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The China Spallation Neutron Source (CSNS) is now in the R&D phase, in which the design of the proton accelerator is an important part. This beam phase and energy measurement system imports the signal from the Drift Tube Linac (DTL) and calculates its phase and energy, which is fed back to tune the beam. The signals received from Fast Current Transformers (FCTs) are modulated pulses of high frequency with a repetition rate of 352.2 MHz for the Accelerator Driven Sub-critical System (ADS) and 324 MHz for CSNS; the leading edge of the signals is hundreds of ps, and the dynamic range of the amplitude varies from 20 mV to 900 mV (peak to peak, before transmission through cables). Therefore, special techniques are required to obtain the phase information. Corresponding simulations and initial tests have been performed, with the result of a phase resolution better than 0.1 degree over 57 dB input signal amplitude range with bandwidth of 367 kHz.