BJT-like transistor symbol - unknown meaning?

Thread Starter

sbixby

Joined May 8, 2010
57
Attached is a snip from a Texas Instruments datasheet for the 74*04 hex inverter chip.

There are three types represented in the datasheet - 7404, 74LS04, 74S04; the original TTL circuit uses the standard BJT transistor symbol, but the other two use a symbol (attached) that I can't seem to find.

What is it??

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By way of explanation, I am working through the AAC book (V4, C3, S2) about "The NOT Gate" and mocking it up in a simulator for sake of understanding the operation of the circuit. (I'm still fuzzy on BJTs, so I like to work through the gate circuits at this level to help strengthen my understanding.) Since the AAC page doesn't show values for the resistors, I though I'd borrow one of the datasheets' values for my simulation.
 

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Papabravo

Joined Feb 24, 2006
13,962
The "S" in the part numbers stands for Schottky. The p-n junctions are implemented with Schottky barriers that have a lower forward voltage drop.
 

Thread Starter

sbixby

Joined May 8, 2010
57
So, then, a related question - is a "Schottky transistor" a discrete part that I could look up for operating curves? I'm not finding one offhand.
 

crutschow

Joined Mar 14, 2008
25,130
The "S" in the part numbers stands for Schottky. The p-n junctions are implemented with Schottky barriers that have a lower forward voltage drop.
If you look at my reference you will see that is not quite correct. ;) A Schottky transistor is a standard junction transistor with a Schottky diode between the base and collection to limit saturation of the transistor and minimize saturation delay.
 

crutschow

Joined Mar 14, 2008
25,130
So, then, a related question - is a "Schottky transistor" a discrete part that I could look up for operating curves? I'm not finding one offhand.
No, it is not a discrete part you can buy. You can emulate one by placing a small Schottky diode between the base and collector of a small switching-type BJT as shown in the reference.
 

Papabravo

Joined Feb 24, 2006
13,962
If you look at my reference you will see that is not quite correct. ;) A Schottky transistor is a standard junction transistor with a Schottky diode between the base and collection to limit saturation of the transistor and minimize saturation delay.
Ah..yes right you are. It is something that is easy to fabricate on a chip however.
 
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