Log-ratio current for beam position monitoring

The logarithmic ratio of the signal amplitudes from beam-position probe-electrodes provides a normalized real-time analog signal that is more linear in beam displacement than other signal-processing techniques for circular cross-section, beam-position monitors. The authors describe work being done to develop a log-ratio circuit using an inexpensive, commercially available, logarithmic-response, integrated-circuit RF-amplifier. The circuit uses two amplifiers in a log (A)-log (B)=log (A/B) configuration to provide the logarithmic ratio of the two RF input signals from the probe. The output is a real-time analog signal proportional to beam displacement.<>