Material Covered in EE247 Where 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 interfaces EECS 247 Lecture 10 Data Converter Intro 2010 H K Page 1 EE247 Lecture 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 11 Intro to Data Converters Performance Metrics 2010 H K Page 2 Data Converter Applications EECS 247 Lecture 10 Data Converter Intro 2010 H K Page 3 Data Converter Basics Analog Input 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 EECS 247 Lecture 10 Data Converter Intro Analog Preprocessing Filters A D Conversion DSP 000 001 110 D A Conversion Analog Postprocessing Filters Analog Output 2010 H K Page 4 A D D A Conversion A D Conversion D A Conversion EECS 247 Lecture 10 Data Converter Intro 2010 H K Page 5 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 Various hand held measurement equipment Low cost digital oscilloscopes EECS 247 Lecture 10 Data Converter Intro 2010 H K Page 6 Data 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 consumption EECS 247 Lecture 10 Data Converter Intro 2010 H K Page 7 Embedded Converters Example Typical Dual Standard Cell Phone Contains in integrated form 4 Rx filters 4 Tx filters 4 Rx ADCs 4 Tx DACs 3 Auxiliary ADCs 8 Auxiliary DACs Dual Standard I Q Audio Tx Rx power control Battery charge control display Total Filters 8 ADCs 7 DACs 12 EECS 247 Lecture 10 Data Converter Intro 2010 H K Page 8 D A Converter Transfer Characteristics MSB b1 b2 An ideal digital toanalog converter Accepts digital inputs b1 bn Produces either an analog output voltage or current Assumption will be revisited bN LSB Nomenclature N of bits VFS full sc ale output Uniform binary digital encoding Unipolar output ranging from 0 to VFS EECS 247 Lecture 10 Vo or Io D A min ste p size 1LSB VFS 2N V or N log2 FS re solution Data Converter Intro 2010 H K Page 9 D A Converter Transfer Characteristics VFS f ul l scal e out put MSB b1 b2 N of bi t s mi n st ep si ze 1L SB V0 VFS D A Vo or Io bN VFS LSB 2N N bi i i 1 2 N bi 2 N i bi 0 or 1 i 1 Note D bi 1 all i Vomax VFS 1 Vomax VFS 1 2N binary weighted EECS 247 Lecture 10 Data Converter Intro 2010 H K Page 10 D A Converter Exampe D A with 3 bit Resolution MSB LSB b1 b2 b3 1 0 1 Example for N 3 and VFS 0 8V input code 101 Find the output value V0 D A V0 b1 22 b2 21 b3 20 The n VFS 23 0 1V V0 0 1V 1 22 0 21 1 20 V0 0 5V V0 Note M SB VFS 2 LSB VFS 2 N EECS 247 Lecture 10 Data Converter Intro 2010 H K Page 11 Ideal 3 Bit D A Transfer Characteristic Ideal DAC introduces no error One to one mapping from input to output Analog Output VFS Ideal Response VFS 2 Step Height 1LSB VFS 8 000 001 010 011 100 101 110 111 EECS 247 Lecture 10 Data Converter Intro Digital Input Code 2010 H K Page 12 A D Converter Transfer Characteristics MSB An ideal analog to digital converter Accepts analog input in the form of either voltage or current A D Vin bN Produces digital output either in serial or parallel form LSB N of bits VFS full sc ale output Assumption will be revisited Unipolar input ranging from 0 to VFS Uniform binary digital encoding EECS 247 Lecture 10 b1 b2 min re solv able input 1LSB VFS 2N V or N log2 FS re solution Data Converter Intro 2010 H K Page 13 Ideal A D Transfer Characteristic Example 3Bit A D Converter Ideal ADC introduces error with max peakto peak 1 2 VFS 2 N N of bits This error is called quantization error For a given VFS as N increases quantization error decreases resolution increases Digital Output 111 110 101 100 011 010 001 1LSB Analog input 000 0 2 3 4 5 6 7 VFS EECS 247 Lecture 10 Data Converter Intro 2010 H K Page 14 Non 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 Voiceband telephony Small signals larger of codes Large signals smaller of codes EECS 247 Lecture 10 Data Converter Intro 2010 H K Page 15 Example Non Linear A D Converter For Voice Band Telephony Applications Non 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 Coder Output DIGITAL VFS VFS 2 VFS 4 Coder Input ANALOG Also called companding SEGMENT 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 10 SIGN BIT Data Converter Intro STEP 2010 H K Page 16 Data Converter Performance Metrics Data Converters are typically characterized by static time domain frequency domain performance metrics Static Offset Full scale error Differential nonlinearity DNL Integral nonlinearity INL Monotonicity 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 10 Data Converter Intro 2010 H K Page 17 Typical Sampling Process C T S D D T time Continuous Time Physical Signals Sampled Data e g T H signal Clock Memory Content Discrete Time EECS 247 Lecture 10 Data Converter
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