what does 74LS stands for, in IC's?

Answer 1

The 74 series of TTL (transistor-transistor logic) was introduced around 1968 by Texas Instruments (TI). Previous logic families included DTL (diode-transistor logic) and SUHL (Sylvania Universal High speed Logic). TTL had the innovation of a multiple emitter input transistor and an active pullup on the output, thereby improving the speed. The 74 series was tested to operate over a temperature range of 0°C to +70°C. TI also introduced a 54 series, which was exactly the same as the 74 series except that it was tested over a temperature range of -55°C to +125°C for military and space applications. Obviously a 54 series device could be substituted for a 74 series device.

As the popularity of the 74 series increased, variations were offered for higher speed (74H) and lower power (74L). These variations are obsolete today.

In 74 series TTL logic, the lower output transistor is fully turned on (saturated) for a low output, or turned off for a high output. The base current into this output transistor has to be sufficient to ensure saturation for any load on the output, which could range from zero to the maximum rated load (generally 16 mA). Of necessity the circuit was designed to have an excess of base current over what was needed for a typical load on the output. This excess current actually reduces the speed of the transistor, because it results in a charge that must be removed from the base before the transistor can be turned off.

However, this loss of speed was minimized by a fabrication step that added a small amount of gold to the transistor. This gold doping reduced the stored charge in the output transistor, allowing it to be turned off more quickly.

As I recall (perhaps incorrectly), the price of gold used to be regulated by the US government at about $35 per ounce, since it was used to back up the value of our currency. Gold was deregulated around 1970, and quickly became very expensive for use in integrated circuit fabrication.

This problem was solved by the addition of a Schottky diode to the lower output transistor. This Schottky diode has a forward voltage drop of only around 0.3 volts, compared with 0.7 volts for a conventional silicon diode. By putting the diode between the base and collector, the transistor is kept from going into saturation, and thus there is no excess charge to slow down the turnoff of the transistor. There is, however, a slightly higher output voltage in the low state. The diode is not usually shown on schematics, but instead a special symbol is used for the transistor.

This series was given the designation 74S. As with its predecessor, a high speed variation was introduced (74AS) as well as two low power variations (74LS and 74ALS). These families were intended to replace the gold-doped families that were being ramped down in production.

A competitor, Fairchild Semiconductor, also introduced their version of Schottky TTL logic, giving it the designation 74F. The performance of this family lies between 74S and 74AS.

Today, most of these bipolar logic families have been replaced by high speed CMOS logic, which is also available in many variations.

Answer 2

There are several families of logic chips numbered from 74xx00 onwards with letters (xx) in the middle of the number to indicate the type of circuitry, eg 74LS00 and 74HC00. The original family (now obsolete) had no letters, eg 7400.
The 74LS (Low-power Schottky) family (like the original) uses TTL (Transistor-Transistor Logic) circuitry which is fast but requires more power than later families. The 74 series is often still called the 'TTL series' even though the latest chips do not use TTL!

Answer 3

The 74xx series was one of the earliest integrated circuits introduced for digital applications and consists of a large number of very useful functions. They are all based on transistor-transistor logic. This can be quite power consuming, so the design was modified (by raising the load resistances) so that less power is consumed, but the circuits are slower than the standard type. These low-power ICs were identified by inserting the letter "L" after the 74 to create the 74Lxx series. Then a high-speed version was developed using Schottky barrier junction transistors; these high speed IC were designated by 74Sxx. They were much faster than standard, and didn't consume more power. Then the two were combined to create low-power Schottky circuits which were as fast as the standard 74xx, but used the low power of the 74Lxx. and these low-power Schottky circuits are designated 74LSxx. This last type offers all the advantages of the standard 74 series but with much less power consumption, and so has supplanted the orginal almost entirely.

Answer 4

Low power Schottkey

Answer 5

It's obsolete, first of all, it has been replaced by the 74ALS family. Advantages and disadvantages compared to what?

Answer 6

hi

74 means the ic belongs to category
& LS means Low Spead for example ----74LS07 & ...

Answer 7

74ls Series

Answer 8

it gives you the number and type