DIGITAL IC
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
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)
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.
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
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
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.
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.
Basic Concepts
Power dissipation Static power dissipation Dynamic power dissipation
Logic Thresholds And Outputs For Different Logic Families
The term threshold is used to specify the voltage in which an electrical signal is determined to be a 1 or 0”
Gate Transition Times And Current Sink Capability For Different Logic Families
Practical digital signal
Thank You