a nalog to d igital c onverters stu godlasky nikita pak james potter
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ANALOG TO DIGITAL CONVERTERS
Stu GodlaskyNikita PakJames Potter
INTRODUCTION
What is an analog to digital converter (ADC)
Going from analog to digital
Types and properties of ADC
WHAT IS AN ANALOG TO DIGITAL CONVERTER
Converts an analog signal to discrete time digital
Computers need digital. (On / Off , High / Low , 1/0)
GOING FROM ANALOG TO DIGITAL
Two step process1) Sampling – Measuring analog signal at
uniform time intervals2) Quantization – Assigning discrete
measurements a binary code (each sample will have a binary number associated with it)
T1 T2 T3 T4
Example of digital signal from 3 bit ADC010 010 011
ALIASING
Every analog signal has a frequency Nyquist Frequency (half sampling frequency) Aliasing occurs when signal above Nyquist
frequency
QUANTIZATION ERROR
Analog (infinite values) – Digital (finite values)
Upon reconstruction of analog signal Increases as resolution decreases
Resolution - Q
EFSR - full scale voltage range
N = Number of discrete voltage intervalsN = 2k where k is the number of bits
QUANTIZATION ERROR
• Quantized signal only has values at midpoint of voltage band
TYPES OF ANALOG TO DIGITAL CONVERTERS
Dual Slope A/D Converter Successive Approximation A/D Converter Flash A/D Converter Delta – Sigma A/D Converter
DUAL SLOPE ANALOG TO DIGITAL CONVERTER
Also referred to as an Integrating ADC
Integrator
DUAL SLOPE ANALOG TO DIGITAL CONVERTER
Converts in two phases (ramp up / ramp down )
Input voltage measurement not dependant on integrator components
DUAL SLOPE ANALOG TO DIGITAL CONVERTER
Pros Conversion result is
insensitive to errors in the component values
Fewer adverse affects from noise
High accuracy
Conso Slowo Accuracy is
dependant on the use of precision external components
o Cost
SUCCESSIVE APPROXIMATION ANALOG TO DIGITAL CONVERTER DAC = Digital to Analog Converter EOC = End of Conversion SAR = Successive Approximation Register S/H = Sample and Hold Circuit Vin = Input Voltage
Vref = Reference Voltage
SUCCESSIVE APPROXIMATION ANALOG TO DIGITAL CONVERTER
Uses an n-bit DAC and original analog results Performs a bit by bit comparison of VDAC and
Vin
If Vin > VREF / 2 MSB set to 1 otherwise 0
If Vin > VDAC Successive Bits set to 1 otherwise 0
SUCCESSIVE APPROXIMATION ADC EXAMPLE
10 bit ADC Vin = 0.6 V
Vref = 1V
N = 2n (n = number of bits)N = 210 = 1024Vref = 1V/ 1024
= 0.0009765625V (resolution)
SUCCESSIVE APPROXIMATION DIGITAL TO ANALOG CONVERTER
Pros Capable of high
speed and reliable Medium accuracy
compared to other ADC types
Good tradeoff between speed and cost
Capable of outputting the binary number in serial (one bit at a time) format.
Conso Higher resolution
successive approximation ADCs will be slower
FLASH ANALOG TO DIGITAL CONVERTER
Also called a parallel ADC 2N – 1 Comparators 2N Resistors Control Logic (encoder)
FLASH ANALOG TO DIGITAL CONVERTER
Uses the resistors to divide reference voltage into intervals
Uses comparators to compare Vin and the reference voltages
Encoder takes the output of comparators and uses control logic to generate binary digital output
FLASH ANALOG TO DIGITAL CONVERTER
Pros Very Fast (Fastest) Very simple operational
theory Speed is only limited
by gate and comparator propagation delay
Conso Expensiveo Prone to produce
glitches in the outputo Each additional bit of
resolution requires twice the comparators and resistors
SIGMA-DELTA ANALOG TO DIGITAL CONVERTER
Input over sampled, goes to integrator Integration compared with ground Iteration drives integration of error to
zeroOutput is a stream of serial bits
SIGMA-DELTA ANALOG TO DIGITAL CONVERTER
Pros High resolution No need for precision
components
ConsoSlow due to over
sampling o Only good for low
bandwidth
COMPARISON OF ADCS
Type Speed (relative)
Cost (relative)
Resolution
Dual Slope Slow Med 12-16
Flash Very Fast High 4-12
Successive Approx
Medium – Fast
Low 8-16
Sigma – Delta
Slow Low 12-24
ANALOG TO DIGITAL CONVERTER APPLICATIONSNikita Pak
ANALOG TO DIGITAL CONVERTER APPLICATIONS
Music recording Data acquisition/measurement devices
thermocouples digital multimeters strain gauges
Consumer Products cell phones digital cameras
MUSIC RECORDING
A to D used to convert sound pressure waves into discrete digital signal (later, D to A used to convert back to an electrical signal for a speaker)
Saves a tremendous amount of space
Ex. CD samples at 44.1 kHz (Nyquist frequency = 22.05 kHz is higher than human ear can detect)
CD recording often done with flash A to D
DATA ACQUISITION
Data acquisition: the process of obtaining signals from sensors that measure physical conditions
Sensors give analog voltage that must be converted to work on a computer
Most National Instruments DAQ’s use successive approximation A to D
MEASUREMENT DEVICES
Thermocouple: a junction of dissimilar metals creates a voltage difference that is temperature dependent
Digital multimeter: converts signal to a voltage and amplifies it for measurement
More accurate than analog counterparts
MEASUREMENT DEVICES
Strain gauge: most common type measures the change in resistance as a metal pattern is deformed
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R =ρL
A
CONSUMER PRODUCTS
Cell phones: convert your voice into a digital signal so it can be more efficiently transmitted by compressing the signal
Digital camera ccd: absorbed photons create charges that are converted into a sequence of voltages
These voltages are converted to a digital signal
Both often use flash A to D
ADC ON YOUR MICROCONTROLLER
Input PinsADC Built-into
MC9S12C32
ADC IN BLOCK DIAGRAMATD 10B8C
Port AD
DETAILS OF ATD 10B8C
Analog-To-Digital Resolution: 8 or 10 Bits (manually chosen) 8-Channel multiplexed inputs
Conversion time: 7 µs (for 10 bit mode) Optional external trigger “Successive approximation” type ADC
ATD 10B8C BLOCK DIAGRAM
ATD 10B8C BLOCK DIAGRAM
Reference Voltages
SourceVsource
Results of Successive Approximation
“Holds” Source Voltage
REGISTERSANDSETTING UP YOUR ATD10B8CJames Potter
ADC REGISTERS
All information about registers found in Chapter 8 of MC9S12C Family Reference
Manual
8 Result Registers 6 Control Registers 2 Status Registers 2 Test Registers 1 Digital Input Enable Register 1 Digital Port Data Register
RESULT REGISTERS
RESULT REGISTERS
8 registers,Each withHigh and low byte
RESULT REGISTERS:LEFT-JUSTIFIED (DEFAULT)
High Byte
Low Byte
RESULT REGISTERS:RIGHT-JUSTIFIED
High Byte
Low Byte
CONTROL REGISTERS
CONTROL REGISTERS:ATDCTL2
CONTROL REGISTERS:ATDCTL2
CONTROL REGISTERS:ATDCTL3
CONTROL REGISTERS:ATDCTL3
CONTROL REGISTERS:ATDCTL4
CONTROL REGISTERS:ATDCTL4
CONTROL REGISTERS:ATDCTL5
CONTROL REGISTERS:ATDCTL5
CONTROL REGISTERS:ATDCTL5
SINGLE CHANNEL (MULT = 0)SINGLE CONVERSION (SCAN = 0)
7 6 5 4 3 2 1 0
Port AD
ATD Converter
ResultRegisterInterface
ATDDR0
ATDDR1
ATDDR2
ATDDR3
ATDDR4
ATDDR5
ATDDR6
ATDDR7
SINGLE CHANNEL (MULT = 0)CONTINUOUS CONVERSION (SCAN = 1)
7 6 5 4 3 2 1 0
Port AD
ATD Converter
ResultRegisterInterface
ATDDR0
ATDDR1
ATDDR2
ATDDR3
ATDDR4
ATDDR5
ATDDR6
ATDDR7
MULTIPLE CHANNEL (MULT = 1)SINGLE CONVERSION (SCAN = 0)
7 6 5 4 3 2 1 0
Port AD
ATD Converter
ResultRegisterInterface
ATDDR0
ATDDR1
ATDDR2
ATDDR3
ATDDR4
ATDDR5
ATDDR6
ATDDR7
SINGLE CHANNEL (MULT = 1)CONTINUOUS CONVERSION (SCAN = 1)
7 6 5 4 3 2 1 0
Port AD
ATD Converter
ResultRegisterInterface
ATDDR0
ATDDR1
ATDDR2
ATDDR3
ATDDR4
ATDDR5
ATDDR6
ATDDR7
STATUS REGISTERS
STATUS REGISTER 0:ATDSTAT0
STATUS REGISTER 0:ATDSTAT0
STATUS REGISTER 1:ATDSTAT1
SETTING UP YOUR ATD10B8C
SETTING UP THE ATD Step 1: Power-up the ATD and define settings in
ATDCTL2ADPU = 1 powers up the ATDASCIE = 1 enables interrupt
Step 2: Wait for ATD recovery time (~ 20μs) before proceeding
Step 3: Set number of successive conversions in ATDCTL3
S1C, S2C, S4C, S8C determine number of conversions (see Table 8-4)
SETTING UP THE ATD Step 4: Configure resolution, sampling time, and ATD
clock speed in ATDCTL4PRS0, PRS1, PRS2, PRS3, PRS4 set sampling rate (see Table 8-6) SRES8 sets resolution to 8-bit (= 1) or 10-bit (= 0)
Step 5: Configure starting channel, single/multiple channel, SCAN and result data signed or unsigned in ATDCTL5
CC, CB, CA determine input channel (see Table 8-12)MULT sets single (= 0) or multiple (= 1) inputsSCAN sets single (= 0) or continuous (= 1) samplingDJM sets output format as left-justified (=0) or right-justified (=1)DSGN sets output data as unsigned (=0) or signed (=1)
THANK YOU
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