Basics of digital ic


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  • TTL = Transistor Transistor Logic, HC / HCT stands for High-speed CMOS Logic (HCL)
  • Basics of digital ic

    1. 1. DIGITAL IC
    2. 2. What is Logic Family? Group of logic gates having compatible logic levels and power supply characteristics. Set of techniques used to implement logic within VLSI integrated circuits
    3. 3. Logic Families Resistor–transistor logic (RTL) Diode–transistor logic (DTL) Emitter-coupled logic (ECL) Transistor–transistor logic (TTL) P-type metal–oxide–semiconductor logic (PMOS) N-type metal–oxide–semiconductor logic (NMOS) Complementary metal–oxide–semiconductor logic (CMOS) Bipolar complementary metal–oxide–semiconductor logic (BiCMOS) Integrated injection logic (I2L)
    4. 4. Basic Concepts Fan In: Maximum no. of inputs of gate  Increase in fan in increases gate delay Fan out: Maximum no. of outputs gate can drive  The fan-out really depends on the amount of electric current a gate can source or sink while driving other gates.  Increase in fan out can affect noise margin, operating temperature, rise time, fall time and propagation delay.
    5. 5. Basic Concepts Gate delay  Delay offered by a gate for the signal appearing at its input, before it reaches the gate output.  Also known as propagation delay. Wire Delay  Delay offered by interconnection between gates  Also known as interconnect delay
    6. 6. Basic Concepts Skew  The same signal arriving at different parts of the design with different phase is known as skew.  Normally refers to clock signals
    7. 7. Basic Concepts Logic levels  VOHmin : The minimum output voltage in HIGH state (logic 1). VOHmin is 2.4 V for TTL and 4.9 V for CMOS.  VOLmax : The maximum output voltage in LOW state (logic 0). VOLmax is 0.4 V for TTL and 0.1 V for CMOS.  VIHmin : The minimum input voltage guaranteed to be recognised as logic 1. VIHmin is 2 V for TTL and 3.5 V for CMOS.  VILmax : The maximum input voltage guaranteed to be recognised as logic 0. VILmax is 0.8 V for TTL and 1.5 V for CMOS.
    8. 8. Basic Concepts Current levels  Source and sink capability Noise Margin  Low noise margin (LNM) = VILmax-VOLmax  High noise margin (HNM) = VOHmin-VIHmin Rise time (tr) Fall time (tf) Propogation delay (tpd)  The time between the logic transition on an input and the corresponding logic transition on the output of the logic gate.
    9. 9. Basic Concepts Power dissipation  Static power dissipation  Dynamic power dissipation
    10. 10. Logic Thresholds And Outputs ForDifferent Logic Families  The term threshold is used to specify the voltage in which an electrical signal is determined to be a 1 or 0”
    11. 11. Gate Transition Times And Current SinkCapability For Different Logic Families
    12. 12. Practical digital signal
    13. 13. Thank You