Analog to Digital Converters (ADC)

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

Output States

Discrete Voltage Ranges (V)

0 0.00-1.251 1.25-2.502 2.50-3.753 3.75-5.004 5.00-6.255 6.25-7.506 7.50-8.757 8.75-10.0

Out-put

Binary Equivalent

0 0001 0012 0103 0114 1005 1016 1107 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 ExampleMike 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

1





• Bit 6• (Vfull scale +5)/2 = 7.5• 7.65 > 7.5 Bit 6 = 1


1 1





• Bit 5• (Vfull scale +7.5)/2 = 8.75• 7.65 < 8.75 Bit 5 = 0


1 1 0





• Bit 4• (8.75+7.5)/2 8.125• 7.65 < 8.125 Bit 4 = 0

Vin = 7.65

1 1 0 0





• Bit 3• (8.125+7.5)/2 = 7.8125• 7.65 < 7.8125 Bit 3 = 0

Vin = 7.65

1 1 0 0 0





• Bit 2• (7.8125+7.5)/2 = 7.65625• 7.65 < 7.65625 Bit 2 = 0

Vin = 7.65

1 1 0 0 0 0





• Bit 1• (7.65625+7.5)/2 = 7.578125• 7.65 > 7.578125 Bit 1 = 1

Vin = 7.65

1 1 0 0 0 0 1





• Bit 0• (7.65625+7.578125)/2 =

7.6171875• 7.65 > 7.6171875 Bit 0 = 1

Vin = 7.65

1 1 0 0 0 0 1 1


• 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

1 1 0 0 0 0 1 1

7 6 5 4 3 2 1 00

0.2

0.4

0.6

0.8

1

Volta

ge

Bit

Vin = 7.65

ADC Applications• Measurements / Data Acquisition• Control Systems• PLCs (Programmable Logic Controllers)• Sensor integration (Robotics)• Cell Phones• Video Devices • Audio Devices

t t

e e*Controller00

1001

0100

1110

11

∆t

e*(∆t)

1001

0010

1010

0101

∆t

u*(∆t)

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 OperationsModes 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 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>.

http://www.me.gatech.edu/mechatronics_course/

Documents

Analog to Digital Converters (ADC)