Re: [ARTIQ] analog extension cards

[Grzegorz Kasprowicz]

I can agree that FMC is not the best idea in case of RF stuff.
There are multipin RF board 2 board coaxial connectors which can be used for 
plugin modules. And such modules can be easily shielded using i.e. Wurth 
shields or EZ-Shields from Harwin that can be easily customized.
Greg

-Original Message-
From: ARTIQ [mailto:artiq-boun...@lists.m-labs.hk] On Behalf Of Slichter, 
Daniel H. (Fed)
Sent: Saturday, March 26, 2016 4:40 PM
To: Sébastien Bourdeauducq ; artiq@lists.m-labs.hk
Subject: Re: [ARTIQ] analog extension cards

To clarify nomenclature, we have been referring to these as "RF daughter cards" 
previously.  These cards could potentially contain components such as RF 
amplifiers, operational/instrumentation amplifiers, filters, 
mixers/modulators/demodulators, splitters/combiners/hybrids, baluns, digital or 
analog attenuators, RF switches, frequency multipliers.  

There are three types of basic card designs that I think should be available 
from the beginning:

1. "Low frequency" - Signal bandwidth of a few MHz, swinging between +/- 10 V 
or so, suitable for ion trap transport waveforms or various DC or quasi-DC bias 
signals in general applications.  This would involve op amps/instrumentation 
amps running off +/- 15V supplies in a similar configuration to the current PDQ 
output stages.  Footprints for discrete component filters both before and after 
the amplifiers should be included.

2. "RF" - For synthesis of tones from a few MHz out to ~3.3 GHz, suitable for 
AOM drive or Be+/Mg+/Ca+/NV center microwave transitions.  This would involve a 
set of filters (common footprint, stuff boards with different cutoff parts to 
define band of interest -- these can be left open for users, or we can choose 
one or two basic frequency sets and they can run their own custom assembly 
order from the fab/layout docs if they want something different) followed by an 
RF amplifier stage (ERA-4SM is a good broadband low-phase-noise selection), a 
digital step attenuator, and a fast high-isolation RF switch.

3. "Upconverting" - For synthesis of tones beyond ~3.3 GHz, suitable for Yb+ or 
superconducting qubit microwave transitions.  The board would have an input 
connector for an externally generated microwave carrier, split and sent to the 
LO ports of a set of mixers/modulators.  We should decide if these needs to be 
IQ mixers or if regular mixers are sufficient.  There will be filters (again, 
common footprint for a choice of frequencies) between the DAC outputs and mixer 
IF ports.  Each mixer RF port will be followed by an amplifier, a digital step 
attenuator, and a fast high-isolation RF switch.

Again, I stress strongly that I am *not* satisfied using FMC connectors for 
these cards until someone has tested and verified properties like crosstalk.  
This issue has the potential the render the entire hardware project useless 
(e.g. if crosstalk levels are too high), and therefore we need to be very 
careful about design here.  

For the "RF" and "upconverting" boards, it will most likely be important to 
have board-level shielding cavities to reduce crosstalk between channels on the 
daughtercards.  It is possible to have these custom designed and produced 
inexpensively at scale (~$15-$20/board).  

Best,
Daniel

> -Original Message-
> From: ARTIQ [mailto:artiq-boun...@lists.m-labs.hk] On Behalf Of 
> Sébastien Bourdeauducq
> Sent: Saturday, March 26, 2016 2:57 AM
> To: artiq@lists.m-labs.hk
> Subject: [ARTIQ] analog extension cards
> 
> Hi,
> 
> any ideas of what analog extensions in FMC form factor for the DSP 
> card should be available first? Mixers I guess, but what are the specs? 
> Amplifiers?
> 
> Sébastien
> 
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Re: [ARTIQ] FW: initial specification of the project

[Grzegorz Kasprowicz]

On Friday, 25 March 2016 12:24:02 PM HKT you wrote:
> * whether or not we use Zynq remains to be decided.
> **The price difference is not that high (a few tens of $) and we get 
> plenty of CPU power

Yes, but Zynq chips are annoying to program (even if we do not use the ARM
cores) and more proprietary. The question is really whether the Zynq 
architecture has technical benefits to the end application that justify the 
trouble. The answer is not straightforward, e.g. CPU power doesn't translate 
linearly to latency reductions.

[GK] If you don't use ARM, you still get hardened SDRAM controller and GBE MACs.

Maybe we should do a quick experiment and map the ARTIQ RTIO core in the 
address space of a Zynq device, and compile (with just gcc or clang, not the 
ARTIQ compiler) the equivalent of the current runtime+kernel system that 
measures the maximum pulse rate. Then we have hard numbers to discuss.

[GK]For time critical apps, one can program these CPUs bare metal. We did it in 
our projects.

> * transceivers on the backplane are acceptable but not necessary; 
> since we have multiple signals we can transmit a clock and use the 
> regular IOSERDES to lower FPGA requirements.
> **Well, IOSERDES can go up to 1.2Gbit n synchronous mode.
> **GTH can go 12Gbit/s easily
> **Are you sure you want to relay only on IOSERDES?

Yes, I think they would be sufficient. The bulk of the data will be processed 
locally on-the-fly by the AMC cards, and a couple Gbps (I suppose we can route 
extra pairs easily) of bandwidth should be plenty for controlling the AMCs.

> * what is the other large BGA chip on the MCH rendering? Is it the 
> Macom
> M21048 48x48 crossbar? Let's not use such a device, which looks 
> unnecessary, complicated, and very proprietary. There isn't even a 
> public datasheet for it.
> We do not need direct communication between the AMCs.
> 
> **At the moment not, but remember that it's going to be research 
> platform

If we use the IOSERDES, the FPGA has plenty of IO pins to perform such direct 
routing (on wider buses and/or with less bandwidth) .

[GK] That' true

> **I can make an option with this chip not mounted. I simply see 
> another potential of this board and the place on the PCB does not cost 
> single $ since we have to use standard module **dimensions:)

OK, but what about the additional routing difficulty, and any additional PCB 
layers?

[GK] It will need 2 extra layers

What is the other application you are thinking of?

[GK] The other application is not related to ARTIQ project - we will need it 
for another project at the WUT related with GEM detectors.
[GK] Generally, it is detector processing electronics

> **In case of the datasheet, I got it easily after I signed the NDA.

The fewer NDAs I sign, the better. And it would make the board less accessible.
[GK] I understand your point. It is not compatible with Open Hardware

> * we want to avoid RTMs and instead put the DAC/ADCs on the AMC card 
> and have analog plug-ins using the FMC form factor (see my document).
> **Are you sure you would get noise performance from such setup that 
> satisfies you?

Unless the FMC connector is particularly bad with analog signals, I think it 
should not be worse than the current hardware.
[GK] All depends how you deliver the clock for such DAC. This is the weakest 
point of such solution.
[GK] Is current HW fully sufficient in terms of SFDR?

Greg


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Re: [ARTIQ] FW: initial specification of the project

[Grzegorz Kasprowicz]

For slow control signals and supplies one can use standard 2.54 golpins and 
headers. 
I saw such solution in the RF group at the university. They pass RF using 
dedicated board to board coaxial connectors, rest is transmitted over standard 
pin headers.
Greg

-Original Message-
From: ARTIQ [mailto:artiq-boun...@lists.m-labs.hk] On Behalf Of Slichter, 
Daniel H. (Fed)
Sent: Monday, March 28, 2016 5:25 PM
To: Sébastien Bourdeauducq 
Cc: Grzegorz Kasprowicz ; artiq@lists.m-labs.hk
Subject: Re: [ARTIQ] FW: initial specification of the project

The beauty of SMP connectors is that they are explicitly designed for 
board-to-board applications with substantial tolerance for misalignment.  Each 
board has a male SMP connector, with a female-female "bullet" in between.  
These connectors, with the bullet in between, can tolerate substantial axial 
and radial misalignment (in excess of .010" - basically considerably larger 
than the fabrication tolerances of typical PCBs and PCB assembly) without 
degrading RF performance.  Then one would have one multipin connector for power 
and digital signals that fixes the board-to-board alignment, and the SMP 
connectors can absorb the slack as necessary based on fabrication/assembly 
tolerances for their placement.  

I agree that if we can get suitable performance out of an FMC or other 
single-connector solution, that would be better from a physical simplicity 
standpoint.  We need to test this.  I may try putting together a board to do so 
in the near term.  

> -Original Message-
> From: Sébastien Bourdeauducq [mailto:s...@m-labs.hk]
> Sent: Saturday, March 26, 2016 10:19 AM
> To: Slichter, Daniel H. (Fed) 
> Cc: Grzegorz Kasprowicz ; 
> artiq@lists.m-labs.hk
> Subject: Re: [ARTIQ] FW: initial specification of the project
> 
> On Saturday, 26 March 2016 4:06:17 PM HKT Slichter, Daniel H. (Fed) wrote:
> > The cost savings from using FMC, which might amount to $50 per AMC, 
> > are not worth if the crosstalk will make the cards not useful for 
> > researchers.
> 
> It's not only about cost of the connector - the RF daughter cards will 
> often need some digital signals (e.g. SPI) for control. FMC provides 
> plenty of pins for that. Mixing two different types of board-to-board 
> connectors will cause mechanical problems and I think we should not do 
> that. If two types of connectors are needed, one of them should use cables.
> 
> Sébastien

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Re: [ARTIQ] FW: initial specification of the project

[Slichter, Daniel H. (Fed)]

> FMC has mounting height of 8 or 10mm.
> Other heights are also possible in case of SEARAY series, but one must order
> large number of them Greg

FMC per VITA 57.1 standard is 8.5 mm stacking height or 10 mm stacking height 
(see section 3.4).  You can get the SEARAY connectors (of which FMC compliant 
connectors are a subset) in a variety of other stacking heights too.  

At the end of the day, I really think that something simple and straightforward 
like pin headers is going to work well and will save us a lot of hassle in 
finding specialized connectors/worrying about longevity/connector 
availability/etc.


> -Original Message-
> From: ARTIQ [mailto:artiq-boun...@lists.m-labs.hk] On Behalf Of Slichter,
> Daniel H. (Fed)
> Sent: Tuesday, March 29, 2016 10:39 PM
> To: Robert Jördens 
> Cc: Grzegorz Kasprowicz ; artiq@lists.m-labs.hk
> Subject: Re: [ARTIQ] FW: initial specification of the project
> 
> Let me make clear that I don't have any specific opposition to FMC for the
> power/digital signals.  The only reason for considering other types of
> connectors would be either if the desired stackup height is not doable (this 
> is
> unlikely -- one .224" bullet e.g. corning A1A1-0001-02, plus two male
> connetors with .051" reference plane distance, e.g. Molex 74315-3312, gives
> a total SMP height of 8.28 mm, which works perfectly with the standard FMC
> stackup height of 8.5 mm board to board), or if there is not enough real
> estate on the board to meet the physical footprint requirements (FMC is
> larger than the QSE connectors I sent along, for example).
> 
> > -Original Message-
> > From: Robert Jördens [mailto:r...@m-labs.hk]
> > Sent: Tuesday, March 29, 2016 11:08 AM
> > To: Slichter, Daniel H. (Fed) 
> > Cc: Sébastien Bourdeauducq ; Grzegorz Kasprowicz
> > ; artiq@lists.m-labs.hk
> > Subject: Re: [ARTIQ] FW: initial specification of the project
> >
> > On Tue, Mar 29, 2016 at 5:16 PM, Slichter, Daniel H. (Fed)
> >  wrote:
> > > Yes, FMC could work but it's overkill in terms of pin count; one
> > > might be
> > able to find a smaller footprint connector with fewer pins, which
> > would be advantageous.  Frankly something as dumb and cheap as 2 mm
> > pin headers would do the job.
> >
> > Yes. A pin header would be dumb if there are better suggestions.
> > LPC FMC with 64 single ended signals is definitely not overkill if 40
> > signals is the estimated need. The grounding is unlikely to hurt.
> > There are certainly many other offers. But if there is such a strong
> > opposition to FMC, I would look for something where we can at least
> > expect a long term availability that is similar to the FMC usage lifespan.
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Re: [ARTIQ] FW: initial specification of the project

[Slichter, Daniel H. (Fed)]

Let me make clear that I don't have any specific opposition to FMC for the 
power/digital signals.  The only reason for considering other types of 
connectors would be either if the desired stackup height is not doable (this is 
unlikely -- one .224" bullet e.g. corning A1A1-0001-02, plus two male connetors 
with .051" reference plane distance, e.g. Molex 74315-3312, gives a total SMP 
height of 8.28 mm, which works perfectly with the standard FMC stackup height 
of 8.5 mm board to board), or if there is not enough real estate on the board 
to meet the physical footprint requirements (FMC is larger than the QSE 
connectors I sent along, for example).  

> -Original Message-
> From: Robert Jördens [mailto:r...@m-labs.hk]
> Sent: Tuesday, March 29, 2016 11:08 AM
> To: Slichter, Daniel H. (Fed) 
> Cc: Sébastien Bourdeauducq ; Grzegorz Kasprowicz
> ; artiq@lists.m-labs.hk
> Subject: Re: [ARTIQ] FW: initial specification of the project
> 
> On Tue, Mar 29, 2016 at 5:16 PM, Slichter, Daniel H. (Fed)
>  wrote:
> > Yes, FMC could work but it's overkill in terms of pin count; one might be
> able to find a smaller footprint connector with fewer pins, which would be
> advantageous.  Frankly something as dumb and cheap as 2 mm pin headers
> would do the job.
> 
> Yes. A pin header would be dumb if there are better suggestions.
> LPC FMC with 64 single ended signals is definitely not overkill if 40 signals 
> is
> the estimated need. The grounding is unlikely to hurt.
> There are certainly many other offers. But if there is such a strong 
> opposition
> to FMC, I would look for something where we can at least expect a long term
> availability that is similar to the FMC usage lifespan.
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Re: [ARTIQ] FW: initial specification of the project

[Slichter, Daniel H. (Fed)]

> > OK. Then mixing SMP with something else is fine IMO.

>

> The other connector can well be FMC. We need at least ~40 signals other

> than the analog ones going to the cards. A bunch of different power supplies,

> SPI control lines, identification buses, switching, attenuation settings etc.

> Also since reliably reflowing SMP connectors manually to three hair widths is

> rather tricky, manual assembly is of the table now anyway. And FMC give us

> at least a form factor that has been tested very well. No need to reinvent the

> mezzanine here.



Yes, FMC could work but it's overkill in terms of pin count; one might be able 
to find a smaller footprint connector with fewer pins, which would be 
advantageous.  Frankly something as dumb and cheap as 2 mm pin headers would do 
the job.



Manual assembly was never really one of the major concerns with these 
daughtercards, as many of the desired components are leadless or QFN packages 
with center ground pads, which are tricky for manual assembly anyway, 
especially if one cares about microwave performance.  However, many SMP 
connectors have a through hole design (see below for an example from Corning 
Gilbert, or from Molex at http://www.molex.com/pdm_docs/sd/734153320_sd.pdf ), 
so it's entirely possible to achieve the kind of lateral alignment tolerances 
required with manual assembly.  Cost-wise, the molex part quoted is less than 
$3 apiece on digikey at qty 750 (and $5 at qty 1), so it’s not like these 
connectors will be a major cost driver on the cards either.



[cid:image001.png@01D1899A.9C6CA5F0]
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Re: [ARTIQ] FW: initial specification of the project

[Slichter, Daniel H. (Fed)]

> If 65 dB between neighboring channels is the requirement, then
> comprehensive board level shielding appears to be required.

Yes, this will be necessary.  See my previous emails.
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Re: [ARTIQ] FW: initial specification of the project

[Robert Jördens]

On Tue, Mar 29, 2016 at 11:56 AM, Sébastien Bourdeauducq  wrote:
> On Monday, 28 March 2016 6:30:52 PM HKT Slichter, Daniel H. (Fed) wrote:
>> Thus for the two examples above, using digital connectors with a 9 mm or 11
>> mm total stackup height would give 250 um axial misalignment (.010"), which
>> is a typical tolerance one would want to use anyway with SMP.
>>
>> More information is available in this application note:
>> https://www.corning.com/media/worldwide/coc/documents/applications/microwave
>> ApplicationNotes.pdf
>
> OK. Then mixing SMP with something else is fine IMO.

The other connector can well be FMC. We need at least ~40 signals
other than the analog ones going to the cards. A bunch of different
power supplies, SPI control lines, identification buses, switching,
attenuation settings etc. Also since reliably reflowing SMP connectors
manually to three hair widths is rather tricky, manual assembly is of
the table now anyway. And FMC give us at least a form factor that has
been tested very well. No need to reinvent the mezzanine here.
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Re: [ARTIQ] FW: initial specification of the project

[Robert Jördens]

On Mon, Mar 28, 2016 at 9:14 PM, Slichter, Daniel H. (Fed)
 wrote:
> http://suddendocs.samtec.com/testreports/hsc-report-seam-seaf-07mm_web.pdf
>
> There is too much crosstalk in FMC connectors (~40-65 dB typical @ 3 GHz) for 
> us to use them for the RF/analog daughterboards.  Recommend dedicated RF 
> connectors (typical crosstalk better than 80 dB) for analog signal 
> transmission.

If 65 dB between neighboring channels is the requirement, then
comprehensive board level shielding appears to be required.
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