EECS 247 Lecture 10 Data Converter Intro. © 2010 H. K. Page 1Material Covered in EE247Where are We?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,….• Self-calibration techniques• Oversampled converters• Systems utilizing analog/digital interfacesEECS 247 Lecture 11: Intro. to Data Converters & Performance Metrics © 2010 H. K. Page 2EE247Lecture 11• Data converters– Areas of application– Data converter transfer characteristics– Sampling, aliasing, reconstruction– Amplitude quantization – Data converter performance metrics:• Static converter error sources – Offset– Full-scale error– Differential non-linearity (DNL)– Integral non-linearity (INL) • Measuring DNL & INL– Servo-loop– Code density testing (histogram testing)EECS 247 Lecture 10 Data Converter Intro. © 2010 H. K. Page 3Data Converter ApplicationsEECS 247 Lecture 10 Data Converter Intro. © 2010 H. K. Page 4Data Converter Basics• DSPs benefited from device scaling• However, real world signals are still analog:– Continuous time– Continuous amplitude• DSP can only process:– Discrete time– Discrete amplitude Need for data conversion from analog to digital and digital to analog Analog PostprocessingD/AConversionDSPA/D ConversionAnalog PreprocessingAnalog InputAnalog Output000...001...110FiltersFilters??EECS 247 Lecture 10 Data Converter Intro. © 2010 H. K. Page 5A/D & D/A ConversionA/D ConversionD/A ConversionEECS 247 Lecture 10 Data Converter Intro. © 2010 H. K. Page 6Data 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• Various hand-held measurement equipment• Low cost digital oscilloscopesEECS 247 Lecture 10 Data Converter Intro. © 2010 H. K. Page 7Data Converters• Embedded data converters– Integration of data conversion interfaces along with DSPs and/or RF circuits Cost, reliability, and performance– Main issues• Feasibility of integrating sensitive analog functions in a technology typically optimized for digital performance• Down scaling of supply voltage as a result of downscaling of feature sizes• Interference & spurious signal pick-up from on-chip digital circuitry and/or high frequency RF circuits• Portable applications dictate low power consumptionEECS 247 Lecture 10 Data Converter Intro. © 2010 H. K. Page 8Embedded ConvertersExample: Typical Dual-Standard Cell PhoneContains in integrated form:• 4 Rx filters• 4 Tx filters• 4 Rx ADCs• 4 Tx DACs• 3 Auxiliary ADCs• 8 Auxiliary DACsTotal: Filters 8ADCs 7DACs 12Dual Standard, I/QAudio, Tx/Rx powercontrol, Battery chargecontrol, display, ...EECS 247 Lecture 10 Data Converter Intro. © 2010 H. K. Page 9D/A Converter Transfer Characteristics• An ideal digital-to-analog converter:– Accepts digital inputs b1-bn– Produces either an analog output voltage or current – Assumption (will be revisited) • Uniform, binary digital encoding • Unipolar output ranging from 0 to VFS…….…b1b2bNVo or IoMSBLSBFSFSNFS2N # of bitsV full scale outputmin. step size 1LSBV2Vor N log resolution Nomenclature:D/AEECS 247 Lecture 10 Data Converter Intro. © 2010 H. K. Page 10D/A Converter Transfer CharacteristicsFSFSNN # of bitsV full scale outputmin. step size 1LSBV2 N0 FSi1Ni1iNibiVV2bi 2 , bi 0 or 1 binary-weighted imaxo FSmaxo FSNNote:Db 1,alliVV11VV2 …….…b1b2bNVo or IoMSBLSBD/AEECS 247 Lecture 10 Data Converter Intro. © 2010 H. K. Page 11D/A Converter Exampe: D/A with 3-bit Resolutionb1b2b3V0MSBLSB 01 2 33FS00NFS FS2 1 02 1 0Vb 2 b 2 b 2Then : V / 2 0.1VV 0.1V1 2 0 2 1 2V 0.5VNote:MSB V / 2 & LSB V / 2 1 0 1Example: for N=3 and VFS=0.8Vinput code 101Find the output value V0D/AEECS 247 Lecture 10 Data Converter Intro. © 2010 H. K. Page 12Ideal 3-Bit D/A Transfer Characteristic• Ideal DAC introduces no error!• One-to-one mapping from input to output000 001 010 011 100 101 110 111Step Height (1LSB =)Ideal ResponseDigital InputCodeAnalog OutputVFSVFS /2VFS /8EECS 247 Lecture 10 Data Converter Intro. © 2010 H. K. Page 13A/D Converter Transfer Characteristics• An ideal analog-to-digital converter:– Accepts analog input in the form of either voltage or current – Produces digital output either in serial or parallel form– Assumption (will be revisited) • Unipolar input ranging from 0 to VFS• Uniform, binary digital encoding …….…b1b2bNMSBLSBVin FSFSNFS2N # of bitsV full scale outputmin. resolvable input 1LSBV2Vor N log resolution A/DEECS 247 Lecture 10 Data Converter Intro. © 2010 H. K. Page 14Ideal A/D Transfer CharacteristicExample: 3Bit A/D Converter• Ideal ADC introduces error with max peak-to-peak:(+-1/2) VFS/2NN= # of bits• This error is called ``quantization error``• For a given VFS as N increases quantization error decreases resolution increases111110101 100011010001000DigitalOutputAnalog input0 2 3 4 5 6 71LSBVFSEECS 247 Lecture 10 Data Converter Intro. © 2010 H. K. Page 15Non-Linear Data Converters• So far data converter characterisitics studied are with uniform, binary digital encoding• For some applications to maximize dynamic range non-linear coding is used e.g. Voice-band telephony, – Small signals larger # of codes– Large signals smaller # of codesEECS 247 Lecture 10 Data Converter Intro. © 2010 H. K. Page 16Example: Non-Linear A/D ConverterFor Voice-Band Telephony ApplicationsNon-linear ADC and DAC used in voice-band CODECs• To maximize dynamic range without need for large # of bits• Non-linear Coding scheme called A-law & m-law is used•
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