Digital Integrate Circuits Logic Families A group of

Digital Integrate Circuits: Logic Families A group of compatible ICs with the same logic levels and supply voltages Fabrication using a specific circuit configuration Same basic logic gate during fabrication Use simple components like – Resistors, diodes, transistors and MOSFETs. Significance of Logic Family Simplicity in the design Members with similar electrical characteristics Reduces the complexity in the design Provides compatibility in digital circuits Easy to expand Classification and Types of Logic Families Logic families can be classified broadly according to the technologies they are built with. In earlier days we had vast number of these technologies, as you can see in the figure below: 125

- DL: Diode Logic. - RTL: Resistor Transistor Logic. - DTL: Diode Transistor Logic. - HTL: High threshold Logic. -TTL: Transistor Logic. -IIL: Integrated Injection Logic. - ECL: Emitter coupled logic. - MOS: Metal Oxide Semiconductor Logic (PMOS and NMOS). - CMOS: Complementary Metal Oxide Semiconductor Logic families are further classified fabricated per chip in IC form • • based on number of logic gates SSI Small Scale Integration MSI Medium Scale Integration LSI Large Scale Integration VLSI Very Large Scale Integration ˂ 12 gates / chip ˂ 100 gates / chip … 1 K gates / chip … 10 K gates/ chip Positive & Negative Logic Positive Logic 0 V 1 Lower voltage to represent a logic 0 Logic 1 V 2 Higher voltage to represent a logic 1 V 2>V 1 0 V Logic 0 V 2 5 V Logic 1 5>0 V 126

Negative Logic: Logic 0 V 1 Higher voltage to represent a logic 0 Logic 1 V 2 Lower voltage to represent a logic 1 V 2>V 1 0 V Logic 1 V 2 5 V Logic 0 5>0 V Example 1: Emitter Coupled logic ECL -0. 8 V logic 1 } - 0. 8 > - 1. 7 V - 1. 7 V logic 0 } higher-- 1 lower – 0 : positive logic P MOS (P channel MOSFET ) 0 V -10 V logic 0 } logic 1 } 0 V > - 10 v higher-- 0 127 lower – 1 : Negative logic