it oscillates!

During this shutdown, I did a little pcb layout for my triggered
common-collector Colpitts oscillator, and had some boards fabbed. A
manufacturing person came in today and built a couple for me.

It's a triggered 125 MHz oscillator that will be used to time delays
in a laser system. We want minimal time jitter so I tried to keep the
Q up. The inductor is a Coilcraft Midi-Spring.

I used a BFT25 super-fast transistor, but it oscillates at more
frequencies than I intended. Tons of jitter. The choice was to add a
base resistor or go with another transistor. A BFS17 seems to work
fine. That's a great little npn, fast but not too fast.

Here's the board

https://www.dropbox.com/s/kalhm9aiq9hal2j/Colpitts_Bench.jpg?raw=1

and here's the roughly 250th rising edge after it's triggered to run

https://www.dropbox.com/s/vjzvh6v8616dt2e/Colpitts_4-15_2us.jpg?raw=1

at 100 ps/div. I haven't figured out how to get that scope to measure
the RMS jitter on that edge; it's obviously smarter than I am, and
lets me know. If I eyeball the p-p jitter and divide by 5 for RMS, I'm
estimating 4 ps RMS jitter at 2 us out from start, which is a ratio of
500K:1. That's unheard of, so I may be doing something wrong.

We plan to phase-lock this to a good OCXO, but it will take a while to
lock, so the better the open-loop Colpitts behavior, the less frantic
we need to be about the DPLL. 2 microseconds is plenty of time to do
the math.

It's out on the bench, so I'll put it in a metal chocloate box with
some feed-thrus for better EMI shielding. Gotta empty the box first.

I need to temperature compensate it and play with the active guard
idea.


Phil H helped me think about this. Thanks.










--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[Mikko OH2HVJ]

jlarkin@highlandsniptechnology.com writes:

https://www.dropbox.com/s/vjzvh6v8616dt2e/Colpitts_4-15_2us.jpg?raw=1

at 100 ps/div. I haven't figured out how to get that scope to measure
the RMS jitter on that edge; it's obviously smarter than I am, and
lets me know. If I eyeball the p-p jitter and divide by 5 for RMS, I'm
estimating 4 ps RMS jitter at 2 us out from start, which is a ratio of
500K:1. That's unheard of, so I may be doing something wrong.

Too good a result feels good for a while always. Then the professional
side starts wondering.

What does 'Trigger on positive edge with Holdoff by time' exactly do, is
it arming on first edge, then triggering on the second edge after
holdoff time ?

I think that would mean that you're triggering on the roughly 250th edge
and thus seeing scope trigger jitter ?

How about triggering on the first edge and scrolling to trigger+2us ? I think
the scope timebase should be quite good compared to oscillator.

--
mikko

 

On Thursday, April 16, 2020 at 2:36:22 AM UTC-4, Mikko OH2HVJ wrote:

jlarkin@highlandsniptechnology.com writes:

https://www.dropbox.com/s/vjzvh6v8616dt2e/Colpitts_4-15_2us.jpg?raw=1

at 100 ps/div. I haven't figured out how to get that scope to measure
the RMS jitter on that edge; it's obviously smarter than I am, and
lets me know. If I eyeball the p-p jitter and divide by 5 for RMS, I'm
estimating 4 ps RMS jitter at 2 us out from start, which is a ratio of
500K:1. That's unheard of, so I may be doing something wrong.

Too good a result feels good for a while always. Then the professional
side starts wondering.

Going off on that point.... Many years ago I was working (peripherally) with a rather intimidating antenna designer. He had just built a radiating element using a 3dB 90 degree hybrid and was launching into the air from each output. He brought me over to the network analyzer and showed me his fantastic return loss. It turns out I had just been doing reading on hybrid couplers and so I pointed out to him that any reflected power at the two launching ends would reflect back into the 4th port with a 50 ohm resistor. He paused for a moment and you could see his countenance drop like a rock. He was nice to me for the rest of the time I worked there.

What does 'Trigger on positive edge with Holdoff by time' exactly do, is
it arming on first edge, then triggering on the second edge after
holdoff time ?

I think that would mean that you're triggering on the roughly 250th edge
and thus seeing scope trigger jitter ?

How about triggering on the first edge and scrolling to trigger+2us ? I think
the scope timebase should be quite good compared to oscillator.

--
mikko

 

[Winfield Hill]

jlarkin@highlandsniptechnology.com wrote...

During this shutdown, I did a little pcb layout for my triggered
common-collector Colpitts oscillator, and had some boards fabbed.
A manufacturing person came in today and built a couple for me.

It's a triggered 125 MHz oscillator that will be used to time delays
in a laser system. We want minimal time jitter so I tried to keep the
Q up. The inductor is a Coilcraft Midi-Spring.

I used a BFT25 super-fast transistor, but it oscillates at more
frequencies than I intended. Tons of jitter. The choice was to add a
base resistor or go with another transistor. A BFS17 seems to work
fine. That's a great little npn, fast but not too fast.

Here's the board ... snip

Phil H helped me think about this. Thanks.

Very interesting, show us the circuit!


--
Thanks,
- Win

 

[Phil Hobbs]

On 2020-04-15 22:30, jlarkin@highlandsniptechnology.com wrote:

During this shutdown, I did a little pcb layout for my triggered
common-collector Colpitts oscillator, and had some boards fabbed. A
manufacturing person came in today and built a couple for me.

It's a triggered 125 MHz oscillator that will be used to time delays
in a laser system. We want minimal time jitter so I tried to keep the
Q up. The inductor is a Coilcraft Midi-Spring.

I used a BFT25 super-fast transistor, but it oscillates at more
frequencies than I intended. Tons of jitter. The choice was to add a
base resistor or go with another transistor. A BFS17 seems to work
fine. That's a great little npn, fast but not too fast.

Here's the board

https://www.dropbox.com/s/kalhm9aiq9hal2j/Colpitts_Bench.jpg?raw=1

and here's the roughly 250th rising edge after it's triggered to run

https://www.dropbox.com/s/vjzvh6v8616dt2e/Colpitts_4-15_2us.jpg?raw=1

at 100 ps/div. I haven't figured out how to get that scope to measure
the RMS jitter on that edge; it's obviously smarter than I am, and
lets me know. If I eyeball the p-p jitter and divide by 5 for RMS, I'm
estimating 4 ps RMS jitter at 2 us out from start, which is a ratio of
500K:1. That's unheard of, so I may be doing something wrong.

Very nice if true. (Nice scope, too.)

We plan to phase-lock this to a good OCXO, but it will take a while to
lock, so the better the open-loop Colpitts behavior, the less frantic
we need to be about the DPLL. 2 microseconds is plenty of time to do
the math.

It's out on the bench, so I'll put it in a metal chocloate box with
some feed-thrus for better EMI shielding. Gotta empty the box first.

I need to temperature compensate it and play with the active guard
idea.


Phil H helped me think about this. Thanks.

Glad to help. It's an interesting problem, for sure.

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 Wednesday, April 15, 2020 at 10:30:51 PM UTC-4, jla...@highlandsniptechnology.com wrote:

During this shutdown, I did a little pcb layout for my triggered
common-collector Colpitts oscillator, and had some boards fabbed. A
manufacturing person came in today and built a couple for me.

It's a triggered 125 MHz oscillator that will be used to time delays
in a laser system. We want minimal time jitter so I tried to keep the
Q up. The inductor is a Coilcraft Midi-Spring.

I used a BFT25 super-fast transistor, but it oscillates at more
frequencies than I intended. Tons of jitter. The choice was to add a
base resistor or go with another transistor. A BFS17 seems to work
fine. That's a great little npn, fast but not too fast.

Here's the board

https://www.dropbox.com/s/kalhm9aiq9hal2j/Colpitts_Bench.jpg?raw=1

and here's the roughly 250th rising edge after it's triggered to run

https://www.dropbox.com/s/vjzvh6v8616dt2e/Colpitts_4-15_2us.jpg?raw=1

at 100 ps/div. I haven't figured out how to get that scope to measure
the RMS jitter on that edge; it's obviously smarter than I am, and
lets me know. If I eyeball the p-p jitter and divide by 5 for RMS, I'm
estimating 4 ps RMS jitter at 2 us out from start, which is a ratio of
500K:1. That's unheard of, so I may be doing something wrong.

We plan to phase-lock this to a good OCXO, but it will take a while to
lock, so the better the open-loop Colpitts behavior, the less frantic
we need to be about the DPLL. 2 microseconds is plenty of time to do
the math.

It's out on the bench, so I'll put it in a metal chocloate box with
some feed-thrus for better EMI shielding. Gotta empty the box first.

I need to temperature compensate it and play with the active guard
idea.


Phil H helped me think about this. Thanks.










--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

What do you mean the first circuit oscillated at more frequencies than you intended? Isn't that circuit tuned?

 

On 16 Apr 2020 03:35:25 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

jlarkin@highlandsniptechnology.com wrote...

During this shutdown, I did a little pcb layout for my triggered
common-collector Colpitts oscillator, and had some boards fabbed.
A manufacturing person came in today and built a couple for me.

It's a triggered 125 MHz oscillator that will be used to time delays
in a laser system. We want minimal time jitter so I tried to keep the
Q up. The inductor is a Coilcraft Midi-Spring.

I used a BFT25 super-fast transistor, but it oscillates at more
frequencies than I intended. Tons of jitter. The choice was to add a
base resistor or go with another transistor. A BFS17 seems to work
fine. That's a great little npn, fast but not too fast.

Here's the board ... snip

Phil H helped me think about this. Thanks.

Very interesting, show us the circuit!

Here's the non-secret oscillator part.

https://www.dropbox.com/s/ct32117dmho0cbr/Z384_Colpitts_3.jpg?raw=1

One key thing to test and tweak is tempco. I cut an island out of the
layer 2 ground plane as an active guard that can float, be grounded,
or be driven from the Q1 emitter. That might mitigate some of the
horrible FR4 capacitance. C3 can tweak tempco too. The real board will
be 10 layers with just 8 mils from the top to the L2 ground plane,
which means it will be different from this proto board. So I'm just
learning principles now.

Varicaps have bad tempcos too, so things will get tangled.

I'd like to make the board thicker and make the dielectrics thicker,
but there are mechanical limits, including the Vbite connectors.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

On Thu, 16 Apr 2020 07:57:06 -0700 (PDT),
bloggs.fredbloggs.fred@gmail.com wrote:

On Wednesday, April 15, 2020 at 10:30:51 PM UTC-4, jla...@highlandsniptechnology.com wrote:
During this shutdown, I did a little pcb layout for my triggered
common-collector Colpitts oscillator, and had some boards fabbed. A
manufacturing person came in today and built a couple for me.

It's a triggered 125 MHz oscillator that will be used to time delays
in a laser system. We want minimal time jitter so I tried to keep the
Q up. The inductor is a Coilcraft Midi-Spring.

I used a BFT25 super-fast transistor, but it oscillates at more
frequencies than I intended. Tons of jitter. The choice was to add a
base resistor or go with another transistor. A BFS17 seems to work
fine. That's a great little npn, fast but not too fast.

Here's the board

https://www.dropbox.com/s/kalhm9aiq9hal2j/Colpitts_Bench.jpg?raw=1

and here's the roughly 250th rising edge after it's triggered to run

https://www.dropbox.com/s/vjzvh6v8616dt2e/Colpitts_4-15_2us.jpg?raw=1

at 100 ps/div. I haven't figured out how to get that scope to measure
the RMS jitter on that edge; it's obviously smarter than I am, and
lets me know. If I eyeball the p-p jitter and divide by 5 for RMS, I'm
estimating 4 ps RMS jitter at 2 us out from start, which is a ratio of
500K:1. That's unheard of, so I may be doing something wrong.

We plan to phase-lock this to a good OCXO, but it will take a while to
lock, so the better the open-loop Colpitts behavior, the less frantic
we need to be about the DPLL. 2 microseconds is plenty of time to do
the math.

It's out on the bench, so I'll put it in a metal chocloate box with
some feed-thrus for better EMI shielding. Gotta empty the box first.

I need to temperature compensate it and play with the active guard
idea.


Phil H helped me think about this. Thanks.










--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

What do you mean the first circuit oscillated at more frequencies than you intended? Isn't that circuit tuned?

I think the NPN was also oscillating at some microwave frequencies,
all on its own. Fast emitter followers do that. It was probably still
oscillating when the 120 MHz tank was quenched and the oscillator
theoretically stopped. Touching various counter-intuitive nodes with a
tiny screwdriver changed things a lot. I even stopped the extra
oscillations by touching something that made no sense.

A series base resistor is the usual fix for an oscillating emitter
follower, but that would need a hack and might reduce Q. Going to a
slower transistor seems like the best fix. It's only 120 MHz.






--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

On Thu, 16 Apr 2020 03:07:53 -0700 (PDT), blocher@columbus.rr.com
wrote:

On Thursday, April 16, 2020 at 2:36:22 AM UTC-4, Mikko OH2HVJ wrote:
jlarkin@highlandsniptechnology.com writes:

https://www.dropbox.com/s/vjzvh6v8616dt2e/Colpitts_4-15_2us.jpg?raw=1

at 100 ps/div. I haven't figured out how to get that scope to measure
the RMS jitter on that edge; it's obviously smarter than I am, and
lets me know. If I eyeball the p-p jitter and divide by 5 for RMS, I'm
estimating 4 ps RMS jitter at 2 us out from start, which is a ratio of
500K:1. That's unheard of, so I may be doing something wrong.

Too good a result feels good for a while always. Then the professional
side starts wondering.


Going off on that point.... Many years ago I was working (peripherally) with a rather intimidating antenna designer. He had just built a radiating element using a 3dB 90 degree hybrid and was launching into the air from each output. He brought me over to the network analyzer and showed me his fantastic return loss. It turns out I had just been doing reading on hybrid couplers and so I pointed out to him that any reflected power at the two launching ends would reflect back into the 4th port with a 50 ohm resistor. He paused for a moment and you could see his countenance drop like a rock. He was nice to me for the rest of the time I worked there.

I almost never trust measurements, especially good ones. Especially
using an oscilloscope that nobody understands, even the LeCroy support
people.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

On Thu, 16 Apr 2020 09:36:18 +0300, Mikko OH2HVJ
<mikko.syrjalahti@nospam.fi> wrote:

jlarkin@highlandsniptechnology.com writes:

https://www.dropbox.com/s/vjzvh6v8616dt2e/Colpitts_4-15_2us.jpg?raw=1

at 100 ps/div. I haven't figured out how to get that scope to measure
the RMS jitter on that edge; it's obviously smarter than I am, and
lets me know. If I eyeball the p-p jitter and divide by 5 for RMS, I'm
estimating 4 ps RMS jitter at 2 us out from start, which is a ratio of
500K:1. That's unheard of, so I may be doing something wrong.

Too good a result feels good for a while always. Then the professional
side starts wondering.

What does 'Trigger on positive edge with Holdoff by time' exactly do, is
it arming on first edge, then triggering on the second edge after
holdoff time ?

LeCroy is always confusing. The oscillator makes a burst, a few us
wide now, and my intent is that the scope triggers on the first rising
edge and captures one burst. Seems to. If there's no holdoff, the
display is a mess.

Holdoff usually means that once a trigger is accepted, triggers are
inhibited for some time. If I set the holdoff greater than the burst
width, I should trigger on the first edge of each burst.

I guess I should trigger the scope from the same pulse that gates the
burst. I got the built board late in the day, and was pleased to see
it oscillate. I need to spend a couple days carefully tweaking it.

I think that would mean that you're triggering on the roughly 250th edge
and thus seeing scope trigger jitter ?

LeCroy claims 1 ps RMS jitter. I checked it with our SRS clock
generator as the input signal, and that has a lot less jitter than my
oscillator, so the scope is good enough.

My old Tek 11802 uses an LC burst oscillator as its timebase, but the
jitter is something like 1/20000 of the delay, which isn't good
enough. The LeCroy just digitizes the input at a constant ADC rate,
pokes it into RAM, and does all the rest in software, including
finding the trigger. I think.

How about triggering on the first edge and scrolling to trigger+2us ? I think
the scope timebase should be quite good compared to oscillator.

That's basically what's happening, probably. But I'll trigger on the
oscillator gate, which is why I included the SMA loop-thru connectors
on the gate input.




--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[Mikko OH2HVJ]

jlarkin@highlandsniptechnology.com writes:

What does 'Trigger on positive edge with Holdoff by time' exactly do, is
it arming on first edge, then triggering on the second edge after
holdoff time ?
....

I guess I should trigger the scope from the same pulse that gates the
burst. I got the built board late in the day, and was pleased to see
it oscillate. I need to spend a couple days carefully tweaking it.

Depends if that's the relevant parameter of the frequency jitter within
the burst. Trigger on gate will also include whatever gating jitters
there might be - which just may be the key performance criteria
depending on application.

I think that would mean that you're triggering on the roughly 250th edge
and thus seeing scope trigger jitter ?

LeCroy claims 1 ps RMS jitter. I checked it with our SRS clock
generator as the input signal, and that has a lot less jitter than my
oscillator, so the scope is good enough.

You might also be able just to use normal trigger delay ?

...

That's basically what's happening, probably. But I'll trigger on the
oscillator gate, which is why I included the SMA loop-thru connectors
on the gate input.

Wonders of modern scopes...

--
mikko

 

[Gerhard Hoffmann]

Am 16.04.20 um 18:48 schrieb bitrex:

Modern DSOs also double as a portable gaming device; Doom runs even
better on this Rigol than some of the Nintendo home video game systems
it was ported to from the PC in the late 90s:

I have booted my Infiniium 54846B scope with a Linux variant to make
backups of its windows disk. It even ran open office, but sloooow.
That looked weird.


Cheers, Gerhard

 

[bitrex]

On 4/16/2020 12:15 PM, jlarkin@highlandsniptechnology.com wrote:

On Thu, 16 Apr 2020 03:07:53 -0700 (PDT), blocher@columbus.rr.com
wrote:

On Thursday, April 16, 2020 at 2:36:22 AM UTC-4, Mikko OH2HVJ wrote:
jlarkin@highlandsniptechnology.com writes:

https://www.dropbox.com/s/vjzvh6v8616dt2e/Colpitts_4-15_2us.jpg?raw=1

at 100 ps/div. I haven't figured out how to get that scope to measure
the RMS jitter on that edge; it's obviously smarter than I am, and
lets me know. If I eyeball the p-p jitter and divide by 5 for RMS, I'm
estimating 4 ps RMS jitter at 2 us out from start, which is a ratio of
500K:1. That's unheard of, so I may be doing something wrong.

Too good a result feels good for a while always. Then the professional
side starts wondering.


Going off on that point.... Many years ago I was working (peripherally) with a rather intimidating antenna designer. He had just built a radiating element using a 3dB 90 degree hybrid and was launching into the air from each output. He brought me over to the network analyzer and showed me his fantastic return loss. It turns out I had just been doing reading on hybrid couplers and so I pointed out to him that any reflected power at the two launching ends would reflect back into the 4th port with a 50 ohm resistor. He paused for a moment and you could see his countenance drop like a rock. He was nice to me for the rest of the time I worked there.




I almost never trust measurements, especially good ones. Especially
using an oscilloscope that nobody understands, even the LeCroy support
people.

Modern DSOs also double as a portable gaming device; Doom runs even
better on this Rigol than some of the Nintendo home video game systems
it was ported to from the PC in the late 90s:

<https://www.youtube.com/watch?v=m2JOs0Aldq0>

 

[TTman]

On 16/04/2020 03:30, jlarkin@highlandsniptechnology.com wrote:

During this shutdown, I did a little pcb layout for my triggered
common-collector Colpitts oscillator, and had some boards fabbed. A
manufacturing person came in today and built a couple for me.

It's a triggered 125 MHz oscillator that will be used to time delays
in a laser system. We want minimal time jitter so I tried to keep the
Q up. The inductor is a Coilcraft Midi-Spring.

I used a BFT25 super-fast transistor, but it oscillates at more
frequencies than I intended. Tons of jitter. The choice was to add a
base resistor or go with another transistor. A BFS17 seems to work
fine. That's a great little npn, fast but not too fast.

Here's the board

https://www.dropbox.com/s/kalhm9aiq9hal2j/Colpitts_Bench.jpg?raw=1

and here's the roughly 250th rising edge after it's triggered to run

https://www.dropbox.com/s/vjzvh6v8616dt2e/Colpitts_4-15_2us.jpg?raw=1

at 100 ps/div. I haven't figured out how to get that scope to measure
the RMS jitter on that edge; it's obviously smarter than I am, and
lets me know. If I eyeball the p-p jitter and divide by 5 for RMS, I'm
estimating 4 ps RMS jitter at 2 us out from start, which is a ratio of
500K:1. That's unheard of, so I may be doing something wrong.

We plan to phase-lock this to a good OCXO, but it will take a while to
lock, so the better the open-loop Colpitts behavior, the less frantic
we need to be about the DPLL. 2 microseconds is plenty of time to do
the math.

It's out on the bench, so I'll put it in a metal chocloate box with
some feed-thrus for better EMI shielding. Gotta empty the box first.

I need to temperature compensate it and play with the active guard
idea.


Phil H helped me think about this. Thanks.

The laser designator that I worked on just used the FPGA to do all the
timing.. Laser diode firing and Q switch opening and range detection...

--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

 

[Phil Hobbs]

On 2020-04-16 12:15, jlarkin@highlandsniptechnology.com wrote:

On Thu, 16 Apr 2020 03:07:53 -0700 (PDT), blocher@columbus.rr.com
wrote:

On Thursday, April 16, 2020 at 2:36:22 AM UTC-4, Mikko OH2HVJ wrote:
jlarkin@highlandsniptechnology.com writes:

https://www.dropbox.com/s/vjzvh6v8616dt2e/Colpitts_4-15_2us.jpg?raw=1

at 100 ps/div. I haven't figured out how to get that scope to measure
the RMS jitter on that edge; it's obviously smarter than I am, and
lets me know. If I eyeball the p-p jitter and divide by 5 for RMS, I'm
estimating 4 ps RMS jitter at 2 us out from start, which is a ratio of
500K:1. That's unheard of, so I may be doing something wrong.

Too good a result feels good for a while always. Then the professional
side starts wondering.


Going off on that point.... Many years ago I was working (peripherally) with a rather intimidating antenna designer. He had just built a radiating element using a 3dB 90 degree hybrid and was launching into the air from each output. He brought me over to the network analyzer and showed me his fantastic return loss. It turns out I had just been doing reading on hybrid couplers and so I pointed out to him that any reflected power at the two launching ends would reflect back into the 4th port with a 50 ohm resistor. He paused for a moment and you could see his countenance drop like a rock. He was nice to me for the rest of the time I worked there.




I almost never trust measurements, especially good ones. Especially
using an oscilloscope that nobody understands, even the LeCroy support
people.

Well, you could test it using a couple of hundred feet of coax, a
trombone line, and one of your fave PECL comparators or a Mini-Circuits
mixer.

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

 

[John Larkin]

On Thu, 16 Apr 2020 15:09:52 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-04-16 12:15, jlarkin@highlandsniptechnology.com wrote:
On Thu, 16 Apr 2020 03:07:53 -0700 (PDT), blocher@columbus.rr.com
wrote:

On Thursday, April 16, 2020 at 2:36:22 AM UTC-4, Mikko OH2HVJ wrote:
jlarkin@highlandsniptechnology.com writes:

https://www.dropbox.com/s/vjzvh6v8616dt2e/Colpitts_4-15_2us.jpg?raw=1

at 100 ps/div. I haven't figured out how to get that scope to measure
the RMS jitter on that edge; it's obviously smarter than I am, and
lets me know. If I eyeball the p-p jitter and divide by 5 for RMS, I'm
estimating 4 ps RMS jitter at 2 us out from start, which is a ratio of
500K:1. That's unheard of, so I may be doing something wrong.

Too good a result feels good for a while always. Then the professional
side starts wondering.


Going off on that point.... Many years ago I was working (peripherally) with a rather intimidating antenna designer. He had just built a radiating element using a 3dB 90 degree hybrid and was launching into the air from each output. He brought me over to the network analyzer and showed me his fantastic return loss. It turns out I had just been doing reading on hybrid couplers and so I pointed out to him that any reflected power at the two launching ends would reflect back into the 4th port with a 50 ohm resistor. He paused for a moment and you could see his countenance drop like a rock. He was nice to me for the rest of the time I worked there.




I almost never trust measurements, especially good ones. Especially
using an oscilloscope that nobody understands, even the LeCroy support
people.

Well, you could test it using a couple of hundred feet of coax, a
trombone line, and one of your fave PECL comparators or a Mini-Circuits
mixer.

Cheers

Phil Hobbs

The SRS clock generator has super low jitter, and using it as the
source in a similar test, I see a couple ps RMS jitter. So it looks
like the scope is good.

One way to check a scope's math is to drive it with an FM'd signal,
where you can calculate the added jitter. Then measure it with the
scope.

Around here, some people were measuring the standard deviation of
cross times, on a Tek sampler. That's not jitter, because the cross
times have already been computed from multiple samples. One of the
LeCroy support people told us to do that too.

I have sucked raw Y-T sample points out of my Tek and done the math
myself. We could do that with the LeCroy too. I'd have more confidence
in that.

https://www.dropbox.com/s/e2ommsccwnkzv3y/Jitter2.gif?raw=1




--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[John Larkin]

On Thu, 16 Apr 2020 19:02:49 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
wrote:

Am 16.04.20 um 18:48 schrieb bitrex:

Modern DSOs also double as a portable gaming device; Doom runs even
better on this Rigol than some of the Nintendo home video game systems
it was ported to from the PC in the late 90s:

I have booted my Infiniium 54846B scope with a Linux variant to make
backups of its windows disk. It even ran open office, but sloooow.
That looked weird.


Cheers, Gerhard

The LeCroy is a Win7 machine.

You really need a mouse to use it.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[John Larkin]

On Thu, 16 Apr 2020 20:36:40 +0100, TTman <kraken.sankey@gmail.com>
wrote:

On 16/04/2020 03:30, jlarkin@highlandsniptechnology.com wrote:

During this shutdown, I did a little pcb layout for my triggered
common-collector Colpitts oscillator, and had some boards fabbed. A
manufacturing person came in today and built a couple for me.

It's a triggered 125 MHz oscillator that will be used to time delays
in a laser system. We want minimal time jitter so I tried to keep the
Q up. The inductor is a Coilcraft Midi-Spring.

I used a BFT25 super-fast transistor, but it oscillates at more
frequencies than I intended. Tons of jitter. The choice was to add a
base resistor or go with another transistor. A BFS17 seems to work
fine. That's a great little npn, fast but not too fast.

Here's the board

https://www.dropbox.com/s/kalhm9aiq9hal2j/Colpitts_Bench.jpg?raw=1

and here's the roughly 250th rising edge after it's triggered to run

https://www.dropbox.com/s/vjzvh6v8616dt2e/Colpitts_4-15_2us.jpg?raw=1

at 100 ps/div. I haven't figured out how to get that scope to measure
the RMS jitter on that edge; it's obviously smarter than I am, and
lets me know. If I eyeball the p-p jitter and divide by 5 for RMS, I'm
estimating 4 ps RMS jitter at 2 us out from start, which is a ratio of
500K:1. That's unheard of, so I may be doing something wrong.

We plan to phase-lock this to a good OCXO, but it will take a while to
lock, so the better the open-loop Colpitts behavior, the less frantic
we need to be about the DPLL. 2 microseconds is plenty of time to do
the math.

It's out on the bench, so I'll put it in a metal chocloate box with
some feed-thrus for better EMI shielding. Gotta empty the box first.

I need to temperature compensate it and play with the active guard
idea.


Phil H helped me think about this. Thanks.


The laser designator that I worked on just used the FPGA to do all the
timing.. Laser diode firing and Q switch opening and range detection...

Did the FPGA initiate each shot? What sort of timing resolution are
you getting?

Our trigger is asynchronous to our main clock, and we have to time
everything off that.

Some lasers just fire when they feel like, or are triggered by someone
not-us.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Clifford Heath]

On 17/4/20 2:42 am, jlarkin@highlandsniptechnology.com wrote:

On Thu, 16 Apr 2020 07:57:06 -0700 (PDT),
bloggs.fredbloggs.fred@gmail.com wrote:
What do you mean the first circuit oscillated at more frequencies than you intended? Isn't that circuit tuned?

I think the NPN was also oscillating at some microwave frequencies,
all on its own. Fast emitter followers do that. It was probably still
oscillating when the 120 MHz tank was quenched and the oscillator
theoretically stopped. Touching various counter-intuitive nodes with a
tiny screwdriver changed things a lot. I even stopped the extra
oscillations by touching something that made no sense.

A series base resistor is the usual fix for an oscillating emitter
follower, but that would need a hack and might reduce Q. Going to a
slower transistor seems like the best fix. It's only 120 MHz.

I've seen (LTSpice and bench) Colpitts oscillators that produce pulses
of much-higher-frequency oscillation near the fundamental's zero
crossing. So you might have 125MHz with synchronously
amplitude-modulated 900Mhz overlaid.

Also beware of paralleling larger and smaller capacitors, as is often
recommended for decoupling. The ESL of the larger capacitor can form a
surprisingly high-Q resonant tank with the smaller capacitor, causing
all kinds of interesting birdies.

Clifford Heath.

 

On Fri, 17 Apr 2020 10:54:54 +1000, Clifford Heath
<no.spam@please.net> wrote:

On 17/4/20 2:42 am, jlarkin@highlandsniptechnology.com wrote:
On Thu, 16 Apr 2020 07:57:06 -0700 (PDT),
bloggs.fredbloggs.fred@gmail.com wrote:
What do you mean the first circuit oscillated at more frequencies than you intended? Isn't that circuit tuned?

I think the NPN was also oscillating at some microwave frequencies,
all on its own. Fast emitter followers do that. It was probably still
oscillating when the 120 MHz tank was quenched and the oscillator
theoretically stopped. Touching various counter-intuitive nodes with a
tiny screwdriver changed things a lot. I even stopped the extra
oscillations by touching something that made no sense.

A series base resistor is the usual fix for an oscillating emitter
follower, but that would need a hack and might reduce Q. Going to a
slower transistor seems like the best fix. It's only 120 MHz.

I've seen (LTSpice and bench) Colpitts oscillators that produce pulses
of much-higher-frequency oscillation near the fundamental's zero
crossing. So you might have 125MHz with synchronously
amplitude-modulated 900Mhz overlaid.

Even worse, Spice transistor models usually exclude wire-bond
inductance.

Also beware of paralleling larger and smaller capacitors, as is often
recommended for decoupling. The ESL of the larger capacitor can form a
surprisingly high-Q resonant tank with the smaller capacitor, causing
all kinds of interesting birdies.

Clifford Heath.

Turns out that I was still having erratic jitter with the slower
transistor. Touching totally illogical nodes with a small screwdriver
sometimes fixed it. As you note, it might have been burst oscillating
on some parts of the main swing. Adding a 50 ohm resistor in series
with the Colpitts base really seems to have fixed it. Exploring the
solution space by soldering is a lot slower than Spicing. This
lockdown does give me lots of time to fiddle.

I bolted it into a chocolate tin, which was a lot of work, but that
didn't make any difference.

Here's the setup:

https://www.dropbox.com/s/c15dx5hu88f96fn/Colpitts_Bench_2.jpg?raw=1

The Tek scope is looking at the sine wave itself, and the LeCroy at
the oscillator digital output. Looks like I have a bit too much
differential-equation-initial-conditions current. The ideal waveform
would be a perfect flat tone burst. More soldering.

I need a big black blanket to huddle under when I photograph that big
scope.









--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard