EE247 Lecture 12 Administrative issues Midterm exam Tues Oct 24th o You can only bring one 8x11 paper with your own written notes please do not photocopy 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 EECS 247 Lecture 12 Data Converters 2006 H K Page 1 EE247 Lecture 12 Today Example of Switched Capacitor filters NOT followed by an ADC Data converters ADC DAC transfer curve Sampling aliasing reconstruction Amplitude quantization Static converter error sources Offset full scale error DNL INL EECS 247 Lecture 12 Data Converters 2006 H K Page 2 Summary of Last Lecture Switched Capacitor Filters continued Effect of non idealities Bilinear switched capacitor filters Filter design summary Comparison of various filter topologies Data Converters continued today EECS 247 Lecture 12 Data Converters 2006 H K Page 3 Last Lecture Questions Based on the CODEC example class may have the impression that S C filters are always followed by an ADC Assumption not accurate Example Switched capacitor filters used in the transmit path of ISDN ICs EECS 247 Lecture 12 Data Converters 2006 H K Page 4 Data Transmission Over Existing Twisted Pair Phone Lines Backbone Digital Network Central Office Xmitter Customer Twisted Pair Xmitter Receiver Receiver 3 to 5km POTS Data transmitted over existing voice grade phone lines covering distances close to 3 5miles Voice band MODEMs ISDN HDSL SDSL ADSL EECS 247 Lecture 12 Data Converters 2006 H K Page 5 Data Transmission Over Twisted Pair Phone Lines ISDN U Interface Transceiver Backbone Digital Network Central Office Xmitter Customer Twisted Pair Xmitter Receiver Receiver 3 to 5km POTS Full duplex transmission RX TX signals sent simultaneously 160kbit sec baseband data 80kHz signal bandwidth Standardized line code 2B1Q 4 level code 3 1 1 3 Max desired loop coverage 18kft 36dB signal attenuation Final required BER bit error rate 10 7 min SNDR 27dB EECS 247 Lecture 12 Data Converters 2006 H K Page 6 Analog Front End 2nd order Butterworth S C Filter 2b S C DAC Class A B Line Driver fs 2 56MHz fs 20 48MHz To avoid stringent requirements for nonlinear echo canceller high linearity analog circuitry needed 75dB EECS 247 Lecture 12 Data Converters 13bit Double Loop Peak signal frequency 80kHz 2006 H K Page 7 Data Converters EECS 247 Lecture 12 Data Converters 2006 H K Page 8 Data 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 oscilloscopes EECS 247 Lecture 12 Data Converters 2006 H K Page 9 Data Converters Embedded data converters Cost reliability and performance 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 consumption EECS 247 Lecture 12 Data Converters 2006 H K Page 10 D A Converter Transfer Characteristics MSB b1 b2 b3 An ideal digital toanalog 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 LSB bn V0 D A Nomenclature N of bits VFS f u l l s cal e o u tp u t mi n s t ep s iz e 1L SB VFS 2N V o r N lo g2 F S r es ol u ti o n EECS 247 Lecture 12 Data Converters 2006 H K Page 11 D A Converter Transfer Characteristics MSB b1 b2 b3 N of bit s VFS f u l l s cal e o u t p u t m i n st ep s i z e 1L S B LSB D A bn V0 VFS 2N V0 VFS N bi i i 1 2 N bi 2 N i i 1 bi 0 or 1 binary weighted EECS 247 Lecture 12 Data Converters 2006 H K Page 12 D A Converter Exampe D A with 3 bit Resolution Exa mp l e N 3 MSB LSB b1 b2 b3 1 0 1 Ass ume VFS 0 8V In put cod e i s 1 01 V0 b1 22 b2 21 b3 20 T hen VF S 23 0 1V V0 D A V0 0 1V 1 22 0 21 1 20 V0 0 5V Note MSB VF S 2 L S B VFS 2 N EECS 247 Lecture 12 Data Converters 2006 H K Page 13 Ideal D A Transfer Characteristic Ideal DAC introduces no error Analog Output VFS Ideal Response One to one mapping VFS 2 from input to output Step Height 1LSB VFS 8 000 001 010 011 100 101 110 111 EECS 247 Lecture 12 Data Converters Digital Input Code 2006 H K Page 14 A D Converter Transfer Characteristic For an ideal analog to digital converter with uniform binary digital encoding a unipolar input range for 0 to VFS MSB b1 b2 b3 LSB bm Vin A D w here N of b i t s VFS f ul l scal e ou t put step s i ze VFS N ot e D bi 1 al l i VFS 1 VFS 1 2N 2N EECS 247 Lecture 12 Data Converters 2006 H K Page 15 Ideal A D Transfer Characteristic Digital Output Ideal ADC introduces error 111 1 2 VFS 2 N N of bits 110 101 100 011 This error is called quantization error 010 001 1LSB Analog input 000 0 EECS 247 Lecture 12 Data Converters 2 3 4 5 6 7 2006 H K Page 16 Example Non Linear A D Converter For Voice Band Telephony Applications Coder Output DIGITAL Non linear ADC and DAC used in voice band CODECs To maximize dynamic range with lower of bits Coding scheme called A law law VFS VFS 2 VFS 4 Coder Input ANALOG Also called companding Ref P R Gray et al Companded pulse code modulation voice codec using monolithic weighted capacitor arrays IEEE Journal of Solid State Circuits vol 10 pp 497 499 December 1975 EECS 247 Lecture 12 Data Converters 2006 H K Page 17 Data Converter Performance Metrics Data Converters are typically characterized by static time domain frequency domain performance metrics Static Monotonicity Offset Full scale error Differential nonlinearity DNL Integral nonlinearity INL Dynamic Delay settling time Aperture uncertainty Distortion harmonic content Signal to noise ratio SNR Signal to noise distortion ratio SNDR Idle channel noise Dynamic range spurious free dynamic range SFDR EECS 247 Lecture 12 Data Converters 2006 H K Page 18 Typical Sampling Process CT SD DT time Continuous Time Physical Signals Sampled Data e g T H signal Clock Memory Content Discrete Time EECS 247 Lecture 12 Data Converters 2006 H K Page 19 Discrete Time Signals A sequence of numbers or vector with discrete index time instants Intermediate signal values not defined not the same as equal to zero Mathematically convenient non physical We will use the term sampled …
View Full Document
Unlocking...