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Bergoz Beam Position Monitors, BPM 
The Bergoz Multiplexed Beam Position Monitor (MX-BPM) is an electronics module with superior performance in a small volume. It is a non-intercepting system that has been optimized for use in electron and positron Storage Rings.

For Beam Position Monitoring of Linacs, transfer lines, first turns, boosters or fast-cycling synchrotrons, please refer to the LR-BPM and the BPM-AFE.

The MX-BPM features
   •  On-board microstrip filters that elminate the need for costly tubular filters
   •  GaAs switches to provide superior button to button isolation and low insertion loss
   •  On-board systhesized local oscillator to elimate the problem of external oscillator signal distribution with power supplies.
   •  Automatic Gain Control with a range of greater than 90dB provides optimum levels for the demodulator, independent of the beam intensity and number of bunches.
   •  phase-locked synchronous demodulation giving high lineariry and noise suppression.
   •  button signal range of -70dBm to +5dBm.
   •  X & Y output level of ±10V.
   •  X & Y resolution of 1µm.
   •  Sample rate of up to 10,000 samples per second.

Operating Principle
Button Scanning Mode
The signals from the four button electrodes are fed in to the BPM module where they are processed sequentially to give three outputs: X, Y and Sum.

Four on-board variable 1dB attenuators are used to equalize the button signals, then the microstrip low-pass filters eliminate the unwanted beam harmonics before the signals are multiplexed by the GaAs switches. The switches close in sequence under the control of the local clock, sampling each button 2,000 times per second. An external clock signal may override the on-board clock, to provide sample rates up to 10,000 times per second. The output of the multiplexer is then filtered by a band-pass filter to allow easy selection of the chosen beam harmonic. A low-noise preamplifier with AGC is used to amplify the signal before it is processed with a superhetrodyne receiver. A mixer gives the intermediate frequency using its own on-board synthesized local oscillator. The local oscillator frequency is given by a string of bits generated by a plug-in programmable frequency key. The automatic gain control of the intermediate frequency amplifier normalizes the sum of all button signals. A PLL synchronous demodulator provides high linearity. The demodulated signal is filtered and memorized by four sample-and-hold circuits under the control of the button scanning clock. The X and Y positions are obtained from the memorized value of the four buttons. Only additions and subtractions are needed to obtain the X and Y positions, because the sum of all four buttons is normalized at all times to a constant value. The Difference over Sum linearity errors are thus avoided.

Single Turn Sampling
The fast gating mode can be enabled with an external command line, and a fast gate can be applied to define the sampling window.
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