Logic Families in Digital Integrated Circuits

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 Transistor Logic. -IIL: Integrated Injection Logic. - ECL: Emitter coupled logic. - MOS: Metal Oxide Semiconductor Logic (PMOS and NMOS). - CMOS: Complementary Metal Oxide Semiconductor Logic. 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 ScaleIntegration 12 gates / chip 100 gates /chip 1K gates /chip 10 K gates/chip Positive & Negative Logic Positive Logic Logic 0 V1 Lower voltage to represent a logic 0 Logic 1 V2 Higher voltage to represent a logic1 V2>V1 V1 0V Logic 0 V2 5V Logic 1 5 > 0 V 126

Negative Logic: Logic 0 V1 Higher voltage to represent a logic0 Logic 1 V2 Lower voltage to represent a logic 1 V2>V1 V1 0V Logic 1 V2 5V Logic 0 5 > 0 V Example 1: Emitter Coupled logic ECL -0.8V logic 1 } - 0.8 > - 1.7V lower 0 : positivelogic -1.7V logic 0 } higher--1 P MOS (P channel MOSFET) 0V logic 0 } 0V > - 10v lower 1 : Negativelogic -10V logic 1 } higher--0 127