数字电路英文版第十三单元.ppt

CHAPTER 13 INTERFACING,KEY TERMS,Acceptor A receiving device on a bus. Analog-to-digital converter (ADC) A device used to convert an analog signal to digital form. Bus A set of interconnections that interface one or more devices based on a standardized specification.,Bus arbitration The process that prevents two sources from using a bus at the same time. Bus contention An adverse condition that could occur if two or more devices try to communicate at the same time on a bus.,Controller An instrument that can specify each of the other instruments on the bus as either a talker or a listener for the purpose of data transfer. DCE Data communications equipment. Digital-to-analog converter (DAC) A device used to convert a digital input to an analog signal .,DTE Data terminal equipment. Flash ADC A simultaneous analog-to-digital converter. Handshaking The process of signal interchange by which two digital devices or systems jointly establish communication.,High-Z The high-impedance state of a tristate circuit in which the output is effectively disconnected from the rest of the circuit. Interfacing The process of making two or more electronic devices or systems operationally compatible with each other so that they can function properly together.,ISA bus Industry standard architecture bus; an internal parallel bus standard. Local bus An internal bus that connects the microprocessor to the cache memory, the main memory, the coprocessor, and the PCI bus controller.,Modem A modulator/demodulator for interfacing digital devices to analog transmission systems such as telephone lines. PCI bus Peripheral control interconnect bus; an internal parallel bus standard.,Peripheral A device or instrument that provides communication with a computer or provides auxiliary services or functions for a computer. Port The physical interface between a computer and a peripheral. SCSI Small computer system interface; an external parallel bus standard.,Source A sending device on a bus. Tristate A type of output in logic circuits that exhibits three states: HIGH, LOW, and High-Z. USB Universal serial bus; an external serial bus standard.,13.1 DIGITAL AND ANALOG INTERFACING,Analog quantities are sometimes called real-world quantities because most physical quantities that we are interested in measuring are analog in nature.,2,3,Many applications of computers and other digital systems require the input of real-world quantities, such as temperature, speed, position, pressure, and force.,Real-world quantities can even include graphic images. Also, digital systems often must produce outputs to control real-world quantities.,4,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,8,9,7,6,5,10,1,2,3,4,15,11,12,13,14,16,17,18,19,20,15,1110,1110,0100,0101,0101,0110,1011,0111,1001,1101,1101,1100,1100,1010,0111,1001,0101,0010,0000,0100,0100,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,8,9,7,6,5,10,1,2,3,4,15,11,12,13,14,16,17,18,19,20,15,5,Application Examples,Address bus,To interface between the digital and analog worlds, two basic processes are required: analog-to-digital ( A/D ) conversion and digital-to-analog ( D/A ) conversion.,6,7,An Electronic Thermostat,1,Amplifier,ADC,Actual temperature,Desired temperature,Control and display logic,7,8,9,4,5,6,1,2,3,0,.,#,On/Off Heat/Cool,Temperature sensor,Digital code,Analog voltage,To HVAC unit,8,CD Player,Amplifier,Digital signal processor,Digital code,Pulses,Amplifier,Amplifier,DAC,Control On/Off, open/close,play,pause, track, search,Laser pick-up head,Right channel audio,Lift channel audio,9,A Digital Audiotape Player/Recorder,Amplifier,Digital signal processor,Audio in,Amplifier,Amplifier,DAC,Control On/Off, open/close,play,pause, track, search,ADC,Right channel audio,Lift channel audio,Tape driver Magnetic read/write heads,Digital code,10,13.2 DIGITAL-TO-ANALOG ( D/A ) CONVERSION,D/A conversion is an important part of many systems. In this section, we will examine the theory of operation of two basic types of digital-to-analog converters ( DACs ) and learn about their performance characteristics.,11,The Operational Amplifier,+,-,+,-,+,-,Inverting input,Noninverting input,Output,Vin,Vin1,Vin2,Vout,Rf,Ri,High internal input R,Vout,(a) Op-amp symbol,(c) Op-amp as a comparator,(b) Op-amp as an inverting amplifier with gain of Rf/Ri,Rf,Vout,= -,Vin,Ri,12,Binary-Weighted-Input Digital-to-Analog Converter,+,-,Rf,8R,4R,2R,R,I1,I0,I2,I3,I0,=,8R,V,I3,=,R,V,I2,=,2R,V,I1,=,4R,V,+,_,20,23,22,21,V,V,V,V,Vout,I = 0,If,Vout = IfRf,Figure 14-37,Thomas L. Floyd Digital Fundamentals, 8e,Copyright 2003 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.,Figure 14-38 Output of the DAC in Figure 14-37.,Thomas L. Floyd Digital Fundamentals, 8e,Copyright 2003 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.,13,The R/2R Ladder Digital-to-Analog Converter,+,-,Rf =2R,R8,R,D0,2R,Vout,D1,D2,D3,R,R,R6,R4,R2,R1,R3,R5,R7,2R,2R,2R,2R,Inputs,14,+,-,Rf =2R,D3 =1,REQ=2R,R7,2R,I,=,2R,5V,+5V,0,Vout = -IfRf =-( )2R,2R,5V,= - 5 V,(a) Equivalent circuit for D3=1,D2=0,D1=0,D0=0,+,-,Rf =2R,D2 =1,R5,2R,I,=,2R,+5V,R7,R8,REQ=2R,R,2R,+,-,Rf =2R,R7,2R,R,R,RTH,R8,2.5V,VTH,2.5V,I =0,0 V,Vout = -IfRf =-( )2R,2R,2.5V,= - 2.5 V,(b) Equivalent circuit for D3=0,D2=1,D1=0,D0=0,15,16,I,=,2R,+,-,Rf =2R,R7,2R,R,R,RTH,R8,1. 25V,VTH,1.25V,I =0,0 V,Vout = -IfRf = -( )2R,2R,1.25V,= - 1.25 V,(c) Equivalent circuit for D3=0,D2=0,D1=1,D0=0,17,I,=,2R,+,-,Rf =2R,R7,2R,R,R,RTH,R8,0.625V,VTH,0.625V,I =0,0 V,Vout = -IfRf = -( )2R=-0.625V,2R,0.625V,(d) Equivalent circuit for D3=0,D2=0,D1=0,D0=1,Resolution. The resolution of a DAC is the reciprocal of the number of discrete steps in the output. The total number of discrete steps equals 2n 1, where n is the number of bits. ( 4-bit DAC, (1/15)* 100 = 6.67% ),Accuracy. Accuracy is a comparison of the actual output of a DAC with the expected output. It is expressed as a percentage of a full-scale, or maximum, output voltage. For example, if a convert has a full-scale output of 10 V and the accuracy is + 0.1%, then the maximum error for any output voltage is (10V)(0.001) = 10 mV.,Ideally, the accuracy should be no worse than + of a least significant bit. For an 8-bit converter, the least significant bit is 0.39% of full scale. The accuracy should be approximately + 0.2%.,Linearity. A linear error is a deviation from the ideal straight-line output of a DAC. A special case is an offset error, which is the amount of output voltage when the input bits are all zeros.,Monotonicity. A DAC is monotonic if it does not take any reverse steps when it is sequenced over its entire range of input bits.,Settling time. Settling time is normally defined as the it takes a DAC to settle within + LSB of its final value when a change occurs in the input code. ( The settling time of a DAC is the time it takes for the DACs analog output settle to 99.95% of its new value after a digital input has been applied.),18,EXAMPLE 13-2 Determine the resolution, expressed as a percentage, of the following: An 8-bit DAC (b) a 12-bit DAC Solution : (a) For the 8-bit converter, x 100= x 100 = 0.392%,1,1,28 - 1,255,(b) For the 12-bit converter,1,1,212 - 1,4095,x 100= x 100 = 0.0244%,If a 4-bit DAC has a 12 V reference applied, calculate each of the following: a. step size b. percent resolution c. the weight of each binary column d. the output voltage when 0010 is applied e. the output voltage when 1011 is applied,a. Step size = V0/2n = 12/16= 0.75 V b. %Res. = s/size/V0 = 0.75/12 = 6.25% c. LSB = 12V/ 16 = 0.75 V 1 = 12V/ 8 = 1. 5 V 1 = 12V/ 4 = 3.0 V MSB = 12V/ 2 = 6.0 V d. 0010 = 1.5 V e. 1011 = 8.25 V,If an 8-bit DAC has a 10 V reference applied, calculate each of the following: a. step size b. percent resolution c. the weight of each binary column d. the output voltage when 0000 0101 is applied e. the output voltage when 1011 0111 is applied,a. Step size = V0/2n = 10/256= 0.039 V b. %Res. = s/size/V0 = 0.039/10 = 0.39% c. LSB = 10V/ 256 = 0.039 V 1 = 10V/ 128 = 0.078 V 2 = 10V/ 64 = 0. 156 V 3 = 10V/ 32 = 0. 3125V 4 = 10V/ 16 = 0. 625 V 5 = 10V/ 8 = 1.25 V 6 = 10V/ 4 = 2.5 V MSB = 10V/ 2 = 5 V,d. 0000 0101 = 0.195 V e. 1011 0111 = 7.137 V,13.3 ANALOG TO DIGITAL (A/D) CONVERSION,Flash ( Simultaneous ) Analog-to-Digital Converter: Disadvantages: too many comparators Advantages: fast conversion time,19,6,7,5,4,3,2,1,0,1,2,4,+,_,+,_,+,_,+,_,+,_,+,_,+,_,R,R,R,R,R,R,R,R,Op amp comparators,D0,D1,D2,+VREF,Sampling pulses,Parallel binary output,Priority encoder,Analog input,20,7 6 5 4 3 2 1 0 4 2 1 0 to 0.9 V 0 0 0 0 0 0 0 0 0 0 0 1 to 1.9 V 0 0 0 0 0 0 1 0 0 0 1 2 to 2.9 V 0 0 0 0 0 1 1 0 0 1 0 3 to 3.9 V 0 0 0 0 1 1 1 0 0 1 1 4 to 4.9 V 0 0 0 1 1 1 1 0 1 0 0 5 to 5.9 V 0 0 1 1 1 1 1 0 1 0 1 6 to 6.9 V 0 1 1 1 1 1 1 1 1 1 0 7 V or Greater 1 1 1 1 1 1 1 1 1 1 1 VREF = 8 V R = 1 k,0,1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7,8,10,11,12,t,V,100,110,111,110,101,010,000,001,011,101,110,111,EXAMPLE 13-3,21,22,Related Problem : 13-3 : 010, 100, 101, 110, 110, 111, 110, 110, 101, 100, 011, 010, 000, 000, 001, 001, 010, 011, 100, 101, 110, 110, 111, 111,23,CLK,Stairstep-Ramp Analog-to-Digital Converter,CLEAR,EN,Q6,Q7,Q5,Q4,Q3,Q2,Q1,Q0,D6,D7,D5,D4,D3,D2,D1,D0,D6,D7,D5,D4,D3,D2,D1,D0,Latch,CTR DIV 256,DAC,Control circuit,Stairstep reference voltage,Analog input,Comparator,C,+,_,24,CLK,Tracking Analog-to-Digital Converter,DOWN,EN,Q6,Q7,Q5,Q4,Q3,Q2,Q1,Q0,D6,D7,D5,D4,D3,D2,D1,D0,D6,D7,D5,D4,D3,D2,D1,D0,Latch,Counter,DAC,Control circuit,Analog input,Comparator,C,+,_,UP,4,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,8,9,7,6,5,10,1,2,3,4,15,11,12,13,14,16,17,18,19,20,15,25,26,D6,D7,D5,D4,D3,D2,D1,D0,Counter,Latches,C,Control logic,Ramp generator,Analog input,CLK,Comparator,Reset,EN,t,V,Ramp,+,_,CLEAR,Binary or BCD output,Chapter 13: Interfacing,True/False 1. A light bulb and switch are examples of an analog circuit. 2. A D/A converter changes something like temperature variations into a digital quantity.,3. An operational amplifier is used as a comparator. 4. An eight- bit D/A converter has a resolution of 0.125. 5. The primary disadvantage of the flash A/D converter is the large number of comparators required.,6. When the analog input to a tracking A/D converter is at a constant level, the digital output will oscillate. 7. The RS-232-C is a serial data transfer system.,Multiple Choice,11. Which of the following characterizes an analog quantity? a. Discrete levels represent changes in a quantity. b. Its values follow a logarithmic response curve. c. Can be described with a finite number of steps. d. Has a continuous set of values over a given range.,12. An analog-to-digital c