SNS BPM RF Electronics and Calibration

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SNS BPMRF Electronicsand Calibration

• Kurt Vetter

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Outline

• Why RF BPM Signal Processing is Necessary
• RF Electronics
• BPM Calibration
• Status

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The Need For RF BPM Signal Processing

• Minimum of two RF BPMs in the baseline
• Baseline AP 1st-Turn requirement
• 1mm resolution over 20mm aperture
• BaseBand Test Results
• Preliminary BaseBand laboratory measurements
  verify 1st-turn SNR of 16dB (require 30dB SNR for
  1mm resolution)
• Expect SNR to degrade in Real System due to
  external noise coupling which desensitizes
  receiver.
• RF BPM Signal Processing
• Achieve 30dB SNR on 1st-Turn (Centered Beam
  lowest SNR)
• Assures 1mm Resolution Requirement on 1st-Turn
• Highly integrated implementation approach will
  fit on existing AFE plug-in board

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1st-Turn Spectral Analysis (M. Kesselman)
Beam Spectrum
BPM Signal Spectrum
Filtered BaseBand Spectrum
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1st-Turn Concept Using 402.5MHz Beam Spectral
Component
1 of 4 Channels
Low Frequency Processing
Diplexor Fc17MHz
To ADC
Mux
From PU
CPL -10dB
1st Few-Turns
(L10)
5Vp
400MHz BP Helical Filter Q20
Cal
3dB Pad
5MHz LPF
3dB Pad
20dB Pad
Cal Signal
PreScaler 1/2
398.5MHz 10dBm
402.5MHz
805MHz
3.3V
7V
Split 4-way 0-deg
Silicon Labs RF/IF Synthesizer Si4133
PWDN
Lo Ch.2
SDATA
From FPGA
Lo Ch.3
SCLK
Lo Ch.4
SEN
SiGe 25dB
Ref Freq 16Frev (16MHz)
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Rf Receiver Calculations

• Noise Floor
• -174dBm/Hz 10Log(5MHz) RF Attenuation
  -55dBm
• Signal Level (1st-Turn) 38mA (ave) Centered Beam
• 27dBm _at_ Pickup
• (1/4) Heliax Cable loss 4dB/100ft _at_ 400MHz
• Assume 300ft of Heliax
• Loss 12dB _at_ 400MHz
• SNR 30dB
• 38mA (ave) 20mm Offset Beam
• 44dBm _at_ Pickup
• SNR 50dB

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RF Receiver 1st-Turn Analysis(38mA average Beam
Current)
SNR 50dB Off Centered Beam
SNR 30dB(min) Centered Beam
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Si4133 Frequency Synthesizer
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Si4133 Synthesizer EVAL Programming Display
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RF PCB Stackup
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BPM Calibration

• Philosophy
• Achieve system gain normalization at BaseBand and
  RF by measuring System Through-Port response to
  remove systematic errors.
• Why This Works
• Using Log-Ratio processing, channel gains can be
  expressed as a constant obtained by measurement
  (S21 or Beam Based Alignment)

Gain Constant Obtained by S21 measurement
Interested in Ratio
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Measurement Setup
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Open Circuit BPM
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S21 H/V Ring BPM (Open 21cm Stripline)
-46dB _at_ 5MHz
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BPM S21 Measurements21cm Open Circuit Ring BPM

• 33dB H/V Sensitivity
• improvement at 400MHz

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BaseBand Calibration Methodology

• Assumptions
• BPM physical and electromagnetic variations
  considered constant (verified by measurement of
  small population)
• Calibration Methodology
• Inject 100ns (5V) Pulse into (1/4) Heliax
  transmission line via 10dB coupler towards
  pickup.
• Measurement capabilities
• S21 of two adjacent orthogonal planes
• S21 of parallel plane
• S11, reflected pulse from open stripline of
  incident port
• Repeat for orthogonal plane (Hor,Vert)

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RF Calibration Methodology

• Assumptions
• BPM physical and electromagnetic variations
  considered constant (verified by measurement of
  small population)
• Calibration Methodology
• Inject 402.5MHz Sinusoid into (1/4) Heliax
  transmission line via 10dB coupler towards
  pickup.
• Measure
• S21 of two adjacent orthogonal planes
• S21 of parallel plane
• Repeat for Orthogonal Plane (Hor, Vert)

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Calibration Implementation
Ch.1
FPGA
S11, S14
CPL -10dB
Cal Pulse (tw100ns)
Horizontal Cal. BB/RF
402.5MHz
LabView Curve Fit Peak Find Gain Normalization
Ch.2
S21, S24
PCI
Ch.3
S31, S34

• BPM
• Open Ckt
• Stripline
• 21cm

Ch.4
S41, S44
CPL -10dB
Cal Pulse (tw100ns)
Vertical Cal. BB/RF
402.5MHz
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H/V Plane Time Domain Transfer Function (S21)
Calibration Pulse
Differentiated Pulse coupled across planes
5V pulse injected into coupled port of 10dB
coupler Approximately 300ft of ¼ Heliax on each
BPM port
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BaseBand Bessel LPF Impulse Response
Calibration Pulse
Gaussian LPF Impulse Response
Same setup as previous slide with Gaussian 5MHz
LPF
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BaseBand Bessel LPF Impulse Response
Expanded Gaussian LPF Impulse Response
2.3mV peak

• Pulse width 74ns
• Acquire 4-samples/pulse (min) for fs64MHz
  (Ts15.625ns)

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Calibration Post Processing

• All calculations done in LabView
• Calibration Algorithm
• Curve-Fit data to determine peak of each channel
• Normalize with respect to maximum channel
• Store normalized gain coefficients
• Scale raw data by normalized gain coefficients
• Calibration Process performed for both RF and
  BaseBand. Two sets of Calibration Coefficients
  required.

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RF Electronics Status

• Detailed Design Complete
• Schematic in shop working on layout
• Completed Proof-of-Principal Calibration
  Concept
• Synthesizer characterization in process