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

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