High Precision Slaved External Clock (HPSEC)
Project description
The aim of this project to upgrade the performance of White Rabbit devices to a level suitable for the Metrology purposes by interfacing the White Rabbit devices to a high precision, ultra stable 10MHz Oven Controlled Crystal Oscillator (OCXO). Metrology institutes may use this Slaved External Clock to make remote copies of their atomic timescales, hence one could also translate HPSEC into High Precision Second.
Ultra stable Oven Controlled Crystal Oscillators typically reach their stability only after a couple of days. Therefor the oscillator is never switched off and has a very clean 12V power supply. A separate 24V input that can connect to an Uninterruptible Power Supply (UPS) to prevent 12V oscillator power-down during a power outage. A buffered copy of the oscillator 10 MHz sine wave is available on three connectors.
The oscillator can be disciplined via Vtune (0-5V) by a DAC which is controlled via an SPI-bus.
The oscillator 10MHz sine wave is fed to two Phase Locked Loop (PLL) Circuits (see Figure 2):
- The first circuit is a Phase Locked Oscillator (PLO) that generates a low phase noise 1 GHz. The PLO is composed of a HMC704 PLL and 1 GHz SAW Oscillator. A divide by 8/(16) creates a 125/(62.5) MHz output clock. White Rabbit devices interface to the High Precision Slaved External Clock via this 125/(62.5) MHz clock output which is disciplined by the 16-bit SPI DAC interface.
- The second circuit consists of a chain of two Phase Locked Loops that generate 100 MHz (HMC1031) and 1 GHz (HMC835). The HMC835 can be initialized to generate an arbitrary (but WR phase locked) frequency.
The SPEC7 is a typical White Rabbit device which can be upgraded with this High Precision Slaved External Clock. The main board contains PCIe connector that fits the SPEC7 and powers the SPEC7 via the PCI bus. High speed D Flip Flops re-sample the 10MHz and 1 PPS signals form the White Rabbit device with the low phase noise 1 GHz clock.
A mezzanine card with a Micro Controller Unit (MCU) serves as a house keeping controller. It has an Ethernet and USB interface. Both Phase Lock Loops (HMC704 and HMC835) can be controlled via the MCU and status information can be retrieved.
All digital interfaces are galvanically isolated from the analog domain to avoid injection of digital noise into the oscilator and PLL circuits.
Figure 1 shows a picture of the 19 inch crate that contains the main oscillator board. The project is currently under development so this is a preliminary picture.
Figure 1: Preliminary view of the HPSEC.
Main Features
Figure 2 shows a block diagram of the HPSEC.
Figure 2: High Precision Slaved External Clock block diagram.
- Power supply system with a separate input for a 12V Uninterruptible Power Supply (UPS)
- ultra stable 10MHz Oven Controlled Crystal Oscillator (OCXO)
- typically used: Morion MV336
Project information
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Official production documentation
- Schematics (Note: Design created with Mentor Graphics using a Xpedition).
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This work is partially funded by the EMPIR 17IND14 WRITE project and the project has received funding from the EMPIR programme co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme.
Contacts
Commercial producers
- The board will be quite expensive and tailored for extreme precision which is usually beyond the specifications needed by ordinary users. Therefor it is not foreseen that the board will be commercially available.
General questions about project
- Guido Visser, Peter Jansweijer - Nikhef
Status
Date | Event |
---|---|
01-07-2019 | Start working on project. Collecting main specifications. |
27-09-2019 | Schematics ready to be reviewed. |
27-09-2019 | Layout started (in parallel). |
14-11-2019 | Schematics reviewed by Peter Jansweijer and Hans Verkooijen (Nikhef). |
28 November 2019