Explanation of output stage types and transitions of signal

[ilop]

want to ask

i have some questions about digital system

1. what is active high?
2 what is active low?
3 what is falling edge?
4 what is rising edge?

 

[Moss]

Re: want to ask

1.Active high is when output stage of logic circuit is biased to high state > In general output stage is some king of push pull circcuit. In active high mode "upper"(Q3) transistor is "opened", and "lower" (Q4) is closed.

In contrast you can have pull up resistor, wich biased output stage to desired condition ( low or hihg)> when you use pull up resistor, output voltage is strongly dependent of output current.
2.Active low is when output stage of logic circuit is biased to low state i.e. lower transistor in output stage is opend, higher is "closed" . Reverse situiatuion to previous.
3.Falling edge is transition of signal from high state to low state.
4. Rissing edge is transition of signal from low to high state.[/img]

 

[gidimiz]

Re: want to ask

Hi,

1. what is active high?

Anything that is regarded as working on "high level" voltage, that is active high. The "High level" is the opposite then the ground of your system. Also, The high level can be any voltage. It is specified in the IC data sheet. For example, some IC have active high of 2.7V, 3.3V, 5V and even 12V.
Example: Take a light bullb and a bettery. Connect the Minus ( - ) of the battery to the light bulb. Now every time you will touch with your plus ( + ) of the battery, the light bulb will turn on. That is active high.

2 what is active low?

Anything that is regarded as working on "low level" voltage. Your ground of your board will be the low level voltage. If you put a low level to your IC or circuit then it will start acteviting.
Example: Take a light bullb and a bettery. Connect the Plus ( + ) of the battery to the light bulb. Now every time you will touch with your minus ( - ) of the battery, the light bulb will turn on. That is active low.

what is falling edge?

That is the exact period/time when you had the change from active high to active low. Think of it as the time when you took out the wire from the light bulb in the first eample.

what is rising edge?

That is the time when you changed from low level to high level. again, from the first example, that is the time when you connected the wire to the light bulb.

Aslo, if you like to learn more, try this site :
Electronics Fundamentals: Circuits, Devices, and Applications
**broken link removed**
Good luck.