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tech / sci.electronics.design / Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and Murata ferrite beads

SubjectAuthor
* Time-Domain Reflectometry: debugging 2.7 GHz oscillations and MurataPhil Hobbs
+* Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and Murata ferriteJohn Larkin
|+* Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations andGerhard Hoffmann
||`* Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations andPhil Hobbs
|| `* Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations andGerhard Hoffmann
||  +- Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and Murata ferriteJohn Larkin
||  `- Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations andehsjr
|`- Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations andPhil Hobbs
+- Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and Murata ferriteClifford Heath
+- Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations andPhil Hobbs
`* Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and Murata ferriteCursitor Doom
 `- Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations andPhil Hobbs

1
Time-Domain Reflectometry: debugging 2.7 GHz oscillations and Murata ferrite beads

<30ac9b94-65cc-7398-0596-288862a6e06c@electrooptical.net>

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From: pcdhSpam...@electrooptical.net (Phil Hobbs)
Subject: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and Murata
ferrite beads
Message-ID: <30ac9b94-65cc-7398-0596-288862a6e06c@electrooptical.net>
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 by: Phil Hobbs - Thu, 31 Mar 2022 16:09 UTC

So I've been wringing out a new APD front end. It's a 500-MHz TIA with
a pHEMT bootstrap, and wants to oscillate at 2.7 GHz with a strong squeg
at about 1 MHz. Changing the drain current changes the duty cycle of
the squegging, and reducing it below about 2 mA makes it stable.

The oscillation frequency doesn't change much (5% or so) with drain
current. All of which suggests that the oscillation is due to some
reasonably-sharp resonance someplace--the squegging gets worse at higher
gain, but the oscillation frequency doesn't move around. The waveform
is more or less sinusoidal-looking, but that's not surprising since the
vertical bandwidth of the scope (a TDS 694C) is about 3.3 GHz. The
oscillation doesn't depend on whether the TIA is connected or not.

Lower-speed front ends based on the same sort of transistor are famously
stable--one of them runs the bootstrap across a two-inch-long FFC cable
going to a MPPC on a cold plate. They also work great as the bottom
device in a cascode with a 45-GHz SiGe NPN. (The NPN needs a
base-stopper bead, but the pHEMT doesn't.)

The difference with this one may be that there's a bootstrapped pour
under the summing junction components, driven by the pHEMT source.

Sooo, I took a bare board, bodged in a U.FL micro coax connector from
the bootstrapped pour to ground, and hung it on the front of one of my
trusty Tek SD-24 TDRs, like so:
<https://electrooptical.net/www/sed/beads/BootstrapPourTDRSetupSm.png>.

(U.FLs are super useful for this sort of thing--far better than coax
pigtails. Not bad for 20 cents.)

Here's the result:
<https://electrooptical.net/www/sed/beads/BootstrapPourTDRsm.png>
(green curve: U.FL unplugged; white curve: board attached).

There's a capacitive dip (3.0 pF as measured on a Boonton 72BD) followed
by a delayed and not-too step open-circuit reflection and some ringing.
Interestingly the reciprocal of the round-trip delay is right around 2.7
GHz, which would make sense with an open-circuit transmission line
resonator.

I also did some measurements of the Murata beads we use as base/gate
stoppers for microwave transistors. Our faves are the Murata BLM1xBA
series.

The following scope photo shows a TDR of a short piece of 0.080"
hardline with various low-Z Murata ferrite beads. From top to bottom at
the beginning of the falling-edge transient:
BLM18BA100SN1D (10 ohms @ 100 MHz, light orange);
BLM15BA050SN1D (5 ohms @ 100 MHz, green);
BLM18BB100SN1D (10 ohms @ 100 MHz, purple); and
BLM15BB050SN1D (10 ohms @ 100 MHz, yellowish).

<https://electrooptical.net/www/sed/beads/MurataBLM15-18-050and100beadsTDRsm.png>

The BA-series beads show a lot better high-frequency impedance than the
BB-series ones, despite their datasheet curves being very similar. The
BLM15BA050 shows a bit of undershoot near 1.5 ns, but the others are all
basically monotonic at late times.

Interestingly the BLM15 (0402) and BLM18 (0603) beads look identical at
this resolution--the traces lie right on top of each other.

Fun stuff, and it'll be more fun once I get the resonance problem
knocked. Putting the pHEMT source connection near the middle of the
pour instead of at one end will help, I expect--this part ought to be
less likely to oscillate at 5 GHz.

Comments welcome.

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

Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and Murata ferrite beads

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From: jlar...@highland_atwork_technology.com (John Larkin)
Newsgroups: sci.electronics.design
Subject: Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and Murata ferrite beads
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 by: John Larkin - Thu, 31 Mar 2022 16:58 UTC

On Thu, 31 Mar 2022 12:09:19 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>So I've been wringing out a new APD front end. It's a 500-MHz TIA with
>a pHEMT bootstrap, and wants to oscillate at 2.7 GHz with a strong squeg
>at about 1 MHz. Changing the drain current changes the duty cycle of
>the squegging, and reducing it below about 2 mA makes it stable.
>
>The oscillation frequency doesn't change much (5% or so) with drain
>current. All of which suggests that the oscillation is due to some
>reasonably-sharp resonance someplace--the squegging gets worse at higher
>gain, but the oscillation frequency doesn't move around. The waveform
>is more or less sinusoidal-looking, but that's not surprising since the
>vertical bandwidth of the scope (a TDS 694C) is about 3.3 GHz. The
>oscillation doesn't depend on whether the TIA is connected or not.
>
>Lower-speed front ends based on the same sort of transistor are famously
>stable--one of them runs the bootstrap across a two-inch-long FFC cable
>going to a MPPC on a cold plate. They also work great as the bottom
>device in a cascode with a 45-GHz SiGe NPN. (The NPN needs a
>base-stopper bead, but the pHEMT doesn't.)
>
>The difference with this one may be that there's a bootstrapped pour
>under the summing junction components, driven by the pHEMT source.
>
>Sooo, I took a bare board, bodged in a U.FL micro coax connector from
>the bootstrapped pour to ground, and hung it on the front of one of my
>trusty Tek SD-24 TDRs, like so:
><https://electrooptical.net/www/sed/beads/BootstrapPourTDRSetupSm.png>.
>
>(U.FLs are super useful for this sort of thing--far better than coax
>pigtails. Not bad for 20 cents.)
>
>Here's the result:
><https://electrooptical.net/www/sed/beads/BootstrapPourTDRsm.png>
>(green curve: U.FL unplugged; white curve: board attached).
>
>There's a capacitive dip (3.0 pF as measured on a Boonton 72BD) followed
>by a delayed and not-too step open-circuit reflection and some ringing.
>Interestingly the reciprocal of the round-trip delay is right around 2.7
>GHz, which would make sense with an open-circuit transmission line
>resonator.
>
>I also did some measurements of the Murata beads we use as base/gate
>stoppers for microwave transistors. Our faves are the Murata BLM1xBA
>series.
>
>The following scope photo shows a TDR of a short piece of 0.080"
>hardline with various low-Z Murata ferrite beads. From top to bottom at
>the beginning of the falling-edge transient:
>BLM18BA100SN1D (10 ohms @ 100 MHz, light orange);
>BLM15BA050SN1D (5 ohms @ 100 MHz, green);
>BLM18BB100SN1D (10 ohms @ 100 MHz, purple); and
>BLM15BB050SN1D (10 ohms @ 100 MHz, yellowish).
>
><https://electrooptical.net/www/sed/beads/MurataBLM15-18-050and100beadsTDRsm.png>
>
>The BA-series beads show a lot better high-frequency impedance than the
>BB-series ones, despite their datasheet curves being very similar. The
>BLM15BA050 shows a bit of undershoot near 1.5 ns, but the others are all
>basically monotonic at late times.
>
>Interestingly the BLM15 (0402) and BLM18 (0603) beads look identical at
>this resolution--the traces lie right on top of each other.
>
>Fun stuff, and it'll be more fun once I get the resonance problem
>knocked. Putting the pHEMT source connection near the middle of the
>pour instead of at one end will help, I expect--this part ought to be
>less likely to oscillate at 5 GHz.
>
>Comments welcome.
>
>Cheers
>
>Phil Hobbs

A bootstrapped pour seems like a great idea. I did that on my
triggered Colpitts oscillator to reduce the effective/terrible FR4
capacitance. But it made things unstable for some reason, so I
reverted to cutting some chunks out of the ground and power planes and
temperature compensating out the positive TC of the FR4.

A couple of those bead TDRs look like capacitors to me.

I like gate resistors to tame phemts, but we mostly work with big
signals so a few more nV of noise is no big deal to us. I'm using 499
ohms in one case! I guess a hi-Z bead makes as much hf Johnson noise
as a resistor.

Gotta study your post in more detail when I have more time.

TDR rocks.
--

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

Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and Murata ferrite beads

<t24olp$79ih$1@solani.org>

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From: dk4...@arcor.de (Gerhard Hoffmann)
Newsgroups: sci.electronics.design
Subject: Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and
Murata ferrite beads
Date: Thu, 31 Mar 2022 19:33:45 +0200
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 by: Gerhard Hoffmann - Thu, 31 Mar 2022 17:33 UTC

Am 31.03.22 um 18:58 schrieb John Larkin:
> On Thu, 31 Mar 2022 12:09:19 -0400, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>
>> So I've been wringing out a new APD front end. It's a 500-MHz TIA with
>> a pHEMT bootstrap, and wants to oscillate at 2.7 GHz with a strong squeg
>> at about 1 MHz. Changing the drain current changes the duty cycle of
>> the squegging, and reducing it below about 2 mA makes it stable.
>>
>> The oscillation frequency doesn't change much (5% or so) with drain
>> current. All of which suggests that the oscillation is due to some
>> reasonably-sharp resonance someplace--the squegging gets worse at higher
>> gain, but the oscillation frequency doesn't move around. The waveform
>> is more or less sinusoidal-looking, but that's not surprising since the
>> vertical bandwidth of the scope (a TDS 694C) is about 3.3 GHz. The
>> oscillation doesn't depend on whether the TIA is connected or not.
>>
>> Lower-speed front ends based on the same sort of transistor are famously
>> stable--one of them runs the bootstrap across a two-inch-long FFC cable
>> going to a MPPC on a cold plate. They also work great as the bottom
>> device in a cascode with a 45-GHz SiGe NPN. (The NPN needs a
>> base-stopper bead, but the pHEMT doesn't.)
>>
>> The difference with this one may be that there's a bootstrapped pour
>> under the summing junction components, driven by the pHEMT source.
>>
>> Sooo, I took a bare board, bodged in a U.FL micro coax connector from
>> the bootstrapped pour to ground, and hung it on the front of one of my
>> trusty Tek SD-24 TDRs, like so:
>> <https://electrooptical.net/www/sed/beads/BootstrapPourTDRSetupSm.png>.
>>
>> (U.FLs are super useful for this sort of thing--far better than coax
>> pigtails. Not bad for 20 cents.)
>>
>> Here's the result:
>> <https://electrooptical.net/www/sed/beads/BootstrapPourTDRsm.png>
>> (green curve: U.FL unplugged; white curve: board attached).
>>
>> There's a capacitive dip (3.0 pF as measured on a Boonton 72BD) followed
>> by a delayed and not-too step open-circuit reflection and some ringing.
>> Interestingly the reciprocal of the round-trip delay is right around 2.7
>> GHz, which would make sense with an open-circuit transmission line
>> resonator.
>>
>> I also did some measurements of the Murata beads we use as base/gate
>> stoppers for microwave transistors. Our faves are the Murata BLM1xBA
>> series.
>>
>> The following scope photo shows a TDR of a short piece of 0.080"
>> hardline with various low-Z Murata ferrite beads. From top to bottom at
>> the beginning of the falling-edge transient:
>> BLM18BA100SN1D (10 ohms @ 100 MHz, light orange);
>> BLM15BA050SN1D (5 ohms @ 100 MHz, green);
>> BLM18BB100SN1D (10 ohms @ 100 MHz, purple); and
>> BLM15BB050SN1D (10 ohms @ 100 MHz, yellowish).
>>
>> <https://electrooptical.net/www/sed/beads/MurataBLM15-18-050and100beadsTDRsm.png>
>>
>> The BA-series beads show a lot better high-frequency impedance than the
>> BB-series ones, despite their datasheet curves being very similar. The
>> BLM15BA050 shows a bit of undershoot near 1.5 ns, but the others are all
>> basically monotonic at late times.
>>
>> Interestingly the BLM15 (0402) and BLM18 (0603) beads look identical at
>> this resolution--the traces lie right on top of each other.
>>
>> Fun stuff, and it'll be more fun once I get the resonance problem
>> knocked. Putting the pHEMT source connection near the middle of the
>> pour instead of at one end will help, I expect--this part ought to be
>> less likely to oscillate at 5 GHz.
>>
>> Comments welcome.
>>
>> Cheers
>>
>> Phil Hobbs
>
> A bootstrapped pour seems like a great idea. I did that on my
> triggered Colpitts oscillator to reduce the effective/terrible FR4
> capacitance. But it made things unstable for some reason, so I
> reverted to cutting some chunks out of the ground and power planes and
> temperature compensating out the positive TC of the FR4.
>
> A couple of those bead TDRs look like capacitors to me.
>
> I like gate resistors to tame phemts, but we mostly work with big
> signals so a few more nV of noise is no big deal to us. I'm using 499
> ohms in one case! I guess a hi-Z bead makes as much hf Johnson noise
> as a resistor.

Yes, at frequencies where it works like a resistor, it creates
noise like a resistor.

V1 is only there as a compiler pleaser, needed for syntax.

<
https://www.flickr.com/photos/137684711@N07/51974219045/in/dateposted-public/
>

chears, Gerhard

Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and Murata ferrite beads

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From: pcdhSpam...@electrooptical.net (Phil Hobbs)
Newsgroups: sci.electronics.design
Subject: Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and
Murata ferrite beads
Date: Thu, 31 Mar 2022 14:50:55 -0400
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 by: Phil Hobbs - Thu, 31 Mar 2022 18:50 UTC

Gerhard Hoffmann wrote:
> Am 31.03.22 um 18:58 schrieb John Larkin:
>> On Thu, 31 Mar 2022 12:09:19 -0400, Phil Hobbs
>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>
>>> So I've been wringing out a new APD front end.  It's a 500-MHz TIA with
>>> a pHEMT bootstrap, and wants to oscillate at 2.7 GHz with a strong squeg
>>> at about 1 MHz.  Changing the drain current changes the duty cycle of
>>> the squegging, and reducing it below about 2 mA makes it stable.
>>>
>>> The oscillation frequency doesn't change much (5% or so) with drain
>>> current.  All of which suggests that the oscillation is due to some
>>> reasonably-sharp resonance someplace--the squegging gets worse at higher
>>> gain, but the oscillation frequency doesn't move around.  The waveform
>>> is more or less sinusoidal-looking, but that's not surprising since the
>>> vertical bandwidth of the scope (a TDS 694C) is about 3.3 GHz.  The
>>> oscillation doesn't depend on whether the TIA is connected or not.
>>>
>>> Lower-speed front ends based on the same sort of transistor are famously
>>> stable--one of them runs the bootstrap across a two-inch-long FFC cable
>>> going to a MPPC on a cold plate.  They also work great as the bottom
>>> device in a cascode with a 45-GHz SiGe NPN.  (The NPN needs a
>>> base-stopper bead, but the pHEMT doesn't.)
>>>
>>> The difference with this one may be that there's a bootstrapped pour
>>> under the summing junction components, driven by the pHEMT source.
>>>
>>> Sooo, I took a bare board, bodged in a U.FL micro coax connector from
>>> the bootstrapped pour to ground, and hung it on the front of one of my
>>> trusty Tek SD-24 TDRs, like so:
>>> <https://electrooptical.net/www/sed/beads/BootstrapPourTDRSetupSm.png>.
>>>
>>> (U.FLs are super useful for this sort of thing--far better than coax
>>> pigtails.  Not bad for 20 cents.)
>>>
>>> Here's the result:
>>> <https://electrooptical.net/www/sed/beads/BootstrapPourTDRsm.png>
>>> (green curve: U.FL unplugged; white curve: board attached).
>>>
>>> There's a capacitive dip (3.0 pF as measured on a Boonton 72BD) followed
>>> by a delayed and not-too step open-circuit reflection and some ringing.
>>> Interestingly the reciprocal of the round-trip delay is right around 2.7
>>> GHz, which would make sense with an open-circuit transmission line
>>> resonator.
>>>
>>> I also did some measurements of the Murata beads we use as base/gate
>>> stoppers for microwave transistors.  Our faves are the Murata BLM1xBA
>>> series.
>>>
>>> The following scope photo shows a TDR of a short piece of 0.080"
>>> hardline with various low-Z Murata ferrite beads.  From top to bottom at
>>> the beginning of the falling-edge transient:
>>> BLM18BA100SN1D (10 ohms @ 100 MHz, light orange);
>>> BLM15BA050SN1D (5 ohms @ 100 MHz, green);
>>> BLM18BB100SN1D (10 ohms @ 100 MHz, purple); and
>>> BLM15BB050SN1D (10 ohms @ 100 MHz, yellowish).
>>>
>>> <https://electrooptical.net/www/sed/beads/MurataBLM15-18-050and100beadsTDRsm.png>
>>>
>>>
>>> The BA-series beads show a lot better high-frequency impedance than the
>>> BB-series ones, despite their datasheet curves being very similar.  The
>>> BLM15BA050 shows a bit of undershoot near 1.5 ns, but the others are all
>>> basically monotonic at late times.
>>>
>>> Interestingly the BLM15 (0402) and BLM18 (0603) beads look identical at
>>> this resolution--the traces lie right on top of each other.
>>>
>>> Fun stuff, and it'll be more fun once I get the resonance problem
>>> knocked.  Putting the pHEMT source connection near the middle of the
>>> pour instead of at one end will help, I expect--this part ought to be
>>> less likely to oscillate at 5 GHz.
>>>
>>> Comments welcome.
>>>
>>> Cheers
>>>
>>> Phil Hobbs
>>
>> A bootstrapped pour seems like a great idea. I did that on my
>> triggered Colpitts oscillator to reduce the effective/terrible FR4
>> capacitance. But it made things unstable for some reason, so I
>> reverted to cutting some chunks out of the ground and power planes and
>> temperature compensating out the positive TC of the FR4.
>>
>> A couple of those bead TDRs look like capacitors to me.
>>
>> I like gate resistors to tame phemts, but we mostly work with big
>> signals so a few more nV of noise is no big deal to us. I'm using 499
>> ohms in one case! I guess a hi-Z bead makes as much hf Johnson noise
>> as a resistor.
>
>
>
> Yes, at frequencies where it works like a resistor, it creates
> noise like a resistor.
>
> V1 is only there as a compiler pleaser, needed for syntax.
>
> <
> https://www.flickr.com/photos/137684711@N07/51974219045/in/dateposted-public/
>      >

Comes up blank for me. But it's true--there's a very general theorem of
classical thermodynamics that states that *in thermal equilibrium* any
process that can dissipate power will also produce fluctuations with
average power kT/2 per classical degree of freedom.

You can derive the sqrt(4kTR) formula by considering an isolated RC
circuit, setting the mean energy on the capacitor as kT/2, and computing
what the resistor's noise power has to be in order to keep the mean
energy constant.

As soon as you apply power, of course, all the nice theorems go
away--for instance, a diode-connected transistor looks like a resistor
whose value is 25 mV/I_C, and whose temperature is T_J/2 (150 K at room
temperature).

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

Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and Murata ferrite beads

<t24ud3$7dj2$1@solani.org>

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From: dk4...@arcor.de (Gerhard Hoffmann)
Newsgroups: sci.electronics.design
Subject: Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and
Murata ferrite beads
Date: Thu, 31 Mar 2022 21:11:30 +0200
Message-ID: <t24ud3$7dj2$1@solani.org>
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 by: Gerhard Hoffmann - Thu, 31 Mar 2022 19:11 UTC

Am 31.03.22 um 20:50 schrieb Phil Hobbs:
> Gerhard Hoffmann wrote:

>> Yes, at frequencies where it works like a resistor, it creates
>> noise like a resistor.
>>
>> V1 is only there as a compiler pleaser, needed for syntax.
>>
>> <
>> https://www.flickr.com/photos/137684711@N07/51974219045/in/dateposted-public/
>>       >
>
> Comes up blank for me.

Works for me. 2k5 * 1k5 screen dump.
called up 7 times upto now.
But Flickr is sloooooow!

Gerhard

Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and Murata ferrite beads

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From: jlar...@highland_atwork_technology.com (John Larkin)
Newsgroups: sci.electronics.design
Subject: Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and Murata ferrite beads
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 by: John Larkin - Thu, 31 Mar 2022 19:59 UTC

On Thu, 31 Mar 2022 21:11:30 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
wrote:

>Am 31.03.22 um 20:50 schrieb Phil Hobbs:
>> Gerhard Hoffmann wrote:
>
>
>>> Yes, at frequencies where it works like a resistor, it creates
>>> noise like a resistor.
>>>
>>> V1 is only there as a compiler pleaser, needed for syntax.
>>>
>>> <
>>> https://www.flickr.com/photos/137684711@N07/51974219045/in/dateposted-public/
>>>       >
>>
>> Comes up blank for me.
>
>Works for me. 2k5 * 1k5 screen dump.
>called up 7 times upto now.
>But Flickr is sloooooow!
>
>Gerhard
>

Fine, fast here with Firefox.

--

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

Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and Murata ferrite beads

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From: ehs...@verizon.net (ehsjr)
Newsgroups: sci.electronics.design
Subject: Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and
Murata ferrite beads
Date: Thu, 31 Mar 2022 18:35:51 -0400
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 by: ehsjr - Thu, 31 Mar 2022 22:35 UTC

On 3/31/2022 3:11 PM, Gerhard Hoffmann wrote:
> Am 31.03.22 um 20:50 schrieb Phil Hobbs:
>> Gerhard Hoffmann wrote:
>
>
>>> Yes, at frequencies where it works like a resistor, it creates
>>> noise like a resistor.
>>>
>>> V1 is only there as a compiler pleaser, needed for syntax.
>>>
>>> <
>>> https://www.flickr.com/photos/137684711@N07/51974219045/in/dateposted-public/
>>>       >
>>
>> Comes up blank for me.
>
> Works for me. 2k5 * 1k5 screen dump.
> called up 7 times upto now.
> But Flickr is sloooooow!
>
> Gerhard
>
>
Works for me too.
Ed

Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and Murata ferrite beads

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Subject: Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and Murata ferrite beads
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From: no.s...@please.net (Clifford Heath)
Date: Fri, 1 Apr 2022 10:32:24 +1100
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 by: Clifford Heath - Thu, 31 Mar 2022 23:32 UTC

On 1/4/22 3:09 am, Phil Hobbs wrote:
> Comments welcome.

No technical comment, just this:

Fascinating post, many thanks for sharing.

CH

Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and Murata ferrite beads

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From: pcdhSpam...@electrooptical.net (Phil Hobbs)
Newsgroups: sci.electronics.design
Subject: Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and
Murata ferrite beads
Date: Thu, 31 Mar 2022 20:09:39 -0400
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 by: Phil Hobbs - Fri, 1 Apr 2022 00:09 UTC

Phil Hobbs wrote:
> So I've been wringing out a new APD front end. It's a 500-MHz TIA
> with a pHEMT bootstrap, and wants to oscillate at 2.7 GHz with a
> strong squeg at about 1 MHz. Changing the drain current changes the
> duty cycle of the squegging, and reducing it below about 2 mA makes
> it stable.
>
> The oscillation frequency doesn't change much (5% or so) with drain
> current. All of which suggests that the oscillation is due to some
> reasonably-sharp resonance someplace--the squegging gets worse at
> higher gain, but the oscillation frequency doesn't move around. The
> waveform is more or less sinusoidal-looking, but that's not
> surprising since the vertical bandwidth of the scope (a TDS 694C) is
> about 3.3 GHz. The oscillation doesn't depend on whether the TIA is
> connected or not.
>
> Lower-speed front ends based on the same sort of transistor are
> famously stable--one of them runs the bootstrap across a
> two-inch-long FFC cable going to a MPPC on a cold plate. They also
> work great as the bottom device in a cascode with a 45-GHz SiGe NPN.
> (The NPN needs a base-stopper bead, but the pHEMT doesn't.)
>
> The difference with this one may be that there's a bootstrapped pour
> under the summing junction components, driven by the pHEMT source.
>
> Sooo, I took a bare board, bodged in a U.FL micro coax connector from
> the bootstrapped pour to ground, and hung it on the front of one of
> my trusty Tek SD-24 TDRs, like so:
> <https://electrooptical.net/www/sed/beads/BootstrapPourTDRSetupSm.png>.
>
> (U.FLs are super useful for this sort of thing--far better than coax
> pigtails. Not bad for 20 cents.)
>
> Here's the result:
> <https://electrooptical.net/www/sed/beads/BootstrapPourTDRsm.png>
> (green curve: U.FL unplugged; white curve: board attached).
>
> There's a capacitive dip (3.0 pF as measured on a Boonton 72BD)
> followed by a delayed and not-too-
steep
> open-circuit reflection and some ringing. Interestingly the
> reciprocal of the round-trip delay is right around 2.7 GHz, which
> would make sense with an open-circuit transmission line resonator.
>
> I also did some measurements of the Murata beads we use as base/gate
> stoppers for microwave transistors. Our faves are the Murata
> BLM1xBA series.
>
> The following scope photo shows a TDR of a short piece of 0.080"
> hardline with various low-Z Murata ferrite beads. From top to bottom
> at the beginning of the falling-edge transient: BLM18BA100SN1D (10
> ohms @ 100 MHz, light orange); BLM15BA050SN1D (5 ohms @ 100 MHz,
> green); BLM18BB100SN1D (10 ohms @ 100 MHz, purple); and
> BLM15BB050SN1D (
5 > ohms @ 100 MHz, yellowish).
>
> <https://electrooptical.net/www/sed/beads/MurataBLM15-18-050and100beadsTDRsm.png>
>
>
>
> The BA-series beads show a lot better high-frequency impedance than
> the BB-series ones, despite their datasheet curves being very
> similar. The BLM15BA050 shows a bit of undershoot near 1.5 ns, but
> the others are all basically monotonic at late times.
>
> Interestingly the BLM15 (0402) and BLM18 (0603) beads look identical
> at this resolution--the traces lie right on top of each other.
>
> Fun stuff, and it'll be more fun once I get the resonance problem
> knocked. Putting the pHEMT source connection near the middle of the
> pour instead of at one end will help, I expect--this part ought to
> be less likely to oscillate at 5 GHz.
>
> Comments welcome.

(Fixed a couple of typos that might impede understanding)

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

Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and Murata ferrite beads

<644d14e8-e79c-5959-741a-8e5e1200e6e0@electrooptical.net>

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From: pcdhSpam...@electrooptical.net (Phil Hobbs)
Newsgroups: sci.electronics.design
Subject: Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and
Murata ferrite beads
Date: Fri, 1 Apr 2022 08:42:50 -0400
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 by: Phil Hobbs - Fri, 1 Apr 2022 12:42 UTC

John Larkin wrote:
> On Thu, 31 Mar 2022 12:09:19 -0400, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>
>> So I've been wringing out a new APD front end. It's a 500-MHz TIA with
>> a pHEMT bootstrap, and wants to oscillate at 2.7 GHz with a strong squeg
>> at about 1 MHz. Changing the drain current changes the duty cycle of
>> the squegging, and reducing it below about 2 mA makes it stable.
>>
>> The oscillation frequency doesn't change much (5% or so) with drain
>> current. All of which suggests that the oscillation is due to some
>> reasonably-sharp resonance someplace--the squegging gets worse at higher
>> gain, but the oscillation frequency doesn't move around. The waveform
>> is more or less sinusoidal-looking, but that's not surprising since the
>> vertical bandwidth of the scope (a TDS 694C) is about 3.3 GHz. The
>> oscillation doesn't depend on whether the TIA is connected or not.
>>
>> Lower-speed front ends based on the same sort of transistor are famously
>> stable--one of them runs the bootstrap across a two-inch-long FFC cable
>> going to a MPPC on a cold plate. They also work great as the bottom
>> device in a cascode with a 45-GHz SiGe NPN. (The NPN needs a
>> base-stopper bead, but the pHEMT doesn't.)
>>
>> The difference with this one may be that there's a bootstrapped pour
>> under the summing junction components, driven by the pHEMT source.
>>
>> Sooo, I took a bare board, bodged in a U.FL micro coax connector from
>> the bootstrapped pour to ground, and hung it on the front of one of my
>> trusty Tek SD-24 TDRs, like so:
>> <https://electrooptical.net/www/sed/beads/BootstrapPourTDRSetupSm.png>.
>>
>> (U.FLs are super useful for this sort of thing--far better than coax
>> pigtails. Not bad for 20 cents.)
>>
>> Here's the result:
>> <https://electrooptical.net/www/sed/beads/BootstrapPourTDRsm.png>
>> (green curve: U.FL unplugged; white curve: board attached).
>>
>> There's a capacitive dip (3.0 pF as measured on a Boonton 72BD) followed
>> by a delayed and not-too step open-circuit reflection and some ringing.
>> Interestingly the reciprocal of the round-trip delay is right around 2.7
>> GHz, which would make sense with an open-circuit transmission line
>> resonator.
>>
>> I also did some measurements of the Murata beads we use as base/gate
>> stoppers for microwave transistors. Our faves are the Murata BLM1xBA
>> series.
>>
>> The following scope photo shows a TDR of a short piece of 0.080"
>> hardline with various low-Z Murata ferrite beads. From top to bottom at
>> the beginning of the falling-edge transient:
>> BLM18BA100SN1D (10 ohms @ 100 MHz, light orange);
>> BLM15BA050SN1D (5 ohms @ 100 MHz, green);
>> BLM18BB100SN1D (10 ohms @ 100 MHz, purple); and
>> BLM15BB050SN1D (10 ohms @ 100 MHz, yellowish).
>>
>> <https://electrooptical.net/www/sed/beads/MurataBLM15-18-050and100beadsTDRsm.png>
>>
>> The BA-series beads show a lot better high-frequency impedance than the
>> BB-series ones, despite their datasheet curves being very similar. The
>> BLM15BA050 shows a bit of undershoot near 1.5 ns, but the others are all
>> basically monotonic at late times.
>>
>> Interestingly the BLM15 (0402) and BLM18 (0603) beads look identical at
>> this resolution--the traces lie right on top of each other.
>>
>> Fun stuff, and it'll be more fun once I get the resonance problem
>> knocked. Putting the pHEMT source connection near the middle of the
>> pour instead of at one end will help, I expect--this part ought to be
>> less likely to oscillate at 5 GHz.
>>
>> Comments welcome.

>
> A bootstrapped pour seems like a great idea. I did that on my
> triggered Colpitts oscillator to reduce the effective/terrible FR4
> capacitance. But it made things unstable for some reason, so I
> reverted to cutting some chunks out of the ground and power planes and
> temperature compensating out the positive TC of the FR4.
>
> A couple of those bead TDRs look like capacitors to me.

The higher-Z BB-series parts are more resistive than the BA-series
ones--poking around on these pages is pretty illuminating.

<https://ds.murata.co.jp/simsurfing/gateway.html?partnumbers=%5B%22BLM18AB050SN1D%22%5D&rgear=suaykx&rgearinfo=com>

(You can replace the part number with the one you actually want to
see--getting the same plot by dorking with the web page is much slower.)

A five-ohm bead that peaks at nearly 100 ohms resisitive out at 4 GHz or
so is a super useful part.

>
> I like gate resistors to tame phemts, but we mostly work with big
> signals so a few more nV of noise is no big deal to us. I'm using 499
> ohms in one case! I guess a hi-Z bead makes as much hf Johnson noise
> as a resistor.
>
> Gotta study your post in more detail when I have more time.
>
> TDR rocks.
>

Yup, especially for time-domain stuff. Stuff like stability analysis is
a bit subtler using TDR vs. a network analyzer. I should break out my
HP 70820A (a 40 GHz scope/network analyzer/spectrum analyzer based on
samplers).

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

Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and Murata ferrite beads

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Newsgroups: sci.electronics.design
Subject: Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and Murata ferrite beads
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 by: Cursitor Doom - Sun, 3 Apr 2022 16:59 UTC

On Thu, 31 Mar 2022 12:09:19 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

[...]

Obviously you do a *lot* of testing and development, Phil. Which
particular area of electronics do you find most stimulating to tackle?
(if any nowadays given your extreme level of familiarity with the
subject, that is).

Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and Murata ferrite beads

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Subject: Re: Time-Domain Reflectometry: debugging 2.7 GHz oscillations and
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From: pcdhSpam...@electrooptical.net (Phil Hobbs)
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 by: Phil Hobbs - Mon, 4 Apr 2022 01:15 UTC

Cursitor Doom wrote:
> On Thu, 31 Mar 2022 12:09:19 -0400, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>
> [...]
>
> Obviously you do a *lot* of testing and development, Phil. Which
> particular area of electronics do you find most stimulating to tackle?
> (if any nowadays given your extreme level of familiarity with the
> subject, that is).
>

I mostly like building complete instruments. I've been doing a lot of
front ends lately, which is getting boring, so we're trying to pour a
bunch of concrete so that we can turn round a customized front end for
folks made from nice tested building blocks.

I thought this oscillation thing was fairly interesting, and was looking
for some input from other folks. (Maybe even Joerg, if I can entice him
away from doing fast laps around his bierkeller on the mountain bike. ;)

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

1
server_pubkey.txt

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