# Presentation: 149953

## SNS BPMRF Electronicsand Calibration

- Kurt Vetter

## Outline

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

## 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

## 1st-Turn Spectral Analysis (M. Kesselman)

- Beam Spectrum

- BPM Signal Spectrum

- Filtered BaseBand Spectrum

## 1st-Turn Concept Using 402.5MHz Beam Spectral Component

- Diplexor
- Fc=17MHz

- Low Frequency
- Processing

- 400MHz BP
- Helical Filter
- Q=20

- 3dB
- Pad

- 5MHz
- LPF

- Silicon Labs
- RF/IF
- Synthesizer
- Si4133

- Split
- 4-way
- 0-deg

- To
- ADC

- Lo Ch.2

- Lo Ch.3

- Lo Ch.4

- PWDN~

- SDATA

- SCLK

- SEN~

- Ref Freq
- 16*Frev
- (16MHz)

- Cal

- From
-  PU

- SiGe
- 25dB

-  (L10)

- +3.3V

- From
- FPGA

- CPL
- -10dB

- Cal Signal

- 398.5MHz
- +10dBm

- 1st Few-Turns

- 3dB
- Pad

- 20dB
- Pad

- Mux

- PreScaler
- 1/2

- 402.5MHz

- 5Vp

- +7V

- 805MHz

- 1 of 4 Channels

## Rf Receiver Calculations

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

## RF Receiver 1st-Turn Analysis(38mA average Beam Current)

- SNR = 30dB(min)
- Centered Beam

- SNR = 50dB
- Off Centered Beam

## Si4133 Frequency Synthesizer

## Si4133 Synthesizer EVAL Programming Display

## RF PCB Stackup

## 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*

## Measurement Setup

## Open Circuit BPM

## S21 “H/V” Ring BPM (Open 21cm Stripline)

- -46dB @ 5MHz

## BPM S21 Measurements21cm Open Circuit Ring BPM

| Frequency | Planes
Measured | S21 Mag. | BPM  | Comments |
| --- | --- | --- | --- | --- |
| 5MHz | H/V | -46.373dB | Ring |  |
| 5MHz | H/H | -59.903dB | Ring |  |
|  |  |  |  |  |
| 400MHz | H/V | -13.842dB | Ring | Sample 1 |
| 400MHz | H/V | -13.847dB | Ring | Sample 2 |
|  |  |  |  |  |
| 400MHz | H/H | -21.059dB | Ring | Sample 1 |
| 400MHz | H/H | -21.089dB | Ring | Sample 2 |

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

## 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)

## 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)

- 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)

*RF Calibration Methodology*

## Calibration Implementation

- CPL
- -10dB

- Ch.4

- Ch.3

- Ch.2

- Ch.1

- FPGA

- S41, S44

- S31, S34

- S21,  S24

- S11,  S14

**BPM**
-  Open Ckt
-    Stripline
-  21cm

- LabView
- Curve Fit
- Peak Find
- Gain Normalization

- PCI

- Cal Pulse (tw=100ns)

- Horizontal Cal.
- BB/RF

- 402.5MHz

- CPL
- -10dB

- Cal Pulse (tw=100ns)

- Vertical Cal.
- BB/RF

- 402.5MHz

## H/V Plane Time Domain Transfer Function (S21)

- 5V pulse injected into coupled port of 10dB coupler
- Approximately 300ft of 1⁄4” Heliax on each BPM port

- Differentiated Pulse
- coupled across planes

- Calibration Pulse

## BaseBand Bessel LPF Impulse Response

- Same setup as previous slide with Gaussian 5MHz LPF

- Gaussian LPF
- Impulse Response

- Calibration Pulse

## BaseBand Bessel LPF Impulse Response

-  Pulse width = 74ns
-  Acquire 4-samples/pulse (min) for fs=64MHz (Ts=15.625ns)

- 2.3mV peak

- Expanded Gaussian LPF
- Impulse Response

## 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.

## RF Electronics Status

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