数字逻辑设计及应用教学英文课件：Lec16-Chap 7.ppt

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1、1Chapter7SequentialLogicDesignPrinciplesLatchesandFlip-FlopsClockedSynchronousState-MachineAnalysisClockedSynchronousState-MachineDesignDigitalLogicDesignandApplication2Question:performan-bitadditionusingonlyone1-bitadder?C1S0X0Y0C0XYCICOSC2S1X1Y1C1反馈C3S2X2Y2C2利用反馈和时钟控制XYCICOSXYCICOSXYCICOSC

2、0S0S1SnX0Y0X1Y1XnYnrippleadderC1C23XYCICOSXYCICOSXYCICOSC0S0S1SnX0Y0X1Y1XnYnrippleadderC1C2暂存XYCICOSCi+1SiXiYiCi时钟控制需要具有记忆功能的逻辑单元，能够暂存运算结果利用反馈和时钟控制4BasicConceptssequentiallogiccircuitOutputsdependsnotonlyonthecurrentinputsbutalsoonthepastsequenceofinputs.Containfeedbackloopsormemorydevice.Fee

3、dbacksequentialcircuit+gatesclockedsynchronousstatemachinelatchandflip-flopMemoryDevicesCombinationalCircuitsExternalInputOutputMemorycircuits:Havestablestatestostorecircuitstates;Changeit’sstateswiththeexternalinputschange.5BasicConcepts“State”embodiesalltheinformationaboutthepastneededtopre

4、dictcurrentoutputbasedoncurrentinput.statevariable,oneormorebitsofinformation.nbit→2nstatesStateinformationisstoredinmemorydevicesMemoryDevicesCombinationalCircuitsExternalInputOutputQnQn+16ClocksignalsVeryimportantwithmostsequentialcircuitsStatevariableschangestateatclockedgeclocktick1.Bi-st

5、abledeviceOscillatortoBi-stablecircuits71Q1oscillation（振荡）Oscillationfrequencydependsonthepropagationdelay00101010Unstable（不稳定）QBi-stable（双稳态）QNQQN=1andQ=0QN=0andQ=18Vin1Vout1Vin2Vout2Vout2Vin2=Vin2=Vout2稳态stable亚稳态metastableQQ_LVin1Vout1Vin2Vout22.AnalogAnalysis达到稳态的条件：反相器得到稳定的反馈输入Vin1=T2(T1

6、(Vin1))Vin2=T1(T2(Vin2))9Allsequentialcircuitsaresusceptibletometastablebehavior.3.MetastableBehaviorThenoisewilltendtodriveacircuitatthemetastablepointtowardoneofthestableoperatingpoint.Applyadefinitepulsewidthfromastablestatetotheother.StableStableMetastableQQ_L1000QQN12QQN113.MetastableBeh

7、aviorQN=0Q=0QN=1Q=1QN=1andQ=0QN=0andQ=1Bi-stable:Meta-stable:振荡的最后结果受两个反相器时延特性的影响，最终可能会稳定到一个双稳态上，或者继续振荡。11ProblemsofBi-stableelementsCan’tdecidetheinitialstateSusceptibletometastablebehavior7.2LatchesandFlip-FlopsQQN12Howtocontrolit……127.2Lat