The aim of this project is 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 10 MHz Oven Controlled Crystal Oscillator (OCXO). Metrology institutes may use the HPSEC to make remote copies of their atomic timescales, hence one could translate HPSEC into High Precision Second.
Ultra stable Oven Controlled Crystal Oscillators typically reach their stability only after a couple of days. Therefore 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 front panel 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 3):
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 or 16 creates a 125/62.5 MHz output clock. White Rabbit devices interface to the HPSEC 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 frequency locked to WR.
The SPEC7 is a typical White Rabbit device which can be upgraded with this HPSEC. 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 ARM-M4) 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 oscillator 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: HPSEC.
Figure 2: HPSEC Front Pannel.
Figure 3 shows a block diagram of the HPSEC.
Figure 3: High Precision Secondary External Clock block diagram.
Power supply system with a separate input for a 24V Uninterruptible Power Supply (UPS)
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.
The board will be quite expensive and tailored for extreme precision which is usually beyond the specifications needed by ordinary users. Therefore it is not foreseen that the board will be commercially available.