Matching Items (7)

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Design of a modified Cherry-Hooper transimpedance amplifier with DC offset cancellation

Description

Optical receivers have many different uses covering simple infrared receivers, high speed fiber optic communication and light based instrumentation. All of them have an optical receiver that converts photons to

Optical receivers have many different uses covering simple infrared receivers, high speed fiber optic communication and light based instrumentation. All of them have an optical receiver that converts photons to current followed by a transimpedance amplifier to convert the current to a useful voltage. Different systems create different requirements for each receiver. High speed digital communication require high throughput with enough sensitivity to keep the bit error rate low. Instrumentation receivers have a lower bandwidth, but higher gain and sensitivity requirements. In this thesis an optical receiver for use in instrumentation in presented. It is an entirely monolithic design with the photodiodes on the same substrate as the CMOS circuitry. This allows for it to be built into a focal-plane array, but it places some restriction on the area. It is also designed for in-situ testing and must be able to cancel any low frequency noise caused by ambient light. The area restrictions prohibit the use of a DC blocking capacitor to reject the low frequency noise. In place a servo loop was wrapped around the system to reject any DC offset. A modified Cherry-Hooper architecture was used for the transimpedance amplifier. This provides the flexibility to create an amplifier with high gain and wide bandwidth that is independent of the input capacitance. The downside is the increased complexity of the design makes stability paramount to the design. Another drawback is the high noise associated with low input impedance that decouples the input capacitance from the bandwidth. This problem is compounded by the servo loop feed which leaves the output noise of some amplifiers directly referred to the input. An in depth analysis of each circuit block's noise contribution is presented.

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  • 2011

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Digitally controlled DC-DC buck converters with lossless current sensing

Description

Current sensing ability is one of the most desirable features of contemporary current or voltage mode controlled DC-DC converters. Current sensing can be used for over load protection, multi-stage converter

Current sensing ability is one of the most desirable features of contemporary current or voltage mode controlled DC-DC converters. Current sensing can be used for over load protection, multi-stage converter load balancing, current-mode control, multi-phase converter current-sharing, load independent control, power efficiency improvement etc. There are handful existing approaches for current sensing such as external resistor sensing, triode mode current mirroring, observer sensing, Hall-Effect sensors, transformers, DC Resistance (DCR) sensing, Gm-C filter sensing etc. However, each method has one or more issues that prevent them from being successfully applied in DC-DC converter, e.g. low accuracy, discontinuous sensing nature, high sensitivity to switching noise, high cost, requirement of known external power filter components, bulky size, etc. In this dissertation, an offset-independent inductor Built-In Self Test (BIST) architecture is proposed which is able to measure the inductor inductance and DCR. The measured DCR enables the proposed continuous, lossless, average current sensing scheme. A digital Voltage Mode Control (VMC) DC-DC buck converter with the inductor BIST and current sensing architecture is designed, fabricated, and experimentally tested. The average measurement errors for inductance, DCR and current sensing are 2.1%, 3.6%, and 1.5% respectively. For the 3.5mm by 3.5mm die area, inductor BIST and current sensing circuits including related pins only consume 5.2% of the die area. BIST mode draws 40mA current for a maximum time period of 200us upon start-up and the continuous current sensing consumes about 400uA quiescent current. This buck converter utilizes an adaptive compensator. It could update compensator internally so that the overall system has a proper loop response for large range inductance and load current. Next, a digital Average Current Mode Control (ACMC) DC-DC buck converter with the proposed average current sensing circuits is designed and tested. To reduce chip area and power consumption, a 9 bits hybrid Digital Pulse Width Modulator (DPWM) which uses a Mixed-mode DLL (MDLL) is also proposed. The DC-DC converter has a maximum of 12V input, 1-11 V output range, and a maximum of 3W output power. The maximum error of one least significant bit (LSB) delay of the proposed DPWM is less than 1%.

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  • 2011

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Digitally controlled average current mode buck converter

Description

During the past decade, different kinds of fancy functions are developed in portable electronic devices. This trend triggers the research of how to enhance battery lifetime to meet the requirement

During the past decade, different kinds of fancy functions are developed in portable electronic devices. This trend triggers the research of how to enhance battery lifetime to meet the requirement of fast growing demand of power in portable devices. DC-DC converter is the connection configuration between the battery and the functional circuitry. A good design of DC-DC converter will maximize the power efficiency and stabilize the power supply of following stages. As the representative of the DC-DC converter, Buck converter, which is a step down DC-DC converter that the output voltage level is smaller than the input voltage level, is the best-fit sample to start with. Digital control for DC-DC converters reduces noise sensitivity and enhances process, voltage and temperature (PVT) tolerance compared with analog control method. Also it will reduce the chip area and cost correspondingly. In battery-friendly perspective, current mode control has its advantage in over-current protection and parallel current sharing, which can form different structures to extend battery lifetime. In the thesis, the method to implement digitally average current mode control is introduced; including the FPGA based digital controller design flow. Based on the behavioral model of the close loop Buck converter with digital current control, the first FPGA based average current mode controller is burned into board and tested. With the analysis, the design metric of average current mode control is provided in the study. This will be the guideline of the parallel structure of future research.

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  • 2011

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A CMOS analog front-end IC for gas sensors

Description

This thesis presents a gas sensor readout IC for amperometric and conductometric electrochemical sensors. The Analog Front-End (AFE) readout circuit enables tracking long term exposure to hazardous gas fumes in

This thesis presents a gas sensor readout IC for amperometric and conductometric electrochemical sensors. The Analog Front-End (AFE) readout circuit enables tracking long term exposure to hazardous gas fumes in diesel and gasoline equipments, which may be correlated to diseases. Thus, the detection and discrimination of gases using microelectronic gas sensor system is required. This thesis describes the research, development, implementation and test of a small and portable based prototype platform for chemical gas sensors to enable a low-power and low noise gas detection system. The AFE reads out the outputs of eight conductometric sensor array and eight amperometric sensor arrays. The IC consists of a low noise potentiostat, and associated 9bit current-steering DAC for sensor stimulus, followed by the first order nested chopped £U£G ADC. The conductometric sensor uses a current driven approach for extracting conductance of the sensor depending on gas concentration. The amperometric sensor uses a potentiostat to apply constant voltage to the sensors and an I/V converter to measure current out of the sensor. The core area for the AFE is 2.65x0.95 mm2. The proposed system achieves 91 dB SNR at 1.32 mW quiescent power consumption per channel. With digital offset storage and nested chopping, the readout chain achieves 500 fÝV input referred offset.

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  • 2011

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Cost-effective integrated wireless monitoring of wafer cleanliness using SOI technology

Description

The thesis focuses on cost-efficient integration of the electro-chemical residue sensor (ECRS), a novel sensor developed for the in situ and real-time measurement of the residual impurities left on the

The thesis focuses on cost-efficient integration of the electro-chemical residue sensor (ECRS), a novel sensor developed for the in situ and real-time measurement of the residual impurities left on the wafer surface and in the fine structures of patterned wafers during typical rinse processes, and wireless transponder circuitry that is based on RFID technology. The proposed technology uses only the NMOS FD-SOI transistors with amorphous silicon as active material with silicon nitride as a gate dielectric. The proposed transistor was simulated under the SILVACO ATLAS Simulation Framework. A parametric study was performed to study the impact of different gate lengths (6 μm to 56 μm), electron motilities (0.1 cm2/Vs to 1 cm2/Vs), gate dielectric (SiO2 and SiNx) and active materials (a-Si and poly-Si) specifications. Level-1 models, that are accurate enough to acquire insight into the circuit behavior and perform preliminary design, were successfully constructed by analyzing drain current and gate to node capacitance characteristics against drain to source and gate to source voltages. Using the model corresponding to SiNx as gate dielectric, a-Si:H as active material with electron mobility equal to 0.4 cm2/V-sec, an operational amplifier was designed and was tested in unity gain configuration at modest load-frequency specifications.

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  • 2010

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Design of a continuous time sigma delta analog-to-digital converter for operation in extreme environments

Description

In this work, a high resolution analog-to-digital converter (ADC) for use in harsh environments is presented. The ADC is implemented in bulk CMOS technology and is intended for space exploration,

In this work, a high resolution analog-to-digital converter (ADC) for use in harsh environments is presented. The ADC is implemented in bulk CMOS technology and is intended for space exploration, mining and automotive applications with a range of temperature variation in excess of 250°C. A continuous time (CT) sigma delta modulator employing a cascade of integrators with feed forward (CIFF) architecture in a single feedback loop topology is used for implementing the ADC. In order to enable operation in the intended application environments, an RC time constant tuning engine is proposed. The tuning engine is used to maintain linearity of a 10 ksps 20 bit continuous time sigma delta ADC designed for spectroscopy applications in space. The proposed circuit which is based on master slave architecture automatically selects on chip resistors to control RC time constants to an accuracy range of ±5% to ±1%. The tuning range, tuning accuracy and circuit non-idealities are analyzed theoretically. To verify the concept, an experimental chip was fabricated in JAZZ .18µm 1.8V CMOS technology. The tuning engine which occupies an area of .065mm2; consists of only an integrator, a comparator and a shift register. It can achieve a signal to noise and distortion ratio (SNDR) greater than 120dB over a ±40% tuning range.

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Date Created
  • 2011

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Effects of low-temperature operation on the performance of MOSFETs

Description

The existing compact models can reproduce the characteristics of MOSFETs in the temperature range of -40oC to 125oC. Some applications require circuits to operate over a wide temperature range consisting

The existing compact models can reproduce the characteristics of MOSFETs in the temperature range of -40oC to 125oC. Some applications require circuits to operate over a wide temperature range consisting of temperatures below the specified range of existing compact models, requiring wide temperature range compact models for the design of such circuits. In order to develop wide temperature range compact models, fourteen different geometries of n-channel and p-channel MOSFETs manufactured in a 0.18μm mixed-signal process were electrically characterized over a temperature range of 40 K to 298 K. Electrical characterization included ID-VG and ID-VD under different drain, body and gate biases respectively. The effects of low-temperature operation on the performance of 0.18μm MOSFETs have been studied and discussed in terms of sub-threshold characteristics, threshold voltage, the effect of the body bias and linearity of the device. As it is well understood, the subthreshold slope, the threshold voltage, drive currents of the MOSFETs increase when the temperature of the MOSFETs is lowered, which makes it advantageous to operate the MOSFETs at low-temperatures. However the internal linearity gm1/gm3 of the MOSFETs degrades as the temperature of the MOSFETs is lowered, and the performance of the MOSFETs can be affected by the interface traps that exist in higher density close to conduction band and valence band energy levels, as the Fermi-level moves closer to bandgap edges when MOSFETs are operated at cryogenic temperatures.

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Date Created
  • 2010