D15 Schmitt Trigger, One-shots, The 555 timer

1、12022-3-6Chapter 7 Latches, Flip-Flops, and Timers17 Schmitt Trigger, One-shots, The 555 timer1. Schmitt trigger working principle and application;2. Two types of one-shot: differentiation/integration;3. Integrated one-shot application.4. The 555 timer5. The 555 timer application22022-3-6Chapter 7 L

2、atches, Flip-Flops, and Timers2CMOS Schmitt Trigger (常用的脈沖整形電路常用的脈沖整形電路)Look at the circuit on the right:Condition #1: vI changes from 0 to a volt just before G1 inverts state. vo is now output 0 volt. Find the relation between vIand vII212221II0vRRRRRRvvAs long as vI VGS(th), vo= 0 VCondition #2: v

3、I , makes vI VGS(th), vo now outputs VDD.Find vI value at this point, denote it as VT+, then)(21)(2211thGSthGSTVRRVRRRV=0Stable state 1Stable state 2Positive going switching threshold 上限觸發(fā)電平上限觸發(fā)電平1 Schmitt trigger 32022-3-6Chapter 7 Latches, Flip-Flops, and Timers3Determine the Hysterisis of a Schmi

4、tt TriggerFind the relation between vIand vI at condition #2.Remember now vo= VDD= VDDI211IDDI)(vRRRvVvVR1As vI goes down, vI also goes down, when vI VGS(th)Gate 1 output HIGH, gate 2 output LOW, vo= 0 VFind vI value at this point, denote it as VT-, then;1GS(th)21DD21GS(th)221TVRRVRRVRRRVDDGS(th)21N

5、ormallyVVNegative going switching thresholdthe HysteresisGS(th)21TTT2VRRVVV下限觸發(fā)電平下限觸發(fā)電平42022-3-6Chapter 7 Latches, Flip-Flops, and Timers4THTIVRRVV)(211THTIVRRVV)(21121212121101RRmustsolockedcircuitVVRRVVRRVRRDDthTthT，時(shí)當(dāng)Analysis of HysterisisWhen locked, output waveform？In-phase output52022-3-6Chapt

6、er 7 Latches, Flip-Flops, and Timers5Schmitt Trigger Application1. Waveform transformation (波形變換波形變換)Inverted output o vI vO1 VOH VOL VT+VT_62022-3-6Chapter 7 Latches, Flip-Flops, and Timers6Schmitt Trigger Application2. Pulse rectification (脈沖整形脈沖整形 )72022-3-6Chapter 7 Latches, Flip-Flops, and Time

7、rs7Schmitt Trigger Application3. Pulse magnitude detection (脈沖鑒幅脈沖鑒幅)82022-3-6Chapter 7 Latches, Flip-Flops, and Timers8Differential and Integral Circuits ReviewRCuinuoRCuinuoDifferential and integral circuits consist of R、C components that are connected in a certain way and parameters are properly

8、selected.Identify which is differential and which is integral?differentialDistinction：1）output from resistor; 2）time constant t t tw92022-3-6Chapter 7 Latches, Flip-Flops, and Timers9RC Circuit Charge-discharge ReviewRCUuotteUUUuuCO)(0Stable voltageInitial voltageconstanttimecalledisRCtAfter time t，

9、capacitor voltage uc(t), find t expression：)(0lntCuUUURCtMore general expression：)()()0()(lntCCCCuuuuRCtKey formula of pulse102022-3-6Chapter 7 Latches, Flip-Flops, and Timers10I. Integral Type 積分型積分型G1, G2 is TTL gate2 One-shot (單穩(wěn)態(tài)觸發(fā)器單穩(wěn)態(tài)觸發(fā)器)Characteristics： only one stable state and one temporal s

10、tate. upon external triggering，state changes from stabletemporal，hold for a while and automatically back to stable. temporary time depends on circuit intrinsic parameter. Recall two features:1）t ttW ； t t= RC2）output from capacitor112022-3-6Chapter 7 Latches, Flip-Flops, and Timers11；：OHOAOHOIVvvVvv

11、statestable1, 0*；，dischargestartscapacitorstatetemporalenteringcircuitvVaboveremainvbutvtochangevOTHAOI, 0, 01*1；，stabletobackvVvtodischargewhenOTHA, 1*；，initialtobackVtorechargeCtobackvOHI,0*Working PrincipleTriggering pulse 顯然，要求顯然，要求vI的寬度的寬度要保證電容放電到要保證電容放電到VTH以下。以下。See demo122022-3-6Chapter 7 Lat

12、ches, Flip-Flops, and Timers12reTRdretttCRRt )(53(0的時(shí)間。的時(shí)間。放電至放電至從從等于等于時(shí)間時(shí)間輸出脈沖寬度輸出脈沖寬度THOHAOVVVV)0(Parameter ComputationTHOHtwVVRCVVVVRCtlnln)()()()(0Output width：C discharge equivalent circuit132022-3-6Chapter 7 Latches, Flip-Flops, and Timers13.,0, 1,121chargingstartsCvvstatetemporalenteringquick

13、lycircuitvvvvvsignaltriggeringwithOOOIOdIDDTHOLDDOHVVVVV21, 0,G1, G2 is CMOS gate；：voltagenohasCVvvVvvvstatestableDDOODDIdI),( , 0, 0, 012II. Differential Type One-shot142022-3-6Chapter 7 Latches, Flip-Flops, and Timers14G1, G2 is CMOS gateII. Differential Type One-shot.0, 0,11222stabletobackvolttod

14、ischargeCVvvstabletoquicklycircuitvvvfeedbackpinducevVvtochargeDDOOOOIITHI，DDTHOLDDOHVVVVV21, 0,152022-3-6Chapter 7 Latches, Flip-Flops, and Timers152ln0lnln)()()0()(RCVVVRCVVVVRCtTHDDDDtwrewdONONDretttCRCRrRt)53()/)(53(1的的時(shí)時(shí)間間。充充電電至至從從時(shí)時(shí)間間）等等于于輸輸出出脈脈沖沖寬寬度度（THIOVVV012Parameter ComputationOutput widt

15、h0.69RCEquivalent charging circuitDischarging circuitdifferentiation time162022-3-6Chapter 7 Latches, Flip-Flops, and Timers16微分型單穩(wěn)微分型單穩(wěn)Control circuit(74 121)電路結(jié)構(gòu)與工作原理電路結(jié)構(gòu)與工作原理3 One-shot IC chip可構(gòu)成上升沿觸發(fā)或下可構(gòu)成上升沿觸發(fā)或下降沿觸發(fā)的輸入方式降沿觸發(fā)的輸入方式上升沿觸發(fā)從上升沿觸發(fā)從B端輸入端輸入A2A1 at least one is lowB normally low分析穩(wěn)定狀態(tài)時(shí)分析穩(wěn)

16、定狀態(tài)時(shí)vO的值的值010010111011暫穩(wěn)態(tài)結(jié)束后暫穩(wěn)態(tài)結(jié)束后Q又被置又被置0下降沿觸發(fā)時(shí)下降沿觸發(fā)時(shí)B接高電平，接高電平， A2A1任一端可接負(fù)脈沖，任一端可接負(fù)脈沖，另一端也接高電平。另一端也接高電平。問：在暫?jiǎn)枺涸跁悍€(wěn)態(tài)期間穩(wěn)態(tài)期間B端輸入端輸入正脈沖有正脈沖有用嗎？用嗎？不起作用不起作用為不可重復(fù)觸發(fā)為不可重復(fù)觸發(fā)型單穩(wěn)態(tài)觸發(fā)器型單穩(wěn)態(tài)觸發(fā)器172022-3-6Chapter 7 Latches, Flip-Flops, and Timers17200lnlnln)()()()(RCVVVRCVVVVRCtTHCCCCtwNon-retriggerable symbolOne-s

17、hots182022-3-6Chapter 7 Latches, Flip-Flops, and Timers18Nonretriggerable One-Shot Action192022-3-6Chapter 7 Latches, Flip-Flops, and Timers19Minimum pulse width = 45 ns with no external components.General formula:RRCtEXTw7 . 0132. 0Note the difference74LS122 Retriggerable One-Shot202022-3-6Chapter

18、7 Latches, Flip-Flops, and Timers20Illustration of Using a 74LS122 One-ShotDetermine the values of REXT and CEXT that will produce a pulse width of 1us when connected to a 74LS122.Solution: Assume CEXT=560pF, solve for REXT.kpFnsCtCCtRCCRRCRtEXTwEXTEXTwEXTEXTEXTEXTEXTEXTEXTw88. 47 . 0560)32. 0(10007

19、 . 032. 032. 0)32. 0)(7 . 0()32. 0)(7 . 0(32. 07 . 0132. 0Use a standard value of 4.7k.212022-3-6Chapter 7 Latches, Flip-Flops, and Timers21Retriggerable One-Shot ActionBefore tW ending, retrigger it，can increase pulse width.See retriggerable demo222022-3-6Chapter 7 Latches, Flip-Flops, and Timers22

20、See demonstrationUse three 74LS122 to form sequential timing generator232022-3-6Chapter 7 Latches, Flip-Flops, and Timers231. Schmitt trigger utilizes hysteresis and internal positive feedback property, and find applications in wave transformation、pulse rectification、and pulse magnitude detection et

21、c；2. A one-shot triggered by an external signal can change state from stable to temporal，then back to stable. The duration of temporal state depends on external resistor and capacitor and thus can be used to generating timing signal;3. From circuit structure, a one-shot can be classified as differen

22、tial and integral. From triggering method, can have retriggerable and nonretriggerable. Retriggerable can generate wide timing signal.Summary24One-ShotsThe one-shot or monostable multivibrator is a device with only one stable state. When triggered, it goes to its unstable state for a predetermined l

23、ength of time, then returns to its stable state.For most one-shots, the length of time in the unstable state (tW) is determined by an external RC circuit.TriggerCEXTREXT+VCXRX/CXQQtWTriggerQ25One-ShotsRetriggerable one-shots respond to any trigger, even if it occurs in the unstable state. If it occu

24、rs during the unstable state, the state is extended by an amount equal to the pulse width.RetriggerstWTriggerQRetriggerable one-shot:Nonretriggerable one-shots do not respond to any triggers that occur during the unstable state.Nonretriggerable one-shot action26One-ShotsAn application for a retrigge

25、rable one-shot is a power failure detection circuit. Triggers are derived from the ac power source, and continue to retrigger the one shot. In the event of a power failure, the one-shot is not triggered and an alarm can be initiated.tWtWtWRetriggersRetriggersTriggers derived from acQMissing trigger

26、due to power failurePower failure indicationRetriggerable one-shot action27Internal functional diagram of a 555 timer (pin numbers are in parentheses).4 The 555 timer28(7)(6)(2)(3)(5)(4)(8)(1)The 555 timer can be configured in various ways, including as a one-shot. A basic one shot is shown. The pul

27、se width is determined by R1C1 and is approximately tW = 1.1R1C1. The trigger is a negative-going pulse.RESETDISCHTHRESTRIGGNDCONTOUTVCC+VCCtW = 1.1R1C1C1R14 The 555 timerone-shot29(7)(6)(2)(3)(5)(4)(8)(1)The 555 timerRESETDISCHTHRESTRIGGNDCONTOUTVCC+VCCtW = 1.1R1C1C1R1Determine the pulse width for

28、the circuit shown. tW = 1.1R1C1 = 1.1(10 k)(2.2 mF) =10 k2.2 mF24.2 ms+15 V30The 555 timerThe 555 can be configured as a basic astable multivibrator with the circuit shown. In this circuit C1 charges through R1 and R2 and discharges through only R2. The output frequency is given by:The frequency and

29、 duty cycle are set by these components.1211.442fRRC(7)(6)(2)(3)(5)(4)(8)(1)RESETDISCHTHRESTRIGGNDCONTOUTVCCC1R1R2+VCCmultivibrator31The 555 timerGiven the components, you can read the frequency from the chart. Alternatively, you can use the chart to pick components for a desired frequency.(7)(6)(2)

30、(3)(5)(4)(8)(1)RESETDISCHTHRESTRIGGNDCONTOUTVCCC1R1R2+VCC10 M1 M100 k10 k1 k101.00.10.010.0010.11.0101001.0k10k100k100C1 (mF)f (Hz)325 The 555 timer application 555定時(shí)器及其應(yīng)用定時(shí)器及其應(yīng)用1 555定時(shí)器定時(shí)器2 用用555定時(shí)器組成施密特觸發(fā)器定時(shí)器組成施密特觸發(fā)器3 用用555定時(shí)器組成定時(shí)器組成單穩(wěn)態(tài)觸發(fā)器單穩(wěn)態(tài)觸發(fā)器 4 用用555定時(shí)器定時(shí)器組成組成多諧振蕩器多諧振蕩器33 555定時(shí)器是一種應(yīng)用方便的中規(guī)模集成電路定

31、時(shí)器是一種應(yīng)用方便的中規(guī)模集成電路, 廣泛用于信號(hào)的廣泛用于信號(hào)的產(chǎn)生、變換、控制與檢測(cè)。產(chǎn)生、變換、控制與檢測(cè)。 555定時(shí)器及其應(yīng)用定時(shí)器及其應(yīng)用電阻分壓器電阻分壓器電壓比較器電壓比較器基本基本SR鎖存器鎖存器輸出緩沖反相器輸出緩沖反相器集電極開路輸出三極管集電極開路輸出三極管 TvovICvI1vI2voC1C2+-+(1)(2)(3)(4)(5)(6)(7)RS&5 k 5 k 5 k &1RDVCC (8)G1、電路、電路 結(jié)構(gòu)結(jié)構(gòu)342、工作原理、工作原理 VCC 5k vIC vI1 C1 5k vI2 C2 5k v O T S R RD & &

32、 & 1 G vO 不變不變不變不變1導(dǎo)通導(dǎo)通01截止截止11導(dǎo)通導(dǎo)通00放電放電管管T輸出輸出(VO)復(fù)位復(fù)位(RD)觸發(fā)輸入觸發(fā)輸入(VI2)閾值輸入閾值輸入(VI1)輸輸 出出輸輸 入入CC31V CC31V CC31V CC32V CC32V CC32V 35 3、555定時(shí)器功能表定時(shí)器功能表不變不變不變不變1導(dǎo)通導(dǎo)通01截止截止11導(dǎo)通導(dǎo)通00放電管放電管T輸出輸出(VO)復(fù)位復(fù)位(RD)觸發(fā)輸入觸發(fā)輸入(VI2)閾值輸入閾值輸入(VI1)輸輸 出出輸輸 入入CC31V CC31V CC31V CC32V CC32V CC32V 36用用555定時(shí)器組成施密特觸發(fā)器定時(shí)器組

33、成施密特觸發(fā)器 VCC 5k vIC vI1 C1 5k vI2 C2 5k v O T S R RD & & & 1 G (3vvI如何改變電路的閾值電壓和回差電壓如何改變電路的閾值電壓和回差電壓? vI VCC 2 3 VCC 1 3 O vO O t t vO O VCC/3 vI 2VCC/3 37 施密特觸發(fā)器的應(yīng)用施密特觸發(fā)器的應(yīng)用 VCC VCC1 8 4 555 6 2 vI R vO2 vO1 VIC 0.01m mF 7 3 5 1 波形變換波形變換 t 1 3 VCC 2 3 VCC vI 0 t vO 1 VO H 0 o vI vO1 VOH

34、VOL VT+VT_電路的頻率可變電路的頻率可變?占空比可變占空比可變?如何改變占空比如何改變占空比?回差電壓減小回差電壓減小,占空比如何變化占空比如何變化?38 波形產(chǎn)生電路波形產(chǎn)生電路( (多諧振蕩器多諧振蕩器 ) C Cv vo ov vI IR R1 1 VCC 8 4 555 6 2 R 0.01m mF 7 3 5 1 C 39v vo ov vI IV VT+T+V VT_T_V VOLOLV VOHOHT T1 1T T2 20 0t t0 0t t12DDTT+DDTTDDTT+DDTT-lnln()lnTTTVVVRCRCRVVVVVCVVVV C Cv vo ov vI

35、IR R1 140用用555定時(shí)器定時(shí)器組成組成單穩(wěn)態(tài)觸發(fā)器單穩(wěn)態(tài)觸發(fā)器 1、電路、電路 VCC vI R vO 0.01m mF C vC 8 4 555 7 6 2 3 5 1 41外加觸發(fā)信號(hào)，電路轉(zhuǎn)換到暫態(tài)，輸出為外加觸發(fā)信號(hào)，電路轉(zhuǎn)換到暫態(tài)，輸出為1觸發(fā)信號(hào)消除后，電容充電電路自動(dòng)轉(zhuǎn)換到穩(wěn)態(tài)輸出為觸發(fā)信號(hào)消除后，電容充電電路自動(dòng)轉(zhuǎn)換到穩(wěn)態(tài)輸出為0沒有觸發(fā)信號(hào)時(shí)沒有觸發(fā)信號(hào)時(shí)( i )電路處于穩(wěn)態(tài)，電路處于穩(wěn)態(tài)，輸出為輸出為0 0 13VCCVCC 5k vIC vI1 C1 5k vI2 C2 5k v O T S R RD & & & 1 G vO vI42

36、 VCC vI R vO 0.01m mF C vC 8 4 555 7 6 2 3 5 1 tw=RC1n31.1RC 4 4、）工作波形及輸出脈寬的計(jì)算、）工作波形及輸出脈寬的計(jì)算電路是可重復(fù)觸發(fā)的單穩(wěn)電路是可重復(fù)觸發(fā)的單穩(wěn)? ?如將如將5腳接電壓腳接電壓V,電路的脈寬會(huì)改變嗎電路的脈寬會(huì)改變嗎?V增加增加,脈寬脈寬如何改變?nèi)绾胃淖?減小減小? vI O vC O vO O 2 3 VCC tW t t t 43 vI O t 8 4 2 5 3 7 6 vI 1 vIC C vO R VCC 脈沖寬度調(diào)制器脈沖寬度調(diào)制器工作波形工作波形 vIC O VCC VCC 2 3 VCC 1 3

37、 t vO O t 555組成的單穩(wěn)態(tài)的應(yīng)用組成的單穩(wěn)態(tài)的應(yīng)用:44 用用555555定時(shí)器組成定時(shí)器組成可重復(fù)觸發(fā)單穩(wěn)可重復(fù)觸發(fā)單穩(wěn) 8 4 7 6 2 1 3 5 R VCC R1 C T vI vO 0.01m mF vI O vC O vO O 2 3 VCC tW t t t tW 45用用555定時(shí)器定時(shí)器組成組成多諧振蕩器多諧振蕩器1 1、電路組成電路組成 VCC vC vO 0.01m mF C 8 4 555 7 6 2 3 5 1 R1R2 TC1C2+-+(4)RS&5 k 5 k 5 k &1RDVCC(8)G(1)(2)(5)(6)(7)vovoC)(

38、-CCV-1R-2R461 1、）、）電路第一暫態(tài)，輸出為電路第一暫態(tài)，輸出為1 1。電容充電，電路轉(zhuǎn)換到。電容充電，電路轉(zhuǎn)換到第二暫態(tài)第二暫態(tài), ,輸出為輸出為0 02 2、工作原理、工作原理2 2、）、）電路第二暫穩(wěn)態(tài)，電容放電，電路轉(zhuǎn)換到第一暫態(tài)電路第二暫穩(wěn)態(tài)，電容放電，電路轉(zhuǎn)換到第一暫態(tài) TC1C2+-+(4)RS&5 k 5 k 5 k &1RDVCC(8)G(1)(2)(5)(6)(7)vovoC)(-CCV-1R-2R473、工作波形與振蕩頻率計(jì)算工作波形與振蕩頻率計(jì)算tPL=R2C1n20.7R2C tpH = (R1+R2)C1n20.7(R1+R2)C PL

39、PH1211.43(2)fttRR C VCC vC v0.01m mF C 8 4 555 7 6 2 3 5 1 R1 R2 vC VCC 2 3 VCC 1 3 O vO O tPL tPH t t 484 4、用用555555定時(shí)器組成定時(shí)器組成占空比可的調(diào)占空比可的調(diào)多諧振蕩器多諧振蕩器tPL=RBC1n20.7RBC tpH = RAC1n20.7RAC RA RB R1 R2 R3 D2 C vC D1 8 4 7 6 2 1 5 3 555 VCC vO 0.01m m F C)RR(.ttfB ApLpH4311%(%)q100A B BA AR RR RR R 49 555定時(shí)器的定時(shí)器的實(shí)例實(shí)例圖是利用多諧振圖是利用多諧振蕩器構(gòu)成的簡(jiǎn)易蕩器構(gòu)成的簡(jiǎn)易溫控報(bào)警電路，溫控報(bào)警電路，利用利用555555構(gòu)成可構(gòu)成可控音頻振蕩電路，控音頻振蕩電路，用揚(yáng)聲器