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
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.
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
The IQA module also performs these additional tasks:
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
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!).
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.
LO Input - The top SMA connector is the input for the 471.2 MHz local oscillator.
The LO is generated by the clock module (slot 2). The nominal LO
power is +13dBm.
RF inputs (1-8) - There are 8 SMA connectors for the 476 MHz RF signals
which the IQ&A module will measure and interlock. The maximum
RF power is 1 watt (+30 dBm).
Detected RF Amplitude - Lemo connector is multiplexed to the 8 envelope
detectors. Multiplexer control is "Signal Selection" on the IQ&A
module EPICS panel. Connect to high impedance scope channel (NOT
- Trip Circuit Speed Switch Settings
The speed of the trip circuit is set by 8 DIP switches (SW2) on the main
circuit board. All channels are set for slow response (3 us) except
for channel 2 of the IQ&A module in slot 7, this channel is protecting
the klystron from reflected power and must be set to respond fast.
The status of the SW2 setting is read by EPICS and displayed as entry "FEST"
on the IQ&A module EPICS panel. Set SW2 for:
Slot 7: FEST = 0xFDFF
Slot 9 or 11: FEST = 0xFFFF
- DDF Coefficient File Names
The bandwidth of the IQ detector is determined by a coefficient file.
Presently all channels except for the klystron output channel are set for
the lowest possible bandwidth (maximum filtering). The klystron output
channel (IQ&A module in slot 7, channel #1) is setup with sufficient
bandwidth to support the ripple loop. File details:
/tbl/iqaDdf_50Hz.rpt: Bandwidth = 5 Hz, Output Rate = 50 Hz
for all channels except klystron output
/tbl/iqaDdf_23KHz.rpt: Bandwidth = 10 kHz, Output Rate = 23 kHz
for the klystron output channel (IQ&A slot 7 channel #1)
- Amplitude History Buffer Settings
AHSZ - Amplitude history buffer size.
This field is set by the EPICS database. The normal value is 512 (k).
AHFS - Amplitude history file name.
This field is set by the EPICS
database. Something like "/dat/FAULTIqadAmp_dd", where the "d" represent
integers that identify the IQ&A module and the fault file number.
- I/Q Data History Buffer Settings
IQHS - I/Q history buffer size.
This field is set by the EPICS database. The normal value is 512 (k).
AHFS - I/Q history file name.
This field is set by the EPICS database.
Something like "/dat/iqaIqHistory.dat"
- IF Mode Setting
On the lower right of the IQ&A EPICS panel there is a button for selecting
the mode of the IQ processing. The IF mode should always be set to
8 chan(nel). The 1 chan(nel) mode is for test purposes and not supported
by the EPICS database.
- Interrupt Mask (IMSK)
Determines what types of interrupts are passed to the
VXI crate processor. The proper value for this field is 0xFFFFFFF8 (248).
- Amplitude Threshold Set Points
These setpoints are set during
IQ&A module calibration. The voltage steeping for
each channel is determined in the EPICS database (Power/Phases panel
then on to the Power Trip Limit panel). If the original steeping
is unknown, the correct value can be restored by placing the cursor
in the associated trip limit entry field on the Power Trip Limit panel
and entering a carriage return. This will force the EPICS database
to recalculate the trip voltage and restore the correct value.
EPICS Panel Details:
- Software Reset
Resets the module and reloads the DDF files and
comparator trip points. The module will become unsynchronized with
the RF reference after a Software Reset. It will be necessary to
force a "resynch" on the clock module panel to restore the proper phase
relationships. This is most important if the IQ&A module is in
slot 7 since the klystron phase is measured in channel 1 and is directly
tied to the phase margins of the direct RF feedback loop.
- Threshold Fault Reset Button
Clears the latched amplitude fault.
This button is pushed by a station Reset and should not need to be activated
from the IQ&A panel (except during testing in the lab).
- Stop Trigger Reset Button
Clears a latched stop trigger.
This trigger stops the internal ADC from writing the IQ and Amplitude information
to the long memories, holding the data until it can be read out to a file.
This button is also pushed by a station Reset and should not need to be
activated from the IQ&A panel (except during testing in the lab).
Contact: Stephanie Allison
Last Modified: Thursday, Jul 11, 2008