Digital Logic Families

INTRODUCTION

The Switching characteristics of the semiconductor devices have been, Basically, there are two types of semiconductor devices; bipolar and unipolar. Based on these devices, the digital integrated circuit has been made which are commercially available. The various digital function is being fabricated in a variety of forms using bipolar and unipolar technologies. A group of compatible ICs with the same logic levels and supply voltage for performing various logic function have been fabricated using a specific circuit configuration which is referred to as a logic family

BIPOLAR LOGIC FAMILIES

The main elements of a bipolar IC are resistors, diodes (which are also capacitors ) and transistors.B basically, there are two types of operation in bipolar ICs

1.Saturated and 

2 Non-saturated 

 In saturated logic, the transistors in the IC are driven to saturation, whereas in the case of non-saturated logic, the transistors are not driven into saturation

The saturated bipolar logic families are;
1 Resistor-transistor logic(RTL)
2 Direct-coupled transistor logic(DCTL)
3 Integrated-injection logic(IL)
4 Diode-transistor logic(DTL)
5 High-transistor logic(HTL)
6 Transistor-transistor logic(TTL)

The non-saturated bipolar logic families are:
1 Schottky TTL, and 
2. Emitter-coupled logic(ECL)

Unipolar Logic Families

MOS devices are unipolar devices and only MOSFETs are employed in MOS logic circuit The  MOS logic Families are ;

1 PMOS

2 NMOS, and 

3 CMOS 

White in PMOS only P-channel MOSFET is used and in NMOS only n-channel MOSFETs are used, in complementary MOS(CMOS), both p and n channel MOSFETs are employed and are fabricated on the same silicon chip 

All the above logic families are discussed in this chapter 

Characteristics of Digital ICs 

With the widespread use of ICT in the digital system and with the development of various technologies for the fabrication of ICs, it has become necessary to be familiar with the characteristics of IC logic families and their relative advantages and disadvantages. digital ICs are classified either according to their relative 

The various characteristics of analog IC's are Input Offset Voltage. ..

• Input Offset Current. ...
• Input Bis Current. ...
• Differential Input Resistance. ...
• Input Capacitance. ...
• Common Mode Rejection Ratio (CMRR) ...
• 8.Supply Voltage Rejection Ratio (SVRR) ...
• Large Signal Voltage Gain.

Digital ICs are classified field either according to the complexity of the circuit, as the relative number of individual basic gates (2input NAND Gates)

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