Design of a generic digital LLRF controller

IUAC operates multiple accelerators consisting of RF structures resonating over a wide range of frequencies, starting from 12.125 MHz to 2860 MHz. Stable cavity fields in terms of amplitude and phase is one of the key requirements of any such accelerating system. The LLRF electronics used for this purpose at IUAC has been operational for a very long time. The current designs make use of analog electronics which are rigid in design and requires frequent maintenance cycles due to recurrent failures on account of components ageing and usage. Component obsolescence also creates hurdles in replacement process. In addition to this, every different type of cavity, requires its own LLRF electronics. In this paper, we will present a completely reconfigurable, low-cost, standalone type of FPGA based Generic Digital LLRF controller which is completely controlled by a remote client over LAN. This is primarily a Generator Driven Resonator based LLRF whose complete operation is synchronized to an external reference signal. Besides the digital signal processing algorithms, it consists of a PI controller as well. The user can dynamically change the frequency of operation (either direct sampling upto 50 MHz or indirect downsampling based), set-points, PI controller gains etc. Additional features like Automatic Frequency Tuner control by the way of motor movement using PWM / variable frequency pulses is also implemented in the same FPGA, which not only reduces the cost and size, but also reduces the overall power consumption. Detailed signal processing chain and the test result with dummy cavity will be presented in this paper. (author)