Browsing by Subject "Operational amplifiers"
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Item A fully differential CMOS operational amplifier implemented with MOS gain boosting technique(Texas Tech University, 1996-05) Lo, PingThis thesis investigates the gain boosting technique proposed by K.Bult and G. Geelen [9]. An improved cascode circuit that combines both high gain and high speed is developed. Using this cascode circuit, a high performance fully differential operational amplifier is designed. A prototype of the cascode circuit and operational amplifier was fabricated in a 2 |im n-well CMOS technology. Simulation results indicate that the cascode circuit has at least 100 MQ output impedance, while the amplifier has an open loop gain of 98 dB and a unity gain frequency of 17 MHz for 10 pF load capacitor.Item Low-power techniques for high-performance pipelined analog to digital converter(2007) Lee, Byung-geun, 1973-; Valvano, Jonathan W., 1953-Low-power and small size analog to digital converters (ADCs) are the strategic building blocks in state of the art mobile wireless communication systems. Various techniques have been developed to reduce both power consumption and die area of the ADC. Among these, the opamp-sharing technique shows the most promise. In opamp-sharing, power and die area are saved by sharing one opamp between two successive pipeline stages. However, this technique suffers from the well-known memory effect drawback due to the absence of the reset phase that discharges the opamp's input parasitics. In this dissertation, this drawback is solved by introducing a discharge phase before the opamp is used for the pipeline stages without compromising speed and resolution of the ADC. Further power and area reduction is achieved by using a capacitor-sharing technique. This technique reduces the effective load capacitance of the opamp by reusing the charge on the feedback capacitor for the MDAC operation of the following stage, resulting in faster settling without increasing opamp power. The proposed low input-capacitance variable-gm opamp also helps to reduce the memory effect and improves the settling behavior of the stage output by increasing the bandwidth of the opamp while input parasitics of the opamp are kept small. The prototype designs of a 10-bit 50MSample/s pipelined ADC and a 14-bit 100MSample/s pipelined ADC implemented in 0.18¹m CMOS technology demonstrate the effectiveness of the proposed techniques. The first ADC achieves 56.2dB SNDR and 72.7dB SFDR for a Nyquist input at full sampling rate while consuming 12 mW from a 1.8-V supply. The FOM, defined as, [power/2[superscript ENOB].Fs], is 0.46 pJ/step with Fin = 24.5MHz at 50MS/s. The second ADC achieves 72.4dB SNR and 88.5dB SFDR at 100MS/s with a 46MHz input and consumes 230mW from a 3V supply. The FOM of the second ADC is 0.69 pJ/step with Fin = 46MHz at 100MS/s.Item Study of operational amplifiers' characteristics for driving the inputs of high performance successive approximation register analog-to-digital converters(Texas Tech University, 2003-08) Lewis, Damian PThis study deals with the requirement for driving the inputs of SAR ADCs used in data acquisition systems. The goal of the study is to develop an analysis technique for selecting amplifiers to drive the inputs of single supply, low power SAR ADCs. One of the conditions is that the amplifier selected must be capable of operating on the same power supply as the SAR ADC. The background and work directed towards achieving the above mentioned goal is outlined in the six chapters of this paper. The first chapter gives an overview of data acquisition systems and ADCs in data acquisition systems. The second chapter discusses the operation of CD AC capacitor array for unipolar, bipolar, differential, and single-ended SAR ADCs. The third chapter goes through the requirements of the SAR ADC and an analysis of operational amplifier's parameters and their required values. The fourth chapter shows how to simulate the selected operational amplifier's performance using Pspice. The fifth chapter describes empirical tests characterizing the amplifier's performance. The last chapter is the analysis of the data, conclusion, and recommendation.