Project 20072002 VIRGO+ Demodulator board (2008 version)

The demodulator board is part of the linear alignment system of the Virgo interferometer at Cascina (near Pisa) in Italy. The goal of the whole project is to measure gravitational waves.
The board receives its 6.26 MHz input signals from a front end module, which is equipped with a quadrant photo diode. The quadrant photo diode is exposed to laser light which is modulated with the 6.26 MHz signal. The control system tries to keep the light spot in the center of the quadrant photo diode.



The demodulator board fits into a two connector VME crate. Only the -12 Volts and +12 Volts are used. On the front there are horizontal and vertical 6.26MHz inputs and horizontal and vertical 6.26 MHz reference inputs. The board has an I&Q detector (quadrature detector) for the horizontal signal and also for the vertical signal. Each I&Q detector has an I-output and a Q-output. The conversion gain of board can be set at four different levels in 12dB steps. This is done by applying the appropriate voltage on the gain-input. To see in what gain setting the board is, one can read the voltage of the gain-output.

Download:

• User Manual 

• Measurement Results

• Measurement setup

• Bill of Materials

Reference documents:

• Schematics

• PCB : Etch layer 1(top)

• PCB : Etch layer 2

• PCB : Etch layer 3

• PCB : Etch layer 4 (bottom)

• Component layout

• Component layout (color)

Previous version(20062001) documents:

• All documents in one zip file