Introduction and classification of Digital Logic Families

 Introduction and classification of Digital Logic Families

Due to the advances in microelectronics, the digital IC technology has rapidly advanced from small scale integration (SSI), through medium scale integration (MSI),large scale integration (LSI), very large scale integration (VLSI), ultra large scale integration(ULSI) and now the technology is entering to giga scale integration (GSI) in which millions of gate equivalent
circuits are integrated on a single chip.The use of ICs has reduced the overall size , the cost and the power consumption due to which the reliability has improved because the number of external  interconnections from one device to another has reduced.

1.Definition  :- A group of compatible IC's (Integrated Circuits) with same logic levels and supply voltages fabricated for performing various logic functions reffered to as digital logic family.These families vary by speed, power consumption, cost, voltage & current levels

2.Classification : The entire digital ICs are fabricated using either bipolar devices or unipolar devices or a combination of the two. Thus, digital logic families are broadly classified under two main categories:

Fig.1. Classification of Digital Logic Families

[A] Bipolar logic families : Those devices in which current conduction is due to both type of charge carriers i.e., electrons and holes. Elements used are resistor, capacitor, diode and transistors. It is further divided into two sub-categories ,they are:

(I). Saturated : In this category the elements are driven into saturation i.e., transistors works in saturation region and cut-off region. In saturation region it will work as ON state and in cut-off region as OFF state.
(i)  RTL ( Resistor Transistor Logic )
(ii). DTL ( Diode Transistor  Logic )
(iii). DCTL Direct Coupled Transistor Logic )
(iv). IIL ( Integrated Injection Logic )
(v). HTL ( High Threshold Logic )
(vi). TTL ( Transistor Transistor Logic )

(II). Unsaturated : In this category the elements are not driven upto saturation region , transistors in active and cut-off region . In active region it will work as ON state and in cut-off region as OFF state.
So, due to this family works fater then saturated family.
(i). Schottky TTL
(ii). ECL ( Emitter coupled Logic )

[B] Unipolar logic families : Those devices in which current conduction is due to only one type of charge carrier i.e., either electrons or holes. Devices used in this families are MOSFET devices. Devices are :
(i). p-MOS ( p channel MOSFET )
(ii). n-MOS (n channel MOSFET )
(iii). CMOS ( complementary MOSFET )