Analog to Digital Converters (ADC) Ben Lester, Mike Steele, Quinn Morrison

Topics Introduction Successive Approximation ADC example Applications 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 Analog systems are typically what engineers need to analyze. ADCs are used to turn analog information into digital data. a system that can produce many different values. Voltmeter, thermometer, spedometer

Process Sampling, Quantification, Encoding Output States Discrete Voltage Ranges (V) 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 Out-put Binary Equivalent 000 1 001 2 010 3 011 4 100 5 101 6 110 7 111 Value of Digital system is taken at determined times, time samples Ts. Use Nyquist Theorem, fs>2*fmax;sampling frequency should be 2 times the max frequency of the analog output. Quantification: Assigning of input to relative output state. Break up based on number of possible states determined by number of bits for the ADC. In this example, since there are 8 states, it is a 3 bit ADC. Encoding is changing the output state to it’s binary equivalent so that it can be used by the computer/circuit.

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. Accuracy- higher sampling rate will increase the number of time intervals and resolution will get the output value closer to the analog value. Speed – varies by type

Comparing types of ADCs Flash ADC Sigma-delta ADC Wilkinson ADC Integrating ADC Successive Approximation Converter

Flash ADC Speed: High Cost: High Accuracy: Low Image: http://www.acclivities.com/images/clip_image007.gif Comparator connected to logic switch to encode. Direct conversion ADC.

Sigma-delta ADC Speed: Low Cost: Low Accuracy: High http://www.maxim-ic.com/app-notes/index.mvp/id/1870 http://www.beis.de/Elektronik/DeltaSigma/SigmaDelta.html

Wilkinson Analog Digital Converter (ADC) circuit schematic diagram Wilkinson ADC Speed: High Cost: High Accuracy: High Wilkinson Analog Digital Converter (ADC) circuit schematic diagram http://fs6.depauw.edu:50080/~akomives/DUNPLweb/summer03/orlayposter.ppt

Integrating ADC Speed: Low Cost: Low Accuracy: High http://www.maxim-ic.com/app-notes/index.mvp/id/1041

Successive Approximation Converter Speed: High Cost: High Accuracy: High but limited “Because the approximations are successive (not simultaneous), the conversion takes one clock-cycle for each bit of resolution desired. The clock frequency must be equal to the sampling frequency multiplied by the number of bits of resolution desired “

Topics Introduction Successive Approximation ADC example Applications 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 Vfull scale = 10, Vin = 7.65 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  

Successive Approximation ADC Example Vfull scale = 10, Vin = 7.65 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  

Successive Approximation ADC Example Vfull scale = 10, Vin = 7.65 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  

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  

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   

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   

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  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  1 

Successive Approximation ADC Example Vin = 7.65 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 1  1  0 0  1 

ADC Applications Measurements / Data Acquisition Control Systems PLCs (Programmable Logic Controllers) Sensor integration (Robotics) Cell Phones Video Devices Audio Devices t e e* Controller 0010 0101 0011 1011 ∆t e*(∆t) 1001 1010 u*(∆t)

ATD10B8C on MC9S12C32 Presented by Quinn Morrison

MC9S12C32 Block Diagram ATD 10B8C

ATD10B8C Block Diagram

ATD10B8C Key Features Resolution Conversion Time 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 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 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. <http://www.beis.de/Elektronik/DeltaSigma/SigmaDelta.html>.