Digital I/Q demodulator

This paper describes the architecture of a digital LLRF system for heavy-ion acceleration developed under the specification of the projected future heavy-ion accelerator facility in Huelva, Spain. A prototype LLRF test bench operating at 80 MHz in CW mode has been designed and built. The core LLRF control has been digitally implemented on a PXIe chassis, including an FPGA for digital signal processing and a real time controller. The test bench is completed with a low phase and amplitude noise signal generator used as master frequency reference, an analog front end for reference modulation and signal conditioning, some RF components completing the circuit, as well as a tunable resonant cavity at 80 MHz, whose RF amplitude, phase and frequency are real-time controlled and monitored. The presented LLRF system is mainly digitally implemented using a PXIe platform provided by National Instruments [1], and is based on IQ modulation and demodulation. The system can be configured to use both direct sampling and undersampling techniques, resulting thus in a high performance and versatile RF control system without the need of excessive computational resources or very high speed acquisition hardware. All the system is programmed using the LabVIEW environment, which makes the prototyping process and its reconfigurability much easier.

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“…It is also advantageous because the symmetry of the I/Q signals [16]. This scheme allows to control both phase and amplitude in a single loop.…”

Section: Test Bench Descriptionmentioning

confidence: 99%

PXIe-Based LLRF Architecture and Versatile Test Bench for Heavy Ion Linear Acceleration

Badillo

Jugo

Portilla

et al. 2015

IEEE Trans. Nucl. Sci.

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“….. This stream, after being demultiplexed and sign corrected, will finally result in two data streams being the I and Q components of the rf signal [9]. This method has been widely used in the past years and has become standard for digital LLRF.…”

Section: Rf Conversion To Digital I and Qmentioning

confidence: 99%

Low level rf system for the European Spallation Source’s Bilbao linac

Hassanzadegan

Garmendia

Etxebarria

et al. 2011

Phys. Rev. ST Accel. Beams

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Design and some performance results of the pulsed digital low level radio frequency (LLRF) for the radio frequency quadrupole (RFQ) systems of Rutherford Appleton Laboratory-front end test stand and the future European Spallation Source Bilbao linac are presented. For rf field regulation, the design is based on direct rf-to-baseband conversion using an analog in-phase quadrature (IQ) demodulator, highspeed sampling of the I/Q components, baseband signal processing in a field-programmable gate array (FPGA), conversion to analog, and IQ modulation. This concept leads to a simple and versatile LLRF system which can be used for a large variety of rf frequencies and virtually any LLRF application including cw, ramping, and pulsed. In order to improve the accuracy of the probe voltage measurement, errors associated with the use of analog IQ demodulators have been identified and corrected by FPGA algorithms and proper setting of the feedback loop parameters. Furthermore, a baseband-equivalent model for the rf plant is developed in MATLAB-SIMULINK to study the RFQ transient response under beam loading in the presence of phase and delay errors. The effect of the unwanted resonant modes on the feedback loop stability and the LLRF considerations to avoid such instabilities are discussed and compared to some other machines such as the ILC and the European free electron laser . The practical results obtained from tests with a mock-up cavity and an RFQ cold model verify that amplitude and phase stabilities down to a fraction of one percent and one degree and phase margins larger than AE50 can be achieved with this method preserving the linearity and bandwidth of the feedback loops.

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“…The network analyzer can be placed in continuous mode to catch RF faults or inject dynamic IQ reference signals from files to FM process the cavities. The IQA detector modules are 8 channel RF receivers using a digital down conversion technique for precise narrow-band measurements (figure 9) [6]. Each RF input is mixed with the LO to produce 4.9 MHz IF.…”

Section: Fig 7 Pep-ii Llrf System Vxi Crate Topology (Her)mentioning

confidence: 99%

Architecture and performance of the PEP-II low-level RF system

Corredoura¹

Proceedings of the 1999 Particle Accelerator Conference (Cat. No.99CH36366)

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Heavy beam loading in the PEP-II B Factory along with large ring circumferences places unique requirements upon the low-level RF (LLRF) system. RF feedback loops must reduce the impedance observed by the beam while ignoring the cavity transients caused by the ion clearing gap. Special attention must be placed on the cavity tuner loops to allow matching the ion clearing gap transients in the high energy ring and the low energy ring. A wideband fiber optic connection to the longitudinal feedback system allows a RF station to operate as a powerful "sub-woofer" to damp residual low order coupled bunch motion.This paper describes the design and performance of the VXI based, EPICS controlled, PEP-II low-level RF system(s). Baseband in-phase and quadrature (IQ) signal processing using both analog and modern digital techniques are used throughout the system. A family of digital down converters provide extremely accurate measurements of many RF signals throughout the system. Each system incorporates a built-in network analyzer and arbitrary RF function generator which interface with Matlab to provide a wide range of functions ranging from automated configuration of each feedback loop to cavity FM processing. EPICS based sequences make the entire system a turn-key operation requiring minimal operator intervention. In the event of a fault, fast history buffers throughout the system write selected RF signals to disk files which can be viewed later to help diagnose problems. Actual data from commissioning runs of PEP-II is presented.

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Digital I/Q demodulator

Cited by 57 publications

References 1 publication

PXIe-Based LLRF Architecture and Versatile Test Bench for Heavy Ion Linear Acceleration

PXIe-Based LLRF Architecture and Versatile Test Bench for Heavy Ion Linear Acceleration

Low level rf system for the European Spallation Source’s Bilbao linac

Architecture and performance of the PEP-II low-level RF system

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