Characteristics of digital logic families:
Propagation delay:
The propagation delay of a gate is basically the time interval between the input pulse and the output pulse.
It limits the speed at which they can operate.
The shorter delay result in high speed and vice-versa.
- tPLH - Output is changing from logic -0 to logic 1(low to high)
- tPHL – Output is changing from logic1 to logic 0(high to low)
Power dissipation:
The amount of power that an IC dissipates is determined by the average supply current (Icc).
Icc is determined based on the 50% duty cycle operation of the gate (LOW half of the time and high half of the time )
Icc =( Icc + IccL)/2
Current and Voltage Parameters:
VIH - High level input voltage
VIL - Low level input voltage
VOH - High level output voltage
VOL - Low level ouput voltage
IIH - High level input current
IIL - Low level input current
IOH - High level output voltage
IOL - Low level output voltage
Fan-out – The maximum number of input of several gate that can be derived by the output of logic gate by a partameter called fan-out.
Fan-in – The Fan-in of a digital logic gate refers to the number of inputs.
Current Sinking – A device output is said to sink current when current flows from the power supply, through the load and though the device output to ground.
Current sourcing – A device output is said to Source current when current flows from the power supply, out of the device output and through the load to ground.
Speed power product – Measuring and comparing the overall performance of an IC family is the Speed power product (SPP).
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