IQ&A Module

Module Description:

LLRF System Description
Vers 3 IQA Module Hardware Changes and Address Map (Bill Ross)
Vers 3 IQA Module Hardware Address Map (Updated by Kukhee Kim)
IQA Module Hardware Documents

Each PEP RF station contains 2 (2-Cavity Station) or 3 (4-Cavity Station) IQ&A modules. Each module measures 8 RF signals. The module performs two main tasks:

  1. The IQ portion (short for in-phase and quadrature) provides very accurate measurement of the real (in-phase) and imaginary (quadrature) component of the RF vector.  Digital down conversion is used to measure both I and Q, the values for each channel are shown on the lower right of the IQ&A module EPICS panel.  The amplitude and phase of the vector are calculated as SQRT(I^2 + Q^2) and ATAN2(I,Q) respectively.  These calculations are performed in the EPICS database.  Slow feedback loops such at the cavity tuners, drive power and station gap voltage set point use IQ data and operate at about a 1 Hz update rate.  The bandwidth of each IQ channel is programmable via a file written to the decimating digital filters (DDF)  for that channel.  Currently all channels are programmed for 5 Hz bandwidth with a 50 Hz update rate, except for the klystron output channel which is set up for 10 kHz bandwidth and 23 kHz update rate needed for the ripple loop.

  2. The Amplitude portion of the module measures the envelope of each RF vector with  8 diode detector circuits.  The output of each detector drives a programmable comparator "trip" circuit.  Any RF signal  whose amplitude exceeds the comparator set point will trigger a fault signal on the VXI crate back plane trigger line representing a station RF fault.  The fault causes the klystron drive to be removed quickly and HVPS turned off.

The IQA module also performs these additional tasks:

  1. The IQ&A module in VXI slot 7 (left most slot is slot 0) has the additional task of measuring the klystron output and sending the information to a DSP in the RF Processing (RFP) module. This information is used to form a feedback loop (the ripple loop) across the  RF modulator (in RFP module), drive amplifier and the klystron.  As the klystron high voltage is changed the phase length of the tube also changes.  The ripple loop keeps the phase length of the path constant.  It was originally intended for the ripple loop to also cancel klystron modulations caused by power line harmonics appearing on the klystron high voltage but this task is now handled by the integral compensation option of the direct RF feedback loop.  The klystron output is assigned to channel 1 of the IQ&A in slot 7.  The klystron output power data is sent to the RFP digitally over a dedicated serial link which operates at 23 kHz.  There are two versions of IQ&A modules.  The IQ&A in slot 7 MUST be a version II to properly send data to the DSP.  IQ&A modules in slot 9 or slot 11 can be either version I or version II.

  2. The output of each diode detector may be directed to the lemo connector located on the IQ&A module front panel for viewing with a scope.  The user must select which channel gets connected by  typing in the channel number (1-8) in the "Signal Selection" box on the IQ&A module EPICS panel.  The amplitude of the selected channel is also digitized and displayed  in volts on the EPICS panel.  Note that if the station is in FM_Processing mode the channel number is constantly being switched by EPICS to measure the amplitude of each channel (the FM signals exceed the 5 Hz bandwidth of the IQ measurements).  The circuit is designed to display the true RF voltage when the signal is viewed with high impedance (NOT 50 ohms!).

  3. The output of both the IQ portion and one envelope detector is constantly being digitized and stored in a long (512K) history buffer.  When a RF fault occurs, these buffers are frozen and can be read out into files for later viewing (see the Fault File Control and Analysis Panel for more detail). Since the IQ channels are low bandwidth, they are probably not very interesting to look at.  The amplitude channel, however, is wide band and can provide a good transient history of the RF fault (provided the "Signal Selection" was preset to the channel  we wanted to review).

Module Inputs and Outputs:

See also the Hardware Setup Procedure for IQA module inputs and output setup information.



Module Setup:

EPICS Panel Details:

EPICS Database:


Contact:  Stephanie Allison
Last Modified:  Thursday, Jul 11, 2008