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
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

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
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
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
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 4
(8.75+7.5)/2 8.125
7.65 < 8.125  Bit 4 = 0
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 3
(8.125+7.5)/2 = 7.8125
7.65 < 7.8125  Bit 3 = 0
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 2
(7.8125+7.5)/2 = 7.65625
7.65 < 7.65625  Bit 2 = 0
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 1
(7.65625+7.5)/2 = 7.578125
7.65 > 7.578125  Bit 1 = 1
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 0
(7.65625+7.578125)/2 = 7.6171875
7.65 > 7.6171875  Bit 0 = 1
Vin = 7.65
Successive Approximation ADC Example
110000112 = 19510
8-bits, 28 = 256
Digital Output
195/256 = 0.76171875
Analog Input
7.65/10 = 0.765

Resolution
(Vmax – Vmin)/2n  10/256 = 0.039
Voltage
Bit
Vin = 7.65
ADC Applications
Measurements / Data Acquisition
Control Systems
PLCs (Programmable Logic Controllers)
Sensor integration (Robotics)
Cell Phones
Video Devices
Audio Devices
ATD10B8C on MC9S12C32
Presented by
Quinn Morrison
MC9S12C32
Block Diagram
ATD 10B8C
ATD10B8C
Block Diagram
ATD10B8C
Key Features
Resolution
8/10 bit (manually chosen)
Conversion Time
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
All clocks halt; conversion aborts; minimum recovery delay
Wait Mode
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
Analog input channel 7
External trigger for ADC
General purpose digital I/O

AN6/PAD6 – AN0/PAD0
Analog input
General purpose digital I/O

VRH, VRL
High and low reference voltages for ADC

VDDA, VSSA
Power supplies for analog circuitry
ATD10B8C
Registers
6 Control Registers ($0080 - $0085)
Configure general ADC operation

2 Status Registers ($0086, $008B)
General status information regarding ADC

2 Test Registers ($0088 - $0089)
Allows for analog conversion of internal states

16 Conversion Result Registers ($0090 - $009F)
Formatted results (2 bytes)

1 Digital Input Enable Register ($008D)
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.
.