Fast edges from cheap logic...

P

Phil Hobbs

Guest
I\'ve been doing some simple test sources, basically just one or other
carefully selected LED driven by fast CMOS. Regular hex inverter
packages (both 74AC04 and 74AC14) look great with resistive loads--clean
250 ps -- 300 ps edges, as measured with an 11801C sampling scope with
SD-26 head.

<https://electrooptical.net/www/sed/MC74AC04-14RisingEdges500ohmLoad.png>

<https://electrooptical.net/www/sed/MC74AC04_14_FallingEdge500ohms.png>

(There\'s a bit of residual inductive rise after the fast edges on the
resistive load tests, but we can fix that.)

They\'re built dead-bug fashion with SO14 packages wired up like this:

10nF +5
C C |
*---C C-------*
| C C |
GND | A
*--|>o--*
in | | 432R
0---|>o---|>o---*--|>o--*---RRRR---0) To sampler
| | |
*--|>o--* GND
| |
*--|>o--*
|
GND

With 82 pF to ground from node A, they fall completely apart--the edges
show an initial fast rise/fall of a volt or so, followed by a ringy mess
for the next 10 ns.

<https://electrooptical.net/www/sed/MC74AC04_14_FallingEdge500ohms82pF.png>

<https://electrooptical.net/www/sed/MC74AC04_14_RisingEdge500ohms82pF.png>

In real life the LEDs won\'t be faster than 2 ns, and will be driven via
a resistor, of course. However, I might well want to use a speedup cap
of the same order, so it\'s very likely to be worthwhile spending an
extra buck or so and using LVC1G04 gates in SC-70, with individual
bypass caps.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
On Fri, 10 Mar 2023 12:56:01 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

I\'ve been doing some simple test sources, basically just one or other
carefully selected LED driven by fast CMOS. Regular hex inverter
packages (both 74AC04 and 74AC14) look great with resistive loads--clean
250 ps -- 300 ps edges, as measured with an 11801C sampling scope with
SD-26 head.

https://electrooptical.net/www/sed/MC74AC04-14RisingEdges500ohmLoad.png

https://electrooptical.net/www/sed/MC74AC04_14_FallingEdge500ohms.png

(There\'s a bit of residual inductive rise after the fast edges on the
resistive load tests, but we can fix that.)

They\'re built dead-bug fashion with SO14 packages wired up like this:

10nF +5
C C |
*---C C-------*
| C C |
GND | A
*--|>o--*
in | | 432R
0---|>o---|>o---*--|>o--*---RRRR---0) To sampler
| | |
*--|>o--* GND
| |
*--|>o--*
|
GND

With 82 pF to ground from node A, they fall completely apart--the edges
show an initial fast rise/fall of a volt or so, followed by a ringy mess
for the next 10 ns.

https://electrooptical.net/www/sed/MC74AC04_14_FallingEdge500ohms82pF.png

https://electrooptical.net/www/sed/MC74AC04_14_RisingEdge500ohms82pF.png

In real life the LEDs won\'t be faster than 2 ns, and will be driven via
a resistor, of course. However, I might well want to use a speedup cap
of the same order, so it\'s very likely to be worthwhile spending an
extra buck or so and using LVC1G04 gates in SC-70, with individual
bypass caps.

Cheers

Phil Hobbs
Click to expand...

For cheap klunky old parts, the AC\'s are fast.

This is the fastest edge I\'ve seen from CMOS:

https://www.dropbox.com/s/7gajbmt923oesli/NC7SV74_2.JPG?raw=1

No, I can\'t explain the asymmetry.

You might consider driving an SAV541 or two from Tiny Logic gates.
Rds-on is about 2 ohms with 0.7 on the gate. Heck, you could drive it
from ECL, like an EP89.

If you drive the SAV gates really hard, like a volt or so, they keep
enhancing. Abs Max is for sissies.
 
On Friday, March 10, 2023 at 12:56:13 PM UTC-5, Phil Hobbs wrote:
I\'ve been doing some simple test sources, basically just one or other
carefully selected LED driven by fast CMOS. Regular hex inverter
packages (both 74AC04 and 74AC14) look great with resistive loads--clean
250 ps -- 300 ps edges, as measured with an 11801C sampling scope with
SD-26 head.

https://electrooptical.net/www/sed/MC74AC04-14RisingEdges500ohmLoad.png

https://electrooptical.net/www/sed/MC74AC04_14_FallingEdge500ohms.png

(There\'s a bit of residual inductive rise after the fast edges on the
resistive load tests, but we can fix that.)

They\'re built dead-bug fashion with SO14 packages wired up like this:

10nF +5
C C |
*---C C-------*
| C C |
GND | A
*--|>o--*
in | | 432R
0---|>o---|>o---*--|>o--*---RRRR---0) To sampler
| | |
*--|>o--* GND
| |
*--|>o--*
|
GND

With 82 pF to ground from node A, they fall completely apart--the edges
show an initial fast rise/fall of a volt or so, followed by a ringy mess
for the next 10 ns.

https://electrooptical.net/www/sed/MC74AC04_14_FallingEdge500ohms82pF.png

https://electrooptical.net/www/sed/MC74AC04_14_RisingEdge500ohms82pF.png

In real life the LEDs won\'t be faster than 2 ns, and will be driven via
a resistor, of course. However, I might well want to use a speedup cap
of the same order, so it\'s very likely to be worthwhile spending an
extra buck or so and using LVC1G04 gates in SC-70, with individual
bypass caps.
Click to expand...

Slightly overcompensated resistive attenuator is what they used in the old days.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
Click to expand...
 
On 2023-03-10 13:29, John Larkin wrote:
On Fri, 10 Mar 2023 12:56:01 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:


I\'ve been doing some simple test sources, basically just one or other
carefully selected LED driven by fast CMOS. Regular hex inverter
packages (both 74AC04 and 74AC14) look great with resistive loads--clean
250 ps -- 300 ps edges, as measured with an 11801C sampling scope with
SD-26 head.

https://electrooptical.net/www/sed/MC74AC04-14RisingEdges500ohmLoad.png

https://electrooptical.net/www/sed/MC74AC04_14_FallingEdge500ohms.png

(There\'s a bit of residual inductive rise after the fast edges on the
resistive load tests, but we can fix that.)

They\'re built dead-bug fashion with SO14 packages wired up like this:

10nF +5
C C |
*---C C-------*
| C C |
GND | A
*--|>o--*
in | | 432R
0---|>o---|>o---*--|>o--*---RRRR---0) To sampler
| | |
*--|>o--* GND
| |
*--|>o--*
|
GND

With 82 pF to ground from node A, they fall completely apart--the edges
show an initial fast rise/fall of a volt or so, followed by a ringy mess
for the next 10 ns.

https://electrooptical.net/www/sed/MC74AC04_14_FallingEdge500ohms82pF.png

https://electrooptical.net/www/sed/MC74AC04_14_RisingEdge500ohms82pF.png

In real life the LEDs won\'t be faster than 2 ns, and will be driven via
a resistor, of course. However, I might well want to use a speedup cap
of the same order, so it\'s very likely to be worthwhile spending an
extra buck or so and using LVC1G04 gates in SC-70, with individual
bypass caps.

Cheers

Phil Hobbs

For cheap klunky old parts, the AC\'s are fast.

This is the fastest edge I\'ve seen from CMOS:

https://www.dropbox.com/s/7gajbmt923oesli/NC7SV74_2.JPG?raw=1

No, I can\'t explain the asymmetry.

You might consider driving an SAV541 or two from Tiny Logic gates.
Rds-on is about 2 ohms with 0.7 on the gate. Heck, you could drive it
from ECL, like an EP89.

If you drive the SAV gates really hard, like a volt or so, they keep
enhancing. Abs Max is for sissies.
Click to expand...

That would be a win for a laser, which is pretty fast--you can put the
quiescent bias just below threshold, and then bang on it. The \'simmer\'
makes its dynamic impedance much lower, and there\'s not a lot of delta-V
on its capacitance, so it can turn off pretty well.

LEDs produce light more or less linearly with current, but it might be
worth thinking about whether it would be better behaved if I didn\'t drop
it all the way to zero current between pulses.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
On Friday, March 10, 2023 at 11:04:50 AM UTC-8, Phil Hobbs wrote:

On Fri, 10 Mar 2023 12:56:01 -0500, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

I\'ve been doing some simple test sources, basically just one or other
carefully selected LED driven by fast CMOS.

LEDs produce light more or less linearly with current, but it might be
worth thinking about whether it would be better behaved if I didn\'t drop
it all the way to zero current between pulses.
Click to expand...

If you want to look at detector fall times, pulling current OUT on the drop
will be beneficial; the alternative, letting the recombination time
determine the light output, doesn\'t show the fast fall time of
the driver, but rather of the (slower?) LED light-emission process that
gradually uses up the minority carriers.

For an oscillator-driven LED, that just means a parallel R-C element in series
with the current limit R, assuming single-supply drive with cathode on the negative rail.
 
On 2023-03-10 15:34, whit3rd wrote:
On Friday, March 10, 2023 at 11:04:50 AM UTC-8, Phil Hobbs wrote:

On Fri, 10 Mar 2023 12:56:01 -0500, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

I\'ve been doing some simple test sources, basically just one or other
carefully selected LED driven by fast CMOS.

LEDs produce light more or less linearly with current, but it might be
worth thinking about whether it would be better behaved if I didn\'t drop
it all the way to zero current between pulses.

If you want to look at detector fall times, pulling current OUT on the drop
will be beneficial;
Click to expand...

Ya\'d think so, but it generally does nothing useful.

Upper state lifetime in direct bandgap semiconductors is short, and the
hole mobility is very low, so you can\'t actually make them drift out of
the junction very fast.

the alternative, letting the recombination time
determine the light output, doesn\'t show the fast fall time of
the driver, but rather of the (slower?) LED light-emission process that
gradually uses up the minority carriers.

For an oscillator-driven LED, that just means a parallel R-C element in series
with the current limit R, assuming single-supply drive with cathode on the negative rail.
Click to expand...

Right, that\'s the speed-up cap I was talking about upthread. Helps a
lot with BJT switching, generally not much with LEDs.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
Am 10.03.23 um 18:56 schrieb Phil Hobbs:
I\'ve been doing some simple test sources, basically just one or other
carefully selected LED driven by fast CMOS.  Regular hex inverter
packages (both 74AC04 and 74AC14) look great with resistive loads--clean
250 ps -- 300 ps edges, as measured with an 11801C sampling scope with
SD-26 head.

https://electrooptical.net/www/sed/MC74AC04-14RisingEdges500ohmLoad.png

https://electrooptical.net/www/sed/MC74AC04_14_FallingEdge500ohms.png

(There\'s a bit of residual inductive rise after the fast edges on the
resistive load tests, but we can fix that.)

They\'re built dead-bug fashion with SO14 packages wired up like this:

        10nF        +5
          C C       |
      *---C C-------*
      |   C C       |
     GND            |   A
                *--|>o--*
in              |       |   432R
0---|>o---|>o---*--|>o--*---RRRR---0) To sampler
                |       |           |
                *--|>o--*          GND
                |       |
                *--|>o--*
                    |
                   GND

With 82 pF to ground from node A, they fall completely apart--the edges
show an initial fast rise/fall of a volt or so, followed by a ringy mess
for the next 10 ns.

https://electrooptical.net/www/sed/MC74AC04_14_FallingEdge500ohms82pF.png

https://electrooptical.net/www/sed/MC74AC04_14_RisingEdge500ohms82pF.png

In real life the LEDs won\'t be faster than 2 ns, and will be driven via
a resistor, of course.  However, I might well want to use a speedup cap
of the same order, so it\'s very likely to be worthwhile spending an
extra buck or so and using LVC1G04 gates in SC-70, with individual
bypass caps.

Cheers
Click to expand...

I got rise = 481 ps trise and 323 ps tfall from just 2
74LVC1G04DCKR, 100 Ohms each, both driving the 50 Ohm input of
an Agilent 54846B scope, 2.25 GHz BW, 156 ps trise.

No need to risk the 2V samplers on 5V logic that does not
deserve it.

That was just a byproduct of a 1pps signal from my GPS-synced
10 MHz source. More intended to be clean than to be fast.

< http://www.hoffmann-hochfrequenz.de/downloads/DoubDist.pdf > page
13 +-

74AC was OK when there was the old Fairchild around. But now
there is 5V tolerant 74LVC on a contemporary process, 30 years
later.

Gerhard
 
On 2023-03-10 17:14, Gerhard Hoffmann wrote:
Am 10.03.23 um 18:56 schrieb Phil Hobbs:

I\'ve been doing some simple test sources, basically just one or other
carefully selected LED driven by fast CMOS.  Regular hex inverter
packages (both 74AC04 and 74AC14) look great with resistive
loads--clean 250 ps -- 300 ps edges, as measured with an 11801C
sampling scope with SD-26 head.

https://electrooptical.net/www/sed/MC74AC04-14RisingEdges500ohmLoad.png

https://electrooptical.net/www/sed/MC74AC04_14_FallingEdge500ohms.png

(There\'s a bit of residual inductive rise after the fast edges on the
resistive load tests, but we can fix that.)

They\'re built dead-bug fashion with SO14 packages wired up like this:

         10nF        +5
           C C       |
       *---C C-------*
       |   C C       |
      GND            |   A
                 *--|>o--*
in              |       |   432R
0---|>o---|>o---*--|>o--*---RRRR---0) To sampler
                 |       |           |
                 *--|>o--*          GND
                 |       |
                 *--|>o--*
                     |
                    GND

With 82 pF to ground from node A, they fall completely apart--the
edges show an initial fast rise/fall of a volt or so, followed by a
ringy mess for the next 10 ns.

https://electrooptical.net/www/sed/MC74AC04_14_FallingEdge500ohms82pF.png


https://electrooptical.net/www/sed/MC74AC04_14_RisingEdge500ohms82pF.png


In real life the LEDs won\'t be faster than 2 ns, and will be driven
via a resistor, of course.  However, I might well want to use a
speedup cap of the same order, so it\'s very likely to be worthwhile
spending an extra buck or so and using LVC1G04 gates in SC-70, with
individual bypass caps.

Cheers

I got rise = 481 ps trise and 323 ps tfall from just 2
74LVC1G04DCKR, 100 Ohms each, both driving the 50 Ohm input of
an Agilent 54846B scope, 2.25 GHz BW, 156 ps trise.

No need to risk the 2V samplers on 5V logic that does not
deserve it.

That was just a byproduct of a 1pps signal from my GPS-synced
10 MHz source. More intended to be clean than to be fast.

  http://www.hoffmann-hochfrequenz.de/downloads/DoubDist.pdf   >  page
13 +-

74AC was OK when there was the old Fairchild around. But now
there is 5V tolerant 74LVC on a contemporary process, 30 years
later.

Gerhard
Click to expand...

Seems slower though!

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
Am 10.03.23 um 23:20 schrieb Phil Hobbs:
On 2023-03-10 17:14, Gerhard Hoffmann wrote:
Am 10.03.23 um 18:56 schrieb Phil Hobbs:

I\'ve been doing some simple test sources, basically just one or other
carefully selected LED driven by fast CMOS.  Regular hex inverter
packages (both 74AC04 and 74AC14) look great with resistive
loads--clean 250 ps -- 300 ps edges, as measured with an 11801C
sampling scope with SD-26 head.

https://electrooptical.net/www/sed/MC74AC04-14RisingEdges500ohmLoad.png

https://electrooptical.net/www/sed/MC74AC04_14_FallingEdge500ohms.png

(There\'s a bit of residual inductive rise after the fast edges on the
resistive load tests, but we can fix that.)

They\'re built dead-bug fashion with SO14 packages wired up like this:

         10nF        +5
           C C       |
       *---C C-------*
       |   C C       |
      GND            |   A
                 *--|>o--*
in              |       |   432R
0---|>o---|>o---*--|>o--*---RRRR---0) To sampler
                 |       |           |
                 *--|>o--*          GND
                 |       |
                 *--|>o--*
                     |
                    GND



I got rise = 481 ps trise and 323 ps tfall from just 2
74LVC1G04DCKR, 100 Ohms each, both driving the 50 Ohm input of
an Agilent 54846B scope, 2.25 GHz BW, 156 ps trise.

No need to risk the 2V samplers on 5V logic that does not
deserve it.

That was just a byproduct of a 1pps signal from my GPS-synced
10 MHz source. More intended to be clean than to be fast.

  http://www.hoffmann-hochfrequenz.de/downloads/DoubDist.pdf  
page 13 +-

74AC was OK when there was the old Fairchild around. But now
there is 5V tolerant 74LVC on a contemporary process, 30 years
later.

Gerhard


Seems slower though!
Click to expand...

Yes, with 4 drivers into 500 Ohms, that\'s easy living.
Not so easy if you need a presentable 1pps...


But just take a look at the quality of these stones...
(Live of Brian)
< https://www.youtube.com/watch?v=OVUwHv43HqM >

> Cheers

Gerhard
 
On 2023-03-10 17:49, Gerhard Hoffmann wrote:
Am 10.03.23 um 23:20 schrieb Phil Hobbs:
On 2023-03-10 17:14, Gerhard Hoffmann wrote:
Am 10.03.23 um 18:56 schrieb Phil Hobbs:

I\'ve been doing some simple test sources, basically just one or
other carefully selected LED driven by fast CMOS.  Regular hex
inverter packages (both 74AC04 and 74AC14) look great with resistive
loads--clean 250 ps -- 300 ps edges, as measured with an 11801C
sampling scope with SD-26 head.

https://electrooptical.net/www/sed/MC74AC04-14RisingEdges500ohmLoad.png


https://electrooptical.net/www/sed/MC74AC04_14_FallingEdge500ohms.png

(There\'s a bit of residual inductive rise after the fast edges on
the resistive load tests, but we can fix that.)

They\'re built dead-bug fashion with SO14 packages wired up like this:

         10nF        +5
           C C       |
       *---C C-------*
       |   C C       |
      GND            |   A
                 *--|>o--*
in              |       |   432R
0---|>o---|>o---*--|>o--*---RRRR---0) To sampler
                 |       |           |
                 *--|>o--*          GND
                 |       |
                 *--|>o--*
                     |
                    GND



I got rise = 481 ps trise and 323 ps tfall from just 2
74LVC1G04DCKR, 100 Ohms each, both driving the 50 Ohm input of
an Agilent 54846B scope, 2.25 GHz BW, 156 ps trise.

No need to risk the 2V samplers on 5V logic that does not
deserve it.

That was just a byproduct of a 1pps signal from my GPS-synced
10 MHz source. More intended to be clean than to be fast.

  http://www.hoffmann-hochfrequenz.de/downloads/DoubDist.pdf  
page 13 +-

74AC was OK when there was the old Fairchild around. But now
there is 5V tolerant 74LVC on a contemporary process, 30 years
later.

Gerhard


Seems slower though!

Yes, with 4 drivers into 500 Ohms, that\'s easy living.
Not so easy if you need a presentable 1pps...


But just take a look at the quality of these stones...
(Live of Brian)
  https://www.youtube.com/watch?v=OVUwHv43HqM 
Click to expand...

Monty Python dubbed in German is a bit surreal.

Yessir, a very nice writeup. Out of curiosity, why did you choose
crystal notch filters, as opposed to an LC tuned amp?

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
Am 11.03.23 um 01:39 schrieb Phil Hobbs:
On 2023-03-10 17:49, Gerhard Hoffmann wrote:
Am 10.03.23 um 23:20 schrieb Phil Hobbs:

But just take a look at the quality of these stones...

Monty Python dubbed in German is a bit surreal.

Yessir, a very nice writeup.  Out of curiosity, why did you choose
crystal notch filters, as opposed to an LC tuned amp?
Click to expand...

When I have a VNA on the table, the inductors are easy,
at least known ones. The plot has been done with
Amidon-Red inductors.
Those from the junk box probably won\'t fit.

Finding the series resonance printed on an xtal will
usually work and if it doesn\'t, it will at least
leave the phase stability of the 10 MHz alone.

> Cheers
Gerhard
 
On a sunny day (Fri, 10 Mar 2023 23:14:16 +0100) it happened Gerhard Hoffmann
<dk4xp@arcor.de> wrote in <tuga3o$1svuu$1@solani.org>:

        10nF        +5
          C C       |
      *---C C-------*
      |   C C       |
     GND            |   A
                *--|>o--*
in              |       |   432R
0---|>o---|>o---*--|>o--*---RRRR---0) To sampler
                |       |           |
                *--|>o--*          GND
                |       |
                *--|>o--*
                    |
                   GND
Click to expand...

Interesting!

The times they are changing...
 
On 2023-03-11 02:12, Gerhard Hoffmann wrote:
Am 11.03.23 um 01:39 schrieb Phil Hobbs:
On 2023-03-10 17:49, Gerhard Hoffmann wrote:
Am 10.03.23 um 23:20 schrieb Phil Hobbs:

But just take a look at the quality of these stones...

Monty Python dubbed in German is a bit surreal.

Yessir, a very nice writeup.  Out of curiosity, why did you choose
crystal notch filters, as opposed to an LC tuned amp?

When I have a VNA on the table, the inductors are easy,
at least known ones. The plot has been done with
Amidon-Red inductors.
Those from the junk box probably won\'t fit.

Finding the series resonance printed on an xtal will
usually work and if it doesn\'t, it will at least
leave the phase stability of the 10 MHz alone.
Click to expand...

Gotcha. How deep a null do you get? I normally think of fundamental
crystals as having 20 ohms or so of series resistance.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
Am 11.03.23 um 18:02 schrieb Phil Hobbs:
On 2023-03-11 02:12, Gerhard Hoffmann wrote:

Finding the series resonance printed on an xtal will
usually work and if it doesn\'t, it will at least
leave the phase stability of the 10 MHz alone.

Gotcha.  How deep a null do you get?  I normally think of fundamental
crystals as having 20 ohms or so of series resistance.
Click to expand...

depends on the impedance level. Maybe 20 dB.
20 Ohms short in a 200 Ohm (50 Ohm* 1:4 xformer) environment.
1 have seen 5 Ohm fundamental crystels @ DigiKey
and 1:9 transformers.

I took what I had here. AFAIR there are 2 traps for the 5 MHz
fundamental.

cheers, Gerhard
 
On Fri, 10 Mar 2023 23:14:16 +0100, Gerhard Hoffmann <dk4xp@arcor.de>
wrote:

Am 10.03.23 um 18:56 schrieb Phil Hobbs:

I\'ve been doing some simple test sources, basically just one or other
carefully selected LED driven by fast CMOS.  Regular hex inverter
packages (both 74AC04 and 74AC14) look great with resistive loads--clean
250 ps -- 300 ps edges, as measured with an 11801C sampling scope with
SD-26 head.

https://electrooptical.net/www/sed/MC74AC04-14RisingEdges500ohmLoad.png

https://electrooptical.net/www/sed/MC74AC04_14_FallingEdge500ohms.png

(There\'s a bit of residual inductive rise after the fast edges on the
resistive load tests, but we can fix that.)

They\'re built dead-bug fashion with SO14 packages wired up like this:

        10nF        +5
          C C       |
      *---C C-------*
      |   C C       |
     GND            |   A
                *--|>o--*
in              |       |   432R
0---|>o---|>o---*--|>o--*---RRRR---0) To sampler
                |       |           |
                *--|>o--*          GND
                |       |
                *--|>o--*
                    |
                   GND

With 82 pF to ground from node A, they fall completely apart--the edges
show an initial fast rise/fall of a volt or so, followed by a ringy mess
for the next 10 ns.

https://electrooptical.net/www/sed/MC74AC04_14_FallingEdge500ohms82pF.png

https://electrooptical.net/www/sed/MC74AC04_14_RisingEdge500ohms82pF.png

In real life the LEDs won\'t be faster than 2 ns, and will be driven via
a resistor, of course.  However, I might well want to use a speedup cap
of the same order, so it\'s very likely to be worthwhile spending an
extra buck or so and using LVC1G04 gates in SC-70, with individual
bypass caps.

Cheers

I got rise = 481 ps trise and 323 ps tfall from just 2
74LVC1G04DCKR, 100 Ohms each, both driving the 50 Ohm input of
an Agilent 54846B scope, 2.25 GHz BW, 156 ps trise.

No need to risk the 2V samplers on 5V logic that does not
deserve it.

That was just a byproduct of a 1pps signal from my GPS-synced
10 MHz source. More intended to be clean than to be fast.

http://www.hoffmann-hochfrequenz.de/downloads/DoubDist.pdf
Click to expand...

The other way to do that would be a PLL. There are some stunning but
affordable VCXOs and OCXOs around now with fs jitter specs.
 
Am 11.03.23 um 18:53 schrieb John Larkin:
On Fri, 10 Mar 2023 23:14:16 +0100, Gerhard Hoffmann <dk4xp@arcor.de
wrote:


That was just a byproduct of a 1pps signal from my GPS-synced
10 MHz source. More intended to be clean than to be fast.

http://www.hoffmann-hochfrequenz.de/downloads/DoubDist.pdf

The other way to do that would be a PLL. There are some stunning but
affordable VCXOs and OCXOs around now with fs jitter specs.
Click to expand...

My GPS already has a 5 MHz double oven,
MTI-260 . Without a heavy effort, I could
not improve that.

Really, it has 2 MTI-260. The other one is
a hot spare for redundancy. Built by HP
for Lucent; I got them as unused spare parts,
still factory sealed.

< http://www.mti-milliren.com/ocxo_260_ocxo.html >

BTW most of the cheap oscillators count the jitter
only from 12 KHz offset & UP. That\'s a telecom spec
that gives friendly numbers.


Cheers,
Gerhard
 
On 2023-03-11 12:32, Gerhard Hoffmann wrote:
Am 11.03.23 um 18:02 schrieb Phil Hobbs:
On 2023-03-11 02:12, Gerhard Hoffmann wrote:

Finding the series resonance printed on an xtal will
usually work and if it doesn\'t, it will at least
leave the phase stability of the 10 MHz alone.

Gotcha.  How deep a null do you get?  I normally think of fundamental
crystals as having 20 ohms or so of series resistance.

depends on the impedance level. Maybe 20 dB.
20 Ohms short in a 200 Ohm (50 Ohm* 1:4 xformer) environment.
1 have seen 5 Ohm fundamental crystels @ DigiKey
and 1:9 transformers.

I took what I had here. AFAIR there are 2 traps for the 5 MHz
fundamental.

cheers, Gerhard
Click to expand...

Absolutely. As a fellow junkbox-builder, I get the ethos.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
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