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# Improvements after first design review
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Following the design and layout review, we were lead to put some
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modifications on the design. Here is explained how we handled the
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different remarks.
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# Detailed comments on schematics
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## General remarks
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- Avoid crossing the wires (use labels)
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- *Done*
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- OHL text in all corners of the pages. Put it on all pages in the
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same place.
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- *Done*
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- Each symbol should be the precise order number. Now clock splitter
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is only in a note that should use -1 version
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- *Done*
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- Add a thermometer to be able to control the temperature influence
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- *Done. Is there any pieces of VHDL code for the DS1BB20U+ ?*
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## Sheet 1 : ADC Board
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- Avoid using the bus connections on the main hierarchical page. It is
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better to make them on the sub-page and then to route the bus on the
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main page. That makes the connections easier to read.
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- *Done*
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- Put connectors on that page
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- *Done. Only for the "analog" inputs. Not for the power supply
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inputs*
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## Sheet 2: Power supplies
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- Add the nominal current at the input
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- *Done. Would probably be around 1A-1.5A depending on the
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microZed and the number of input used.*
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- Capacitors marked Cin1-Cin11 and Cout1-Cout10. Number normally (C1
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etc). Same for Rset1, Cbias1 etc.
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- *Done*
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- Comment Vout (MAX) = -\> Vout =, should remove the "MAX" or should
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be a min value also
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- *Done*, for further informations see the "Realisation of a low
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noise acquisition board : design choices"
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- Specify PGFP = IN: “power good and fast start-up functionalities are
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not needed”
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- *Will be taken into account for the next design*
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- How are heatsinks fixed?
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- *This [application
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note](http://www.farnell.com/datasheets/1581390.pdf) gives some
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indications about the heatsink footprint*
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- Put a figure of the used heatsink on the schematic
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- *Done*
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- Put a comment on for the two bridges
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- *Done*
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- Use symbol of Schottky diodes, while likely use normal ones.
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- *According to us it is already the symbol of the Schottky
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diodes*
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- Specify Diodes used.
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- *Already in the detailed schematics PDF. Will be put in the not
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detailed schematics PDF for the next design*
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## Sheet 3 & 4: ADC and inputs
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- Add TVS on all inputs
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- *We have not found a TVS with a capacitance low enougth, we will
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rely on the diodes inside the ADC*
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- As the input are always the same circuit, make an hierarchical page
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for them.
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- *Will be taken into account for the next schematic*
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- What is the signalling rate of the ADC digital output? Mention in
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comment on schematics page. Is that compatible to the max rate of
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the MicroZED?
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- *Unfortunately, with the new ADC, the sampling rate must be
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bellow 118 MHz to be compatible with the rate of MicroZed. This
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is the worst-case value*
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- Remove the labels for the same net (AVDD1-AVDD6)
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- *They are changed on text now*
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- Resistor values marked as 30E, 200E, 49E9 -\> 49R9, 30
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- *Done*
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- Over-design of decoupling. Make it simpler, 10nF not needed. But
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suggest to add an inductor. (Cf. ADC100M: just two 100nF and 4.7uH
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inductor: 67.7 dB, 70.8 dB, 72.2 dB (@ */-50mV,*/-0.5V, +/-5V range)
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measured, while it has 4 channels and full front-end. AD9645 spec:
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SNR = 74 dBFS (to Nyquist).)
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- *We will probably do two different cards with different
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decoupling scheme to be able to see the influence of decoupling*
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- Specify input range
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- *Done*
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- Specify transformer type and tell which winding ratio.
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- *Already in the detailed schematics PDF*
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- Why 30 Ohm and not 33 Ohm as specified in datasheet on VINA/B?
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- *These resistor have to be in Metal Film (less noisy). We have
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not found them in 33 ohm. That is why we use 30 ohm instead. The
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input impedance is a bit modified but still acceptable*
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- Why not use a 4-channel ADC so that there can be no skew problems?
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- *The biggest change for the new design*
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## Sheet 5: ADC Clock splitter
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* **As we have decided to use an other ADC with 4 input channels, we
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no longer need a clock splitter circuit. However, the LTC6957 is now
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used as a clock driver.**
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- Note of version IC: add below component.
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- *Done*
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- Max speed 300 MHz, specify on schematics
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- *Done*
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- Repeat table of input filter. Tell what are the default settings.
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- *Done*
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- J1 not specified what type of connector.
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- *These connectors are jumpers. The references are added*
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- As want to sample with 125 MHz, and max 300 MHz on splitter, may
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possibly limit.
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- *The ADC only needs a clock signal of 125 MHz if we do not use
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the internal clock divider. As we have decided to use a high
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quality 125 MHz clock at the input, this feature is not used and
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we do not use a clock input greater than 125 MHz*
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- Why no local clock oscillator and require a stable external one? Add
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one.
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- *Done*
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- Use a power splitter instead of a clock splitter IC
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- *The component is not used as clock splitter anymore*
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- Link the filter inputs to vcc using pull-ups to have a default
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configuration
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- *I preferred to connect them to the ground to get the maximum
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cut off frequency*
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## Sheet 6: Connections to the MicroZED board
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- What are all L1-L6 etc? Not specified.
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- *Already in the detailed schematics PDF. Will be put in the not
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detailed schematics PDF for the new design*
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- Why are the double labels for? Makes schematics look weird.
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- *These labels are there to be able to show the connections
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between the ADC and the MicroZed on the main hierarchical page
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but also to be able to connect these pins to the external
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connectors at the same time. This has been removed for the new
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design*
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- Maybe add some buffers between the ADC and the FPGA
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- *We will not add some buffer between the ADC and the FPGA. These
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buffer would isolate the ADC from the noisy MicroZed,bu this
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would complicate the design*
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## Sheet 7: Connections to the MicroZED board 2
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- 10nF not of much use as connectors to it. Better have 10uF as is
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consuming a lot and may have large peaks
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- *Done*
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- Why comment PG\_MODULE?
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- *this pin can be connected to a LED to tell the user the startup
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sequence is finished. This pin has been linked to a LED in the
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new schematics*
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- Banks that are not used for the ADC should be connected to the 3.3 V
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instead of 1.8 V (more common)
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- *Done*
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- Add a reset switch on the pin CARRIER\_SRST (see carrier card
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datasheet)
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- *Not usefull, there is also a restart button on the MicroZed
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itself*
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- Add a note concerning the MicroZed compatibilities
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- *Done. The prototype will be realised with the MicroZed*
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## Sheet 8: Connectors on the side of the board
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- Remove some GPIO connections (40 pins are enough)
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- *Only the GPIO for the bank 35 are provided (powered with 3.3
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V)*
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- Put the GPIO connectors to be compatible with designs done for the
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MicroZed [GPIO carrier
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card](http://zedboard.org/sites/default/files/documentations/IOCC_HW_UG_1p2.pdf)
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- *These connectors using the same connectors as the IO carrier
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card ones. Unfortunately, we only provide the connectors for the
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bank 35. The bank 34 is used for the ADC is powered with 1.8 V*
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# Bill of Materials
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- Made by hand and not extracted from schematics. Prone to errors when
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modifying.
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- *Done by hand but corrected using the BOM list export from
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Kicad*
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- Missing manufacturer name
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- *Will be taken into account for the next design*
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- Very expensive components used everywhere. Almost 100 Euro on C and
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R alone.
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- *Will be taken into account for the next design*
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- Really 0.1% needed?
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- *Not everywhere, this remark will be taken into account for the
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next design*
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- 16 C values (for the ADC100M only 12 C values, and has a full
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front-end) (R: 9 types, for the ADC100M : 18, so is good)
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- *Will be taken into account for the next design*
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- MicroZED should likely be put on BOM
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- *Will be taken into account for the next design*
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- Why two types of SMA?
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- *We need two types of SMA : for the connectors at the edges of
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the board : these connectors are horizontal, and for the
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connectors which are in the middle of the board (these are
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vertical)*
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- Prices, have fixed two digits (69, 4.6, 0.58)
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- *Will be taken into account for the next design*
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# Comments on the layout
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- Avoid small angles while crossing the tracks (better to cross with
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90°)
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- *Will be taken into account for the next design*
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- Avoid to cross the power junction with the differential tracks
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(local impedance mismatch)
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- *Will be taken into account for the next design*
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- Put the decoupling capacitors on the top of the board if possible.
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- *Will be taken into account for the next design*
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- Bigger distance between the SMA connectors to be able to screw the
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male connector easier
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- *Will be taken into account for the next
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design*
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# Other Comments on the written documentation: "Realisation of a low noise acquisition board : design choices"
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- Missing name of author.
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- *Will be corrected as soon as possible*
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- Choices not made clear (The minimum specifications are 12 bits with
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an LVDS output.)
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- *Will be taken into account for the next design*
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- Texas InstrumentS, some French words used, some typos (MicroZeb
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Board)
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- *Will be corrected as soon as possible*
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