AD8045 mystery...

[Phil Hobbs]

Hi, all.

So I have this SiPM/MPPC front end. It has pop options to use either an
On Semi MicroFC-10010 1-mm SiPM chip or a packaged Hamamatsu
S13362-3050DG 3-mm MPPC with integral TE cooler, both bootstrapped by a
SAV-551+ running at 20 mA. So far, it all works.

(The SAV-551+ is amazingly stable--I\'ve got a shipping product that runs
a very similar bootstrap across a 2-inch FFC cable. Bandwidth suffers a
bit, but it shows no tendency to oscillate.)

The mystery is in the TIA stage. It\'s a vanilla op amp TIA made from
either an ADA4899 (600 MHz, 300 V/us) or AD8045 (1 GHz, 1300 V/us @
Av=1), which are pin compatible in the 3-mm LFCSP package. Both are
voltage feedback amps.

I\'m seeing a 3 dB bandwidth of 220 MHz, together with a faster rolloff
than I expect: -3 dB @ 220 MHz, -9 dB @ 320 MHz. It\'s not slew
limiting, because the waveform looks pretty good on a 3-GHz scope (TDS
694C) and the rolloff stays the same when I drop the input by 6 dB.

The layout is pretty tight (the whole board is only an inch square), so
getting enough stray capacitance across R_F to account for it is
implausible--it would need about 1.4 pF. DecouplingBypassing is good--

For test, I removed the 0-ohm jumper that connects the bootstrapped SiPM
to the summing junction, and added a 1k input resistor, forming an
inverting amp with a nominal gain of -0.5.

That\'s connected to the terminated end of an RG-174/U cable going to a
PTS-500 synthesizer. The output goes via a 10-ohm resistor into a
properly-terminated 50-ohm cable (the TDS 694C is 50-ohm only).

Here I\'m expecting a bandwidth somewhere between the datasheet\'s 1 GHz @
Av=1 and 400 MHz @ Av=-1, but it\'s way off. There\'s no visible change
when I put the jumper back in, on account of the swoopy bootstrap.

So where do you suppose the missing factor of ~3 in bandwidth went?

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

 

[John Larkin]

On Wed, 18 Nov 2020 14:27:21 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

Hi, all.

So I have this SiPM/MPPC front end. It has pop options to use either an
On Semi MicroFC-10010 1-mm SiPM chip or a packaged Hamamatsu
S13362-3050DG 3-mm MPPC with integral TE cooler, both bootstrapped by a
SAV-551+ running at 20 mA. So far, it all works.

(The SAV-551+ is amazingly stable--I\'ve got a shipping product that runs
a very similar bootstrap across a 2-inch FFC cable. Bandwidth suffers a
bit, but it shows no tendency to oscillate.)

The mystery is in the TIA stage. It\'s a vanilla op amp TIA made from
either an ADA4899 (600 MHz, 300 V/us) or AD8045 (1 GHz, 1300 V/us @
Av=1), which are pin compatible in the 3-mm LFCSP package. Both are
voltage feedback amps.

I\'m seeing a 3 dB bandwidth of 220 MHz, together with a faster rolloff
than I expect: -3 dB @ 220 MHz, -9 dB @ 320 MHz. It\'s not slew
limiting, because the waveform looks pretty good on a 3-GHz scope (TDS
694C) and the rolloff stays the same when I drop the input by 6 dB.

The layout is pretty tight (the whole board is only an inch square), so
getting enough stray capacitance across R_F to account for it is
implausible--it would need about 1.4 pF. DecouplingBypassing is good--

For test, I removed the 0-ohm jumper that connects the bootstrapped SiPM
to the summing junction, and added a 1k input resistor, forming an
inverting amp with a nominal gain of -0.5.

That\'s connected to the terminated end of an RG-174/U cable going to a
PTS-500 synthesizer. The output goes via a 10-ohm resistor into a
properly-terminated 50-ohm cable (the TDS 694C is 50-ohm only).

Here I\'m expecting a bandwidth somewhere between the datasheet\'s 1 GHz @
Av=1 and 400 MHz @ Av=-1, but it\'s way off. There\'s no visible change
when I put the jumper back in, on account of the swoopy bootstrap.

So where do you suppose the missing factor of ~3 in bandwidth went?

Thanks

Phil Hobbs

Do you have enough bootstrap gain?

 

[Phil Hobbs]

On 11/18/20 3:07 PM, John Larkin wrote:

On Wed, 18 Nov 2020 14:27:21 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

Hi, all.

So I have this SiPM/MPPC front end. It has pop options to use either an
On Semi MicroFC-10010 1-mm SiPM chip or a packaged Hamamatsu
S13362-3050DG 3-mm MPPC with integral TE cooler, both bootstrapped by a
SAV-551+ running at 20 mA. So far, it all works.

(The SAV-551+ is amazingly stable--I\'ve got a shipping product that runs
a very similar bootstrap across a 2-inch FFC cable. Bandwidth suffers a
bit, but it shows no tendency to oscillate.)

The mystery is in the TIA stage. It\'s a vanilla op amp TIA made from
either an ADA4899 (600 MHz, 300 V/us) or AD8045 (1 GHz, 1300 V/us @
Av=1), which are pin compatible in the 3-mm LFCSP package. Both are
voltage feedback amps.

I\'m seeing a 3 dB bandwidth of 220 MHz, together with a faster rolloff
than I expect: -3 dB @ 220 MHz, -9 dB @ 320 MHz. It\'s not slew
limiting, because the waveform looks pretty good on a 3-GHz scope (TDS
694C) and the rolloff stays the same when I drop the input by 6 dB.

The layout is pretty tight (the whole board is only an inch square), so
getting enough stray capacitance across R_F to account for it is
implausible--it would need about 1.4 pF. DecouplingBypassing is good--

330 ohm bead and 1 uF 0603 to ground from both supply pins. Supplies
are +5/-4.

For test, I removed the 0-ohm jumper that connects the bootstrapped SiPM
to the summing junction, and added a 1k input resistor, forming an
inverting amp with a nominal gain of -0.5.

That\'s connected to the terminated end of an RG-174/U cable going to a
PTS-500 synthesizer. The output goes via a 10-ohm resistor into a
properly-terminated 50-ohm cable (the TDS 694C is 50-ohm only).

Here I\'m expecting a bandwidth somewhere between the datasheet\'s 1 GHz @
Av=1 and 400 MHz @ Av=-1, but it\'s way off. There\'s no visible change
when I put the jumper back in, on account of the swoopy bootstrap.

So where do you suppose the missing factor of ~3 in bandwidth went?

Do you have enough bootstrap gain?

Yes, the BW hardly changes when I disconnect/reconnect the whole
PD/bootstrap thing by way of the 0402 jumper. I also verified that the
step response gives about the same answer. Using a very nice 30-ps Leo
Bodnar pulser, the amp\'s rise time is about 1.5 ns, underdamped with
~20% overshoot. (Initially I had 0.3 pF across the 511-ohm R_F, but
ripped it out to verify that it hadn\'t been mis-stuffed.)

This board has solder flux about 2 inches deep at this point.

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

 

[Uwe Bonnes]

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

Hi, all.

So I have this SiPM/MPPC front end. It has pop options to use either an
On Semi MicroFC-10010 1-mm SiPM chip or a packaged Hamamatsu
S13362-3050DG 3-mm MPPC with integral TE cooler, both bootstrapped by a
SAV-551+ running at 20 mA. So far, it all works.

Sorry, no help here. But curious what you mean by \"bootstrap\"ing a MPPC diode?

Thanks!
--
Uwe Bonnes bon@elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik Schlossgartenstrasse 9 64289 Darmstadt
--------- Tel. 06151 1623569 ------- Fax. 06151 1623305 ---------

 

[Phil Hobbs]

On 11/18/20 4:28 PM, Uwe Bonnes wrote:

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
Hi, all.

So I have this SiPM/MPPC front end. It has pop options to use either an
On Semi MicroFC-10010 1-mm SiPM chip or a packaged Hamamatsu
S13362-3050DG 3-mm MPPC with integral TE cooler, both bootstrapped by a
SAV-551+ running at 20 mA. So far, it all works.

Sorry, no help here. But curious what you mean by \"bootstrap\"ing a MPPC diode?

Thanks!

Same as an ordinary PIN. You get rid of the effect of its capacitance
by using a follower to force the anode to follow the cathode at AC.

That way the high frequency noise floor is set by

omega Cdiode e_Nbootstrap

and not

omega Cdiode e_Nopamp

Those numbers are more than 20 dB different, so a bootstrap is a win.

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 Wed, 18 Nov 2020 17:22:41 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 11/18/20 4:28 PM, Uwe Bonnes wrote:
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
Hi, all.

So I have this SiPM/MPPC front end. It has pop options to use either an
On Semi MicroFC-10010 1-mm SiPM chip or a packaged Hamamatsu
S13362-3050DG 3-mm MPPC with integral TE cooler, both bootstrapped by a
SAV-551+ running at 20 mA. So far, it all works.

Sorry, no help here. But curious what you mean by \"bootstrap\"ing a MPPC diode?

Thanks!

Same as an ordinary PIN. You get rid of the effect of its capacitance
by using a follower to force the anode to follow the cathode at AC.

That is equivalent to connecting a negative capacitor across the
photodiode. Of course, the cap value is exactly correct.

 

[Phil Hobbs]

On 11/18/20 8:41 PM, John Larkin wrote:

On Wed, 18 Nov 2020 17:22:41 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 11/18/20 4:28 PM, Uwe Bonnes wrote:
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
Hi, all.

So I have this SiPM/MPPC front end. It has pop options to use either an
On Semi MicroFC-10010 1-mm SiPM chip or a packaged Hamamatsu
S13362-3050DG 3-mm MPPC with integral TE cooler, both bootstrapped by a
SAV-551+ running at 20 mA. So far, it all works.

Sorry, no help here. But curious what you mean by \"bootstrap\"ing a MPPC diode?

Thanks!

Same as an ordinary PIN. You get rid of the effect of its capacitance
by using a follower to force the anode to follow the cathode at AC.

That is equivalent to connecting a negative capacitor across the
photodiode. Of course, the cap value is exactly correct.

Yes, because the photodiode capacitance is what governs the value of the
negative C, and the follower\'s voltage gain is always less than unity.

My best one has a gain of 0.9997 at DC, and better than 0.995 out to a
few megahertz, as measured by the bootstrap bandwidth increase. (It\'s
hard to measure it any other way.)

You don\'t usually need it that good for noise purposes. If the op amp\'s
voltage noise is N times the bootstrap\'s, the two e_N C noise
contributions become equal when the bootstrap gain is

A_V = 1-1/N,

and another factor of 2 knocks the op amp down to a 1-dB perturbation.
Thus a gain of 0.95 is usually enough for noise purposes unless the op
amp is horribly noisy.

In our QL01 quantum-limited nanowatt photoreceiver, we use an LM6171 for
the TIA stage despite its fairly gross e_N of 12 nV in 1 Hz (typical).
The noise of the 10M feedback resistor is 400 nV in 1 Hz, so you might
think we were fairly safe with no bootstrap, but no.

The e_N C noise starts growing linearly (in volts) at the RC corner
frequency of the feedback resistor times the total input capacitance
(diode plus circuit), which might be

f_N = 1 / ( 2 pi (20 pF) (10 Mohm)) = 800 Hz,

so with a 1-MHz bandwidth the output noise would be around 15 uV in 1
Hz, except that the LM6171 would run out of gain and bandwidth before it
got there.

With a BF862 or equivalent bootstrap device (e_N ~ 0.9 nV in 1 Hz), we\'d
only need a gain of 0.96 or so for the TIA noise to be a 1-dB level
perturbation. So why worry about getting so close to 1.0?

The reason is a hidden gotcha: In a bootstrap there\'s a pole/zero pair
near f_N that doesn\'t quite cancel. This leads to to whoopdedoos of
order (1-A_V) in the impulse response at late times, a matter of a few
percent with A_V = 0.96.

A bootstrap gain of 0.995 makes for dramatically better measurements.

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

 

[George Herold]

On Wednesday, November 18, 2020 at 2:27:39 PM UTC-5, Phil Hobbs wrote:

Hi, all.

So I have this SiPM/MPPC front end. It has pop options to use either an
On Semi MicroFC-10010 1-mm SiPM chip or a packaged Hamamatsu
S13362-3050DG 3-mm MPPC with integral TE cooler, both bootstrapped by a
SAV-551+ running at 20 mA. So far, it all works.

(The SAV-551+ is amazingly stable--I\'ve got a shipping product that runs
a very similar bootstrap across a 2-inch FFC cable. Bandwidth suffers a
bit, but it shows no tendency to oscillate.)

The mystery is in the TIA stage. It\'s a vanilla op amp TIA made from
either an ADA4899 (600 MHz, 300 V/us) or AD8045 (1 GHz, 1300 V/us @
Av=1), which are pin compatible in the 3-mm LFCSP package. Both are
voltage feedback amps.

I\'m seeing a 3 dB bandwidth of 220 MHz, together with a faster rolloff
than I expect: -3 dB @ 220 MHz, -9 dB @ 320 MHz. It\'s not slew
limiting, because the waveform looks pretty good on a 3-GHz scope (TDS
694C) and the rolloff stays the same when I drop the input by 6 dB.

The layout is pretty tight (the whole board is only an inch square), so
getting enough stray capacitance across R_F to account for it is
implausible--it would need about 1.4 pF. DecouplingBypassing is good--

For test, I removed the 0-ohm jumper that connects the bootstrapped SiPM
to the summing junction, and added a 1k input resistor, forming an
inverting amp with a nominal gain of -0.5.

That\'s connected to the terminated end of an RG-174/U cable going to a
PTS-500 synthesizer. The output goes via a 10-ohm resistor into a
properly-terminated 50-ohm cable (the TDS 694C is 50-ohm only).

Here I\'m expecting a bandwidth somewhere between the datasheet\'s 1 GHz @
Av=1 and 400 MHz @ Av=-1, but it\'s way off. There\'s no visible change
when I put the jumper back in, on account of the swoopy bootstrap.

I was going to suggest looking at the \'speed\' of the light source.
But the above seems to point to something \'in\' the amp stage...
(Is that right?) (And maybe check the light source rise time anyway?)

George H.

So where do you suppose the missing factor of ~3 in bandwidth went?

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

 

[Phil Hobbs]

On 11/19/20 8:22 AM, George Herold wrote:

On Wednesday, November 18, 2020 at 2:27:39 PM UTC-5, Phil Hobbs wrote:
Hi, all.

So I have this SiPM/MPPC front end. It has pop options to use either an
On Semi MicroFC-10010 1-mm SiPM chip or a packaged Hamamatsu
S13362-3050DG 3-mm MPPC with integral TE cooler, both bootstrapped by a
SAV-551+ running at 20 mA. So far, it all works.

(The SAV-551+ is amazingly stable--I\'ve got a shipping product that runs
a very similar bootstrap across a 2-inch FFC cable. Bandwidth suffers a
bit, but it shows no tendency to oscillate.)

The mystery is in the TIA stage. It\'s a vanilla op amp TIA made from
either an ADA4899 (600 MHz, 300 V/us) or AD8045 (1 GHz, 1300 V/us @
Av=1), which are pin compatible in the 3-mm LFCSP package. Both are
voltage feedback amps.

I\'m seeing a 3 dB bandwidth of 220 MHz, together with a faster rolloff
than I expect: -3 dB @ 220 MHz, -9 dB @ 320 MHz. It\'s not slew
limiting, because the waveform looks pretty good on a 3-GHz scope (TDS
694C) and the rolloff stays the same when I drop the input by 6 dB.

The layout is pretty tight (the whole board is only an inch square), so
getting enough stray capacitance across R_F to account for it is
implausible--it would need about 1.4 pF. DecouplingBypassing is good--

For test, I removed the 0-ohm jumper that connects the bootstrapped SiPM
to the summing junction, and added a 1k input resistor, forming an
inverting amp with a nominal gain of -0.5.

That\'s connected to the terminated end of an RG-174/U cable going to a
PTS-500 synthesizer. The output goes via a 10-ohm resistor into a
properly-terminated 50-ohm cable (the TDS 694C is 50-ohm only).

Here I\'m expecting a bandwidth somewhere between the datasheet\'s 1 GHz @
Av=1 and 400 MHz @ Av=-1, but it\'s way off. There\'s no visible change
when I put the jumper back in, on account of the swoopy bootstrap.

I was going to suggest looking at the \'speed\' of the light source.
But the above seems to point to something \'in\' the amp stage...
(Is that right?) (And maybe check the light source rise time anyway?)

George H.

So where do you suppose the missing factor of ~3 in bandwidth went?

This has the SiPM and bootstrap disconnected (0 ohm jumper removed) and
a 1/20W leaded 1k resistor bodged in to make an inverting amp with a
gain of -0.5.

I\'m looking at the trace capacitance to figure out if that might be it.
There\'s about 3/4 inch of 10-mil trace on the summing junction, but
that ought to produce a high frequency peak if anything. hard to find
1.4 pF across the feedback resistor. Once I\'m back in the lab I\'ll
measure a bare board with a Boonton and see.

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

 

[server]

On Thu, 19 Nov 2020 10:30:17 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 11/19/20 8:22 AM, George Herold wrote:
On Wednesday, November 18, 2020 at 2:27:39 PM UTC-5, Phil Hobbs wrote:
Hi, all.

So I have this SiPM/MPPC front end. It has pop options to use either an
On Semi MicroFC-10010 1-mm SiPM chip or a packaged Hamamatsu
S13362-3050DG 3-mm MPPC with integral TE cooler, both bootstrapped by a
SAV-551+ running at 20 mA. So far, it all works.

(The SAV-551+ is amazingly stable--I\'ve got a shipping product that runs
a very similar bootstrap across a 2-inch FFC cable. Bandwidth suffers a
bit, but it shows no tendency to oscillate.)

The mystery is in the TIA stage. It\'s a vanilla op amp TIA made from
either an ADA4899 (600 MHz, 300 V/us) or AD8045 (1 GHz, 1300 V/us @
Av=1), which are pin compatible in the 3-mm LFCSP package. Both are
voltage feedback amps.

I\'m seeing a 3 dB bandwidth of 220 MHz, together with a faster rolloff
than I expect: -3 dB @ 220 MHz, -9 dB @ 320 MHz. It\'s not slew
limiting, because the waveform looks pretty good on a 3-GHz scope (TDS
694C) and the rolloff stays the same when I drop the input by 6 dB.

The layout is pretty tight (the whole board is only an inch square), so
getting enough stray capacitance across R_F to account for it is
implausible--it would need about 1.4 pF. DecouplingBypassing is good--

For test, I removed the 0-ohm jumper that connects the bootstrapped SiPM
to the summing junction, and added a 1k input resistor, forming an
inverting amp with a nominal gain of -0.5.

That\'s connected to the terminated end of an RG-174/U cable going to a
PTS-500 synthesizer. The output goes via a 10-ohm resistor into a
properly-terminated 50-ohm cable (the TDS 694C is 50-ohm only).

Here I\'m expecting a bandwidth somewhere between the datasheet\'s 1 GHz @
Av=1 and 400 MHz @ Av=-1, but it\'s way off. There\'s no visible change
when I put the jumper back in, on account of the swoopy bootstrap.

I was going to suggest looking at the \'speed\' of the light source.
But the above seems to point to something \'in\' the amp stage...
(Is that right?) (And maybe check the light source rise time anyway?)

George H.

So where do you suppose the missing factor of ~3 in bandwidth went?


This has the SiPM and bootstrap disconnected (0 ohm jumper removed) and
a 1/20W leaded 1k resistor bodged in to make an inverting amp with a
gain of -0.5.

I\'m looking at the trace capacitance to figure out if that might be it.
There\'s about 3/4 inch of 10-mil trace on the summing junction, but
that ought to produce a high frequency peak if anything. hard to find
1.4 pF across the feedback resistor. Once I\'m back in the lab I\'ll
measure a bare board with a Boonton and see.

Cheers

Phil Hobbs

What\'s the board stackup? Not the specified one, but the real one.
I\'ve been burned by what some of the fast-turn proto houses do.

https://www.dropbox.com/s/p3vpbaofzqurebz/Z462_PCB_Way_2.png?raw=1







--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[dalai lamah]

Un bel giorno Phil Hobbs digitò:

The layout is pretty tight (the whole board is only an inch square), so
getting enough stray capacitance across R_F to account for it is
implausible--it would need about 1.4 pF. DecouplingBypassing is good--

Are you using vias through internal planes? Each via may add 0.5 pF stray
capacitance or even more.

--
Fletto i muscoli e sono nel vuoto.

 

[server]

On Thu, 19 Nov 2020 17:09:07 +0100, dalai lamah
<antonio12358@hotmail.com> wrote:

Un bel giorno Phil Hobbs digitò:

The layout is pretty tight (the whole board is only an inch square), so
getting enough stray capacitance across R_F to account for it is
implausible--it would need about 1.4 pF. DecouplingBypassing is good--

Are you using vias through internal planes? Each via may add 0.5 pF stray
capacitance or even more.

The Saturn PCB design software does via calculations. A big one can be
many pF.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[Fred Bloggs]

On Wednesday, November 18, 2020 at 2:27:39 PM UTC-5, Phil Hobbs wrote:

Hi, all.

So I have this SiPM/MPPC front end. It has pop options to use either an
On Semi MicroFC-10010 1-mm SiPM chip or a packaged Hamamatsu
S13362-3050DG 3-mm MPPC with integral TE cooler, both bootstrapped by a
SAV-551+ running at 20 mA. So far, it all works.

(The SAV-551+ is amazingly stable--I\'ve got a shipping product that runs
a very similar bootstrap across a 2-inch FFC cable. Bandwidth suffers a
bit, but it shows no tendency to oscillate.)

The mystery is in the TIA stage. It\'s a vanilla op amp TIA made from
either an ADA4899 (600 MHz, 300 V/us) or AD8045 (1 GHz, 1300 V/us @
Av=1), which are pin compatible in the 3-mm LFCSP package. Both are
voltage feedback amps.

I\'m seeing a 3 dB bandwidth of 220 MHz, together with a faster rolloff
than I expect: -3 dB @ 220 MHz, -9 dB @ 320 MHz. It\'s not slew
limiting, because the waveform looks pretty good on a 3-GHz scope (TDS
694C) and the rolloff stays the same when I drop the input by 6 dB.

The layout is pretty tight (the whole board is only an inch square), so
getting enough stray capacitance across R_F to account for it is
implausible--it would need about 1.4 pF. DecouplingBypassing is good--

For test, I removed the 0-ohm jumper that connects the bootstrapped SiPM
to the summing junction, and added a 1k input resistor, forming an
inverting amp with a nominal gain of -0.5.

That\'s connected to the terminated end of an RG-174/U cable going to a
PTS-500 synthesizer. The output goes via a 10-ohm resistor into a
properly-terminated 50-ohm cable (the TDS 694C is 50-ohm only).

Here I\'m expecting a bandwidth somewhere between the datasheet\'s 1 GHz @
Av=1 and 400 MHz @ Av=-1, but it\'s way off. There\'s no visible change
when I put the jumper back in, on account of the swoopy bootstrap.

So where do you suppose the missing factor of ~3 in bandwidth went?

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

Can you tap that PTS-500 synthesizer input right at its loading on your board and verify its not rolling off for some reason?

 

[Phil Hobbs]

On 11/19/20 10:44 AM, jlarkin@highlandsniptechnology.com wrote:

On Thu, 19 Nov 2020 10:30:17 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 11/19/20 8:22 AM, George Herold wrote:
On Wednesday, November 18, 2020 at 2:27:39 PM UTC-5, Phil Hobbs wrote:
Hi, all.

So I have this SiPM/MPPC front end. It has pop options to use either an
On Semi MicroFC-10010 1-mm SiPM chip or a packaged Hamamatsu
S13362-3050DG 3-mm MPPC with integral TE cooler, both bootstrapped by a
SAV-551+ running at 20 mA. So far, it all works.

(The SAV-551+ is amazingly stable--I\'ve got a shipping product that runs
a very similar bootstrap across a 2-inch FFC cable. Bandwidth suffers a
bit, but it shows no tendency to oscillate.)

The mystery is in the TIA stage. It\'s a vanilla op amp TIA made from
either an ADA4899 (600 MHz, 300 V/us) or AD8045 (1 GHz, 1300 V/us @
Av=1), which are pin compatible in the 3-mm LFCSP package. Both are
voltage feedback amps.

I\'m seeing a 3 dB bandwidth of 220 MHz, together with a faster rolloff
than I expect: -3 dB @ 220 MHz, -9 dB @ 320 MHz. It\'s not slew
limiting, because the waveform looks pretty good on a 3-GHz scope (TDS
694C) and the rolloff stays the same when I drop the input by 6 dB.

The layout is pretty tight (the whole board is only an inch square), so
getting enough stray capacitance across R_F to account for it is
implausible--it would need about 1.4 pF. DecouplingBypassing is good--

For test, I removed the 0-ohm jumper that connects the bootstrapped SiPM
to the summing junction, and added a 1k input resistor, forming an
inverting amp with a nominal gain of -0.5.

That\'s connected to the terminated end of an RG-174/U cable going to a
PTS-500 synthesizer. The output goes via a 10-ohm resistor into a
properly-terminated 50-ohm cable (the TDS 694C is 50-ohm only).

Here I\'m expecting a bandwidth somewhere between the datasheet\'s 1 GHz @
Av=1 and 400 MHz @ Av=-1, but it\'s way off. There\'s no visible change
when I put the jumper back in, on account of the swoopy bootstrap.

I was going to suggest looking at the \'speed\' of the light source.
But the above seems to point to something \'in\' the amp stage...
(Is that right?) (And maybe check the light source rise time anyway?)

George H.

So where do you suppose the missing factor of ~3 in bandwidth went?


This has the SiPM and bootstrap disconnected (0 ohm jumper removed) and
a 1/20W leaded 1k resistor bodged in to make an inverting amp with a
gain of -0.5.

I\'m looking at the trace capacitance to figure out if that might be it.
There\'s about 3/4 inch of 10-mil trace on the summing junction, but
that ought to produce a high frequency peak if anything. hard to find
1.4 pF across the feedback resistor. Once I\'m back in the lab I\'ll
measure a bare board with a Boonton and see.

Cheers

Phil Hobbs

What\'s the board stackup? Not the specified one, but the real one.
I\'ve been burned by what some of the fast-turn proto houses do.

https://www.dropbox.com/s/p3vpbaofzqurebz/Z462_PCB_Way_2.png?raw=1

The SJ capacitance is 2.4 pF, as measured on a Boonton, which is about
twice what I expected. That seems to be the issue--in simulation it
produces a pretty big gain peak, which reduces the bandwidth.

Time to Dremel the ground plane.

Cheers

Phil Hobs


--
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

 

[George Herold]

On Friday, November 20, 2020 at 10:36:14 PM UTC-5, Phil Hobbs wrote:

On 11/19/20 10:44 AM, jla...@highlandsniptechnology.com wrote:
On Thu, 19 Nov 2020 10:30:17 -0500, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

On 11/19/20 8:22 AM, George Herold wrote:
On Wednesday, November 18, 2020 at 2:27:39 PM UTC-5, Phil Hobbs wrote:
Hi, all.

So I have this SiPM/MPPC front end. It has pop options to use either an
On Semi MicroFC-10010 1-mm SiPM chip or a packaged Hamamatsu
S13362-3050DG 3-mm MPPC with integral TE cooler, both bootstrapped by a
SAV-551+ running at 20 mA. So far, it all works.

(The SAV-551+ is amazingly stable--I\'ve got a shipping product that runs
a very similar bootstrap across a 2-inch FFC cable. Bandwidth suffers a
bit, but it shows no tendency to oscillate.)

The mystery is in the TIA stage. It\'s a vanilla op amp TIA made from
either an ADA4899 (600 MHz, 300 V/us) or AD8045 (1 GHz, 1300 V/us @
Av=1), which are pin compatible in the 3-mm LFCSP package. Both are
voltage feedback amps.

I\'m seeing a 3 dB bandwidth of 220 MHz, together with a faster rolloff
than I expect: -3 dB @ 220 MHz, -9 dB @ 320 MHz. It\'s not slew
limiting, because the waveform looks pretty good on a 3-GHz scope (TDS
694C) and the rolloff stays the same when I drop the input by 6 dB.

The layout is pretty tight (the whole board is only an inch square), so
getting enough stray capacitance across R_F to account for it is
implausible--it would need about 1.4 pF. DecouplingBypassing is good--

For test, I removed the 0-ohm jumper that connects the bootstrapped SiPM
to the summing junction, and added a 1k input resistor, forming an
inverting amp with a nominal gain of -0.5.

That\'s connected to the terminated end of an RG-174/U cable going to a
PTS-500 synthesizer. The output goes via a 10-ohm resistor into a
properly-terminated 50-ohm cable (the TDS 694C is 50-ohm only).

Here I\'m expecting a bandwidth somewhere between the datasheet\'s 1 GHz @
Av=1 and 400 MHz @ Av=-1, but it\'s way off. There\'s no visible change
when I put the jumper back in, on account of the swoopy bootstrap.

I was going to suggest looking at the \'speed\' of the light source.
But the above seems to point to something \'in\' the amp stage...
(Is that right?) (And maybe check the light source rise time anyway?)

George H.

So where do you suppose the missing factor of ~3 in bandwidth went?


This has the SiPM and bootstrap disconnected (0 ohm jumper removed) and
a 1/20W leaded 1k resistor bodged in to make an inverting amp with a
gain of -0.5.

I\'m looking at the trace capacitance to figure out if that might be it.
There\'s about 3/4 inch of 10-mil trace on the summing junction, but
that ought to produce a high frequency peak if anything. hard to find
1.4 pF across the feedback resistor. Once I\'m back in the lab I\'ll
measure a bare board with a Boonton and see.

Cheers

Phil Hobbs

What\'s the board stackup? Not the specified one, but the real one.
I\'ve been burned by what some of the fast-turn proto houses do.

https://www.dropbox.com/s/p3vpbaofzqurebz/Z462_PCB_Way_2.png?raw=1
The SJ capacitance is 2.4 pF, as measured on a Boonton, which is about
twice what I expected. That seems to be the issue--in simulation it
produces a pretty big gain peak, which reduces the bandwidth.

Time to Dremel the ground plane.

Hah, my first TIA I took a belt sander to the ground plane.
(Terrible layout on my part I had the input trace snaking around.)

Finding the trouble is good.
George H.

Cheers

Phil Hobs
--
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

 

[server]

On Fri, 20 Nov 2020 22:35:52 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 11/19/20 10:44 AM, jlarkin@highlandsniptechnology.com wrote:
On Thu, 19 Nov 2020 10:30:17 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 11/19/20 8:22 AM, George Herold wrote:
On Wednesday, November 18, 2020 at 2:27:39 PM UTC-5, Phil Hobbs wrote:
Hi, all.

So I have this SiPM/MPPC front end. It has pop options to use either an
On Semi MicroFC-10010 1-mm SiPM chip or a packaged Hamamatsu
S13362-3050DG 3-mm MPPC with integral TE cooler, both bootstrapped by a
SAV-551+ running at 20 mA. So far, it all works.

(The SAV-551+ is amazingly stable--I\'ve got a shipping product that runs
a very similar bootstrap across a 2-inch FFC cable. Bandwidth suffers a
bit, but it shows no tendency to oscillate.)

The mystery is in the TIA stage. It\'s a vanilla op amp TIA made from
either an ADA4899 (600 MHz, 300 V/us) or AD8045 (1 GHz, 1300 V/us @
Av=1), which are pin compatible in the 3-mm LFCSP package. Both are
voltage feedback amps.

I\'m seeing a 3 dB bandwidth of 220 MHz, together with a faster rolloff
than I expect: -3 dB @ 220 MHz, -9 dB @ 320 MHz. It\'s not slew
limiting, because the waveform looks pretty good on a 3-GHz scope (TDS
694C) and the rolloff stays the same when I drop the input by 6 dB.

The layout is pretty tight (the whole board is only an inch square), so
getting enough stray capacitance across R_F to account for it is
implausible--it would need about 1.4 pF. DecouplingBypassing is good--

For test, I removed the 0-ohm jumper that connects the bootstrapped SiPM
to the summing junction, and added a 1k input resistor, forming an
inverting amp with a nominal gain of -0.5.

That\'s connected to the terminated end of an RG-174/U cable going to a
PTS-500 synthesizer. The output goes via a 10-ohm resistor into a
properly-terminated 50-ohm cable (the TDS 694C is 50-ohm only).

Here I\'m expecting a bandwidth somewhere between the datasheet\'s 1 GHz @
Av=1 and 400 MHz @ Av=-1, but it\'s way off. There\'s no visible change
when I put the jumper back in, on account of the swoopy bootstrap.

I was going to suggest looking at the \'speed\' of the light source.
But the above seems to point to something \'in\' the amp stage...
(Is that right?) (And maybe check the light source rise time anyway?)

George H.

So where do you suppose the missing factor of ~3 in bandwidth went?


This has the SiPM and bootstrap disconnected (0 ohm jumper removed) and
a 1/20W leaded 1k resistor bodged in to make an inverting amp with a
gain of -0.5.

I\'m looking at the trace capacitance to figure out if that might be it.
There\'s about 3/4 inch of 10-mil trace on the summing junction, but
that ought to produce a high frequency peak if anything. hard to find
1.4 pF across the feedback resistor. Once I\'m back in the lab I\'ll
measure a bare board with a Boonton and see.

Cheers

Phil Hobbs

What\'s the board stackup? Not the specified one, but the real one.
I\'ve been burned by what some of the fast-turn proto houses do.

https://www.dropbox.com/s/p3vpbaofzqurebz/Z462_PCB_Way_2.png?raw=1

The SJ capacitance is 2.4 pF, as measured on a Boonton, which is about
twice what I expected. That seems to be the issue--in simulation it
produces a pretty big gain peak, which reduces the bandwidth.

Time to Dremel the ground plane.

How many layers?

Maybe section the board to see what the stackup actually is.

Here is a Dremel-optimized SMA connector.

https://www.dropbox.com/s/gc5j45995nqiftu/Isola_Right_Trim.jpg?raw=1

https://www.dropbox.com/s/t0cnfe9do4slvvf/Isola_Trimmed_Right_TDR.jpg?raw=1




--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[Phil Hobbs]

On 11/21/20 12:39 AM, jlarkin@highlandsniptechnology.com wrote:

On Fri, 20 Nov 2020 22:35:52 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 11/19/20 10:44 AM, jlarkin@highlandsniptechnology.com wrote:
On Thu, 19 Nov 2020 10:30:17 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 11/19/20 8:22 AM, George Herold wrote:
On Wednesday, November 18, 2020 at 2:27:39 PM UTC-5, Phil
Hobbs wrote:
Hi, all.

So I have this SiPM/MPPC front end. It has pop options to
use either an On Semi MicroFC-10010 1-mm SiPM chip or a
packaged Hamamatsu S13362-3050DG 3-mm MPPC with integral
TE cooler, both bootstrapped by a SAV-551+ running at 20
mA. So far, it all works.

(The SAV-551+ is amazingly stable--I\'ve got a shipping
product that runs a very similar bootstrap across a 2-inch
FFC cable. Bandwidth suffers a bit, but it shows no
tendency to oscillate.)

The mystery is in the TIA stage. It\'s a vanilla op amp TIA
made from either an ADA4899 (600 MHz, 300 V/us) or AD8045
(1 GHz, 1300 V/us @ Av=1), which are pin compatible in the
3-mm LFCSP package. Both are voltage feedback amps.

I\'m seeing a 3 dB bandwidth of 220 MHz, together with a
faster rolloff than I expect: -3 dB @ 220 MHz, -9 dB @ 320
MHz. It\'s not slew limiting, because the waveform looks
pretty good on a 3-GHz scope (TDS 694C) and the rolloff
stays the same when I drop the input by 6 dB.

The layout is pretty tight (the whole board is only an
inch square), so getting enough stray capacitance across
R_F to account for it is implausible--it would need about
1.4 pF. DecouplingBypassing is good--

For test, I removed the 0-ohm jumper that connects the
bootstrapped SiPM to the summing junction, and added a 1k
input resistor, forming an inverting amp with a nominal
gain of -0.5.

That\'s connected to the terminated end of an RG-174/U
cable going to a PTS-500 synthesizer. The output goes via
a 10-ohm resistor into a properly-terminated 50-ohm cable
(the TDS 694C is 50-ohm only).

Here I\'m expecting a bandwidth somewhere between the
datasheet\'s 1 GHz @ Av=1 and 400 MHz @ Av=-1, but it\'s way
off. There\'s no visible change when I put the jumper back
in, on account of the swoopy bootstrap.

I was going to suggest looking at the \'speed\' of the light
source. But the above seems to point to something \'in\' the
amp stage... (Is that right?) (And maybe check the light
source rise time anyway?)

George H.

So where do you suppose the missing factor of ~3 in
bandwidth went?


This has the SiPM and bootstrap disconnected (0 ohm jumper
removed) and a 1/20W leaded 1k resistor bodged in to make an
inverting amp with a gain of -0.5.

I\'m looking at the trace capacitance to figure out if that
might be it. There\'s about 3/4 inch of 10-mil trace on the
summing junction, but that ought to produce a high frequency
peak if anything. hard to find 1.4 pF across the feedback
resistor. Once I\'m back in the lab I\'ll measure a bare board
with a Boonton and see.

Cheers

Phil Hobbs

What\'s the board stackup? Not the specified one, but the real
one. I\'ve been burned by what some of the fast-turn proto houses
do.

https://www.dropbox.com/s/p3vpbaofzqurebz/Z462_PCB_Way_2.png?raw=1



The SJ capacitance is 2.4 pF, as measured on a Boonton, about
twice what I expected. That seems to be the issue--in simulation
it produces a pretty big gain peak, which reduces the bandwidth.

Time to Dremel the ground plane.

How many layers?

Only four, but of course ground is L2 and there\'s an L3 ground pour in
that area. It is PCBway, so maybe they did the same thing to me. (A
generally very good outfit in many ways, especially price and delivery.)

Maybe section the board to see what the stackup actually is.

Monday I\'ll look at it under the good microscope. (About three years
ago, I got a beautiful Mitutoyo FS-110 with 2x-50x long working-distance
objectives for $2k on eBay. Apparently the guy didn\'t know what he had,
because he shipped this massive precision instrument in a cardboard box
with foam peanuts. The box was a mess when it got here, but the scope
survived because it\'s a beast.)

Here is a Dremel-optimized SMA connector.


https://www.dropbox.com/s/gc5j45995nqiftu/Isola_Right_Trim.jpg?raw=1

https://www.dropbox.com/s/t0cnfe9do4slvvf/Isola_Trimmed_Right_TDR.jpg?raw=1

Nice.

We\'ve had that problem too--you need some extra pad area for the
solder fillet, but that makes a nasty capacitive discontinuity at the
connector.

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

 

[server]

On Sat, 21 Nov 2020 07:05:11 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 11/21/20 12:39 AM, jlarkin@highlandsniptechnology.com wrote:
On Fri, 20 Nov 2020 22:35:52 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 11/19/20 10:44 AM, jlarkin@highlandsniptechnology.com wrote:
On Thu, 19 Nov 2020 10:30:17 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 11/19/20 8:22 AM, George Herold wrote:
On Wednesday, November 18, 2020 at 2:27:39 PM UTC-5, Phil
Hobbs wrote:
Hi, all.

So I have this SiPM/MPPC front end. It has pop options to
use either an On Semi MicroFC-10010 1-mm SiPM chip or a
packaged Hamamatsu S13362-3050DG 3-mm MPPC with integral
TE cooler, both bootstrapped by a SAV-551+ running at 20
mA. So far, it all works.

(The SAV-551+ is amazingly stable--I\'ve got a shipping
product that runs a very similar bootstrap across a 2-inch
FFC cable. Bandwidth suffers a bit, but it shows no
tendency to oscillate.)

The mystery is in the TIA stage. It\'s a vanilla op amp TIA
made from either an ADA4899 (600 MHz, 300 V/us) or AD8045
(1 GHz, 1300 V/us @ Av=1), which are pin compatible in the
3-mm LFCSP package. Both are voltage feedback amps.

I\'m seeing a 3 dB bandwidth of 220 MHz, together with a
faster rolloff than I expect: -3 dB @ 220 MHz, -9 dB @ 320
MHz. It\'s not slew limiting, because the waveform looks
pretty good on a 3-GHz scope (TDS 694C) and the rolloff
stays the same when I drop the input by 6 dB.

The layout is pretty tight (the whole board is only an
inch square), so getting enough stray capacitance across
R_F to account for it is implausible--it would need about
1.4 pF. DecouplingBypassing is good--

For test, I removed the 0-ohm jumper that connects the
bootstrapped SiPM to the summing junction, and added a 1k
input resistor, forming an inverting amp with a nominal
gain of -0.5.

That\'s connected to the terminated end of an RG-174/U
cable going to a PTS-500 synthesizer. The output goes via
a 10-ohm resistor into a properly-terminated 50-ohm cable
(the TDS 694C is 50-ohm only).

Here I\'m expecting a bandwidth somewhere between the
datasheet\'s 1 GHz @ Av=1 and 400 MHz @ Av=-1, but it\'s way
off. There\'s no visible change when I put the jumper back
in, on account of the swoopy bootstrap.

I was going to suggest looking at the \'speed\' of the light
source. But the above seems to point to something \'in\' the
amp stage... (Is that right?) (And maybe check the light
source rise time anyway?)

George H.

So where do you suppose the missing factor of ~3 in
bandwidth went?


This has the SiPM and bootstrap disconnected (0 ohm jumper
removed) and a 1/20W leaded 1k resistor bodged in to make an
inverting amp with a gain of -0.5.

I\'m looking at the trace capacitance to figure out if that
might be it. There\'s about 3/4 inch of 10-mil trace on the
summing junction, but that ought to produce a high frequency
peak if anything. hard to find 1.4 pF across the feedback
resistor. Once I\'m back in the lab I\'ll measure a bare board
with a Boonton and see.

Cheers

Phil Hobbs

What\'s the board stackup? Not the specified one, but the real
one. I\'ve been burned by what some of the fast-turn proto houses
do.

https://www.dropbox.com/s/p3vpbaofzqurebz/Z462_PCB_Way_2.png?raw=1



The SJ capacitance is 2.4 pF, as measured on a Boonton, about
twice what I expected. That seems to be the issue--in simulation
it produces a pretty big gain peak, which reduces the bandwidth.

Time to Dremel the ground plane.

How many layers?

Only four, but of course ground is L2 and there\'s an L3 ground pour in
that area. It is PCBway, so maybe they did the same thing to me. (A
generally very good outfit in many ways, especially price and delivery.)

Several of the chinese quick-turn houses make 4-layer boards with very
thin (like 4 mil) outer dielectrics. Maybe they roll process the
outers and glue them to a core or something.

Maybe section the board to see what the stackup actually is.


Monday I\'ll look at it under the good microscope. (About three years
ago, I got a beautiful Mitutoyo FS-110 with 2x-50x long working-distance
objectives for $2k on eBay. Apparently the guy didn\'t know what he had,
because he shipped this massive precision instrument in a cardboard box
with foam peanuts. The box was a mess when it got here, but the scope
survived because it\'s a beast.)

I sheared and sandpapered the example I posted, and shot it with my
super-good microscope

https://www.amazon.com/gp/product/B01IV0TV50/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Here is a Dremel-optimized SMA connector.


https://www.dropbox.com/s/gc5j45995nqiftu/Isola_Right_Trim.jpg?raw=1

https://www.dropbox.com/s/t0cnfe9do4slvvf/Isola_Trimmed_Right_TDR.jpg?raw=1

Nice.

We\'ve had that problem too--you need some extra pad area for the
solder fillet, but that makes a nasty capacitive discontinuity at the
connector.

The impedance of that SMA edge-launch connector, center pin to the
four ground pins, is about 100 ohms in free air. So the PCB has to be
about 100 in the pin region too. We\'ve worked that out, cutting away
inners and paving over the bottom with ground. We simulated the whole
geometry with ATLC to get the dims right. That was cool.

The case I posted was testing a laminate sample, 20 mils thick.

The $1.50 edge-launches are just as good as the $12 microwave
connectors if the layout is right, at least as far as we can resolve
with 30 ps TDR.

I sometimes cut away layer 2 (or more) under critical circuit nodes.
My triggered Colpitts oscillator has a driven guard patch on layer 5.

You bootstrap photodiodes, so you might bootstrap the PCB too.



--

John Larkin Highland Technology, Inc

The best designs are necessarily accidental.

 

[Lasse Langwadt Christensen]

lørdag den 21. november 2020 kl. 17.05.34 UTC+1 skrev jla...@highlandsniptechnology.com:

On Sat, 21 Nov 2020 07:05:11 -0500, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

On 11/21/20 12:39 AM, jla...@highlandsniptechnology.com wrote:
On Fri, 20 Nov 2020 22:35:52 -0500, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

On 11/19/20 10:44 AM, jla...@highlandsniptechnology.com wrote:
On Thu, 19 Nov 2020 10:30:17 -0500, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

On 11/19/20 8:22 AM, George Herold wrote:
On Wednesday, November 18, 2020 at 2:27:39 PM UTC-5, Phil
Hobbs wrote:
Hi, all.

So I have this SiPM/MPPC front end. It has pop options to
use either an On Semi MicroFC-10010 1-mm SiPM chip or a
packaged Hamamatsu S13362-3050DG 3-mm MPPC with integral
TE cooler, both bootstrapped by a SAV-551+ running at 20
mA. So far, it all works.

(The SAV-551+ is amazingly stable--I\'ve got a shipping
product that runs a very similar bootstrap across a 2-inch
FFC cable. Bandwidth suffers a bit, but it shows no
tendency to oscillate.)

The mystery is in the TIA stage. It\'s a vanilla op amp TIA
made from either an ADA4899 (600 MHz, 300 V/us) or AD8045
(1 GHz, 1300 V/us @ Av=1), which are pin compatible in the
3-mm LFCSP package. Both are voltage feedback amps.

I\'m seeing a 3 dB bandwidth of 220 MHz, together with a
faster rolloff than I expect: -3 dB @ 220 MHz, -9 dB @ 320
MHz. It\'s not slew limiting, because the waveform looks
pretty good on a 3-GHz scope (TDS 694C) and the rolloff
stays the same when I drop the input by 6 dB.

The layout is pretty tight (the whole board is only an
inch square), so getting enough stray capacitance across
R_F to account for it is implausible--it would need about
1.4 pF. DecouplingBypassing is good--

For test, I removed the 0-ohm jumper that connects the
bootstrapped SiPM to the summing junction, and added a 1k
input resistor, forming an inverting amp with a nominal
gain of -0.5.

That\'s connected to the terminated end of an RG-174/U
cable going to a PTS-500 synthesizer. The output goes via
a 10-ohm resistor into a properly-terminated 50-ohm cable
(the TDS 694C is 50-ohm only).

Here I\'m expecting a bandwidth somewhere between the
datasheet\'s 1 GHz @ Av=1 and 400 MHz @ Av=-1, but it\'s way
off. There\'s no visible change when I put the jumper back
in, on account of the swoopy bootstrap.

I was going to suggest looking at the \'speed\' of the light
source. But the above seems to point to something \'in\' the
amp stage... (Is that right?) (And maybe check the light
source rise time anyway?)

George H.

So where do you suppose the missing factor of ~3 in
bandwidth went?


This has the SiPM and bootstrap disconnected (0 ohm jumper
removed) and a 1/20W leaded 1k resistor bodged in to make an
inverting amp with a gain of -0.5.

I\'m looking at the trace capacitance to figure out if that
might be it. There\'s about 3/4 inch of 10-mil trace on the
summing junction, but that ought to produce a high frequency
peak if anything. hard to find 1.4 pF across the feedback
resistor. Once I\'m back in the lab I\'ll measure a bare board
with a Boonton and see.

Cheers

Phil Hobbs

What\'s the board stackup? Not the specified one, but the real
one. I\'ve been burned by what some of the fast-turn proto houses
do.

https://www.dropbox.com/s/p3vpbaofzqurebz/Z462_PCB_Way_2.png?raw=1



The SJ capacitance is 2.4 pF, as measured on a Boonton, about
twice what I expected. That seems to be the issue--in simulation
it produces a pretty big gain peak, which reduces the bandwidth.

Time to Dremel the ground plane.

How many layers?

Only four, but of course ground is L2 and there\'s an L3 ground pour in
that area. It is PCBway, so maybe they did the same thing to me. (A
generally very good outfit in many ways, especially price and delivery.)
Several of the chinese quick-turn houses make 4-layer boards with very
thin (like 4 mil) outer dielectrics. Maybe they roll process the
outers and glue them to a core or something.

I believe the common process for 4 layers is first a core with the inner
layers and then sandwiched with pre-peg and copper to make the outer layers

thin outer dielectrics means traces to things like DDR ram does have to be mile wide

 

[server]

On Sat, 21 Nov 2020 13:11:36 -0800 (PST), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

lørdag den 21. november 2020 kl. 17.05.34 UTC+1 skrev jla...@highlandsniptechnology.com:
On Sat, 21 Nov 2020 07:05:11 -0500, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

On 11/21/20 12:39 AM, jla...@highlandsniptechnology.com wrote:
On Fri, 20 Nov 2020 22:35:52 -0500, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

On 11/19/20 10:44 AM, jla...@highlandsniptechnology.com wrote:
On Thu, 19 Nov 2020 10:30:17 -0500, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

On 11/19/20 8:22 AM, George Herold wrote:
On Wednesday, November 18, 2020 at 2:27:39 PM UTC-5, Phil
Hobbs wrote:
Hi, all.

So I have this SiPM/MPPC front end. It has pop options to
use either an On Semi MicroFC-10010 1-mm SiPM chip or a
packaged Hamamatsu S13362-3050DG 3-mm MPPC with integral
TE cooler, both bootstrapped by a SAV-551+ running at 20
mA. So far, it all works.

(The SAV-551+ is amazingly stable--I\'ve got a shipping
product that runs a very similar bootstrap across a 2-inch
FFC cable. Bandwidth suffers a bit, but it shows no
tendency to oscillate.)

The mystery is in the TIA stage. It\'s a vanilla op amp TIA
made from either an ADA4899 (600 MHz, 300 V/us) or AD8045
(1 GHz, 1300 V/us @ Av=1), which are pin compatible in the
3-mm LFCSP package. Both are voltage feedback amps.

I\'m seeing a 3 dB bandwidth of 220 MHz, together with a
faster rolloff than I expect: -3 dB @ 220 MHz, -9 dB @ 320
MHz. It\'s not slew limiting, because the waveform looks
pretty good on a 3-GHz scope (TDS 694C) and the rolloff
stays the same when I drop the input by 6 dB.

The layout is pretty tight (the whole board is only an
inch square), so getting enough stray capacitance across
R_F to account for it is implausible--it would need about
1.4 pF. DecouplingBypassing is good--

For test, I removed the 0-ohm jumper that connects the
bootstrapped SiPM to the summing junction, and added a 1k
input resistor, forming an inverting amp with a nominal
gain of -0.5.

That\'s connected to the terminated end of an RG-174/U
cable going to a PTS-500 synthesizer. The output goes via
a 10-ohm resistor into a properly-terminated 50-ohm cable
(the TDS 694C is 50-ohm only).

Here I\'m expecting a bandwidth somewhere between the
datasheet\'s 1 GHz @ Av=1 and 400 MHz @ Av=-1, but it\'s way
off. There\'s no visible change when I put the jumper back
in, on account of the swoopy bootstrap.

I was going to suggest looking at the \'speed\' of the light
source. But the above seems to point to something \'in\' the
amp stage... (Is that right?) (And maybe check the light
source rise time anyway?)

George H.

So where do you suppose the missing factor of ~3 in
bandwidth went?


This has the SiPM and bootstrap disconnected (0 ohm jumper
removed) and a 1/20W leaded 1k resistor bodged in to make an
inverting amp with a gain of -0.5.

I\'m looking at the trace capacitance to figure out if that
might be it. There\'s about 3/4 inch of 10-mil trace on the
summing junction, but that ought to produce a high frequency
peak if anything. hard to find 1.4 pF across the feedback
resistor. Once I\'m back in the lab I\'ll measure a bare board
with a Boonton and see.

Cheers

Phil Hobbs

What\'s the board stackup? Not the specified one, but the real
one. I\'ve been burned by what some of the fast-turn proto houses
do.

https://www.dropbox.com/s/p3vpbaofzqurebz/Z462_PCB_Way_2.png?raw=1



The SJ capacitance is 2.4 pF, as measured on a Boonton, about
twice what I expected. That seems to be the issue--in simulation
it produces a pretty big gain peak, which reduces the bandwidth.

Time to Dremel the ground plane.

How many layers?

Only four, but of course ground is L2 and there\'s an L3 ground pour in
that area. It is PCBway, so maybe they did the same thing to me. (A
generally very good outfit in many ways, especially price and delivery.)
Several of the chinese quick-turn houses make 4-layer boards with very
thin (like 4 mil) outer dielectrics. Maybe they roll process the
outers and glue them to a core or something.

I believe the common process for 4 layers is first a core with the inner
layers and then sandwiched with pre-peg and copper to make the outer layers

thin outer dielectrics means traces to things like DDR ram does have to be mile wide

Thin, actually?

A 50 ohm microstrip on 4 mils thick FR4 dielectric is 6 mils wide. A
75 ohm trace would be 2 mils wide.



--

John Larkin Highland Technology, Inc

The best designs are necessarily accidental.