Mounting
Components needed to mount the board
The following components are needed to mount the board correctly:
-
SAMTEC QSS-025-01-L-D-A (http://fr.farnell.com/samtec/qss-025-01-l-d-a/connect-rcpt-50-voies-2-rangees/dp/2504993) or QSS-016-01-L-D-DP
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U.FL connector (http://fr.farnell.com/hirose-hrs/u-fl-r-smt-01/embase-u-fl/dp/3908021)
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U.FL to SMA cable 150mm (http://fr.farnell.com/multicomp/r-132g7210150cc/cable-u-fl-sma-150mm/dp/1699242)
-
U.FL Cable (http://fr.farnell.com/hirose-hrs/u-fl-2lp-088k1t-a-150/cable-plug-plug-1-37mm-150mm/dp/1688073)
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2x M3 25mm screw
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2x M3 12mm screw
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4x 5mm spacer
The board mounted
Instructions to mount the SAMTEC connector
The SAMTEC connector has been mounted with 100% success rate on the WRS PCB. The trick is to use an heat gun and to cover with aluminum foils all the board except the bottom of the board, under the connector. When using the heat gun, a slight smoke can arise from the SAMTEC connector, which it's fine.
Instructions to mount the U.FL connector on the WR Switch board
Remove the VM53S3 oscillator and then place an U.FL connector, as show
by the following image
WARNING*: since the U.FL connector is soldered on the pads of the
VCXO, it has weak mechanical strength. Do not attempt to remove the
U.FL cable when mated to the U.FL connector. Remove the soldered U.FL
connector from the PCB. If you try to remove the U.FL cable when mated,
you'll likely rip-off the PCB pads
https://www.ohwr.org/project/wrs-low-jitter/uploads/c29e1cf16d099fabc200ce5f5600bce6/ufl_vctcxo.jpg!
Instruction to mount an OCXO
If the client request an OCXO, the resistor R10 must be removed and R11
must be soldered. This is because the 3.3V of the VCTCXO is provided by
a 150 mA LDO. An OCXO must be powered with the general 3.3V LDO.
A current up to 1A can be used by the OCXO.
Instructions to set the jumpers
There are two sets of jumpers on the board, as shown in red on this picture:
- SW1, SW2 & SW3: these jumpers – also named ID0, ID1 and ID2 respectively – are located in the top left corner of the daughterboard. Their purpose is to indicate the main carrier board what is the frequency of the oscillator (OSC1 / OSC2) mounted on the daughterboard. Because there are no pull resistors connected to these three lines, it is mandatory to place the jumpers. By default, the oscillator frequency is 20MHz (ID0 = 1, ID1 = 0, ID2 = 0). The different configurations are listed below:
ID0 (SW1) | ID1 (SW2) | ID2 (SW3) | Frequency |
---|---|---|---|
0 | 0 | 0 | 10MHz |
1 | 0 | 0 | 20MHz (default) |
0 | 1 | 0 | 25MHz |
1 | 1 | 0 | 50MHz |
0 | 0 | 1 | 100MHz |
- SW4 & SW5: these jumpers – also named FILTB and FILTA respectively – are located in the bottom right corner of the board. Their purpose is to control the input bandwidth of the early amplifier stages of the low phase noise output buffer (IC8 – LTC6957-2). For slow slewing signals, substantially lower phase noise is achieved by using this feature. Bandwidth limiting is useful because it limits the impact of all of the spectral energy that will alias down to (on top of) the fundamental frequency. The best filter setting to use for a given application will depend on the clock frequency, amplitude, and waveform shape, with the single biggest determinant being the slew rate at the input of the LTC6957. For more information, see LTC6957 datasheet, p.23 and p.24, section “Input Filtering”. Because there are no pull resistors connected to these three lines, it is mandatory to place the jumpers. By default, the input bandwidth is set to 160MHz (FILTB = 1, FILTA = 0). The different configurations are listed below:
FILTB (SW4) | FILTA (SW5) | Bandwidth | Input Slew Rate (V/µs) |
---|---|---|---|
0 | 0 | 1200MHz (Full Bandwidth) | >400 |
0 | 1 | 500MHz (-3dB) | 125 to 400 |
1 | 0 | 160MHz (-3dB, default) | 40 to 125 |
1 | 1 | 50MHz (-3dB) | <40 |
26 December 2016