A beam position monitor for low intensity beams

To detect the position of lower intensity beams, the gain of a beam position monitor needs to be increased, and the bandwidth also needs to be reduced in order to suppress noise. The increased gain and reduced bandwidth often result in the instability of instrument zero. To solve this problem, the conventional signal processing scheme of one-step AM-to-PM conversion is modified into a two-step conversion of AM-to-Δ/Σ and then Δ/Σ-to-PM. The signal amplification, filtering, and frequency down-converting are done between the two conversions. As the result, the zero-drift caused by the changes in channel balance is reduced