Active low vs active high

[ArdyNT]

What is the principle difference between active low and active high ? What is the advantages and disadvantages ? What is their relation with sourcing ?

 

[pjmelect]

TTL, bipolar technology uses active low because it saves on power, CMOS devices on the other hand tend to use active high as it does not matter whether you use active high or active low as regards power dissipation and people tend to think as high being on or active.