《電子技術(shù)數(shù)字基礎(chǔ) digital fundamentals》雙語(yǔ)課件 introduction to digital signal processing

1、11 Interfacing (接口)1ContentsIntroductionDigital and Analog InterfacingDigital-to-Analog (D/A) Conversion (DAC)The operational amplifier: op-amp Binary-Weighted-Input DAC The R/2R Ladder DAC Performance Characteristics of DACA specific DAC DAC08082ContentsAnalog-to-Digital (A/D) Conversion (ADC)Stair

2、 step-Ramp ADCTracking ADCSingle-slope ADCDual-slope ADCSuccessive-approximation ADCPerformance Characteristics of ADCTroubleshooting DACs and ADCs311-0 IntroductionElectronic circuits can be divided into two broad categories, digital and analog .An analog quantity (模擬量)is one having continuous valu

3、es.411-0 IntroductionA digital quantity (數(shù)字量) is one having a discrete (離散的) (discontinuous 不連續(xù)的) set of values.511-0 IntroductionMany quantities are analog in nature; that is, they are continuous quantities. Physical quantities such as temperature (溫度), pressure (壓力), time (時(shí)間), velocity(速度), and s

4、ound (聲音) are examples of analog quantities.611-0 IntroductionAn analog electronic system: - a public address systemAmplifier711-0 IntroductionNow most of modern electronic devices and systems are digital system. 811-0 Introduction911-0 IntroductionInterfacing is the process of making two or more de

5、vices or systems compatible with each other so that they function together as required. (接口是使兩個(gè)或多個(gè)設(shè)備或系統(tǒng)性能兼容地工作)Q: How can different kinds of systems work together?Interfacing1011-0 IntroductionTo interface between the digital and analog worlds, two basic processes are required: analog-to-digital con

6、version (ADC) (模擬到數(shù)字轉(zhuǎn)換器，簡(jiǎn)稱為模數(shù)轉(zhuǎn)換器) and digital-to-analog conversion (DAC) (數(shù)字到模擬轉(zhuǎn)換器，簡(jiǎn)稱為數(shù)模轉(zhuǎn)換器) 1111-1 Digital and Analog InterfacingADC: analog-to-digital conversion/converter (模擬信號(hào)到數(shù)字信號(hào)的轉(zhuǎn)換，其器件簡(jiǎn)稱為模數(shù)轉(zhuǎn)換器). Analog valuesDigital codes0011ADC010001011211-1 Digital and Analog InterfacingBasic block diagram

7、of a CD player (CD播放器).Digital codeAnalogsignal1311-1 Digital and Analog InterfacingBasic block diagram of an electronic thermostat (溫度控制器) that uses an ADC.Digital codeADCAmp.Actual temp.Desired temp. CDU19.422.222.2Analog value1411-1 Digital and Analog InterfacingDigital Codes0011,0100,0101DAC: di

8、gital-to-analog conversion/converter (數(shù)字信號(hào)到模擬信號(hào)的轉(zhuǎn)換，其器件簡(jiǎn)稱為數(shù)模轉(zhuǎn)換器)DACAnalog values15Basic block diagram of a digital audiotape (DAT) player/recorder (數(shù)字磁帶式錄放機(jī)) 11-1 Digital and Analog Interfacing16Amp.ADCDSPDACAmp.ControlOn/offPlayRecord010 1Tape DriverMagnetic read/write headAnalog valueDigital codeAn

9、alog value11-1 Digital and Analog InterfacingIn the record modeIn the play mode1711-2 Digital-to-Analog Conversion DACBefore getting into DACs, lets look briefly at an element that is common to most types of DACs and ADCs.This element is the operational amplifier (運(yùn)算放大器), or op-amp for short.1811-2-

10、1 The operational amplifier: op-ampAn op-amp is a linear amplifier (線性放大器) that has one output and two inputs (inverting (反相輸入端) and noninverting (同相輸入端).1911-2-1 The operational amplifier: op-ampThe ideal op-amp has a very high voltage gain (高電壓增益/電壓放大倍數(shù)) and a very high input impedance (高輸入阻抗) as

11、well as a very low output impedance (低輸出阻抗).2011-2-1 The op-ampop-amp symbolAs an inverting amplifierAs a comparator2111-2-1 The op-ampThe op-amp used as an inverting amplifier (作為反相放大器)The feedback resistor Rf (反饋電阻)input resistor Ri (輸入端電阻)Virtual short (虛短)Virtual open (虛斷)Virtual ground (虛地)Inte

12、rnally input impedance Ri (輸入阻抗)2211-2-1 The op-ampThe relationship formula between the input and output voltages:The negative sign indicates inversion2311-2-2 Binary-Weighted-Input DAC (權(quán)電阻網(wǎng)絡(luò)D/A轉(zhuǎn)換器)DAC methodsThe R/2R Ladder DAC(倒T形DAC)Binary-Weighted-Input DAC(權(quán)電阻網(wǎng)絡(luò)D/A轉(zhuǎn)換器)Others2411-2-2 Binary-Wei

13、ghted-Input DAC (權(quán)電阻網(wǎng)絡(luò)D/A轉(zhuǎn)換器)This method uses a resistor network with resistance values that represent the binary weights of the input bits of the digital code.25Each of the input resistors will either have current or have no current, depending on the input voltage level. The input voltage is 0, the

14、 current is also 0; The input is 1, the amount of current depends on the input resistor value and is different for each input resistor.2611-2-2 Binary-Weighted-Input DACFor 4-bit binary-weight-input DAC, the input current of the op-amp is approximately zero, 2711-2-2 Binary-Weighted-Input DAC2811-2-

15、2 Binary-Weighted-Input DACFor a n-bit binary-weight-input DAC,2911-2-2 Binary-Weighted-Input DAC3011-2-2 Binary-Weighted-Input DACExample. Determine the output of the DAC if the waveforms representing a sequence of 4-bit numbers shown in the following figure are applied to the inputs. Input D0 is L

16、SB.3111-2-2 Binary-Weighted-Input DAC3211-2-2 Binary-Weighted-Input DAC3311-2-2 Binary-Weighted-Input DACBecause VREF can be positive or negative voltage, Vo is positive or negative according to what it is needed.Advantage: not too many resistors are included.Disadvantage: not easy to be integrated

17、because the distinct resistance difference among them.3411-2-3 The R/2R Ladder DAC (倒T形DAC)This methods overcomes the problems in the binary-weight-input DAC in that it requires only two resistor values.3511-2-3 The R/2R Ladder DAC3611-2-3 The R/2R Ladder DAC3713-2-3 The R/2R Ladder DAC3811-2-4 Perf

18、ormance Characteristics of DAC (DAC 的性能參數(shù))The performance characteristics of a DAC include resolution, accuracy, linearity, monotonicity, and settling time.Resolution (分辨率). It is the reciprocal (倒數(shù)) of the number of discrete steps in the output. This, of course, is dependent on the number of input

19、bits. e.g. a 4-bit DAC has a resolution of one part in (24-1) (one part in fifteen) (1/15).3911-2-4 Performance Characteristics of DACFor a 10-bit DAC, the resolution is 4011-2-4 Performance Characteristics of DAC2. Accuracy (轉(zhuǎn)換精度). It is a comparison of the actual output of a DAC with the expected

20、output (實(shí)際輸出值與期望值的比較). 4111-2-4 Performance Characteristics of DAC The accuracy is expressed as a percentage of a full-scale, or maximum, output voltage (精度采用輸出電壓最大量程或最大值的百分比表示). e.g. If a DAC has a full-scale output of 10V and the accuracy is 0.1%, then the maximum error for any output voltage is 1

21、0V0.1%=10mV. 4211-2-4 Performance Characteristics of DAC3. Linearity (線性度). A linear error (線性誤差) is a deviation (偏差) from the ideal straight-line output of a DAC. An offset error is the amount of output voltage when the input ones are all zeros (偏移量誤差是指當(dāng)所有輸入均為0時(shí)的輸出電壓值).4311-2-4 Performance Characte

22、ristics of DAC4. Monotonicity (單調(diào)性). A DAC is monotonic if it does not take any reverse steps when it is sequenced over its entire range of input bits.5. Settling time (建立時(shí)間, 轉(zhuǎn)換速度). It is normally defined as the time it takes a DAC to settle within 1/2 LSB of its final value when a change occurs in

23、the input code. 4411-3 Analog-to-Digital Conversion (ADC)ADC is the process by which an analog quantity is converted to digital form.Because the analog signal is continuous, and the digital form is discrete, the analog signal is sampled (采樣) at a sampled interval time (采樣間隔), and the sampled signal

24、is converted to digital signal. 4511-3 Analog-to-Digital Conversion (ADC)Flash analog-to-digital converter (快速ADC) The flash method utilizes comparators that compare reference voltages with the analog input voltage. When the analog voltage exceeds the reference voltage for a given comparator, a HIGH

25、 is generated.4611-3 Analog-to-Digital Conversion (ADC)A 3-bit converter that uses seven comparator circuits; a comparator is not needed for the all-0s condition.4711-3 Analog-to-Digital Conversion (ADC)In general, 2n-1 comparators are required for conversion to an n-bit binary code.The large number

26、 of comparators necessary for a reasonable-sized binary number is one of the disadvantage of the flash ADCAdvantage: fast conversion.4811-3 Analog-to-Digital Conversion (ADC)The reference voltage for each comparator is set by the resistive voltage-divided circuit.The output of each comparator is con

27、nected an input of the priority encoder.The encoder is sampled by a pulse on the enable input.4911-3 Analog-to-Digital Conversion (ADC)The sampling rate determines the accuracy with which the sequence of digital codes represents the analog input of the ADC. The more samples taken in a given unit of

28、time, the more accurately the analog signal is represented in digital form.5011-3 Analog-to-Digital Conversion (ADC)Ex. 13-3 Determine the binary code output of the 3-bit flash ADC for the analog input signal and the sampling pulses shown. For this example, VREF=+8V.5111-3 Analog-to-Digital Conversi

29、on (ADC)5211-3 Analog-to-Digital Conversion (ADC)2. Tracking analog-to-digital converterThe tracking method uses an up/down counter, tends to track the analog input.The figure shows a typical 8-bit tracking ADC53As long as the output reference voltage is less than the analog input, the comparator output is HIGH, putting the counter in the UP mode.This causes an increasing stairstep reference voltage output of the DAC, which continues until th