Multi-frequency point supported LLRF front-end for CiADS wide-bandwidth application

The China initiative Accelerator Driven System, CiADS, physics design adopts 162.5 MHz, 325 MHz, and 650 MHz cavities, which are driven by the corresponding radio frequency (RF) power system, requiring frequency translation front-end for the RF station. For that application, a general-purpose design front-end prototype has been developed to evaluate the multi-frequency point supported design feasibility. The difficult parts to achieve the requirements of the general-purpose design are reasonable device selection and balanced design. With a carefully selected low-noise wide-band RF mixer and amplifier to balance the performance of multi-frequency supported down-conversion, specially designed LO distribution net to increase isolation between adjacent channels, and external band-pass filter to realize expected up-conversion frequencies, high maintenance and modular front-end general-purpose design has been implemented. Results of standard parameters show an $$R^2$$ value of at least 99.991% in the range of − 60–10 dBm for linearity, up to 18 dBm for P1dB, and up to 89 dBc for cross talk between adjacent channels. The phase noise spectrum is lower than 80 dBc in the range of 0–1 MHz; cumulative phase noise is 0.006°; and amplitude and phase stability are 0.022% and 0.034°, respectively.