Abstract

Abstract Within the Helmholtz Validation Fund Project "MicroTCA.4 for Industry", DESY together with collaboration partners from industry and research developed a compact fully MicroTCA chassis-integrated local RF oscillator module. The local oscillator and clock generation module generates a low noise local oscillator out of the global reference that is distributed over the accelerator. The module includes a splitting section which provides 9 local oscillator signals which are distributed over the RF-Backplane to the rear-transition modules. Similarly, the clock signal is also generated out of a single reference input by means of low-noise dividers. The clock is then fan-out to 22 differential lines that are routed over the RF backplane to the rear-transition modules. The functional block is implemented such that it fits in the rear slots 15 and 14 of a standard MTCA.4 crate. In the paper the commissioning results measured on the L3 lowlevel RF stations of the European XFEL will be presented. SYSTEM ARCHITECTURE The basic RF field detection scheme for the XFEL imposes specific requirements on the local oscillator (LO) and clock (CLK) generation circuits. The main design parameters are large number of tap-points and performance in terms of phase and amplitude stability. The decision was taken that each crate will have its own LO and CLK generation module. If one LO/CLK generation circuit would be serving multiple crates, this would cause issues with cable-drifts and reliability. On the other hand, having one LO/CLK generation circuits per one down-converter unit (8 field detectors) would increase the performance that could be achieved by vector-sum processing gain. The last option will be investigated in the future. The LO/CLK module presented in this paper is located in the rear side of a standard MTCA.4 crate in slot 15. It uses a dedicated RF backplane [1] for distributing the LO and CLK signals. This reduces the amount of cables needed. The crate environment provides also the power, hardware management and data communication to the module. One of the main functions of the LO/CLK generation module for the XFEL is to provide the local oscillator (LO) frequency at 1354 MHz. The LO frequency is generated by means of splitters and dividers as shown in Even if other architectures such as PLL-based circuits cover a wider frequency range of possible LO frequencies the method using dividers-only can practically achieve a lower residual phase noise while keeping the circuit simple. Because of the high number of tap-points the RF power before the splitting has to be in the order of 1 W which represents also a challenge in terms of shielding and DC power dissipation. The generation of the CLK signals is implemented via simple clock dividers. The reasons for such architecture are similar to the ones for the LO generation. HARDWARE OVERVIEW The module is composed of several subsystems. The carrier hosts the RF splitting section, the CLK signal generation, the digital management section, the application processing unit and the low-noise linear regulators. Other functionalities such as DC/DC converters, the temperature controllers and the local oscillator generation are moved off the carrier board on daughter cards and connected to the main board through multi-pin connectors. Carrier Board The carrier board's primary function is frequency and clock distribution to the RF back plane (see The carrier also provides DC power generation for the system via a shielded 'DC/DC-Mezzanine' card that hosts two 8 A switch-mode convertors. One convertor provides a 5.9 V output used by the numerous LDO's on both RF and carrier card, the other convertor provides a 5.0 V output used exclusively for temperature control via thermoelectric controllers (TEC's) and Peltier elements.