EE 435 Lect 27 Spring 2010

EE 435 Lect 27 Spring 2010 - EE 435 Lecture 27 Data...

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EE 435 Lecture 27 Data Converters • Differential Nonlinearity • Spectral Performance
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Performance Characterization of Data Converters • Static characteristics – Resolution – Least Significant Bit (LSB) – Offset and Gain Errors – Absolute Accuracy – Relative Accuracy – Integral Nonlinearity (INL) – Differential Nonlinearity (DNL) – Monotonicity (DAC) – Missing Codes (ADC) – Low-f Spurious Free Dynamic Range (SFDR) – Low-f Total Harmonic Distortion (THD) – Effective Number of Bits (ENOB) – Power Dissipation .• • • Review from last lecture .•
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Integral Nonlinearity (DAC) Nonideal DAC IN X G C 0 C 1 C 2 C 3 C 4 C 5 C 6 C 7 X REF INL X OUT • At design stage, INL characterized by standard deviation of the random variable • Closed-form expressions for INL almost never exist because PDF of order statistics of correlated random variables is extremely complicated • Simulation of INL very time consuming if n is very large (large sample size required to establish reasonable level of confidence) Model parameters become random variables Process parameters affect multiple model parameters causing model parameter correlation Simulation times can become very large • INL can be readily measured in laboratory but often dominates test costs because of number of measurements needed when n is large • Expected of INL k at k=(N-1)/2 is largest for many architectures • Major effort in DAC design is in obtaining acceptable yield ! .• • • Review from last lecture .•
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Integral Nonlinearity (ADC) Nonideal ADC IN ± X ( ) INF IN X X With this definition of INL, the INL of an ideal ADC is X LSB /2 (for X T1 = X LSB ) This is effective at characterizing the overall nonlinearity of the ADC but does not vanish when the ADC is ideal and the effects of the breakpoints is not explicit .• • • Review from last lecture .•
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Integral Nonlinearity (ADC) Nonideal ADC X IN OUT X G X REF C 0 C 1 C 2 C 3 C 4 C 5 C 6 C 7 X T1 X T2 X T3 X T4 X T5 X T6 X T7 X IN X FT1 X FT2 X FT3 X FT4 X FT5 X FT6 X FT7 INL 3 Break-point INL definition { } max k 2kN - 2 INL INL ≤ ≤ = Often expressed in LSB 1 Tk FTl k LSB - INL = k N-2 ≤≤ XX X For an ideal ADC, INL is ideally 0 .• • • Review from last lecture .•
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INL-based ENOB Consider initially the continuous INL definition for an ADC where the INL of an ideal ADC is X LSB /2 Assume Define the LSB by EQ REF LSB n = 2 X X Thus EQ n LSB INL= θ 2X Since an ideal ADC has an INL of X LSB /2, express INL in terms of ideal ADC 1) 2 EQ (n LSB X INL= θ 2 + ⎛⎞ ⎡⎤ ⎜⎟ ⎢⎥ ⎣⎦ ⎝⎠ Setting term in [ ] to 1, can solve for n EQ to obtain () EQ 2 R 2 1 ENOB = n = log n -1-log 2 θ υ = REF LSBR INL= θ X = X where X LSBR is the LSB based upon the defined resolution where n R is the defined resolution .• • • Review from last lecture .•
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INL-based ENOB () R2 ENOB = n -1-log υ ν ENOB ½n 1n - 1 2n - 2 4n - 3 8n - 4 16 n-5 Consider an ADC with specified resolution of n R and INL of ν LSB .• • • Review from last lecture .•
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Manufacturers of Catalog Data Converter Components
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This note was uploaded on 01/31/2012 for the course EE 345 taught by Professor Geiger during the Fall '11 term at Iowa State.

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EE 435 Lect 27 Spring 2010 - EE 435 Lecture 27 Data...

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