adaptation: The inner product computes in 10 μs, whereas the weight normalization takes minutes to hours     

A Complementary Pair of Four-Terminal Silicon Synapses

We have developed a complementary pair of pFETand nFET floating-gate silicon MOS transistors foranalog learning applications. The memory storage is nonvolatile;hot-electron injection and electron tunneling permit bidirectionalmemory updates. Because these updates depend on both the storedmemory value and the transistor terminal voltages, the synapsescan implement a learning function. We have derived a memory-updaterule for both devices, and have shown that the synapse learningfollows a simple power law. Unlike conventional EEPROMs, thesynapses allow simultaneous memory reading and writing. Synapsetransistor arrays can therefore compute both the array output,and local memory updates, in parallel. We have fabricated prototypesynaptic arrays; because the tunneling and injection processesare exponential in the transistor terminal voltages, the writeand erase isolation between array synapses is better than 0.01 percentThe synapses are small, and typically are operated at subthresholdcurrent levels; they will permit the development of dense, low-powersilicon learning systems.     

Whey beverages decrease blood pressure in prehypertensive and hypertensive young men and women

Whey protein beverages reduced blood pressure in young men and women in a six week controlled intervention. There were no differences in systolic blood pressure (SBP), diastolic blood pressure (DBP), or mean arterial pressure (MAP) observed between groups consuming 28 g per day of either hydrolyzed or non-hydrolyzed whey protein in a beverage. However, in young adults with elevated DBP and SBP, whey beverage consumption significantly decreased SBP, DBP, and MAP by 8.0, 8.6, and 6.4 mm Hg, respectively (P ≤ 0.001 for all comparisons). In subjects with elevated SBP only, SBP significantly decreased by 3.8 mm Hg (P ≤ 0.04) after the whey beverage intervention. Subjects with normal blood pressure had no change in SBP, DBP, and MAP. Whey beverages also significantly decreased total and low-density lipoprotein cholesterol concentrations (P ≤ 0.001 and 0.05, respectively). Whey protein beverages may be useful for the dietary treatment of prehypertension and/or stage 1 hypertension.     

Theory and experiment on the amplified spontaneous emission fromdistributed-feedback lasers

The amplified spontaneous emission (ASE) of a strained quantum-well distributed feedback (DFB) laser biased below laser threshold is used to extract the gain and refractive index spectra in a systematic manner. A modified Hakki-Paoli method is used to obtain the gain and differential gain spectra. The refractive index change due to carrier injection is obtained from the shift of the Fabry-Perot peaks in the ASE spectrum. The measured ASE spectrum, gain, refractive index change, and linewidth enhancement factor are then compared with our theoretical model for strained quantum-well lasers. Our model takes into account the realistic band structure and uses the material and quantum-well dimensions directly in the calculation of the electronic and optical properties. The theory agrees very well with the experiment     

Charge-based chemical sensors: a neuromorphic approach with chemoreceptive neuron MOS (C/spl nu/MOS) transistors

A novel chemoreceptive neuron MOS (C/spl nu/MOS) transistor with an extended floating-gate structure has been designed with several individual features that significantly facilitate system integration of chemical sensing. We have fabricated C/spl nu/MOS transistors with generic molecular receptive areas and have characterized them with various fluids. We use an insulating polymer layer to provide physical and electrical isolation for sample fluid delivery. Experimental results from these devices have demonstrated both high sensitivity via current differentiation and large dynamic range from threshold voltage shifts in sensing both polar and electrolytic liquids. We have established electrochemical models for both steady-state and transient analyses. Our preliminary measurement results have confirmed the basic design and operations of these devices, which show potential for developing silicon olfactory and gustatory units that are fully compatible with current CMOS technology.     

Implementing the Lorenz oscillator with translinear elements

Nonlinear processing is often more suitable than the traditional linear approach is for analyzing biological signals. Unfortunately, digital nonlinear operations are computationaly expensive. In contrast, a large variety of nonlinear operations can efficiently be implemented in analog electronics, operating at real-time speeds. The low level of accuracy generally associated with analog processing is not a concern in this scenario, as biological signals themselves typically have low signal-to-noise ratios. One challenge of analog processing is in its apparently-ad hoc design, and the fact that there is very little wide-spread knowledge of systematically implementing analog electronics to perform arbitrary nonlinear computations. Another issue is the integrity of the analog components; the analog properties of electronic devices are prone to a large amount of mismatch. In this paper, we examine multiple-input translinear element (MITE) networks, a class of analog circuits that addresses the two concerns of a structured synthesis procedure and component mismatch. We test the ability of these MITE networks for accurately realizing linear and nonlinear systems with prescribed dynamics by attempting to implement the Lorenz equations. We will present the theoretical procedure, address practical implementation issues, and then show experimental results from a version of the circuit fabricated in a 0.5 μm CMOS technology through MOSIS.     

Paleolithic and Neolithic lineages in the European mitochondrial gene pool

PURPOSE: This article presents a new optimization method for stereotactic radiosurgery treatment planning for gamma unit treatment system. METHODS AND MATERIALS: The gamma unit has been utilized in stereotactic radiosurgery for about 30 years, but the usual procedure for a physician-physicist team to design a treatment plan is a trial-and-error approach. Isodose curves are viewed on two-dimensional computed tomography (CT) or magnetic resonance (MR) image planes, which is not only time consuming but also seldom achieves the optimal treatment plan, especially when the isocenter weights are regarded. We developed a treatment-planning system on a computer workstation in which Powell's optimization method is realized. The optimization process starts with the initial parameters (the number of isocenters as well as corresponding 3D isocenters' coordinates, collimator sizes, and weight factors) roughly determined by the physician-physicist team. The objective function can be changed to consider protection of sensitive tissues. RESULTS: We use the plan parameters given by a well-trained physician-physicist team, or ones that the author give roughly as the initial parameters for the optimization procedure. Dosimetric results of optimization show a better high dose-volume conformation to the target volume compared to the doctor's plan. CONCLUSION: This method converges quickly and is not sensitive to the initial parameters. It achieves an excellent conformation of the estimated isodose curves with the contours of the target volume. If the initial parameters are varied, there will be a little difference in parameters' configuration, but the dosimetric results proved almost to be the same.