Hex Schmitt Trigger Ic's

whats the difference between the different ic's ??

i had thought that the 74hc14 was the ttl version, and the 40106 was the cmos version, and the 74c14 was interchangeable with the 40 series.

but now that i look, 74hc14 datasheet calls it a cmos schmitt trigger.

so whats the real difference between the 74hc series, the 74c series, and the 40 series?

TTL doesn't have the letter C in the part number. So yes, 74HC is CMOS. The H stands for high speed. 74HC is much faster than 74C but it's still CMOS.

In the early days, I believe it was RCA who first introduced CMOS logic and used the 4000 numbering system. Other companies brought out their own lines, but used the 74C numbering because everyone was already familiar with the TTL logic series numbering. So, for the most part there is no functional difference between 74C and 4000 parts, though there may be a difference in pinouts in some cases. Some parts are dual numbered with both 4000 and 74C numbers.

74Cxx is essentially CD4000 technology ("metal gate CMOS") used to build familiar TTL-family devices and pinouts. Both are typically used at 5-15V supply.

HC came later (built with "amorphous gate CMOS"). It goes faster, drives harder, and only operates up to TTL voltages (7V abs. max.). It also has buffering, meaning the inputs are less critical of whatever crummy waveform you supply, and the outputs produce a much nicer, more reliable waveform (symmetrical drive, consistent rise/fall time), at a small expense in propagation delay.

Any 74xxx series has familiar functions and pinouts (give or take), so you'll find the 7414 schmitt trigger in 74, LS, C, HC, LVC, and so on. Some functions aren't provided in all families, or can't be (the 7406 had 30V tolerant open-collector outputs, impossible in 74HC), while others are provided for convenience (TTL muxes are unidirectional, whereas CMOS muxes like 74HC4051 are actually "analog switches" and can be used in either direction, or for analog signals!).

Tim

thanks!

74, 74L, 74S, 74LS, 74AS, 74F, 74ALS... I think that's it... are actual TTL.

74C, 74HC, 74AC, 74LV, 74LVX, 74LVC, 74VHC, etc, are CMOS.

74ABT is CMOS with bipolar outputs IIRC. "BiCMOS".


Any of the CMOS ones with 'T' (ie. 74HC -> 74HCT) is CMOS with TTL level inputs (0 = <0.8V, 1 > 2V), as opposed to CMOS (uh.. 0.3 Vdd and 0.7 Vdd, usually, i think.)

Those were the good ol' days *sigh*

The different brands have different threshold values for the Schmitt trigger function. If you make oscillator circuit from them, you should be aware of that, since the frequency may/will be different between the brands/ families. This is mainly a logistic problem if you make several production runs over time.

TOK

Speaking of which -- CMOS schmitt inputs will toggle somewhere in the 0.3-0.7 range (or maybe it's 0.4-0.6, depends on how clean their process is). I think TTL toggled in the ~1.2V range (corresponding to somewhere between the default 0.8-2V "don't know" range).

Tim