Analog to Digital Converters
(ADC)
Ben Lester, Mike Steele, Quinn
Morrison
Topics

Introduction





Why?
Types and Comparisons
Successive Approximation ADC example
Applications
ADC System in the CML-12C32 Microcontroller

Analog systems are typically what
engineers need to analyze. ADCs are
used to turn analog information into
digital data.
Process

Sampling, Quantification, Encoding
Outpu Discrete
t
Voltage
States Ranges (V)
0
0.00-1.25
1
1.25-2.50
2
2.50-3.75
3
3.75-5.00
4
5.00-6.25
5
6.25-7.50
6
7.50-8.75
7
8.75-10.0
Output
Binary
Equivalent
0
000
1
001
2
010
3
011
4
100
5
101
6
110
7
111
Resolution, Accuracy, and
Conversion time



Resolution – Number of discrete values
it can produce over the range of analog
values; Q=R/N
Accuracy – Improved by increasing
sampling rate and resolution.
Time – Based on number of steps
required in the conversion process.
Comparing types of ADCs





Flash ADC
Sigma-delta ADC
Wilkinson ADC
Integrating ADC
Successive Approximation Converter
Flash ADC



Speed: High
Cost: High
Accuracy: Low
Sigma-delta ADC



Speed: Low
Cost: Low
Accuracy: High
Wilkinson ADC



Speed: High
Cost: High
Accuracy: High
Wilkinson Analog
Digital Converter
(ADC) circuit
schematic diagram
Integrating ADC



Speed: Low
Cost: Low
Accuracy: High
Successive Approximation
Converter



Speed: High
Cost: High
Accuracy: High but limited
Topics

Introduction





Why?
Types and Comparisions
Successive Approximation ADC example
Applications
ADC System in the CML-12C32 Microcontroller
Successive Approximation ADC
Example Mike Steele
Goal: Find digital value Vin
• 8-bit ADC
• Vin = 7.65
• Vfull scale = 10
Successive Approximation ADC
Example
• MSB  LSB
• Average high/low limits
• Compare to Vin
• Vin > Average  MSB = 1
• Vin < Average  MSB = 0
• Bit 7
• (Vfull scale +0)/2 = 5
• 7.65 > 5  Bit 7 = 1
1
Vfull scale = 10, Vin = 7.65
Successive Approximation ADC
Example
• MSB  LSB
• Average high/low limits
• Compare to Vin
• Vin > Average  MSB = 1
• Vin < Average  MSB = 0
• Bit 6
• (Vfull scale +5)/2 = 7.5
• 7.65 > 7.5  Bit 6 = 1
1
1
Vfull scale = 10, Vin = 7.65
Successive Approximation ADC
Example
• MSB  LSB
• Average high/low limits
• Compare to Vin
• Vin > Average  MSB = 1
• Vin < Average  MSB = 0
• Bit 5
• (Vfull scale +7.5)/2 = 8.75
• 7.65 < 8.75  Bit 5 = 0
1
1
0
Vfull scale = 10, Vin = 7.65
Successive Approximation ADC
Example
Vin = 7.65
• MSB  LSB
• Average high/low limits
• Compare to Vin
• Vin > Average  MSB = 1
• Vin < Average  MSB = 0
• Bit 4
• (8.75+7.5)/2 8.125
• 7.65 < 8.125  Bit 4 = 0
1
1
0
0
Successive Approximation ADC
Example
Vin = 7.65
• MSB  LSB
• Average high/low limits
• Compare to Vin
• Vin > Average  MSB = 1
• Vin < Average  MSB = 0
• Bit 3
• (8.125+7.5)/2 = 7.8125
• 7.65 < 7.8125  Bit 3 = 0
1
1
0
0
0
Successive Approximation ADC
Example
Vin = 7.65
• MSB  LSB
• Average high/low limits
• Compare to Vin
• Vin > Average  MSB = 1
• Vin < Average  MSB = 0
• Bit 2
• (7.8125+7.5)/2 = 7.65625
• 7.65 < 7.65625  Bit 2 = 0
1
1
0
0
0
0
Successive Approximation ADC
Example
Vin = 7.65
• MSB  LSB
• Average high/low limits
• Compare to Vin
• Vin > Average  MSB = 1
• Vin < Average  MSB = 0
• Bit 1
• (7.65625+7.5)/2 = 7.578125
• 7.65 > 7.578125  Bit 1 = 1
1
1
0
0
0
0
1
Successive Approximation ADC
Example
Vin = 7.65
• MSB  LSB
• Average high/low limits
• Compare to Vin
• Vin > Average  MSB = 1
• Vin < Average  MSB = 0
• Bit 0
• (7.65625+7.578125)/2 =
7.6171875
• 7.65 > 7.6171875  Bit 0 = 1
1
1
0
0
0
0
1
1
Successive Approximation ADC
Example
0.8
Voltage
• 110000112 = 19510
• 8-bits, 28 = 256
• Digital Output
• 195/256 = 0.76171875
• Analog Input
• 7.65/10 = 0.765
Vin = 7.65
1
0.6
0.4
0.2
0
7
6
5
4
3
Bit
• Resolution
• (Vmax – Vmin)/2n  10/256 = 0.039
1
1
0
0
0
0
1
1
2
1
0
ADC Applications
• Measurements / Data Acquisition
• Control Systems
• PLCs (Programmable Logic Controllers)
• Sensor integration (Robotics)
• Cell Phones
• Video Devices
• Audio Devices
e*(∆t)
t
t
∆t
Controller
1001
0010
1010
0101
e*
0010
0101
0011
1011
e
u*(∆t)
∆t
ATD10B8C on MC9S12C32
Presented by
Quinn Morrison
MC9S12C32
Block Diagram
ATD 10B8C
ATD10B8C
Block Diagram
ATD10B8C
Key Features

Resolution


Conversion Time



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8/10 bit (manually chosen)
7 usec, 10 bit
Successive Approximation ADC architecture
8-channel multiplexed inputs
External trigger control
Conversion modes


Single or continuous sampling
Single or multiple channels
ATD10B8C
Modes and Operations
Modes

Stop Mode


Wait Mode


All clocks halt; conversion aborts; minimum recovery delay
Reduced MCU power; can resume
Freeze Mode

Breakpoint for debugging an application
Operations

Setting up and Starting the A/D Conversion

Aborting the A/D Conversion

Resets

Interrupts
ATD10B8C External Pins

There Are 12 External Pins

AN7 / ETRIG / PAD7



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AN6/PAD6 – AN0/PAD0



Analog input
General purpose digital I/O
VRH, VRL


Analog input channel 7
External trigger for ADC
General purpose digital I/O
High and low reference voltages for
ADC
VDDA, VSSA

Power supplies for analog circuitry
ATD10B8C
Registers

6 Control Registers ($0080 - $0085)


2 Status Registers ($0086, $008B)


Formatted results (2 bytes)
1 Digital Input Enable Register ($008D)


Allows for analog conversion of internal states
16 Conversion Result Registers ($0090 - $009F)


General status information regarding ADC
2 Test Registers ($0088 - $0089)


Configure general ADC operation
Convert channels to digital inputs
1 Digital Port Data Register ($008F)

Contains logic levels of digital input pins
ATD10B8C
Control Register 2
ATD10B8C
Control Register 3
ATD10B8C
Control Register 4
ATD10B8C
Control Register 5
ATD10B8C
Single Channel Conversions
ATD10B8C
Multi-channel Conversions
ATD10B8C
Status Register 0
ATD10B8C
Status Register 1
ATD10B8C
Results Registers
ATD10B8C
Results Registers
ATD10B8C
ATD Input Enable Register
ATD10B8C
Port Data Register
ATD10B8C
Setting up the ADC
References
• Dr. Ume, http://www.me.gatech.edu/mechatronics_course/
• Maxim Integrated Products, AN1870, AN 1870, APP1870, Appnote1870, Appnote
1870
• "An Introduction to Sigma Delta Converters." Die Homepage Der Familie Beis. 10
June 2008. Web. 27 Sept. 2010.
<http://www.beis.de/Elektronik/DeltaSigma/SigmaDelta.html>.