Stu Godlasky Nikita Pak James 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 ID: 151994
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Slide1
Analog to Digital Converters
Stu Godlasky
Nikita Pak
James PotterSlide2
Introduction
What is an analog to digital converter (ADC)
Going from analog to digital
Types and properties of ADCSlide3
What is an Analog to Digital Converter
Converts an analog signal to discrete time digital
Computers need digital. (On / Off , High / Low , 1/0)Slide4
Going from Analog to Digital
Two step process
Sampling – Measuring analog signal at uniform time intervals
Quantization – Assigning discrete measurements a binary code (each sample will have a binary number associated with it)
T
1
T2 T3 T4Example of digital signal from 3 bit ADC010 010 011Slide5
Aliasing
Every analog signal has a frequency
Nyquist Frequency (half sampling frequency)
Aliasing occurs when signal above Nyquist frequencySlide6
Quantization Error
Analog (infinite values) – Digital (finite values)
Upon reconstruction of analog signal
Increases as resolution decreases
Resolution - Q
EFSR - full scale voltage rangeN = Number of discrete voltage intervalsN = 2k where k is the number of bitsSlide7
Quantization Error
Quantized signal only has values at midpoint of voltage bandSlide8
Types of Analog to Digital Converters
Dual Slope A/D Converter
Successive Approximation A/D Converter
Flash A/D Converter
Delta – Sigma A/D ConverterSlide9
Dual Slope Analog to Digital Converter
Also referred to as an Integrating ADC
IntegratorSlide10
Dual Slope Analog to Digital Converter
Converts in two phases (ramp up / ramp down )
Input voltage measurement not dependant on integrator components Slide11
Dual Slope Analog to Digital Converter
Pros
Conversion result is insensitive to errors in the component values
Fewer adverse affects from noise
High accuracy
Cons Slow Accuracy is dependant on the use of precision external components CostSlide12
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 VoltageSlide13
Successive Approximation Analog to Digital Converter
Uses an n-bit DAC and original analog results
Performs a bit by bit comparison of V
DAC
and V
in If Vin > VREF / 2 MSB set to 1 otherwise 0 If Vin > VDAC Successive Bits set to 1 otherwise 0Slide14
Successive Approximation ADC Example
10 bit ADC
V
in
= 0.6 V
Vref = 1VN = 2n (n = number of bits)N = 210 = 1024Vref = 1V/ 1024 = 0.0009765625V (resolution)Slide15
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.Cons Higher resolution successive approximation ADCs will be slowerSlide16
Flash Analog to Digital Converter
Also called a parallel ADC
2
N
– 1 Comparators
2N ResistorsControl Logic (encoder) Slide17
Flash Analog to Digital Converter
Uses the resistors to divide reference voltage into intervals
Uses comparators to compare V
in
and the reference voltages
Encoder takes the output of comparators and uses control logic to generate binary digital outputSlide18
Flash Analog to Digital Converter
Pros
Very Fast (Fastest)
Very simple operational theory
Speed is only limited by gate and comparator propagation delay
Cons Expensive Prone to produce glitches in the output Each additional bit of resolution requires twice the comparators and resistorsSlide19
Sigma-Delta Analog to Digital Converter
Input over sampled, goes to integrator
Integration compared with ground
Iteration drives integration of error to zero
Output is a stream of serial bitsSlide20
Sigma-Delta Analog to Digital Converter
Pros
High resolution
No need for precision components
Cons
Slow due to over sampling Only good for low bandwidthSlide21
Comparison of ADCs
Type
Speed (relative)
Cost (relative)
Resolution
Dual Slope
SlowMed12-16FlashVery FastHigh4-12Successive ApproxMedium – FastLow8-16Sigma – DeltaSlowLow12-24Slide22
Analog to Digital Converter Applications
Nikita PakSlide23
Analog to Digital Converter Applications
Music recording
Data acquisition/measurement devices
thermocouples
digital
multimetersstrain gaugesConsumer Productscell phonesdigital camerasSlide24
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 spaceEx. 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 DSlide25
Data Acquisition
D
ata acquisition: the
process of obtaining signals from sensors that measure physical
conditions
Sensors give analog voltage that must be converted to work on a computerMost National Instruments DAQ’s use successive approximation A to DSlide26
Measurement Devices
T
hermocouple: a
junction of dissimilar metals creates a voltage difference that is temperature
dependent
Digital multimeter: converts signal to a voltage and amplifies it for measurementMore accurate than analog counterpartsSlide27
Measurement Devices
S
train gauge: most common type measures the change in resistance as a metal pattern is deforme
dSlide28
Consumer Products
C
ell 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 voltagesThese voltages are converted to a digital signalBoth often use flash A to DSlide29
ADC on Your Microcontroller
Input Pins
ADC Built-into
MC9S12C32Slide30
ADC in Block Diagram
ATD 10B8C
Port ADSlide31
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 ADCSlide32
ATD 10B8C Block DiagramSlide33
ATD 10B8C Block Diagram
Reference Voltages
Source
V
source
Results of Successive Approximation
“Holds” Source VoltageSlide34
Registersand
Setting Up Your ATD10B8C
James PotterSlide35
ADC Registers
All information about registers found in
Chapter 8 of
MC9S12C Family Reference Manual
8 Result Registers
6 Control Registers2 Status Registers2 Test Registers1 Digital Input Enable Register1 Digital Port Data RegisterSlide36
Result RegistersSlide37
Result Registers
8 registers
,
Each with
High and low byteSlide38
Result Registers:Left-Justified (Default)
High Byte
Low ByteSlide39
Result Registers:Right-Justified
High Byte
Low ByteSlide40
Control RegistersSlide41
Control Registers:ATDCTL2 Slide42
Control Registers:ATDCTL2 Slide43
Control Registers:ATDCTL3Slide44
Control Registers:ATDCTL3Slide45
Control Registers:ATDCTL4Slide46
Control Registers:ATDCTL4Slide47
Control Registers:ATDCTL5Slide48
Control Registers:ATDCTL5Slide49
Control Registers:ATDCTL5Slide50
Single Channel (MULT = 0)Single Conversion (SCAN = 0)
7
6
5
4
3
210
Port ADATD ConverterResultRegister
InterfaceATDDR0ATDDR1ATDDR2ATDDR3ATDDR4ATDDR5
ATDDR6
ATDDR7Slide51
Single Channel (MULT = 0)Continuous Conversion (SCAN = 1)
7
6
5
4
3
210
Port ADATD ConverterResult
RegisterInterfaceATDDR0ATDDR1ATDDR2ATDDR3ATDDR4ATDDR5
ATDDR6
ATDDR7Slide52
Multiple Channel (MULT = 1)Single Conversion (SCAN = 0)
7
6
5
4
3
210
Port ADATD ConverterResultRegister
InterfaceATDDR0ATDDR1ATDDR2ATDDR3ATDDR4ATDDR5
ATDDR6
ATDDR7Slide53
Single Channel (MULT = 1)Continuous Conversion (SCAN = 1)
7
6
5
4
3
210
Port ADATD ConverterResult
RegisterInterfaceATDDR0ATDDR1ATDDR2ATDDR3ATDDR4ATDDR5
ATDDR6
ATDDR7Slide54
Status RegistersSlide55
Status Register 0:ATDSTAT0Slide56
Status Register 0:ATDSTAT0Slide57
Status Register 1:ATDSTAT1Slide58
Setting Up Your ATD10B8CSlide59
Setting Up the ATD
Step 1: Power-up the ATD and define settings in
ATDCTL2
ADPU
= 1 powers up the ATDASCIE = 1 enables interruptStep 2: Wait for ATD recovery time (~ 20μs) before proceedingStep 3: Set number of successive conversions in ATDCTL3S1C,
S2C, S4C, S8C determine number of conversions (see Table 8-4) Slide60
Setting Up the ATD
Step 4: Configure resolution, sampling time, and ATD clock speed in
ATDCTL4
PRS0
,
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 ATDCTL5CC
, 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)Slide61
Thank You