数字逻辑3-2n.ppt

1、Structure : complement switchs steady state : voltage and current Dynamic state : Speed and cost,Chapter 3 Digital circuit,When Vx is increased, Rp will be increased and Rn decreased !,The resistors model of CMOS,Figure 3-8 3-9 The output voltage is changed When input voltage changed.,The resistors

2、model of CMOS,Steady-state behavior,Ideal behavior,Real behavior,The input between VIL and VIH : Amplified area !,Logic level and noise margin,The input limit : to avoid the noise be amplified!,Device informations from the data sheet,Use Table 3-3 : 74HC00 (NAND2x4) Commercial: Vcc 4.75 Military:Vcc

3、4.5,Get resistor value from the data sheet,For commercial device High level output (use minimal value),Output driven ability,For NAND2 in Table 3-3: If VOHmin= 3.84 V Then IOHmax=4 mA R 3.84/4 = 0.96 k,Limitation for output current and resistive load.,Use NAND2 to drive LED,Fig 3-54 74AC Device : VO

4、Lmax = 0.37 V,If 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 input,Use feedback circuit to shift the switching threshold depending on the input changing ways.,Hysteresis: the difference between the