Questions for Training

• Digital Logic families
• Characteristics of digital circuits:
– fan in, fan-out, power dissipation, propagation delay, noise margin;
• Transistor-transistor Logic(TTL),
– TTL NAND Gate with active pull up,
– its input and output Characteristics,
– Types of TTL Gates (Schottky, standard, low power, high speed).
• Emitter Coupled Logic(ECL),
– ECL gate,
– its transfer characteristics,
– Level translation in ECL & TTL.
Characteristics of digital circuits
Fan in
Fan in is the number of inputs connected to the gate without any
degradation in the voltage level.
Fan-out
Fan out specifies the number of standard loads that the output of the gate
can drive without impairment of its normal operation
Power dissipation
Power dissipation is measure of power consumed by the gate when fully
driven by all its inputs.
Propagation delay
Propagation delay is the average transition delay time for the signal to
propagate from input to output when the signals change in value. It is
expressed in ns.
Noise margin
It is the maximum noise voltage added to an input signal of a digital circuit
that does not cause an undesirable change in the circuit output. It is
expressed in volts.