Silicon delay lines

[[email protected]]

Is it "good practice" to design with delay lines? I assume somebody
must be buying all those 74ls31 and DS1100s.

Anybody ever used some of these and for what? Just curious.

 

[John Larkin]

Is it "good practice" to design with delay lines? I assume somebody
must be buying all those 74ls31 and DS1100s.

Anybody ever used some of these and for what? Just curious.

Good practice is anything that works.

Delay lines can be very handy. The LS31 is pretty sloppy, but there
are more precise parts around, like the Dallas thing... Bel Fuse and
Data Delay have some too. Micrel makes an astonishing ECL delay line,
SY89295, which has 1024 internal 10 ps delay elements and guaranteed
monotic setability.

We program delay lines inside FPGAs now and then; you have to fight
the Xilinx tools to do it. Some of the new Vertex chips include
legally-sanctioned delay blocks.

All-synchronous design is sort of a severe ancient religion.

John

 

[[email protected]]

Good practice is anything that works.

Guess so, as long as you know what you're getting into. I've got this
personal thing that's been bugging me like a splinter under a
fingernail for a while.
I'd like to try a delay line, but I'm wary of things I don't
understand. Want to learn, you see.

Delay lines can be very handy. The LS31 is pretty sloppy, but there
are more precise parts around, like the Dallas thing... Bel Fuse and

If only Digikey carried them. I hate specifying parts that other
people will have trouble ordering. And I don't want to be in the parts
business.

Data Delay have some too. Micrel makes an astonishing ECL delay line,
SY89295, which has 1024 internal 10 ps delay elements and guaranteed
monotic setability.

Ah yes, Micrel. A bit too much for a 32MHz CMOS clock...

We program delay lines inside FPGAs now and then; you have to fight
the Xilinx tools to do it. Some of the new Vertex chips include
legally-sanctioned delay blocks.

No PLDs in my design. Just a few flip-flops and a PIC.

All-synchronous design is sort of a severe ancient religion.

Heh.
I'm planning on some pretty good power supply bypassing on the delay
line chip. I understand there's some kind of ramp/comparator thingy in
there. I'm hoping that overall it's less sensitive to power supply
noise than the VCO I've got right now.
Would you heavily filter the VCC to a delay line?

 

[Joerg]

Is it "good practice" to design with delay lines? I assume somebody
must be buying all those 74ls31 and DS1100s.

Anybody ever used some of these and for what? Just curious.

I never do and have designed some out. Got less noise that way and the
BOM cost total plummeted impressively. The latter made that client
really happy. They were kind of expecting that I'd solve their noise
issues and later didn't really want to know why the noise was now gone.
But they sure didn't expect a serious cost reduction, especially because
it just "happened" they didn't have to pay extra for that service.

If, for example, there had to be a precise summation of signals over
staggered delays I used Belfuse LC lines as John mentioned. For anything
else it's the good old LC, RC, LR, whatever is practical. IOW nickel and
dime parts. Then again my background is analog so maybe I am a bit
biased here.

 

[Joel Kolstad]

Is it "good practice" to design with delay lines? I assume somebody
must be buying all those 74ls31 and DS1100s.

Anybody ever used some of these and for what? Just curious.

Sure... I used some DS1000-series delay line (and some logic) once to create a
double-speed clock to extract bytes from a 16-bit word-wide parallel data bus.
The clock speed was fixed, the DS1000 part had decent tolerances, so after
sitting down and checking the timing margins, it really was a solid,
repeatable design.

In fact, the main advantage of something being sold as a delay line over just
using some handful of spare gates is -- generally -- the much tighter
tolerance you get on the delay.

 

[[email protected]]

If, for example, there had to be a precise summation of signals over
staggered delays I used Belfuse LC lines as John mentioned. For anything

"NOTIFICATION OF DISCONTINUANCE
END OF LIFE: DELAY LINES
ALL PRODUCT FAMILIES

Bel is issuing this Notification of Discontinuance regarding the End
of Life status of our delay line products. This unilateral
discontinuance is in support of rather than in lieu of any prior
notification you may have received from Bel. Original notification
dates are in no way superceded by this announcement."

Oh dear. I suspect 100000 transistors on an ASIC are cheaper than a LC
delay line.

 

[Joerg]

"NOTIFICATION OF DISCONTINUANCE
END OF LIFE: DELAY LINES
ALL PRODUCT FAMILIES

Bel is issuing this Notification of Discontinuance regarding the End
of Life status of our delay line products. This unilateral
discontinuance is in support of rather than in lieu of any prior
notification you may have received from Bel. Original notification
dates are in no way superceded by this announcement."

Oh dear. I suspect 100000 transistors on an ASIC are cheaper than a LC
delay line.

Yeah, mine had been a long time ago. They were used in ultrasound
beamformers (that's what I often design for a living). Then, with
digital beamforming becoming economical the market for delay lines has
shriveled to the point where it just doesn't make sense anymore. But you
can still get similar delay lines from others. Be prepared for sticker
shock though. IMHO these have become boutique parts. While it may be ok
to use one in a rocket controller it might not be the right thing to do
in regular electronics.

As I wrote, personally I'd stay away from a "canned solution" and roll
my own. It ain't that hard. Heck, we even roll our own pizza dough
instead of buying anything "ready to bake"

Besides noise and a painful sticker price there is another reason why I
avoid commercial delay lines if at all possible: Neither I nor my
clients like single-sourced parts. Over my career I have heard the
clanging of too many last order bells and seen the demise of whole
companies along with their otherwise superb products. Remember Plessey
and their excellent mixer chips? Luckily I was able to secure a small
stash of those before the ship sank.

 

[[email protected]]

Guess so, as long as you know what you're getting into. I've got this
personal thing that's been bugging me like a splinter under a
fingernail for a while.
I'd like to try a delay line, but I'm wary of things I don't
understand. Want to learn, you see.


If only Digikey carried them. I hate specifying parts that other
people will have trouble ordering. And I don't want to be in the parts
business.


Ah yes, Micrel. A bit too much for a 32MHz CMOS clock...


No PLDs in my design. Just a few flip-flops and a PIC.


Heh.
I'm planning on some pretty good power supply bypassing on the delay
line chip. I understand there's some kind of ramp/comparator thingy in
there. I'm hoping that overall it's less sensitive to power supply
noise than the VCO I've got right now.
Would you heavily filter the VCC to a delay line?

Monostables have ramps and comparators and can have nasty
sensitivities to noise. Some of the Dallas parts that Dallas list as
delay lines are actually strings of monostables.

Proper delay lines don't have ramps and comparators, and are much less
noise sensitive. I've used them in a few applications, but they do
tend to come out expensive.

Farnell stocked the Newport lumped constant delay lines for some
twenty years - they were still in the catalogue last year, albeit as
C&D Technology parts - but they've vanished from the 2007 catalogue.

These parts were just passive linear phase phase low pass filters,
built as thick film hyrids, and - as passive parts - they were totally
insensitive to power supply noise. If you get hold of a book on filter
theory, you can design your own delay line as an "all-pass" filter,
but you get twice as much delay out of the same capacitance and
inductance if you design your delay line as a low-pass filter. You do
have to make sure that the high frequency cut-off of you low pass
filter doesn't excessively slow down the transition times of the wave-
train you plan on delaying.

 

[Joerg]

Monostables have ramps and comparators and can have nasty
sensitivities to noise. Some of the Dallas parts that Dallas list as
delay lines are actually strings of monostables.

Proper delay lines don't have ramps and comparators, and are much less
noise sensitive. I've used them in a few applications, but they do
tend to come out expensive.

Farnell stocked the Newport lumped constant delay lines for some
twenty years - they were still in the catalogue last year, albeit as
C&D Technology parts - but they've vanished from the 2007 catalogue.

These parts were just passive linear phase phase low pass filters,
built as thick film hyrids, and - as passive parts - they were totally
insensitive to power supply noise. If you get hold of a book on filter
theory, you can design your own delay line as an "all-pass" filter,
but you get twice as much delay out of the same capacitance and
inductance if you design your delay line as a low-pass filter. You do
have to make sure that the high frequency cut-off of you low pass
filter doesn't excessively slow down the transition times of the wave-
train you plan on delaying.

You can still get those types of delay lines today:
http://www.susumu.co.jp/english/pdf/products-j05-01.pdf
http://www.susumu.co.jp/english/pdf/products-j05-02.pdf

Digikey has that series in stock. But sit down before looking to the
right where the prices are. Big bucks. Key "Susumu" into search, then
first item under "Inductors".

 

[Ian]

Proper delay lines don't have ramps and comparators, and are much less
noise sensitive. I've used them in a few applications, but they do
tend to come out expensive.

Farnell stocked the Newport lumped constant delay lines for some
twenty years - they were still in the catalogue last year, albeit as
C&D Technology parts - but they've vanished from the 2007 catalogue.

These parts were just passive linear phase phase low pass filters,
built as thick film hyrids, and - as passive parts - they were totally
insensitive to power supply noise. If you get hold of a book on filter
theory, you can design your own delay line as an "all-pass" filter,
but you get twice as much delay out of the same capacitance and
inductance if you design your delay line as a low-pass filter. You do
have to make sure that the high frequency cut-off of you low pass
filter doesn't excessively slow down the transition times of the wave-
train you plan on delaying.

It's the other way round, you get twice the delay of the low-pass
version using the components as an all-pass.
You probably wouldn't like the shape of the output edge, though;-)

Regards
Ian

 

[[email protected]]

<snip>






It's the other way round, you get twice the delay of the low-pass
version using the components as an all-pass.

That's not the way it seemed to be working when we looked into this at
Cambridge Instruments around 1985 - which is why we went ofr the low-
pass filter.

You probably wouldn't like the shape of the output edge, though;-)

A phase linear low pass filter may degrade the steepness of the output
edge, but since the delay will remain constant with frequency up to
the cut-off point, it won't degrade the shape.

A phase linear all-pass filter wouldn't - in theory - have a cut-off
point, so it ought to be better.

 

[Fred Bartoli]

[email protected] a écrit :

That's not the way it seemed to be working when we looked into this at
Cambridge Instruments around 1985 - which is why we went ofr the low-
pass filter.

For a normalized 1st order APF Hap= (1-p)/(1+p)
For a first order LPF Hlp= 1/(1+p)

The APF has twice the LPF phase shift for the same cut off frequency.