İzmir University of Economics EEE 332 Digital Electronics Lab

EXPERIMENT 1 Logic

A. Background

Diode logic (DL) or diode resistor logic (DRL) is a that uses only and the resistors in the implementation of the logic functions. AND and OR functions can be implemented using the very easily. The main drawback of the diode logic family is that it is not complete. The (NOT) function cannot be implemented using diode logic. A.1. OR Gate The OR gate diode logic implementation is given in Fig. 1.1.

DA VA VY

DB VB

R

Fig. 1.1. OR Gate Diode Logic Implementation

Assuming the diodes are ideal, the voltage as given in Table 1.1.a is obtained. The corresponding logic truth table is given in Table 1.1.b

Table 1.1. Voltage Truth Table and Logic Truth Table of the OR Gate

VA VB VY (volt) (volt) (volt) A B Y 0 0 0 0 0 0 0 5 5 0 1 0 5 0 5 1 0 0 5 5 5 1 1 1 (a) (b)

A.2. AND Gate The diode logic implementation of the AND Gate is given in Fig. 1.2.

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VCC

R

DA VA VY

DB VB Fig. 1.2. AND Gate Diode Logic Implementation

Assuming the diodes are ideal, the voltage truth table of the above AND gate is as given in Table 1.2.a. The corresponding logic truth table is in Table 1.2.b

Table 1.1. Voltage Truth Table and Logic Truth Table of the AND Gate

VA VB VY (volt) (volt) (volt) A B Y 0 0 0 0 0 0 0 5 0 0 1 0 5 0 0 1 0 0 5 5 5 1 1 1 (a) (b)

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B. Preliminary Work

B. 1. Consider the OR gate implemented using practical diodes with V D(on) = 0.7 V as given in Fig. 1.3. DA VA VY

DB VB

R

Fig. 1.3. OR Gate Implemented Using Practical Diodes with V D(on) = 0.7 V

Complete the missing entries in the voltage and logic truth tables given below..

VA VB VY (volt) (volt) (volt) A B Y 0 0 …… 0 0 … 0 5 …… 0 1 … 5 0 …… 1 0 .. 5 5 …… 1 1 … Voltage Truth Table Logic Truth Table

B. 2. The AND gate implemented using practical diodes with V D(on) = 0.7 V using diode logic is given below in Fig. 1.4. VCC

R

DA VA VY

DB V B

Fig. 1.4. AND Gate Implemented Using Practical Diodes with V D(on) = 0.7 V

Complete the missing entries in the voltage and logic truth tables given below.

VA VB VY (volt) (volt) (volt) A B Y 0 0 …… 0 0 … 0 5 …… 0 1 … 5 0 …… 1 0 .. 5 5 …… 1 1 … Voltage Truth Table Logic Truth Table

B. 3. Consider the serially connected AND gates (implemented using diode logic with practical diodes, V D(on) = 0.7 V) as given in Fig. 1.5. Determine and write down the voltage values at the outputs indicated.

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0 V …. V …. V 0 V …. V 5 V …. V 5 V 5 V

Fig. 1.5. Voltage Degradation in the serially connected AND Gates using practical diodes with V D(on) = 0.7 V

B. 4. The voltage degradation problem may be overcomed by adding a diode and a resistor as shown in level shifted AND gate as shown in Fig. 1.6. For the choice of R1 = 10 k Ω and R 2 = 100 k Ω, the low output voltage is 0 volt compared to the 0.7 volts output for the normal AND gate. However the high output voltage is very close to 5 V. VCC =5V

R1 1 k Ω DA DY VA VY

DB R2 Ω VB 100 k

Fig. 1.6. Level Shifted AND Gate

Complete the missing entries in the voltage truth table given below.

VA VB VY (volt) (volt) (volt) 0 0 …… 0 5 …… 5 0 …… 5 5 …… Voltage Truth Table

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C. Experimental Work

C. 1. Conctruct the OR gate diode logic given below in Fig. 1.7.

DA VA VY

DB VB

R=10 k Ω

Fig. 1.7. OR Gate Diode Logic Implementation

Apply the given inputs and complete the missing entries in the voltage and logic truth tables given below..

VA VB VY (volt) (volt) (volt) A B Y 0 0 …… 0 0 … 0 5 …… 0 1 … 5 0 …… 1 0 .. 5 5 …… 1 1 … Voltage Truth Table Logic Truth Table

C. 2. Conctruct the AND gate diode logic given below in Fig. 1.8.

VCC

R = 10 k Ω

DA VA VY

DB V B

Fig. 1.8. AND Gate Diode Logic Implementation

Apply the given inputs and complete the missing entries in the voltage and logic truth tables given below..

VA VB VY (volt) (volt) (volt) A B Y 0 0 …… 0 0 … 0 5 …… 0 1 … 5 0 …… 1 0 .. 5 5 …… 1 1 … Voltage Truth Table Logic Truth Table

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C. 3. Contruct the Level Shifted AND Gate given in Fig. 1.9.

VCC =5V

R1 1 k Ω DA DY VA VY

DB R2 Ω VB 100 k

Fig. 1.9. Level Shifted AND Gate

Apply the given inputs and complete the missing entries in the voltage and logic truth tables given below..

VA VB VY (volt) (volt) (volt) A B Y 0 0 …… 0 0 … 0 5 …… 0 1 … 5 0 …… 1 0 .. 5 5 …… 1 1 … Voltage Truth Table Logic Truth Table

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