Ground trampolines and Phase Locked Loops

A customer was using the UPduino v2.1 low-cost Lattice iCE40 FPGA board in their prototype to check out some IP in the FPGA. This IP required the use of a Phase Locked Loop (PLL) within the FPGA to generate specific frequencies that the design required.

The customer reported that the FPGA PLL was going out of lock intermittently.


Phase locked loops are useful blocks (and there is one in the Lattice iCE40 UP5K FPGA) used to generate specific clock frequencies that may not necessarily be an integer multiple of a reference clock. The principle of operation is covered very well in this Wikipedia article.

The UPduino 2.1 is a low cost FPGA board thats designed for fast prototyping. The board has a couple of voltage regulators, an FT232H USB to SPI bridge, flash for FPGA code storage and supporting passives. The board is laid out on 2 layers.


Test Case

I was able to duplicate the failure mode on my setup which consisted of an UPduino connected to the customers test board. By a process of elimination, I was able to get the PLL to fail with an FPGA design consisting of the PLL, an output clock from the PLL, a GPIO input and an LED output from the FPGA. This rather minimal design exhibited the symptoms described by the user in a significantly more complex design.

On to Debug

Now that I had the test case, it was time to delve deeper: why would such a simple design cause the PLL to lose lock and that too by toggling a switch to the FPGA! This strange behavior was also not consistent: pushing the switch would intermittently cause the PLL to go out of lock. There didn't appear to be any pattern to the behavior either.

I was also able to eliminate the customer board as the source of the issue. I checked all DC power supplies on the UPduino and customer board with a multi-meter, things looked good. Searching online gave me a hint on what to pursue next, (isn't information sharing a wonderful thing!) ie. clock quality and board layout.

From my experience, I knew that PLL's were finicky analog creatures and had to be cared for by low jitter input clocks and proper filtering of the power supply.

A simple change I made was to source a clean 12MHz clock from an external crystal instead of using the on-board resonator which has poor phase noise in comparison. This seemed to reduce the probability of PLL unlocking but didnt make the issue go away.

Power and Ground

The dedicated power supply on the PLL and the ground near it looked good with about 10-15mV of digital noise, not too bad. Its important to follow proper probing guidelines when making such measurements!

I probed the DC voltages and noticed a substantial noise of >50mV or so on the supplies. This was significantly reduced by adding 10uF caps on the LDO's. However, this didnt seem to improve the probability of the PLL losing lock.

I then measured the ground plane from one end of the board to the other. I was shocked to see huge spikes on the ground plane! This meant that the various circuits on the board had a different view of what they considered a reference.

The UPduino is a small board, about 2.2cm x 5.1cm. Having the ground plane be different by hundreds of mV across such a small board, that too with such a simple design on the FPGA, not consuming much power seemed to indicate something was very wrong!

I analyzed the board layout in Eagle and noticed that the Ground plane was routed on the bottom side as follows:

The solid filled areas are the ground plane in the above picture. As you can see, the ground plane is split into multiple discrete sections, never a good idea! This gave me a good idea of what to try next. I used copper braid to short across various sections of the ground plane and was able to get the noise down significantly. More importantly, this correlated well with a decreasing probability of the PLL failing to lock. A good indication that I was on the right track.

Unfortunately, all the hacking was not able to restore a reliable PLL lock on this board. Needless to say, the customer was unable to use this board for their design as the board design was to blame.

Next Steps and a New Beginning!

I had inherited the design from the original manufacturer/designer. This experience, as well as the feedback from users about various features missing from the UPduino, got me thinking about coming up with the next generation of the board.

UPduino 3.0!

I kicked off the next generation: the UPduino 3.0, with a goal of not just fixing the layout but adding significant features as documented on this GitHub site.

The ground plane on the UPduino 3.0 is a solid plane with no cuts. This was a hard requirement on the layout. The power plane does have some cuts but shouldn't be too significant as shown in the plots below. A detailed review was done to ensure that power and grounds had sufficiently thick traces and decoupling caps were placed close to the pins being decoupled. A 0.1uF/4.7uF capacitor combination was settled on as a standard decoupling strategy. Going to a 4 layer board made the design implementable: it was clear during routing of this board that the original design with 2 layers was simply not feasible and a bad design choice in the first place. The extra cost of going to 4 layers vs. 2 layers was simply not worth the risk.

UPduino 3.0 ground plane

UPduino 3.0 power plane

The first version of the design is now complete and will be fabricated soon with a high expectation that the PLL will lock!

If you would like to be involved, please feel free to browse Discourse and/or join the Discord channel!


  • download free full games for pc hidden objectsfree google pc games downloaddownload tema pc windows 10computer pc game free downloadwindows virtual pc download for windows 10best browser for windows 8 pc free downloadadobe photoshop cs3 download for windows 10vlc media player windows xp latest version free download freefree download windows 10 for dell laptopdownload windows 7 isos free
    [url=]ace of spades battle builder free download pc
    [url=]elite dangerous pc game download
    [url=]coloring games download for pc
    [url=]download cisco anyconnect vpn client for windows 10 free
    [url=]facebook for pc windows 7 free download filehippo
    [url=]download windows 10 version 1709 free
    [url=]download unlocker for windows 8.1 free
    [url=]emacs download for windows 10
    [url=]download kaspersky for windows 10 free
    [url=]download rdpwrap windows 10 pro
    free windows download 7 free
    download photoshop cs4 for windows 10
    download itunes 64 bit for windows 10 latest version
    itunes 10 64 bit free download for windows
    mcafee free download for windows 10 full version

    download windows 10 november 2019 update
    epson es-400 driver download windows 10 free
    chrome app launcher free download for pc
    logitech software download windows 10
    download a free vpn for windows 10

    best action and adventure games for pc free download
    directx 11.2 download windows 10
    amd radeon r3 graphics driver download windows 10
    cuphead game pc download free
    command and conquer ultimate collection windows 10 free download

    download minecraft laptop windows 10
    download car game for pc full version free
    big mutha truckers free download pc
    download windows vista windows xp free
    download windows 10 64 bit free for pc

    itunes for windows 10 pro 64 bit [/url] asio driver download windows 10 [/url] wallpaper download for windows 10 [/url] oracle 8i setup for windows 10 [/url] dalmatians pc game free download [/url] maps windows 10 download free [/url] file player free download for windows 7 free [/url] office download free windows 7 free [/url] easy games download for pc [/url] windows 8.1 for pc 64 bit [/url]
  • windows mobile 6.5.3 os download free100 in 1 games free download for pcrome total war free download full game pc windows 7mobile intel 965 express chipset family driver download windows xp freeacer empowering technology framework 3.0 windows 10 downloadindesign free download windows 10microsoft freecell download windows xp freecandy crush soda saga game free download for pc framework 2.0 free download for windows xp 32 bit freecod modern warfare pc free download
    [url=]jre 1.6 download windows xp free
    [url=]realvnc viewer free download for windows 7 free
    [url=]download fighting games free for pc
    [url=]windows desktop calculator download free
    [url=]dollhouse pc game download
    [url=]dx10 download for windows 7 free
    [url=]gba emulator for pc windows 10 free download
    [url=]can you escape game free download for pc
    [url=]download asphalt 8 for pc windows 10
    [url=]free download final fantasy xiv full version game pc
    chaos faction 2 download free for pc
    ps3 remote play pc windows 10 download
    gmail pc download windows 10
    download windows mediaplayer classic free
    easy driver download windows 10

    new windows free download free
    download shopee for windows 10
    hp pavilion dv9000 drivers for windows xp free download free
    gta vice city for pc windows 10 free download
    windows 7 home basic 64 bit download free

    pc junk file cleaner for windows 10 free download
    windows movie maker free download for windows free
    gta 5 download pc windows 7 ultimate
    freestyle street soccer pc game free download
    kies 3 download for windows 7 free

    logitech options download windows 10
    windows loader 2.2.1 free download free
    download pale moon for windows 7 free
    free download microsoft chess titans game for windows 8 free
    decklink mini recorder driver windows 10 download

    dll download for windows 10 [/url] audition free download windows 10 [/url] download windows 10 64 bit [/url] flipper free download windows 10 [/url] latest internet browser download for windows xp free [/url] net framework 1.1 windows 10 [/url] flash cs6 free download full version for windows 7 free [/url] download windows xp free [/url] download wamp server for windows 10 64 bit [/url] cpu meter windows 7 free [/url]
  • quote auto insurance
    auto insurance agent
    get car insurance quote
    get car insurance quotes
    car insurance near me

  • asus p4p800-vmwhat is ai suite iigrow castle gold castlehotspot shield 7.4.6 crackati firegl v7200 driver windows 7 64 bitsamsung chronos 7 driversgames4theworld bestgoo t18086 sims ultimate fixepson workforce 325 driveruniversity of arkansas computer storestand of food 2
    the crew wild run motorcycle

    the last weekend game download

    the clipboard can store up to 36 text items.

    windows xp daylight savings patch

    dell inspiron one 2330 drivers

    windows 10 anniversary update failed to install

    intel 4400 graphics driver

    sound blaster omni driver

    call of duty ghosts achievements

    riders of icarus hack

    netgear fa310tx driver windows 7
    ffx-2 save editor pc
    final fantasy x cheat table
    panda internet security 2016 key
    battlefield 4 squad join not working ps4

    monster hunter end game
    canon ir adv c5240 drivers
    intel 1217-lm
    skyrim assassin mod armor
    alienware x51 bios update

    7601.17514 101119 1850_update_sp_wave1 grmsp1 1_dvd
    sharp blu ray player update
    asus p8b75 m csm drivers
    amd radeon hd 6550d
    how to play mmf files

    boom beach cryo bomb
    asus m5a99fx pro r2.0 driver
    engenius 802.11n wireless usb adapter
    dap-1650 firmware
    samsung note 7 ebay

    two worlds 2 trainer

    nvidia gtx 560m drivers

    dvdfab converter not working

    d-link wua-2340 driver windows 7

    halo wars collector’s edition

    angry birds airfield chase 30

    what is an hp wireless button driver

    hp stream 7 drivers

    moultrie m990i gen 2

    how to update skyrim xbox 360

  • amd radeon hd 7540d drivercth-490/kshadowrun dragonfall essence cheathalo 4 preorder bonusfootball manager 2015 transferwindows xp high cpu usagepioneer avh-x2700bs firmware updatethemer launcher hd wallpaperm5a97 le r2.0 cpu supportmsi 760gm p23 fx
    terrarium tv 1.8 6

    nvidia geforce 9500 gt driver windows 10

    injection moulding cycle time calculations

    gigabyte z97m-ds3h

    amd radeon hd 8670d drivers

    mad games tycoon trainer

    i’m scared of girls

    window mobile 6.5 downloads

    amd smbus driver update failed

    mushkin ssd firmware update

    presonus universal control not working
    samsung xpress m2825dw driver
    toshiba satellite c55 bluetooth
    how to update firmware on canon 5d mark iii
    intel me driver not installingзаработок для новичков/

    amd radeon software crimson edition 16.3.2
    rocketfish bluetooth adapter driver
    gateway camera assistant software download
    samsung xpress m2825dw driver
    tsstcorp cddvdw sh-224fb

    ffx remaster cheat table
    amd hd 6310 driver
    the powder toy controls
    ga-z170-hd3 ddr3
    cod aw all royalty guns

    dota 2 roshpit champions
    laserjet 1012 windows 7
    ga 970a ds3p drivers
    heroes of the storm kael’thas bug
    gigabyte z270 gaming k3

    graphic accelerator for windows 7

    cisco powerline av utility

    standard dual channel pci ide controller driver windows 7

    epubor vitalsource downloader crack

    deus ex directx 10

    ms comfort keyboard 5000

    samsung blu ray player bd d5300

    broadcom netlink gigabit ethernet driver windows 7 64 bit

    zte zmax 2 marshmallow

    google play services 12.6.88


Leave a comment