©2008 The McGraw-Hill Companies, Inc. All rights reserved. Digital Electronics Principles & Applications Seventh Edition Chapter 14 Connecting with Analog Devices Roger L. Tokheim ©2008 The McGraw-Hill Companies, Inc. All rights reserved.

INTRODUCTION Hybrid System (analog-to-digital-to-analog) A/D and D/A Converters (block diagrams) Simple 4-bit D/A Converter Simple D/A Converter Operation Counter-ramp-type A/D Converter Ramp-type A/D Converter Successive-approximation A/D Converter Flowcharting- Successive Approximation A/D Converter Specifications Digital Light Meter Digitizing temperature

©2008 The McGraw-Hill Companies, Inc. All rights reserved. Hybrid System (Both Analog and Digital) Digital Processing Unit Decoder D/A Converter Encoder A/D Converter Analog output Analog input Converts from analog input to digital output Converts from digital input to analog output

©2008 The McGraw-Hill Companies, Inc. All rights reserved. QUIZ 1. The encoder in block A is a(n) __________. A/D converter 2. The decoder in block B is a(n) __________. D/A converter Analog input Digital Processing Unit Analog output AB Hybrid System- both Analog and Digital Components

©2008 The McGraw-Hill Companies, Inc. All rights reserved. A/D and D/A Converters Resistor Network Summing Amplifier Analog Voltage Digital-to-analog converter INPUT A/D Analog-to-digital converter Digital Processing Unit Decoder D/A Converter Encoder A/D Converter Analog output Analog input

©2008 The McGraw-Hill Companies, Inc. All rights reserved. Simple D/A Converter 10 k  3 V Input resistors Feedback resistor Binary inputs N = 4 Summing amplifier (inverting) 37.5 k  150 k  75 k  18.7 k  2 N = 16 This circuit can produce 16 different analog output voltages. V reference

©2008 The McGraw-Hill Companies, Inc. All rights reserved. D/A Converter Operation 10 k  3 V 37.5 k  150 k  75 k  18.7 k  Binary input = 0000 = 0 V V out = x 3 V = 0.2 V 10 k  150 k  The smallest step size for this circuit is 0.2 V = 0.2 V

©2008 The McGraw-Hill Companies, Inc. All rights reserved. 4-Bit D/A Converter 10 k  3 V The total span for this circuit is from 0 to 3 V. As the binary input steps from 0000 to 1111 V out steps from 0 V to 3 V 0 V 3 V V out(max) = (2 N - 1) x 0.2 V = 3 V

©2008 The McGraw-Hill Companies, Inc. All rights reserved. V QUIZ 0V 0 0 Q#1- If the binary input to the D/A converter is 0000, then the output voltage will be ___. Summing Amplifier Resistor network D/A converter- (output steps by 0.2V per binary count) ANS: 0V Q#2- If the binary input to the D/A converter is 0001, then the output voltage will be ___ ANS: 0.2V 0.2V Q#3- If the binary input to the D/A converter is 1111, then the output voltage will be ___. 1 1 ANS: 3V 3V Q#4- If the binary input to the D/A converter is 0111, then the output voltage will be ___ ANS: 1.4V 1.4V Q#5- The main active component in the summing amplifier is a(n) ___ (audio, operational) amplifier. ANS: operational

©2008 The McGraw-Hill Companies, Inc. All rights reserved. Counter-Ramp Type A/D Converter When the ramp exceeds V in the comparator output goes LOW and the clock is disabled. V in ramp Binary output V in Clock ramp Comparator Counter D/A Converter HIGH LOW

©2008 The McGraw-Hill Companies, Inc. All rights reserved. QUIZ A C B Binary output V in Clock ramp Counter-ramp type A/D converter (0.2V per step of ramp voltage) Q#1- The block labeled A is a(n) ___ (4-bit counter, op amp). ANS: 4-bit counter Q#2- The block labeled C is a(n) ___ (D/A converter, A/D converter). ANS: D/A converter Q#3- The block labeled B is a(n) ___ (serial-load shift register, voltage comparator). ANS: voltage comparator

©2008 The McGraw-Hill Companies, Inc. All rights reserved. Ramp-type A/D Converter 0 1 Clock pulses to counter Comparator output V in = + 5 V V in Clock Counter Comparator Ramp Generator Binary output LOW

©2008 The McGraw-Hill Companies, Inc. All rights reserved. QUIZ V in Clock A C B Binary output Ramp-type A/D Converter Q#1- The block labeled A in the A/D converter is a(n) ___ (binary counter, op amp). ANS: binary counter Q#2- The block labeled B in the A/D converter is a(n) ___ (ramp generator, shift register). ANS: ramp generator Q#3- The block labeled C in the A/D converter is a(n) ___ (decade counter, voltage comparator). ANS: voltage comparator

©2008 The McGraw-Hill Companies, Inc. All rights reserved. Successive-approximation type A/D Converter V in Successive Approximation Logic Voltage Comparator D/A Converter Clock Binary output 7V input

©2008 The McGraw-Hill Companies, Inc. All rights reserved. Set 1s place to 1 STOP Final result= 0111 Is 0110 high or low? HIGH LOW Set 2s place to 1 Is 0100 high or low? HIGH LOW 7 V input Flowcharting Successive Approximation Assume an input of 7V to a 4-bit binary output A/D converter using successive approximation Clear 8s. Set 4s to 1. Is 1000 high or low? LOW HIGH Set MSB to 1 Start

©2008 The McGraw-Hill Companies, Inc. All rights reserved. QUIZ A C B Clock Binary output 7V input Successive-approximation type A/D converter Q#1- The block labeled A contains the ___ (shift register, successive-approximation logic) unit. ANS: successive-approximation logic Q#2- The block labeled B contains the ___ (D/A converter, successive-approximation logic) unit. ANS: D/A converter Q#3- The block labeled C contains the ___ (ramp generator, voltage comparator) unit. ANS: voltage comparator

©2008 The McGraw-Hill Companies, Inc. All rights reserved. A/D Converter Specifications Type of output Binary (microprocessor-type) Decimal (digital meter type) Resolution Binary output- number of bits (such as 4, 6, 8, 12, 14 or 16) Decimal output- number of digits on display (such as 3 1/2 or 4 1/2) Accuracy Binary output- (ranges from +/- 1/2 LSB to about +/- 2 LSB) Decimal output- (ranges from about 0.01 to 0.05 percent) Conversion time is the time it takes for the IC to convert the analog input voltage to digital output. Binary output A/D converters commonly have faster conversion times than decimal output types.

©2008 The McGraw-Hill Companies, Inc. All rights reserved. QUIZ 2. The resolution of a commercial A/D converter with microprocessor-type output (binary output) would be the number of bits in the output (such as 8-bits for the ADC0804 IC). (True or False) 1.One classification of commercial A/D converters is by the type of output which include either __________ (analog-, binary-) or decimal-type outputs. binary- True 3. The time required for a commercial A/D converter to transform the analog input to a digital output is a characteristic called __________ (access time, conversion time). conversion time 4. Generally, decimal output commercial A/D converters have faster conversion times than binary output types. (True or False) False

©2008 The McGraw-Hill Companies, Inc. All rights reserved. Digital Light Meter Photocell (photoresistive cell) More I = More Vin = Higher binary output Less I = Less Vin = Lower binary output Increase light Lower R Increase I Higher Vin Higher binary output Decrease light Higher R Lower I Decrease Vin Lower binary output

©2008 The McGraw-Hill Companies, Inc. All rights reserved. QUIZ Q#1- Increasing the light striking the photocell will cause a(n) ___ (decrease, increase) in its resistance. ANS: decrease Q#2- Increasing the light striking the photocell will cause a(n) ___ (decrease, increase) in current (I) flowing through resistor R2. ANS: increase Q#3- Increasing the light striking the photocell will cause a(n) ___ (decrease, increase) in voltage across resistor R2 (Vin). ANS: increase Q#4- Increasing the light striking the photocell will cause a(n) ___ (decrease, increase) in the binary value at the outputs of the ADC. ANS: increase Increase light Q#5- Decreasing the light striking the photocell will cause a(n) ___ (decrease, increase) in the binary value at the outputs of the ADC. Decrease light ANS: decrease ©2008 The McGraw-Hill Companies, Inc. All rights reserved.

Digitizing Temperature using a Thermistor Thermistor- Temperature-sensitive Resistor As temperature inceases the resistance of the thermistor decreases Analog Input (Vin) Digital Output Increase in temperature causes decreased resistance Causing increase in I & increase in Vin Low output Decrease in temperature causes increased resistance Causing decrease in I & decrease in Vin High Output

©2008 The McGraw-Hill Companies, Inc. All rights reserved. QUIZ Q#1- Component R3 is a temperature transducer called a _____ (Hall-effect resistor, thermistor). ANS: thermistor Q#2- The Schmitt-trigger inverter converts an analog input voltage to a digital (HIGH or LOW) output. (True or False) ANS: True Q#3- Decreasing the temperature of thermistor R3 will cause its resistance to _____ (decrease, increase). ANS: increase Q#4- Decreasing the temperature of thermistor will cause Vin to decrease and the output of the inverter will go _____ (HIGH, LOW). ANS: HIGH Q#5- Increasing the temperature of thermistor will cause its resistance to decrease and Vin to _____ (decrease, increase). ANS: increase Q#6- Increasing the temperature of thermistor will cause its resistance to decrease, Vin to increase and the output to go _____ (HIGH, LOW). ANS: LOW Vin Output

©2008 The McGraw-Hill Companies, Inc. All rights reserved. REVIEW Hybrid System (analog-to-digital-to-analog) A/D and D/A Converters (block diagrams) Simple 4-bit D/A Converter Simple D/A Converter Operation Counter-ramp-type A/D Converter Ramp-type A/D Converter Successive-approximation A/D Converter Flowcharting- Successive Approximation A/D Converter Specifications Digital Light Meter Digitizing temperature