TTL inverters

[Kevin Weddle]

I looked at the schematic for the inverter and am having trouble with it. The input transistor is not biased to work like a transistor and I have seen a representation of two diodes in a book. Why doesn't the schematic show these two diodes instead of the transistor?

 

[ante1]

Kevin,

Which is

 

[Kevin Weddle]

http://www.ee.washington.edu/stores/DataSheets/74ls/74ls04.pdf

 

[ante1]

Kevin,

I don

 

[nishanth_aks]

hai,
thie reason for showing a transistor is exactly that the other guy has said.It is because , in manufacturing, they dont bother to make two independent diodes connected back to back.Keep in mind that the diodes themselves are made from transistors in wafer.So, why should they use two transistors to make a pair of back to back connected diodes when they can reasile the same effect with just one transistor!!!
Well, some documents show it as two seperate diodes and not as transistor because the authors of the document wants to make the reader aware that the functionality is just that of two diodes and not that of the transistor.Hope you understand the probelem.Even you where confused about why the transistor is not biased, because you have a prejudice that all transistor should work in actie region or something like that.Well, actually they can be used as diodes also.

nishi

 

[MP1]

would someone like to post a link or schematic of theTTL inverter you are talking about so that the rest of us can follow?
Thanks.
MP

 

[ante1]

MP,

Kevin posted it in post #3.

Ante :

 

[Kevin Weddle]

Could someone explain this circuit in terms of the overall design. Why do they use a low current source and a high current sink? Why do they use the totem pole, which has an emitter follower and a common emitter. The idea I have is that logic is designed to handle the 0 to 5volts. This is a good voltage spread. The second idea is that the gain must be high to give a good transition. So what is the intention of the overall design?

 

[MP1]

Thanks, ante. I saw the link for the inverter chip. I thought you were discussing an inverter schematic which used this chip in it. My mistake.

MP