speed of ttl ic

[payam]

What is the highest kind of TTL ices , and frequency range of them ?(
ALS ,HC, H,f,act, LS, S? ) CAN YOU SORT THEM ACCORDING TO THE SPPED
AND HIGHER FREQUENCY RANGE?
Which kind can work higher than 10MHZ?
[email protected]

 

[John Fields]

What is the highest kind of TTL ices , and frequency range of them ?(
ALS ,HC, H,f,act, LS, S? ) CAN YOU SORT THEM ACCORDING TO THE SPPED
AND HIGHER FREQUENCY RANGE?
Which kind can work higher than 10MHZ?

 

[CFoley1064]

What is the highest kind of TTL ices , and frequency range of them ?(

ALS ,HC, H,f,act, LS, S? ) CAN YOU SORT THEM ACCORDING TO THE SPPED
AND HIGHER FREQUENCY RANGE?
Which kind can work higher than 10MHZ?
[email protected]

Start with Fairchild App Note 319:

http://www.fairchildsemi.com/an/AN/AN-319.pdf

Go to the manufacturer web sites. Read their app notes and data sheets.

Please post questions of this type on sci.electronics.basics.

Good luck.
Chris

 

[Bill Sloman]

What is the highest kind of TTL ices , and frequency range of them ?(
ALS ,HC, H,f,act, LS, S? ) CAN YOU SORT THEM ACCORDING TO THE SPPED
AND HIGHER FREQUENCY RANGE?
Which kind can work higher than 10MHZ?

This should have been posted on sci.electronics.basics

H and LS are slow, and HC isn't much faster.

S is faster, but obsolete. Don't use it.

ALS, F, and ACT are all fairly fast, and have counters that can clock
at up to about 50MHz and single bistables that can get up to about
125MHz, but you have to read the data sheet for the part that you want
to use, and think about the critical propagation delays, set-up times
and hold times in the particular circuit you are putting together.

The manufacturers guaranteed maximum frequencies are always for very
artificial test circuits - the parts can never go that fast in
circuits that do anything useful.

 

[Winfield Hill]

Bill Sloman wrote...

The manufacturers guaranteed maximum frequencies are always
for very artificial test circuits - the parts can never go
that fast in circuits that do anything useful.

Good conservative advice for a novice I suppose, but talking
about "guaranteed maximum frequency" is rather misleading, and
not very accurate in my experience. For example the spec is
usually a maximum delay time or a minimum "maximum" frequency,
and it's measured in a test circuit with added capacitance
(e.g. 50pF) that's much higher than one usually encounters in
a real application, and at a lower voltage, (e.g. 4.5V instead
of 5V). As a result actual circuits usually can go _faster_
(not slower) than these conservative "specs." For example, TI
gives 21MHz for their 74hc191 counter, but I bet one would be
hard pressed to find a real part with such a slow upper limit.

Thanks,
- Win

 

[Bill Sloman]

Bill Sloman wrote...

Good conservative advice for a novice I suppose, but talking
about "guaranteed maximum frequency" is rather misleading, and
not very accurate in my experience. For example the spec is
usually a maximum delay time or a minimum "maximum" frequency,
and it's measured in a test circuit with added capacitance
(e.g. 50pF) that's much higher than one usually encounters in
a real application, and at a lower voltage, (e.g. 4.5V instead
of 5V). As a result actual circuits usually can go _faster_
(not slower) than these conservative "specs." For example, TI
gives 21MHz for their 74hc191 counter, but I bet one would be
hard pressed to find a real part with such a slow upper limit.

I should hope so. The guaranteed maximum frequency ought to be the
2.5- or 3-sigma tail of the distribution, so fewer than one part in a
thousand should fall over at that frequency, at worst case temperature
and supply voltage.

In a production environment, that is what you design for, so that very
few of your boards fall over under worst case conditions.

At Nijmegen University, one of my colleagues designed a board around
the actual performance of 74F, and he got it back about once a year,
as one or other of his chips drifted back from its initially measured
performance.

Okay for a reasearch one-off, perhaps. But when the client started
complaining about systematic pattern-related clock jitter, I
redesigned the board using ECL for the critical clocks, and never had
to touch it again - going over from DIP packaging to surface mount for
most of the components to made enough room for the extra ECLinPS chips
(only available in surface mount anyway).

 

[Fred Bloggs]

I should hope so. The guaranteed maximum frequency ought to be the
2.5- or 3-sigma tail of the distribution, so fewer than one part in a
thousand should fall over at that frequency, at worst case temperature
and supply voltage.

In a production environment, that is what you design for, so that very
few of your boards fall over under worst case conditions.

At Nijmegen University, one of my colleagues designed a board around
the actual performance of 74F, and he got it back about once a year,
as one or other of his chips drifted back from its initially measured
performance.

74F is different from the other logic family Tpd characterizations in
that it is measured with the output loaded to VoH=3.5V or less- and this
makes it look better by a few nanoseconds.

 

[Winfield Hill]

Bill Sloman wrote...

At Nijmegen University, one of my colleagues designed a board around
the actual performance of 74F, and he got it back about once a year,
as one or other of his chips drifted back from its initially measured
performance.

Whew, the design must have indeed been very much on the edge to
have a failure mode sensitive to modest changes in propagation
delay. Or perhaps the changes weren't so modest? I wonder what
the mechanisms are for slowing of a chip's speed with time.

Thanks,
- Win

 

[Michael A. Terrell]

Bill Sloman wrote...

Whew, the design must have indeed been very much on the edge to
have a failure mode sensitive to modest changes in propagation
delay. Or perhaps the changes weren't so modest? I wonder what
the mechanisms are for slowing of a chip's speed with time.

Thanks,
- Win

I'd like to know, as well. I used to repair a lot of Commodore 64s,
and early memory cards built with 4164 type DRAM. I found a lot of bad
chips on the boards that still worked, but at a slower speed. I had the
old Startek DRAM tester with a variable clock, and some parts were 20 to
50% slower than marked. I also found some surplus 300 ns chips that
would pass at 150 ns.