Application as a diode AND logic function A diode circuit that can generate an AND logic function is shown in Fig. 4.3. A positive–logic convention denotes logic 0 for 0 V and logic 1 for a positive voltage, typically 5 V. Show the truth table that illustrates the logic output.

Question

Application as a diode AND logic function A diode circuit that can generate an AND logic function is shown in Fig. 4.3. A positive–logic convention denotes logic 0 for 0 V and logic 1 for a positive voltage, typically 5 V. Show the truth table that illustrates the logic output.

Accepted Answer

If input [latex] V_{ A } ext { or } V_{ B } [/latex] (or both) is 0, the corresponding diode [latex] \left( D _{1} ext { or } D _{2} ext { or both } ight) [/latex] will conduct, and the output voltage will be 0. In practice, a diode has a finite voltage drop of approximately 0.7 V, and the output voltage will be approximately 0.7 V (or logic 0). If both inputs are high [latex] ext { (i.e., } V_{ A }=5 V ext { and } V_{ B }=5 V ext { ) } [/latex], both diodes will be reverse biased (off), and the output voltage will be high at [latex] V_{ C }=5 V [/latex]. The output will be logic 1.
The truth table for an AND logic gate is shown in Table 4.2.

TABLE 4.2 Truth table for Example 4.2

Voltages			Logic Levels
[latex] V_{ A } [/latex]	[latex] V_{ B } [/latex]	[latex] V_{ C } [/latex]	A	B	C
0 (V)	0 (V)	0.7 (V)	0	0	0
0 (V)	5 (V)	0.7 (V)	0	1	0
5 (V)	0 (V)	0.7 (V)	1	0	0
5 (V)	5 (V)	5 (V)	1	1	1

Question 4.2: Application as a diode AND logic function A diode circuit th...

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