BPM - AFE Analog Front End

The Beam Position Monitor Analog Frontend (BPM-AFE) is an electronics module for fast analog processing of beam pickup signals.

BPM - AFE delivers an output signal which can be directly entered into fast 14-bit ADCs. It is specially developed for transfer lines and linacs. It can be customized to any RF frequency up to 1 GHz.


  • Non-interceptive beam position measurement
  • Four parallel processing path
  • Mezzanine board to PCI specifications
  • Four input signals processed in parallel, allows single-pass position measurement
  • Input signals are down-converted by independent superheterodyne receivers to an intermediate frequency (IF)
  • IF output signals are differential and galvanically isolated, for direct input into fast ADC (e.g. AD6644)
  • Output signals are adjustable up to 4Vpp to take advantage of full ADC input aperture
  • High phase accuracy and low harmonic distortion by current feedback amplifiers
  • IF bandwidth adjustable by separate independent high-pass and low-pass filters provide flexibility
  • Low power dissipation and temperature drift are achieved with passive mixers
  • Excellent in-band transient response


Signal processing:


Input signals into each superheterodyne channel can either be the Calibration signal or the signal from the lobe, controlled by the Lobe, Input and Calibration switches. Each channel switches are controlled individually.
Calibration signals are balanced to identical level for each receiver, and can be sent to any lobe for detection by another channel, under the control of the switches. Calibration signal frequency is independent of the superheterodyne receiver frequency.
Switch-selected input signals are summed to produce a phase reference signal. Each channel is otherwise processed independently. Two successive trap filters reject unwanted harmonics.
A passive double-balanced mixer processes the signal with a common Local Oscillator (LO) signal. The common LO signal is distributed to each mixer after buffering. The resulting Intermediate Frequency (IF) is filtered by two cascaded high-pass and low-pass filters to reject the unwanted mixing products.
The IF filtered signal is amplified by two stages of high gain x bandwidth current-feedback amplifiers. The first stage can be switched between two gain levels, while the second stage gain is adjustable by potentiometer in a range 1:4.
A balun at the output produces a balanced signal with floating ground reference from each single-ended IF signal.