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Journal Article•DOI•

Design and evaluation of a low-level RF control system analog/digital receiver for the ILC main Linacs

U. Mavric1, Brian Chase1, Matjaz Vidmar•
Fermilab1
21 Aug 2008-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment (North-Holland)-Vol. 594, Iss: 1, pp 90-96
TL;DR: This paper presents a balanced design approach to the specifications of each receiver section, the design choices made to fulfill the goals and a description of the prototyped system.
Abstract: The proposed RF distribution scheme for the two 15 km long ILC LINACs uses one klystron to feed 26 superconducting RF cavities operating at 1.3 GHz. For a precise control of the vector sum of the signals coming from the SC cavities, the control system needs a high-performance, low-cost, reliable and modular multichannel receiver. At Fermilab we developed a 96-channel, 1.3 GHz analog/digital receiver for the ILC LINAC LLRF control system. In this paper we present a balanced design approach to the specifications of each receiver section, the design choices made to fulfill the goals and a description of the prototyped system. The design is tested by measuring standard performance parameters, such as noise figure, linearity and temperature sensitivity. Measurements show that the design meets the specifications and it is comparable to other similar systems developed at other laboratories, in terms of performance.

Summary (4 min read)

Jump to: [1. Introduction] – [2. Installation] – [3. xTensor basics] – [4. Examples] – [4.1. Spin 2 on a flat background] – [5. xTras functions] – [5.1.1. AllContractions] – [5.1.2. MakeTraceless] – [5.1.3. ConstructDDIs] – [5.1.4. IndexConfigurations] – [5.1.5. MakeAnsatz] – [5.2. Tensor algebra] – [5.2.1. CollectTensors] – [5.2.2. CollectConstants] – [5.2.3. SolveConstants] – [5.2.4. SolveTensors] – [5.3. Young tableaux] – [5.3.1. YoungProject] – [5.3.3. TableauSymmetric] – [5.4.1. VarL] – [5.4.2. FullSimplification] – [5.4.3. EulerDensity] and [Acknowledgments]

1. Introduction

  • XAct [1] is a free collection of powerful Mathematica packages for tensor computer algebra.
  • On this solid basis a great number of applications have been built [7–13] that range from tensor spherical harmonics to perturbations around homogeneous cosmological backgrounds.

2. Installation

  • XTras can be installed by downloading the package from its website www.xact.es/xtras, unzipping it, and following the supplied instructions.
  • Once installed, xTras can be loaded with the following command:.
  • Note that the authors have suppressed some print messages in the Mathematica output above, and have only shown the package info.

3. xTensor basics

  • Before the authors discuss xTras, it is convenient to go over the basics of xTensor [3].
  • After defining a manifold, it is possible to define a metric on that manifold with the command DefMetric: In := DefMetric[-1, metric[-a,-b], CD, PrintAs -> "g"].
  • The minus signs in front of the indices indicate that they are covariant indices.
  • Contractions of the Riemann tensor are automatically converted to Ricci tensors2: In := RiemannCD[-c, -b, -a, b] Out = Rca 10 Note, however, that xTensor also does not automatically rewrite Rca to Rac , even though the Ricci tensor is symmetric.

4. Examples

  • The authors will now demonstrate the features of xTras, or at least some of them, on the basis of two examples.
  • The functions used here are described in more detail in Section 5.

4.1. Spin 2 on a flat background

  • In this section the authors will construct a gauge invariant theory of a free spin 2 field on a flat background.
  • Up to total derivatives, this should be zero.

5. xTras functions

  • This section documents the most important functions in xTras.
  • The list of functions below is not exhaustive, nor are the functions described in full detail (for example, most options are not described here).
  • Throughout this section, the authors assume they have a manifold M, a metric metric, a covariant derivative CD and associate curvature tensors (RiemannCD, RicciCD, etc.).
  • These can be defined with the commands In := DefManifold[M, dim, IndexRange[a,m]].

5.1.1. AllContractions

  • AllContractions[expr] returns a sorted list of all possible full contractions of expr over its free indices.
  • The problem of finding all possible contractions of the input expression is equivalent to enumerating all double coset representatives of K \ Sn/H , where n is the number of indices of the input expression, K its symmetry group, and H the symmetry group of n2 metrics.
  • Take for instance the Riemann tensor: In := AllContractions[RiemannCD[-a, -b, -c, -d]].
  • AllContractions takes an optional second argument, which specifies what free indices the final contractions should have.
  • As is obvious from the previous example, there are none.

5.1.2. MakeTraceless

  • MakeTraceless[expr] returns the traceless version of expr.
  • And if the authors enter the Riemann tensor, it returns the Weyl tensor: In := MakeTraceless[RiemannCD[-a, -b, -c, -d]].
  • This is what the Sym objects in the above output do.

5.1.3. ConstructDDIs

  • ConstructDDIs[expr] constructs all scalar dimensional dependent identities that can be build out of expr. ConstructDDIs[expr, frees] constructs all dimensional dependent identities that can be build out of expr and that have free indices frees.
  • The same holds true for other contractions.

5.1.4. IndexConfigurations

  • IndexConfigurations[expr] gives a list of all independent index configurations of expr.
  • The commandIndexConfigurations gives all possible independent permutations of the free indices of the input expression.
  • A right transversal is the set of representatives of the right cosets H\Sn, which in turn is in one-to-one correspondence to the set of independent index configurations.
  • For two metrics the authors get: In := IndexConfigurations[metric[a, b] metric[c, d]].
  • Out = {Rabcd, Racbd, Radbc} 63 Note that IndexConfigurations does not take multi-term symmetries like the Bianchi identity into account, and hence it does not see that the last term can actually be written in terms of the first two.

5.1.5. MakeAnsatz

  • MakeAnsatz is a convenience function that, out of a list of terms, constructs an Ansatz with constant Symbols.
  • Even though the constant symbols print as Ci, their Mathematica symbol name is Ci: In := {C1, C2} Out = {C1, C2} 65 In combination with other functions such as IndexConfigurations or AllContractions, MakeAnsatz becomes very handy: In := MakeAnsatz @ IndexConfigurations[metric[a, b] metric[c, d]].

5.2. Tensor algebra

  • This section describes the functions in xTras that can be used for doing basic algebra with tensors.
  • There are two functions for rewriting expressions (CollectTensors and CollectConstants), and two functions for solving equations (SolveTensors and SolveConstants).

5.2.1. CollectTensors

  • CollectTensors[expr] collects all tensorial terms in expr.
  • CollectTensors works like the Mathematica function Collect, with the difference that you do not have to specify a second argument: it collects all tensorial terms it can find in the input expression.
  • A ‘tensorial term’ is a single tensor, or a product of tensors that cannot be expanded into a sum.

5.2.2. CollectConstants

  • CollectConstants[expr] collects all constant symbols in expr.
  • Instead of collecting all tensorial terms in the input expression, it collects all constant symbols it can find.

5.2.3. SolveConstants

  • SolveConstants[expr] attempts to solve the system expr of tensorial equations for all constant symbols appearing in expr.
  • The function SolveConstants solves equations with respect to constant symbols.
  • Not only does it do that, it also makes sure no tensors appear on the right-hand-side of the solutions.
  • The second step is to read off equations for the constant symbols from each tensorial term.

5.2.4. SolveTensors

  • SolveTensors[expr] attempts to solve the system expr of tensorial equations for all tensors in expr. SolveTensors[expr, tens] attempts to solve the system expr of tensorial equations for the tensors tens.
  • This does not always return the most general space of solutions, but a subset of it.
  • Hence SolveTensors should more be used as a way to easily obtain proper xAct tensor replacement rules than as a method to solve generic tensorial equations.
  • It is worth mentioning that the second argument of SolveTensors, which specifies what tensors to solve for, also takes patterns: In := SolveTensors[ RicciCD[-a, -b] - 1/2 metric[-a, -b] RicciScalarCD[] == 0, metric[__] ].

5.3. Young tableaux

  • Conspicuously absent in xAct are functions that deal with Young tableaux and multi-term symmetries.
  • XTras provides a few functions in an attempt to partly fill this void, but it is by no means a complete treatment of the subject.

5.3.1. YoungProject

  • YoungProject[expr, tab] projects the tensorial expression expr onto the Young tableau tab.
  • The projection can be donewith so-called Young projectors [19], which are sequential row-by-row symmetrizations and column-by-column antisymmetrizations of the Young tableau.
  • And indeed, the Bianchi identity is manifest after projection: In := ToCanonical @ Antisymmetrize[%, {-a, -b, -c}].

5.3.3. TableauSymmetric

  • TableauSymmetric[tab] gives the symmetry of the tableau tab.
  • TableauSymmetric generalizes the xAct functions Symmetric, Antisymmetric, and RiemannSymmetric to arbitrary Young tableaux.
  • This is because the tensor T abcdef now has all the mono-term symmetries that come from its Young diagram.

5.4.1. VarL

  • VarD[g[-a,-b], cd][S] returns δS δgab while integrating by parts with respect to the covariant derivative cd. VarL[g[-a,-b], cd][L] returns 1√ |g| δ √ |g|L δgab while integrating by parts with respect to the covariant derivative cd.
  • Computing the total variation is the first step towards reading off δF δg , and is carried out by the xPert commands Perturbation and ExpandPerturbation: In := ExpandPerturbation @ Perturbation[RicciScalarCD[]].
  • If the authors want, they have to do this ourselves afterwards.

5.4.2. FullSimplification

  • FullSimplification[][expr] tries to simplify expr as much as possible, taking Bianchi identities into account and sorting covariant derivatives.
  • The Bianchi identities are however implemented in the simplification methods of the Invar package [9,10].
  • The function FullSimplification extends the capabilities of Invar slightly by also simplifying the contracted second Bianchi identities in any expression, not just scalar monomials.
  • Apply the contracted second Bianchi identities ∇aRbcda = ∇cRbd − ∇bRcd and ∇aRba = 12∇bR. 3. Sort covariant derivatives.
  • This is a contraction of the identity the authors found in Section 5.3.2.

5.4.3. EulerDensity

  • EulerDensity[cd] gives the Euler density associated to the covariant derivative cd. EulerDensity[cd, dim] gives the Euler density associated to the covariant derivative cd in the dimension dim if the underlying manifold has a generic dimension.
  • Note that this technically is not a density because it has zero weight.
  • In order to prevent dummy index collisions, the results of EulerDensity are wrapped in a special head Scalar, which is indicated by a bracket.
  • In six dimensions the Euler density becomes: In := EulerDensity[CD, 6].

Acknowledgments

  • I would like to thank Thomas Bäckdahl, José M. Martín-García, and Leo Stein for useful discussions and their contributions to the xAct mailing list, and Cyril Pitrou for his suggestion to use xPert for computingmetric variations.
  • Furthermore, I thank Andrea Campoleoni, Massimo Taronna, and Pan Kessel for their feedback on initial versions of xTras.

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Design and Evaluation of a Low-Level RF Control System Analog/Digital Receiver for the ILC Main
LINACs
Keywords: ILC M
ain LINACs, LLRF, Digital Receiver, Vector Sum, high frequency electronics design
Uros Mavric; Matjaz Vidmar, prof.dr.; Brian Chase
Fermi National Accelerator Laboratory
Abstract: The proposed RF distribution scheme for the two 15 km long ILC LINACs, uses one klystron to
feed 26 superconducting RF cavities operating at 1.3 GHz. For a precise control of the vector sum of the
signals coming from the SC cavities, the control system needs a high performance, low cost, reliable and
modular multichannel receiver. At Fermilab we developed a 96 channel, 1.3 GHz analog/digital receiver for
the ILC LINAC LLRF control system. In the paper we present a balanced design approach to the
specifications of each receiver section, the design choices made to fulfill the goals and a descrip
tion of the
prototyped system. The design is tested by measuring standard performance parameters, such as noise
figure, linearity and temperature sensitivity. Measurements show that the design meets the specifications
and it is comparable to other similar systems developed at other laboratories, in terms of performance.
FERMILAB-PUB-08-157-AD
1
1. Introduction
The proposed international linear collider (ILC) will be an electron/positron
collider operating at 500 GeV (possible upgrade to 1 TeV) and it will be composed of
two damping rings, electron/positron source, detectors and two LINACs. The study in
this paper applies also to other ILC-style LINACs, where one klystron drives multiple
superconducting (SC) cavities. As presented in the reference design report for the ILC
(RDR) [1], the RF distribution for the LINACs foresees 560 RF units, each of them
composed of one klystron driving 26 SC cavities. The low power section of the RF
system, also denoted as the low-level RF (LLRF), takes care of the control of the vector
sum of signals coming from the SC cavities. The LLRF stabilizes the amplitude and
phase of the vector sum at the desired set point by means of feedback and feedforward
regulation techniques. In order to calculate the correction that is applied to the klystron,
the LLRF control uses 96 RF signals coming from one RF station (26 cavities). As a
result, for the two LINACs, the overall sum of the RF signals that are processed by the
multichannel receiver system equals 50 000. The high channel count has a major impact
on the design of the LLRF receiver section, where all the incoming signals need to be
downconverted and digitized. The process of downconversion and digitalization suffers
from noise, nonlinearities, and temperature dependent processes. In this paper we present
the design strategies to address these problems and we exploit these strategies to
implement a possible solution for the multichannel analog/digital receiver for an ILC
style LINAC LLRF control system.
Manuscript
2
2. Requirements
The two main parameters that have the biggest impact on the design of the
receiver are the performance and the high number of channels. In the RDR, the
performance requirements are given in terms of controlled amplitude and phase of the RF
fields and they are derived from the requirements for luminosity of the collider. These
numbers equal to 0.5 % and 0.24º for correlated errors (e.g. ground motion, reference line
drifts, beam loading, etc.) and 1.6 % and 0.48º for uncorrelated errors (e.g. noise in one
channel of the receiver). The errors are partitioned among the reference system (drifts of
the reference line between RF stations), the perturbation sources of the cavity
(microphonics, Lorentz force detuning and beam loading) and the LLRF electronics. The
error from the LLRF electronics is mainly defined by the errors from the receiver and the
error from the LO generation/distribution [2, 3]. The uncorrelated error introduced by one
channel of the receiver (with the LO generation and distribution) that we aim for must be
at least 20 times lower than the overall uncorrelated errors given in the RDR. This equals
to 0.08 % RMS and 0.024 º RMS for amplitude and phase respectively. Other
disturbances like harmonics generated by the nonlinear electronics, coupling among
adjacent channels and temperature dependent drifts also have considerable effects on the
system performance. However, they are not explicitly given in the RDR. In order to
define some values for these parameters, as our design goals, we followed the philosophy
that they must be limited by the most expensive part in the receiver chain, which is the
analog-to-digital converter (ADC). We therefore aim for an isolation among channels that
is higher than 90 dB and the second and third harmonics generated by the receiver must
3
not exceed -75 dBc. Furthermore we demand that the change of amplitude and phase over
large temperature swings (15 °C) meets uncorrelated amplitude and phase error values
given above. We also expect that the resolution of the ADC will define the uncorrelated
noise spectral density (NSD) of the receiver system at the output.
In addition to performance, the design has to account for the high number of RF
channels that need to be processed. Due to the higher probability of failure, the high
number of channels calls for a robust design to fit mean time between failure (MTBF)
requirements and a modular design to minimize the mean time to repair (MTTR). In
order to minimize MTBF we need to minimize the number of components in the system,
which also means we aim for a simpler and lower cost design. Modularity can be
achieved by properly grouping processing sections of the system which will eventually
result in a more versatile design, with the possibility to be reused on other RF systems.
The system with high number of channels also demands a high degree of automation,
which would otherwise be impossible to calibrate, reprogram or diagnose in a short time
period. Finally, the high channel count requires a cost and power sensitive design. The
power consumption of the LLRF electronics that we aim for is less than 200 W per one
RF station (96 channels).
3. System Design Strategy
The first step towards meeting the requirements for good performance, versatility
and ease of automation is achieved by choosing the digital approach to system design.
The commonly adopted digital architecture used in modern LLRF systems [4, 5] is based
Citations
More filters
Journal Article•DOI•
High-Accuracy Amplitude and Phase Measurements for Low-Level RF Systems

[...]

Zheng Wang1, Luhong Mao1, Rong Liu•
Tianjin University1
12 Jan 2012-IEEE Transactions on Instrumentation and Measurement
TL;DR: Experimental results at different frequencies prove that the detection system can meet the demands of state-of-the-art RF control systems for modern particle accelerators.
Abstract: This paper presents a detection system for high-accuracy amplitude and phase measurements on RF signals. It is typically used to set up the low-level RF system for particle accelerators. The proposed detector employs the principle of a heterodyne receiver and uses the digital IF architecture with a high oversampling rate to increase the SNR. A discrete Fourier transform-based quadrature demodulator is used to suppress the analog-to-digital converter (ADC) quantization noise and IF harmonics. The system has been evaluated at an IF of 1 MHz and in an RF range of 500-3000 MHz. A graphical user interface is developed to display and record the measured values. The detection accuracy achieved on 500-MHz signals in a 250-kHz bandwidth is better than ±0.0051% for the amplitude and better than ±0.0032 ° for the phase. Experimental results at different frequencies prove that the detection system can meet the demands of state-of-the-art RF control systems for modern particle accelerators.

12 citations

Cites methods from "Design and evaluation of a low-leve..."

  • ...References [3]–[5] use a heterodyne architecture to demodulate the RF signal, and the signal is digitized by ADC at IF....

    [...]

  • ...52-MHz clock is used for an ADC to sample a 13-MHz IF signal in [5]....

    [...]

Journal Article•DOI•
Multi-frequency Point Supported LLRF Front-end for CiADS Wide-bandwidth Application

[...]

Qi Chen1, Zheng Gao1, Z. A. Zhu1, Zongheng Xue1, Yuan He1, Xian-Wu Wang1 •
Chinese Academy of Sciences1
04 Nov 2020-arXiv: Accelerator Physics
TL;DR: In this article, a general-purpose design front-end prototype has been developed to evaluate the multi-frequency point supported design feasibility, with a carefully selected low-noise wide-band RF mixer and amplifier to balance the performance of multichannel supported downconversion, specially designed local oscillator (LO) distribution net to increase isolation between adjacent channels, and external band-pass filter to realize expected up-conversion frequencies.
Abstract: The China initiative Accelerator Driven System, CiADS, physics design adopts $162.5 \,\mathrm{MHz}$, $325 \,\mathrm{MHz}$, and $650 \,\mathrm{MHz}$ cavities, which are driven by the corresponding radio frequency (RF) power system, requiring frequency translation front-end for the RF station. For that application, a general-purpose design front-end prototype has been developed to evaluate the multi-frequency point supported design feasibility. The difficult parts to achieve the requirements of the general-purpose design are reasonable device selection and balanced design. With a carefully selected low-noise wide-band RF mixer and amplifier to balance the performance of multi-frequency supported down-conversion, specially designed local oscillator (LO) distribution net to increase isolation between adjacent channels, and external band-pass filter to realize expected up-conversion frequencies, high maintenance and modular front-end general-purpose design has been implemented. Results of standard parameters show an $R^2$ value of at least $99.991\%$ in the range of $-60 \sim 10\,\mathrm{dBm}$ for linearity, up to $18\,\mathrm{dBm}$ for P1dB, and up to $89\,\mathrm{dBc}$ for crosstalk between adjacent channels. The phase noise spectrum is lower than $80\,\mathrm{dBc}$ in the range of $0 \sim 1\,\mathrm{MHz}$, and cumulative phase noise is $0.006^\circ$; amplitude and phase stability are $0.022\%$ and $0.034^\circ$, respectively.

10 citations

Journal Article•DOI•
Advanced topics on RF amplitude and phase detection for low-level RF systems

[...]

Zheqiao Geng1, Roger Kalt1•
Paul Scherrer Institute1
01 Oct 2019-Nuclear Science and Techniques
TL;DR: In this paper, different sampling strategies and demodulation algorithms have been developed for low-level radio frequency (LLRF) systems, including accurate RF transient measurement, wideband RF detection, and detection with an asynchronous trigger, local oscillator, or clock.

8 citations

Cites background from "Design and evaluation of a low-leve..."

  • ...There are already quite a few articles to discuss the RF signal detection focusing on the accuracy, precision and latency requirements described above [24-28]....

    [...]

Proceedings Article•
Module management controller for MicroTCA-based controller board

[...]

Piotr Perek, Aleksander Mielczarek, Pawel Predki, Dariusz Makowski, Andrzej Napieralski 
16 Jun 2011
TL;DR: These new specifications define a number of extensions to the Advanced Telecommunications Computing Architecture (ATCA) and Micro Telecommunications Computing architecture (μTCA) standards, specifically dedicated to control and data acquisition systems of HEP applications.
Abstract: As a result of a growing interest in the xTCA systems by research centers conducting High Energy Physics (HEP) experiments, the PICMG xTCA for Physics Coordinating Committee is developing a new, attractive standards. They are specifically dedicated to control and data acquisition systems of HEP applications. These new specifications define a number of extensions to the Advanced Telecommunications Computing Architecture (ATCA) and Micro Telecommunications Computing Architecture (μTCA) standards.

8 citations

Cites background from "Design and evaluation of a low-leve..."

  • ...An essential problem in case of complex control systems of HEP machines is a large number of signals which must be supplied to the system from the outside [9], [ 10 ]....

    [...]

Journal Article•DOI•
Multi-frequency point supported LLRF front-end for CiADS wide-bandwidth application

[...]

Qi Chen1, Zheng Gao1, Z. A. Zhu1, Zongheng Xue1, Yuan He1, Xian-Wu Wang1 •
Chinese Academy of Sciences1
01 Mar 2020-Nuclear Science and Techniques
TL;DR: A carefully selected low-noise wide-band RF mixer and amplifier to balance the performance of multi-frequency supported down-conversion, specially designed LO distribution net to increase isolation between adjacent channels, and external band-pass filter to realize expected up-converting frequencies, high maintenance and modular front-end general-purpose design has been implemented.

5 citations

Cites background or methods from "Design and evaluation of a low-leve..."

  • ...F [20] U....

    [...]

  • ...Therefore, the digital and RF front-end separation design is adopted [20]....

    [...]

  • ...As described in [20], using the LO amplifier directly on the LO port increases the coupling between the channels and the near-center phase noise, thus, the leakage of the active mixer with the internal LO amplifier from the LO port to the RF port increases....

    [...]

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Abstract: A class of digital linear phase finite impulse response (FIR) filters for decimation (sampling rate decrease) and interpolation (sampling rate increase) are presented. They require no multipliers and use limited storage making them an economical alternative to conventional implementations for certain applications. A digital filter in this class consists of cascaded ideal integrator stages operating at a high sampling rate and an equal number of comb stages operating at a low sampling rate. Together, a single integrator-comb pair produces a uniform FIR. The number of cascaded integrator-comb pairs is chosen to meet design requirements for aliasing or imaging error. Design procedures and examples are given for both decimation and interpolation filters with the emphasis on frequency response and register width.

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Lawrence Doolittle, H. Ma, Mark Champion
01 Jan 2006
TL;DR: A collaborative effort is developing a digital LLRF control evaluation platform to experiment using coherent sampling with much longer synchronous periods, on the order of the cavity closed-loop bandwidth, to meet greater future RF control challenges.
Abstract: The success of digital feedback with synchronous IQ sampling for cavity field control in recent accelerator projects make this LLRF control scheme a popular choice. This short-period synchronous sampling does not, however, average out well-known defects in modern ADC and DAC hardware. That limits the achievable control precision for digital IQ LLRF controllers, while demands for precision are increasing for future accelerators such as International Linear Collider. For this reason, a collaborative effort is developing a digital LLRF control evaluation platform to experiment using coherent sampling with much longer synchronous periods, on the order of the cavity closed-loop bandwidth. This exercise will develop and test the hardware and software needed to meet greater future RF control challenges.

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TL;DR: This paper primarily addresses the usefulness of phase-modulation noise measurements versus noise figure (NF) measurements in characterizing the merit of an amplifier, and concludes that, although NF is sometimes used as a selection criteria for an amplifier for low-level signal, NF yields no information about potentially important close-to-carrier 1/f noise of an amplifier nor broadband noise in the presence of a high- level signal.
Abstract: This paper primarily addresses the usefulness of phase-modulation (PM) noise measurements versus noise figure (NF) measurements in characterizing the merit of an amplifier. The residual broadband (white PM) noise is used as the basis for estimating the NF of an amplifier. We have observed experimentally that many amplifiers show an increase in the broadband noise of 1 to 5 dB as the signal level through the amplifier increases. This effect is linked to input power through the amplifier's nonlinear intermodulation distortion. Consequently, this effect is reduced as linearity is increased. We further conclude that, although NF is sometimes used as a selection criteria for an amplifier for low-level signal, NF yields no information about potentially important close-to-carrier 1/f noise of an amplifier nor broadband noise in the presence of a high-level signal, but a PM noise measurements does. We also have verified experimentally that the single-sideband PM noise floor of an amplifier due to thermal noise is -177 dBc/Hz, relative to a carrier input power of 0 dBm

34 citations

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Frequently Asked Questions (19)
Q1. What are the main advantages of using two amplifiers?

The main advantages are good matching, low coupling between RF channels, compactness, low power dissipation, low cost and no need for high power amplifiers. 

In the paper the authors present a balanced design approach to the specifications of each receiver section, the design choices made to fulfill the goals and a description of the prototyped system. 

The mixer parameters that affect the presented design the most are the mixer linearity, the RF to LO isolation and the input impedance at the mixer ports. 

Using the N-type RF connector in the front of the board, allows connection of the rigid cables that come from the cavities directly to the analog board. 

The high channel count has a major impact on the design of the LLRF receiver section, where all the incoming signals need to be downconverted and digitized. 

Standard coupling reduction design techniques, like proper shielding of each high frequency section and channelization of ground and power planes, have also been used. 

The two main parameters that have the biggest impact on the design of the receiver are the performance and the high number of channels. 

Due to the higher probability of failure, the high number of channels calls for a robust design to fit mean time between failure (MTBF) requirements and a modular design to minimize the mean time to repair (MTTR). 

Among all the different modules that compose the LLRF control system, the receiver is the most critical in terms of noise contribution. 

Due to a modular, robust, cost effective and high performance design, this receiver is suitable for machines like the ILC main LINACs and the ILC bunch compressor. 

As mentioned in the introduction, the authors expect the NSD at the output of the receiver system to be equal to the NSD of the ADC, which was measured to be -147 dBc/Hz. 

This minimizes the number of boards needed per one RF station, decreases the group delay, simplifies the interconnections between the boards and reduces the possibility of failure. 

They were not measured in Fig. 3 because the residual phase noise measurement, adopted for this measurement, cancels out all coherent disturbances. 

amplitude and phase drifts are likely to be several percent in amplitudeand several degrees in phase according to measurements in Fig. 

An additional problem associated with the high number of channels is finding an RF connector with satisfying isolation between channels that is compact and has acceptable return loss at 1.3 GHz. 

Using two amplifiers that are placed in between three 1:4 power splitters (see Fig. 2 LO distribution module), turns out to have several advantages over the single input amplifier option. 

The remainder of the coupling is caused by the transmission lines that connect the IF circuitry and the output mini-coax IF connector. 

The system with high number of channels also demands a high degree of automation, which would otherwise be impossible to calibrate, reprogram or diagnose in a short time period. 

The integrated RMS amplitude and phase uncertainties for the spectra shown in Fig. 4 are 0.0022% and 0.0044º RMS from 100 Hz to 100 kHz.