Reply by Phil Hobbs ●December 8, 20212021-12-08
John Larkin wrote:

> On Tue, 7 Dec 2021 22:53:21 -0500, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
> 
>> John Larkin wrote:
>>> https://www.dropbox.com/s/tugwe4mnoj2ri80/Z508_AC_Coupling.jpg?raw=1
>>>
>>> 0306 cap, capacitive bump. 0603 cap, inductive bump. No surprise that
>>> the 0204 is best. In the 25 ps sort of domain, on FR4, there's no need
>>> to buy exotic caps.
>>>
>>> That 0204 is a 0.47 uF 16 volt cap. With 9 volts DC bias from my
>>> distributed amplifier, it loses 80% of its capacitance.
>>>
>>
>> Dropbox found the picture again.  It does look like the 0204 is a good
>> fit to the 50-ohm line.  Do you have the TDRs handy?
>>
>> Thanks
>>
>> Phil Hobbs
> 
> https://www.dropbox.com/sh/w4qqa260o7wu4vg/AADWbTl1sr3ZBEzha1TIlvIla?dl=0
> 
> The caps are at cm 7 in the upper/TDR trace. The Mueller edge-launch
> SMA connectors are worse than the caps. We did nail 50 ohms pretty
> good on this one.


Very nice!

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
Reply by John Larkin ●December 8, 20212021-12-08
On Tue, 7 Dec 2021 22:53:21 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:


>John Larkin wrote:
>> https://www.dropbox.com/s/tugwe4mnoj2ri80/Z508_AC_Coupling.jpg?raw=1
>> 
>> 0306 cap, capacitive bump. 0603 cap, inductive bump. No surprise that
>> the 0204 is best. In the 25 ps sort of domain, on FR4, there's no need
>> to buy exotic caps.
>> 
>> That 0204 is a 0.47 uF 16 volt cap. With 9 volts DC bias from my
>> distributed amplifier, it loses 80% of its capacitance.
>> 
>
>Dropbox found the picture again.  It does look like the 0204 is a good 
>fit to the 50-ohm line.  Do you have the TDRs handy?
>
>Thanks
>
>Phil Hobbs


https://www.dropbox.com/sh/w4qqa260o7wu4vg/AADWbTl1sr3ZBEzha1TIlvIla?dl=0

The caps are at cm 7 in the upper/TDR trace. The Mueller edge-launch
SMA connectors are worse than the caps. We did nail 50 ohms pretty
good on this one.



-- 

If a man will begin with certainties, he shall end with doubts, 
but if he will be content to begin with doubts he shall end in certainties.
Francis Bacon
Reply by John Doe ●December 8, 20212021-12-08
That sounds dirty...
Reply by Gerhard Hoffmann ●December 8, 20212021-12-08
Am 08.12.21 um 04:53 schrieb Phil Hobbs:

> John Larkin wrote:
>> https://www.dropbox.com/s/tugwe4mnoj2ri80/Z508_AC_Coupling.jpg?raw=1
>>
>> 0306 cap, capacitive bump. 0603 cap, inductive bump. No surprise that
>> the 0204 is best. In the 25 ps sort of domain, on FR4, there's no need
>> to buy exotic caps.
>>
>> That 0204 is a 0.47 uF 16 volt cap. With 9 volts DC bias from my
>> distributed amplifier, it loses 80% of its capacitance.
>>
> 
> Dropbox found the picture again.&nbsp; It does look like the 0204 is a good 
> fit to the 50-ohm line.&nbsp; Do you have the TDRs handy?


How wide a 50 Ohm line is depends on eps-r of the board and the
stackup. We got excellent results for the eye diagrams @ 10 GBps
with 0402 AVX capacitors > 10 years ago.

And I wonder why the CV product is so much worse for the short &
fat capacitors vs. the normal slim & long ones.

I have a lot of 0612 10u 6V3 here, DK 445-4072-1-ND, never used them.

cheers, Gerhard
Reply by Phil Hobbs ●December 7, 20212021-12-07
John Larkin wrote:

> https://www.dropbox.com/s/tugwe4mnoj2ri80/Z508_AC_Coupling.jpg?raw=1
> 
> 0306 cap, capacitive bump. 0603 cap, inductive bump. No surprise that
> the 0204 is best. In the 25 ps sort of domain, on FR4, there's no need
> to buy exotic caps.
> 
> That 0204 is a 0.47 uF 16 volt cap. With 9 volts DC bias from my
> distributed amplifier, it loses 80% of its capacitance.
> 


Dropbox found the picture again.  It does look like the 0204 is a good 
fit to the 50-ohm line.  Do you have the TDRs handy?

Thanks

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
Reply by Phil Hobbs ●December 7, 20212021-12-07
boB wrote:

> On Tue, 07 Dec 2021 11:16:37 -0800, John Larkin
> <jlarkin@highland_atwork_technology.com> wrote:
> 
>> https://www.dropbox.com/s/tugwe4mnoj2ri80/Z508_AC_Coupling.jpg?raw=1
>>
>> 0306 cap, capacitive bump. 0603 cap, inductive bump. No surprise that
>> the 0204 is best. In the 25 ps sort of domain, on FR4, there's no need
>> to buy exotic caps.
>>
>> That 0204 is a 0.47 uF 16 volt cap. With 9 volts DC bias from my
>> distributed amplifier, it loses 80% of its capacitance.
> 
> 
> Where do you find these sideways capacitors ?
> 
> 
> 
> 


Digikey.  Search on "0204 capacitor" and 98 part numbers come up, 
including this one:

<https://www.digikey.com/en/products/detail/murata-electronics/LLL153C80G105ME21D/4905678>

0.47 uF, 4V, with most of the capacitance remaining at the rated 
voltage, 3 cents in reels.

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
Reply by boB ●December 7, 20212021-12-07
On Tue, 07 Dec 2021 11:16:37 -0800, John Larkin
<jlarkin@highland_atwork_technology.com> wrote:


>https://www.dropbox.com/s/tugwe4mnoj2ri80/Z508_AC_Coupling.jpg?raw=1
>
>0306 cap, capacitive bump. 0603 cap, inductive bump. No surprise that
>the 0204 is best. In the 25 ps sort of domain, on FR4, there's no need
>to buy exotic caps.
>
>That 0204 is a 0.47 uF 16 volt cap. With 9 volts DC bias from my
>distributed amplifier, it loses 80% of its capacitance.



Where do you find these sideways capacitors ?
Reply by John Larkin ●December 7, 20212021-12-07
On Tue, 7 Dec 2021 16:05:09 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:


>John Larkin wrote:
>> https://www.dropbox.com/s/tugwe4mnoj2ri80/Z508_AC_Coupling.jpg?raw=1
>> 
>> 0306 cap, capacitive bump. 0603 cap, inductive bump. No surprise that
>> the 0204 is best. In the 25 ps sort of domain, on FR4, there's no need
>> to buy exotic caps.
>> 
>> That 0204 is a 0.47 uF 16 volt cap. With 9 volts DC bias from my
>> distributed amplifier, it loses 80% of its capacitance.
>> 
>
>Comes up 500 at the moment.
>
>Cheers
>
>Phil Hobbs


Strange; that link used to work.

Dropbox used to just work. They have fancied it up and mostly broke
it.

-- 

If a man will begin with certainties, he shall end with doubts, 
but if he will be content to begin with doubts he shall end in certainties.
Francis Bacon
Reply by Phil Hobbs ●December 7, 20212021-12-07
John Larkin wrote:

> https://www.dropbox.com/s/tugwe4mnoj2ri80/Z508_AC_Coupling.jpg?raw=1
> 
> 0306 cap, capacitive bump. 0603 cap, inductive bump. No surprise that
> the 0204 is best. In the 25 ps sort of domain, on FR4, there's no need
> to buy exotic caps.
> 
> That 0204 is a 0.47 uF 16 volt cap. With 9 volts DC bias from my
> distributed amplifier, it loses 80% of its capacitance.
> 


Comes up 500 at the moment.

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
Reply by John Larkin ●December 7, 20212021-12-07
https://www.dropbox.com/s/tugwe4mnoj2ri80/Z508_AC_Coupling.jpg?raw=1

0306 cap, capacitive bump. 0603 cap, inductive bump. No surprise that
the 0204 is best. In the 25 ps sort of domain, on FR4, there's no need
to buy exotic caps.

That 0204 is a 0.47 uF 16 volt cap. With 9 volts DC bias from my
distributed amplifier, it loses 80% of its capacitance.

-- 

If a man will begin with certainties, he shall end with doubts, 
but if he will be content to begin with doubts he shall end in certainties.
Francis Bacon