数字逻辑3-2n.ppt

1、u Structure:complement switchsu steady state:voltage and current u Dynamic state:Speed and costChapter 3 Digital circuitWhen Vx is increased,Rp will be increased and Rn decreased!The resistors model of CMOSFigure 3-8 3-9The output voltage is changed When input voltage changed.The resistors model of

2、CMOSSteady-state behaviorIdeal behaviorReal behaviorThe input between VIL and VIH:Amplified area!Logic level and noise marginThe input limit:to avoid the noise be amplified!Device informations from the data sheetUse Table 3-3:74HC00 (NAND2x4)Commercial:Vcc 4.75 Military:Vcc4.5Get resistor value from

3、 the data sheetnpRR4.402.035.0npRR84.3491.0For commercial device High level output(use minimal value)151151.0kRpOutput driven abilityFor NAND2 in Table 3-3:If VOHmin=3.84 VThen IOHmax=4 mAR 3.84/4=0.96 kLimitation for output current and resistive load.Use NAND2 to drive LED Fig 3-54 74AC Device:VOLm

4、ax=0.37 V 303303.010/)6.137.05(kRIf an input is not used?If an input keep floating,the output will be undecided,or the gate may be damaged!Must connected it to some where!More than one outputs connect to a single line?Never Yes,but only one is not Z!Yes,but need pull up resistor!Schmitt Trigger inputUse feedback circuit to shift the switching threshold depending on the input changing ways.Hysteresis:the difference between the threshold Schmitt Trigger inputIt can be used to eliminate noise!