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Optimization of Capacitor Based DAC  

Authors
 Rybakov A.A.
 Shliakhova N.F.
Date of publication
 2018
DOI
 10.31114/2078-7707-2018-4-82-87

Abstract
 The capacitor matrix makes a significant contribution to the SAR ADC conversion error realized by capacitor based DAC. Reducing the influence of imperfections on the accuracy of conversion is achieve by the optimal arrangement of the matrix elements on the chip. The criterion of optimality is the objective function Τ, which takes into account the influence of two types of non-idealities (systematic and random errors), while reducing the number of metals used for wiring between pairs of adjacent vertical columns of the matrix. The search for optimal locations is carried out automatically according to the algorithm implemented in the C++ programming language. The optimal criterion is the objective function Φ, which takes into account the influence of two types of non-idealities (systematic and random errors), while reducing the number of metals used for wiring between pairs of neighboring vertical columns of the matrix. The systematic error is due to the presence of oxide thickness gradients and is minimized using a simple integrated model. A random error caused by local and global variations in the edges of the capacitor, the oxide thickness and its dielectric constant, and is minimized by increasing the overall correlation coefficient. Also, the error caused by the parasitic capacitances arising between the upper and lower plates of the DAC capacitors is minimized due to using the "interdigital" metallization rule. Based on the simulation results, the value of the discrepancy factor L is improved by 30% and overall correlation coefficient R is improved by 0.25% compared with the typical topology of the matrix. The proposed method provides a simplified search for the best arrangement of the elements of the capacitors matrix in which the total error is minimal.
Keywords
 SAR ADC, capacitor based DAC, oxide-gradient-induced mismatch, overall correlation coefficient.
Library reference
 Rybakov A.A., Shliakhova N.F. Optimization of Capacitor Based DAC // Problems of Perspective Micro- and Nanoelectronic Systems Development - 2018. Issue 4. P. 82-87. doi:10.31114/2078-7707-2018-4-82-87
URL of paper
 http://www.mes-conference.ru/data/year2018/pdf/D011.pdf

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