SEPTENTRIO mosaic Series, Руководство по оборудованию

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Pinout and I/O Description
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4.7 Clock Frequency Reference
The module can use its internal TCXO frequency reference, or can accept an external
frequency reference, bypassing the internal TCXO.
Pin Name Type Level Description Comment
REF_I Clk 0.5-1.7Vp-p Main frequency reference input, DC-decoupled, input capacitance
is 8 pF See section 4.7.2.
REF_O Clk 1.2Vp-p Frequency reference output from the internal TCXO See section 4.7.1.
2V8_OUT P,O 2.8V 2.8V supply output for the internal TCXO. Do not power any external device from
this pin. It is only intented to connect
to 2V8_IN.
2V8_IN P,I 2.8V 2.8V supply input for the internal TCXO. Typically connected to
2V8_OUT.
VTUNE I Reserved Leave unconnected.
4.7.1 Using the internal TCXO
To have the module run on its own TCXO:
•
REF_I must be connected to REF_O (those pins are next to each other);
• 2V8_IN must be connected to 2V8_OUT (those pins are next to each other). Do not
use the 2V8_OUT for another purpose and do not apply another 2.8V supply to
2V8_IN than the one from 2V8_OUT.
The 10-MHz signal from the internal TCXO is available at the REF_O pin, with peak-to-peak
amplitude of 1.2V. The waveform is illustrated in the oscilloscope screen capture below.
4.7.2 Using and external frequency reference
To use an external frequency reference:
•
2V8_IN must be tied to ground
• REF_O and 2V8_OUT are not used and should be left unconnected
•
The 10-MHz reference must be fed into the REF_I pin. It is preferably a sine wave
or a band-limited square wave. If CMOS or LVTTL signals are used, it is
recommended to filter them at the source with an RC filter with a pole near 100
MHz. The level at the REF_I input has to be between 0.5 and 1.7 Vp-p. If a higher
signalling voltage is divided with a resistive divider, the impedance level shall be