EE 435. Lecture 25. Data Converters. Architectures. Characterization

Transcription

1 EE 435 Lecture 5 Data Coverters Architectures Characterizatio

2 . eview from last lecture. Data Coverters Types: A/D (Aalog to Digital) Coverts Aalog Iput to a Digital Output D/A (Digital to Aalog) Coverts a Digital Iput to a Aalog Output A/D is the world s most widely used mixed-sigal compoet D/A is ofte icluded i a FB path of a A/D A/D ad D/A fields will remai hot idefiitely techology advaces make data coverter desig more challegig embedded applicatios desigs ofte very applicatio depedet

3 . eview from last lecture. D/A Coverters DAC C 0 C 1 C C 3 C 4 C 5 C 6 C 7 For this ideal DAC X X b b b b b OUT=X EF b -j OUT=XEF j j=1 Number of outputs gets very large for large Spacig betwee outputs is X EF / ad gets very small for large

4 . eview from last lecture. A/D Coverters Quatizatio Errors ADC X T1 =X LSB C 7 C 6 C 5 C 4 C 3 C C 1 C 0 X LSB X LSB 3X LSB 4X LSB 5X LSB 6X LSB 7X LSB ε Q X T1 X T X T3 X T4 X T5 X T6 X T7 X EF X -X Q OUT IN X T1 X T X T3 X T4 X T5 X T6 X T7 X EF -X LSB Magitude of ε Q bouded by X LSB for a ideal A/D

5 . eview from last lecture. Data Coverter Architectures ADC DAC Nyquist ate Flash Charge edistributio Pipelie Two-step ad Multi-Step Iterpolatig Algorithmic/Cyclic Successive Approximatio (egister) SA Sigle Slope / Dual Slope Subragig Folded Iterleaved Over-Sampled (Delta-Sigma) Discrete-time First-order/Higher Order Cotiuous-time Curret Steerig -strig Charge edistributio Algorithmic - (ladder) Pipelied Subragig Discrete-time First-order/Higher Order Cotiuous-time

6 . eview from last lecture. Data Coverter Architectures ADC Flash V EF V IN Thermometer to Biary Decoder

7 Data Coverter Architectures ADC Successive Approximatio egister (SA) C LK V IN V EF DAC DAC Cotroller

8 Data Coverter Architectures Charge edistributio ADC V ICOMP C -1 C - C -3 C C -4 C C C C C C C 0 S 1 f A d-1 φb d-1 φb f f A d d -1 φb -1 φb A f A d- φb d - φ B f A d-3 φb d-3 φb f A d0 φb d 0 φ B f A φ B f A V IN V EF Successive Approximatio Block f A t 1 1 ' C C QSAM VIN Ci C 0 VIN V i INC i0 i0 1 C Q V d EDIS EF i i i0 f B d -1 VCOMP=0 T CONV t Q SAM Q EDIS d - T CLK VCOMP=1 VCOMP=0 t 1 C V d V C V EF i i IN i0 d 1 i IN VEF i i0 d 0 VCOMP=1 VCOMP=0 VCOMP=1 t t

9 Data Coverter Architectures Sigle Slope ADC S S C LK V EF Itegrator V OUT V IN V E E Biary Couter c Comparator Chages States whe t T V I V dt I t V IN 0 EF 0 T EF 0 Couter stops whe VIN ttvef I0 COUNT TCLK VEF I0 COUNT V V IN f I CLK EF 0 If calibrate so that fclk I0 V IN COUNT VEF V IN COUNT V EF

10 Data Coverter Architectures DAC -Strig V FF S 1 S V OUT S N- S N-1 S N is decoded to close oe switch

11 Data Coverter Architectures DAC Curret Steerig V FF I 1 I I k S 1 S S k V OUT

12 Data Coverter Architectures DAC - (4-bits) V OUT d 3 d d 1 d 0 V EF By superpositio: d V =V d +V d +V d +V d = V V 3 4 k 4-k OUT EF 3 EF EF 1 EF 0 EF 4-k EF k k=0 k=1 d

13 Data Coverter Architectures Charge edistributio DAC C -1 C - C -3 C C -4 C C C C C C C 0 S 1 f A f B d-1 φa d-1 φa f B d-1 φa d-1 φa f B d- φ d - φ A A f B d d-3 φ -3 φa A f B d0 φa d 0 φ A φ B f A f A V OUT V EF Successive Approximatio Block 1 Q V d C SET EF i i i0 1 1 ' C C QDIS VOUT Ci C 0 VOUT V i OUTC i0 i0 f A t Q SET Q DIS T CONV f B 1 C V d V C V EF i i OUT i0 d 1 i OUT VEF i i0 t

14 Performace Characterizatio of Data Coverters ADC DAC A very large umber of parameters ( ) characterize the static performace of a ADC! Ad eve more parameters eeded to characterize the dyamic performace of a ADC A large (but much smaller) umber of parameters are ivariably used to characterize a data coverter Performace parameters of iterest deped strogly o the applicatio Very small umber of parameters of iterest i may/most applicatios Catalog data coverters are geerally iteded to satisfy a wide rage of applicatios ad thus have much more striget requiremets placd o their performace Custom applicatio-specific data coverter will geerally perform much better tha a catalog part i the same applicatio

15 Performace Characterizatio of Data Coverters Static characteristics esolutio Least Sigificat Bit (LSB) Offset ad Gai Errors Absolute Accuracy elative Accuracy Itegral Noliearity (INL) Differetial Noliearity (DNL) Mootoicity (DAC) Missig Codes (ADC) Low-f Spurious Free Dyamic age (SFD) Low-f Total Harmoic Distortio (THD) Effective Number of Bits (ENOB) Power Dissipatio

16 Performace Characterizatio of Data Coverters Dyamic characteristics Coversio Time or Coversio ate (ADC) Settlig time or Clock ate (DAC) Samplig Time Ucertaity (aperture ucertaity or aperture jitter) Dyamic age Spurious Free Dyamic age (SFD) Total Harmoic Distortio (THD) Sigal to Noise atio (SN) Sigal to Noise ad Distortio atio (SND) Sparkle Characteristics Effective Number of Bits (ENOB)

17 Dyamic characteristics Degradatio of dyamic performace parameters ofte due to oideal effects i time-domai performace Dyamic characteristics of high resolutio data coverters ofte challegig to measure, to simulate, to uderstad source of cotributios, ad to miimize Example: A -bit ADC would ofte require SFD at the 6+6 bit level or better. Thus, cosiderig a 14-bit ADC, the SFD would be expected to be at the -90dB level or better. If the iput to the ADC is a 1V p-p siusoidal waveform, the secod harmoic term would 90 db / 0dB eed to be at the 10 3μV level. A 3uV level is about 1part i 30,000. Sigals at this level are difficult to accurately simulate i the presece of a 1V level sigal. For example, covergece parameters i simulators ad sample (strobe) poits used i data acquisitio adversely affect simulatio results ad observig the time domai waveforms that cotribute to oliearity at this level ad relatioships betwee these waveforms ad the sources of oliearity is ofte difficult to visualize. Simulatio errors that are at the 0dB level or worse ca occur if the simulatio eviromet is ot correctly established.

18 Performace Characterizatio of Data Coverters What is meat by low frequecy? Operatio at frequecies so low that further decreases i frequecy cause o further chages i a parameter of iterest Low frequecy operatio is ofte termed Pseudostatic operatio

19 Low-frequecy or Pseudo-Static Performace Paramater Pseudo-Static egio f

20 Ed of Lecture 5