Maesaka, H. Dewa, H. Fujita, T. Fukui, T. Masaki, M. Saji, C. Takano, S. JACoW Publishing Geneva, Switzerland 2673-5350 978-3-95450-204-2 10.18429/JACoW-IBIC2019-WEBO03 English 471-474 WEBO03 electron electronics FPGA LLRF low-level-rf Contribution to a conference proceedings 2019 2019-11 https://doi.org/10.18429/JACoW-IBIC2019-WEBO03 http://jacow.org/ibic2019/papers/webo03.pdf We have developed a new button-BPM readout electronics based on the MTCA.4 standard for the low-emittance upgrade of SPring-8 [*]. Requirements for the BPM system are a high single-pass BPM resolution of better than 100 µm for a 100 pC injected bunch to achieve first-turn steering in the commissioning of the upgraded ring and a highly stable COD BPM within 5 µm error for 1 month to maintain the optical axis of brilliant x-rays for users [**]. We designed an rf front-end rear transition module (RTM) having band-pass filters, low-noise amplifiers, step attenuators, and calibration tone generators. The rf signal is detected by a 16-bit 370 MSPS high-speed digitizer advanced mezzanine card (AMC) developed for the new low-level rf system of SPring-8 [***]. The firmware of the FPGA on the digitizer AMC was newly developed to implement various functions of the BPM system. We evaluated the readout system at a laboratory and then tested at the present SPring-8 storage ring with a prototype BPM head for the SPring-8 upgrade. We confirmed that the new readout system satisfies the requirements for the single-pass BPM resolution and the COD BPM stability.