Browsing by Subject "OTA"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Design techniques for high intermediate frequency bandpass (sigma/delta) modulator.(Texas A&M University, 2008-10-10) Kode, PraveenaThe focus of the present thesis is the circuit-level implementation of an excess loop delay compensation scheme which optimizes excess loop delay in Analog-to-Digital Converter(ADC) by using a programmable delay block and synchronizes the signal passing through Dynamic Element Matching block, used to mitigate mismatch effects of multi-bit Digital-to-Analog Converter(DAC). The proposed delay block has tuning range of T/10 to T/2 seconds, with a step size of T/30 seconds, where T is the time period (1.25 nanoseconds) of sampling signal (800 MHz) in high IF (200 MHz) Bandpass [sigma delta] ADC. The implementation details of the element rotation scheme used to calibrate the multi-bit DAC static error mismatch are also presented. Also presented is the design of high frequency highly linear Operational Transconductance Amplifier(OTA) targeted for continuous-time filters in a high resolution High Intermediate Frequency (200 MHz) Bandpass [sigma delta] ADC for Software Radio applications. Proposed OTA uses super source follower input stage to enhance its voltage-to-current conversion linearity. The design has been simulated using TSMC 0.18 ?m CMOS process. The OTA has small signal transconductance of 0.9 mA/V, IM3 below -79 dB (for 0.3 Vpp input), Signal-to-Noise Ratio of 82 dB and power consumption of 6.8 mW, when tested in unity gain configuration.Item Nonlinearity and noise modeling of operational transconductance amplifiers for continuous time analog filters(Texas A&M University, 2006-08-16) Ramachandran, ArunA general framework for performance optimization of continuous-time OTA-C (Operational Transconductance Amplifier-Capacitor) filters is proposed. Efficient procedures for evaluating nonlinear distortion and noise valid for any filter of arbitrary order are developed based on the matrix description of a general OTA-C filter model . Since these procedures use OTA macromodels, they can be used to obtain the results significantly faster than transistor-level simulation. In the case of transient analysis, the speed-up may be as much as three orders of magnitude without almost no loss of accuracy. This makes it possible to carry out direct numerical optimization of OTA-C filters with respect to important characteristics such as noise performance, THD, IM3, DR or SNR. On the other hand, the general OTA-C filter model allows us to apply matrix transforms that manipulate (rescale) filter element values and/or change topology without changing its transfer function. The above features are a basis to build automated optimization procedures for OTA-C filters. In particular, a systematic optimization procedure using equivalence transformations is proposed. The research also proposes suitable software implementations of the optimization process. The first part of the research proposes a general performance optimization procedure and to verify the process two application type examples are mentioned. An application example of the proposed approach to optimal block sequencing and gain distribution of 8th order cascade Butterworth filter (for two variants of OTA topologies) is given. Secondly the modeling tool is used to select the best suitable topology for a 5th order Bessel Low Pass Filter. Theoretical results are verified by comparing to transistor-level simulation withCADENCE. For the purpose of verification, the filters have also been fabricated in standard 0.5mm CMOS process. The second part of the research proposes a new linearization technique to improve the linearity of an OTA using an Active Error Feedforward technique. Most present day applications require very high linear circuits combined with low noise and low power consumption. An OTA based biquad filter has also been fabricated in 0.35mm CMOS process. The measurement results for the filter and the stand alone OTA have been discussed. The research focuses on these issues.