Commissioning and status of new BPM electronics for COD measurement at the SPring-8 storage ring

At SPring-8 storage ring,BPM electronics for closed orbit measurement and a part of its control system were replaced during summer shutdown period of 2006. In the new electronics,one of four beam signals at the frequency of 508.58 MHz, which is the acceleration frequency of the SPring-8, is selected by a multiplexer and down-converted to IF frequency.The IF signal is sampled by 2 MSPS 16-bit ADC and detected with DSP. On the DSP, spurious frequencies are eliminated by digital filter and effective band-width can be changed by averaging. During the commissioning of the new circuit after the summer shutdown,DSP parameters such as number of averaging were decided to measure beam positions at all BPMs in 3 seconds, although the new circuit was designed with a target repetition of a few 10 Hz or around 100 Hz with resolution of sub-microns. With the DSP parameters, position resolution of less than 0.5 micron is achieved. In this paper, we also describe current dependence and gain dependence of the amplifier of the new circuit in addition to the position resolution and measurement repetition.