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Berkeley ELENG 247A - Lecture 12

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EECS 247 Lecture 12: Data Converters © 2005 H. K. Page 1EE247Lecture 12• Administrative issues§ Midterm exam Oct. 20tho You can only bring one 8x11 paper with your own written notes (please do not copy)o No books, class or any other kind of handouts/notes, calculators, computers, PDA, cell phones....o Midterm includes material covered to end of lecture 14– EE247 final exam date has changed to: December 13th, 12:30-3:30 pm (group 2)- please check your other class finals to ensure no conflictEECS 247 Lecture 12: Data Converters © 2005 H. K. Page 2EE247Lecture 12Today:–Summary switched-capacitor filters–Comparison of various filter topologies–Data convertersEECS 247 Lecture 12: Data Converters © 2005 H. K. Page 3SC Filter Summaryü Pole and zero frequencies proportional to – Sampling frequency fs– Capacitor ratiosØ High accuracy and stability in responseØ Long time constants realizable without large R, Cü Compatible with transconductance amplifiers– Reduced circuit complexity, power dissipationü Amplifier bandwidth requirements less stringent compared to CT filters (low frequencies only)L Issue: Sampled-data filters à require anti-aliasing prefilteringEECS 247 Lecture 12: Data Converters © 2005 H. K. Page 4SummaryFilter Performance versus Filter Topology_1-5%1-5%1-5%1-5%Freq. tolerance+ tuning<<1%40-90dB~ 10MHzSwitched Capacitor+-40-60%40-70dB~ 100MHzGm-C+-30-50%50-90dB~ 5MHzOpamp-MOSFET-RC+-30-50%40-60dB~ 5MHzOpamp-MOSFET-C+-30-50%60-90dB~10MHzOpamp-RCFreq. tolerance w/o tuningSNDRMax. Usable BandwidthEECS 247 Lecture 12: Data Converters © 2005 H. K. Page 5Data ConvertersEECS 247 Lecture 12: Data Converters © 2005 H. K. Page 6Material Covered in EE247ü Filters – Continuous-time filters• Biquads & ladder type filters• Opamp-RC, Opamp-MOSFET-C, gm-C filters• Automatic frequency tuning– Switched capacitor (SC) filters• Data Converters– D/A converter architectures– A/D converter • Nyquist rate ADC- Flash, Pipeline ADCs,….• Oversampled converters• Self-calibration techniques• Systems utilizing analog/digital interfaces– Wireline communication systems- ISDN, XDSL…– Wireless communication systems- Wireless LAN, Cellular telephone,…– Disk drive electronics– Fiber-optics systemsEECS 247 Lecture 12: Data Converters © 2005 H. K. Page 7Data Converter Topics• Basic Operation of Data Converters – Uniform sampling and reconstruction– Uniform amplitude quantization• Characterization and Testing• Common ADC/DAC Architectures• Selected Topics in Converter Design– Practical Implementations– Desensitization to Analog Circuit Non-Idealities• Figures of Merit and Performance TrendsEECS 247 Lecture 12: Data Converters © 2005 H. K. Page 8Suggested Reference Texts• R. v. d. Plassche, CMOS Integrated Analog-to-Digital and Digital-to-Analog Converters, 2nd ed., Kluwer, 2003.• B. Razavi, Data Conversion System Design, IEEE Press, 1995.• S. Norsworthy et al (eds), Delta-Sigma Data Converters, IEEE Press, 1997.Extensive treatment of oversampled converters including stability, tones, bandpass converters.• J. G. Proakis, D. G. Manolakis, Digital Signal Processing, Prentice Hall, 1995.EECS 247 Lecture 12: Data Converters © 2005 H. K. Page 9Converter ApplicationsEECS 247 Lecture 12: Data Converters © 2005 H. K. Page 10Example: Typical Cell PhoneContains in integrated form:• 4 Rx filters• 4 Tx filters• 4 Rx ADCs• 4 Tx DACs• 3 Auxiliary ADCs• 8 Auxiliary DACsTotal: Filters à 8ADCs à 7DACs à 12Dual Standard, I/QAudio, Tx/Rx powercontrol, Battery chargecontrol, display, ...EECS 247 Lecture 12: Data Converters © 2005 H. K. Page 11Data Converter Basics• DSP is wonderful, but...• Real world signals are analog:– Continuous time– Continuous amplitude• DSP can only process:– Discrete time– Discrete amplitudeà Need for data conversion from analog to digital and digital to analogAnalog PostprocessingD/AConversionDSPA/D ConversionAnalog PreprocessingAnalog InputAnalog Output000...001...110FiltersFilters??EECS 247 Lecture 12: Data Converters © 2005 H. K. Page 12A/D & D/A ConversionA/D ConversionD/A ConversionEECS 247 Lecture 12: Data Converters © 2005 H. K. Page 13Data Converters• Stand alone data converters– Used in variety of systems– Example: Analog Devices AD9235 12bit/ 65Ms/s ADC- Applications:• Ultrasound equipment• IF sampling in wireless receivers• Hand-held scopemeters• Low cost digital oscilloscopesEECS 247 Lecture 12: Data Converters © 2005 H. K. Page 14Data Converters• Embedded data converters– Cost, reliability, and performance à integration of data conversion interfaces along with DSPs– Main challenges• Feasibility of integrating sensitive analog functions in technologies optimized for digital performance• Down scaling of supply voltage• Interference & spurious signal pick-up from on-chip digital circuitry• Portable applications dictate low power consumptionEECS 247 Lecture 12: Data Converters © 2005 H. K. Page 15D/A Converter Transfer Characteristics• For an ideal digital-to-analog converter with uniform, binary digital encoding & a unipolar output range from 0 to VFSNN0FSi1i1NiibiVVbi2,bi0or12==−==∆×=∑∑D/A……..…b1 b2 b3bnV0()0FSFSNNote:VVbi1,alli11V2=−∆=−=MSBLSB( )0210Example:N3Vb1.2b2.2b3.2==∆++FSFSNwhereN#ofbitsVfullscaleoutputLSBstepsizeV2==∆=∆=EECS 247 Lecture 12: Data Converters © 2005 H. K. Page 16Ideal D/A Transfer Characteristic• Ideal DAC introduces no error!• One-to-one mapping from input to output001 010 011 100 101 110 111Step Height (1LSB=∆)Ideal ResponseDigital InputCodeAnalog OutputVFSVFS /2VFS /8EECS 247 Lecture 12: Data Converters © 2005 H. K. Page 17A/D Converter Transfer Characteristic• For an ideal analog-to-digital converter with uniform, binary digital encoding & a unipolar input range for 0 to VFS……..…b1 b2 b3bmVin()FSFSmNote:DVbi1,alli11V2→−∆=−→MSBLSBA/DFSFSmwherem#ofbitsVfullscaleoutputstepsizeV2==∆=∆=EECS 247 Lecture 12: Data Converters © 2005 H. K. Page 18Ideal A/D Transfer Characteristic• Ideal ADC introduces error àmax error = (+ -1/2∆) ∆= VFS/2m m= # of bits• This error is called ``quantization error``111110101 1000110100010001LSBDigital OutputAnalog input∆ 2∆ 3∆ 4∆ 5∆ 6∆ 7∆EECS 247 Lecture 12: Data


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