100 MHz In The Loop V1.0¶

Project description¶

General¶

Figure 1 shows a preliminary picture of the 100MHzInTheLoop PCB.

Figure 1: Preliminary picture of the 100MHzInTheLoop PCB

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Figure 2 shows a block diagram of the 100MHzInTheLoop board.

Figure 2: A Block diagram of the 100MHzInTheLoop board

This Board contains a 100 MHz high precision low phase noise OCXO. The oscillator can be used as an external high precision oscillator for White Rabbit (WR) applications that need to generate low phase noise clocks.
The OCXO can be tuned via a DAC. The 100 MHz output of the oscillator is the reference for a PLL (LTC6950) that has a low phase noise 1 GHz Surface Wave Acoustic (SAW) VCO.
The PLL needs initialization via SPI. Therefore the SPI bus is connected to a Spartan-7 FPGA such that the firmware implementation of this FPGA can either feed forward an external SPI bus or drive the SPI bus stand alone via a MicroBlaze implementation.

The PLL generates a 125 MHz clock that is used as WR reference clock. It can also generate 10 and 100 MHz clock that are used in the Virgo demonstrator and ET-Pathfinder. An auxiliary frequency can be generated as well.

Lock-Sweep¶

In the current WR implementation (wr-cores v4.2) it is not possible to phase align the 100 MHz OCXO with the WR master. The WR phase aligned clock exists in the WR FPGA implementation and can have 5 arbitrary phase offsets w.r.t. the 100 MHz OCXO. It is planned to update WR with "lock-sweep" (wr-cores v5) which enables the external high precision OCXO to be phase aligned with the WR master.
For the time being the 10, 100 MHz and PPS signals are generated by the WR implementation. The phase noise quality of these signals is enhanced by re-clocking them with a clean 1 GHz signal from the PLL.

Design details¶

• Schematics (Note: Design created with Mentor Graphics using a Xpedition).
• Manufacturing files 11500.04.02 100MHzInTheLoop (Note: Design created with Mentor Graphics using a Xpedition).
• Repository containing firmware/software implementation for Spartan-7 MicroBlaze"

Older versions¶

• 100MHzInTheLoop_V1.0

Contacts¶

General questions about project¶

• Guido Visser -Nikhef
• Peter Jansweijer - Nikhef

Status¶

Date	Event
29-09-2020	Initial Meeting with LAPP.
17-03-2021	Start working on project. Collecting main specifications.
15-10-2021	100 MHz In The Loop ready for production.
15-11-2021	After survey of quotes; 4 boards ordered.
07-02-2022	4 boards received.
23-02-2022	100MHzInTheLoop operational with SPEC7 + FMCBreakout_extended.

05 October 2023