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## The whole board
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[![](/uploads/369b5e642651608cb4aff7b81e7fc982/WholeBoard-small.jpg)](/uploads/6f9f326e441e218162874dad9568cef2/WholeBoard-big.jpg)
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[![](/uploads/a8e8adf16dbc98e8ebaaa87f89e080f8/top_small.jpg)](/uploads/f3d7d01ea75b53cbefadb523371c500f/top_big.jpg)
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On this card will be connected all the future time measurement elements.
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So, the goal of this board is only to convert the analog data in
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numerical ones. As we want the best possible resolution for the ADC, we
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pay extremely attention to the noise generated by other components. This
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On this card will be connected all the future analogue time measurement
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elements. The output of these elements has first to be converted in
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numerical data before being processed: that is where the ADC board comes
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in. As we want the best possible resolution for the ADC, we pay
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extremely attention to the noise generated by other components. This
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board is a carrier card for the
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[MicroZed](http://zedboard.org/product/microzed) board which will be
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used to process incoming data.
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The design schematics are divided into 4 different parts :
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The design schematics are divided into 5 different parts :
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\> \# the two ADC,
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\> \# the clock splitter circuitry,
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\> \# the ADC and the inputs,
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\> \# the clock circuitry,
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\> \# the MicroZed Board connections,
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\> \# the power supply
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\> \# the miscellaneous
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This first picture is only to show the different connections between
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these different parts. In addition to the power lines and data lines, we
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can see the SPI bus between the MicroZed and both the ADC. This bus can
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be used to configure the ADC.
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This first picture, the top level of the schematics, is only to show the
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different connections between these different parts. In addition to the
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power lines and data lines, we can see the SPI bus between the MicroZed
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and both the ADC. This bus can be used to configure the ADC.
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-----
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## The two ADC
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## The ADC and the Inputs
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As the schematics for the two ADC are the same, we only put one of them
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here. The other one is available
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[here](https://www.ohwr.org/project/r19-tdc-del-a/uploads/d4972bdb52d3b358c6df2f48d8250dc1/ADC2-big.jpg).
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The AD9253 is able to sample data at a rate of 125 MHz. Its resolution
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is 14
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bits.
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[![](/uploads/be538d3b15b7d7d3ff8e085a8a8b3b90/ADC1-small.jpg)](/uploads/9ecece2c4a642460784a03269e83037a/ADC1-big.jpg)
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[![](/uploads/d167fc7519b5a77a27b03ad150ded720/adc_small.jpg)](/uploads/9220efeb3bf4382a369f8e56e77976a6/adc_big.jpg)
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We have two inputs for each ADC. On each input are one SMA connector for
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ground referenced signals and two others for differential ones. All
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inputs have an impedance around 50 ohm on a two decades bandwidth
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(200kHz to 20MHz).
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The AD9253 has four inputs. On the previous verion of the board, we
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chose the AD9645 which has more or less the same properties. This one
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has only two channels. Using two ADC, even if they are synchronized with
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the same sampling clock, may increase the error jitter on the
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measurements. It is in order to reduce this jitter that we finally chose
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to use the AD9253.
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A particular attention is given to the power supply decoupling. Multiple
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capacitors with multiple values are placed to reduce the impedance on a
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large bandwidth and then avoid the noise to disturb the measurements.
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This has been done as well for the analog power lines as for the digital
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ones. To have the lowest ESR and the highest SRF, we only use ceramic
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capacitors (C0G/NP0 when possible, otherwise we use X7R).
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ones. To have the lowest ESR (Equivalent Serie Resistor) and the highest
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SRF (Self Resonant Frequency), we only use ceramic capacitors (C0G/NP0
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when possible, otherwise we use X7R).
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All the resistors are in metal film to give the best performance (less
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noisy, lower temperature coefficient).
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noisy, lower temperature
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coefficient).
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The clock signal arrives from the splitter on a differential
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line.
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[![](/uploads/ff0184d8ed14950ebb4fc10887e18612/input_small.jpg)](/uploads/9b129d4588dcb549e918033d284f5128/input_big.jpg)
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On each input are one SMA connector for ground referenced signals and
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two others for differential ones. All inputs have an impedance around 50
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ohm and a bandwidth of 400 kHz to 175
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MHz.
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-----
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## The clock splitter
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## The Clock Circuitry
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[![](/uploads/a52c62fec5d5b09e185621ca93c64524/ClockSplitter-small.jpg)](/uploads/ad68744d2997997adbbf77a926ebbb46/ClockSplitter-big.jpg)
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[![](/uploads/00a105a2dd37bdf7aace13b4fdb679b0/clock_small.jpg)](/uploads/8874a5702ef84095073fb253c23bee6d/clock_big.jpg)
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This part is used to synchronise both the ADC by giving them the same
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clock signal. This clock splitter allows us to use different clock
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frequencies in a range from 5 MHz to 125 MHz. This component can also
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filter the input clock signal. The parameters of the filter can be set
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using the `FILTA` and `FILTB` inputs. To be able to change the filter
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and to adjust it to our needs, we put these inputs on
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By default, the sampling frequency is 100 MHz given by the local
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oscillator. Another frequency can be set using an external oscillator.
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By this way, we can set the frequency in a range from 5 MHz up to 125
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MHz.
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The clock splitter (LTC6957) is used to send the clock signal both to
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the ADC and to a trigger (see miscellaneous part). . This component can
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also filter the input clock signal. The parameters of the filter can be
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set using the `FILTA` and `FILTB` inputs. To be able to change the
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filter and to adjust it to our needs, we put these inputs on
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jumpers.
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-----
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## The power Supply
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[![](/uploads/fae232a9cd87431b8b132382262a27a8/PowerSupply-small.jpg)](/uploads/2870c6f8c043692b5f6da0a46030adce/PowerSupply-big.jpg)
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[![](/uploads/e929b88be82a7cc5b2f4553797e06a69/power1_small.jpg)](/uploads/34cbcc1afa0aa6a6e0362bde9881319b/power1_big.jpg)
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We need enough power to supply all the components on the board but also
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the MicroZed board. Furthermore, these components needs different
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voltage levels.
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the MicroZed board. Furthermore, these components need different voltage
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levels.
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The first stage is a buck converter. It is used to convert the voltage
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from 12 V to 5V DC. These 5 V are needed by the MicroZed board. We then
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convert these 5 V in a 3.3 V one. This last is used to supply the clock
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splitter. Finally, two LDO are used to regulate the digital and analog
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power supplies of the ADC.
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from 12 V to 5V DC. These 5 V are needed by the MicroZed board.
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We put two different connectors for the power : a DC barrel jack and a
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MINI DIN 4. To be sure to have the right voltage polarity, we put a
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... | ... | @@ -112,19 +122,46 @@ converter, we decided to use different values to catch the high |
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harmonics and then improve the noise
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rejection.
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[![](/uploads/df06807ebf1d165facf32721eb8124f7/power2_small.jpg)](/uploads/61a2cf211895bcf4de5496a649b6640d/power2_big.jpg)
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We then convert these 5 V in a 3.3 V one. This last is used to supply
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the clock splitter. Finally, two LDO are used to regulate the digital
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and analog power supplies of the
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ADC.
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-----
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## External connections
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[![](/uploads/165d0de00a4b0e7dfa01a2de62245bcb/FCI-Small.jpg)](/uploads/bfb5ed7b77ab47591077dcf598819075/FCI-big.jpg)
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[![](/uploads/727841d84385ae27bc1cf51f62d36d2e/connections1_small.jpg)](/uploads/c53bdb22f6e8c398a8641539df607df5/connections1_big.jpg)
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The connections to the MicroZed board are done via its FCI connectors.
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All these inputs can be configured to work in LVDS. As the outputs of
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our ADC are already in LVDS, this configuration fits ideally with our
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project.
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There are two connectors. Only one is represented here. The [other
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connector](https://www.ohwr.org/project/r19-tdc-del-a/uploads/6841e4bd942c7a6d0e9700829c390d6d/connections2_big.jpg)
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is powered with the 3.3V and is used to communicate with the components
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in the miscellaneous part and the external GPIO ports.
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In addition to these connections to the ADC, we also provide the board
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other connections to be able to use the other MicroZed GPIO.
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other connections to be able to use the other MicroZed
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GPIO.
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-----
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## Miscellaneous
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[![](/uploads/ddd128b75f8885d37a1683e789c03316/misc_small.jpg)](/uploads/e1abc2d9aa7ad2e376f8cff41f9fe754/misc_big.jpg)
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Some other components have been added to the board. First, we have the
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trigger. This trigger is used to send a clock synchronized signal to an
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external device. We also have a thermometer to be able to measure the
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card temperature. This chip has also a unique ID and allow to make the
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difference between similar boards.
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-----
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Nicolas Boucquey 19th of October 2016
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