BPM Signal Processing withLog Amps

DITANET WorkshopCERN

16-18 January 2012

José Luis Gonzalez – CERN/BE/BI

JL Gonzalez - CERN/BE/BI 2

Outline

• Introduction• Logarithmic Amplifiers Basics• Position Measurement– Electrostatic BPM Principle– Log Derivation

• Position Measurement with Log-Amps– Shoe-box and Button BPM– Applications

• Summary

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Introduction

• BPM signal processing methods– Difference over Sum– Multiplexing (RF Receivers)– Normalization (Amplitude to Time Conversion)– Log processing (High Dynamic Range)

• Main Applications– Orbit Measurements– Trajectory

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Logarithmic Amplifiers

• What do they do?– Convert signals of high dynamic range to a

substantially smaller dynamic range – The output is readily scaled to represent the

decibel value of the input– This is a nonlinear conversion of the signal

representation

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From Barrie Gilbert (Analog Devices)

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Logarithmic Amplifiers

• Fundamental Function

whereVW is the Output voltageVX . . . . . Input voltage VY . . . . . Slope voltageVZ . . . . . Log Intercept voltage

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Z

XYW V

VVV log

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The Basic Logarithmic Relationship

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Z

XYW V

VVV log

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Logarithmic Function Approximation

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• The backbone is a chain of simple Amplifier Cells• FUNCTION is a type of PIECEWISE LINEAR APPROXIMATION

2AEK

3AEK

4AEK

A EK

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The A/0 Amplifier (Limiter)

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KINKOUT

KININOUT

EVforEAVEVforVAV

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Progressive Compression 4-Stage Example

Vx very low (< EK)• Linear response: VW = (1+A+A2+A3+A4)VX

• EK remains hidden

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Progressive Compression 4-Stage Example

• For Vx = EK/A3

• Then VW = (A+1+A-1+A-2+A-3)EK

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Progressive Compression 4-Stage Example

• For Vx = EK/A2

• Then VW = (2A+1+A-1+A-2)EK

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Progressive Compression 4-Stage Example

• For Vx = EK

• Then VW = (4A+1)EK

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Progressive Compression 4-Stage Example

• For Vx > EK

• Then VW = 4AEK + Vx

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Z

XYW V

VVV log

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Log-Amp Slope and Intercept

• Slope (V/dB):

• Intercept (V):

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AEAV K

Y log

11

NN

KZ

A

EV

Adding an offset to the outputlowers the intercept

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Position Measurement Principle

• Electrostatic BPM

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ydownup

downup

y UUUU

Sy

1

xleftright

leftright

x UUUU

Sx

1

From P. Forck et al. (GSI, Darmstadt, DE)

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Position Measurement Principle

• Logarithmic derivation of normalized position

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10ln2log

lnlnlog

...53

211ln

53

xBA

aXX

xxxxx

a

xx

BA

BABAx

11

210ln

loglog

K

BAKx

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Position Measurement Principle

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A

B

LogAmp

Diff. Amp.

Position = K*Vout

BPFilter

LogAmp

BPFilter

ADCVout

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Theoretical Log Response

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-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

LinearLog(A/B)1.5Log(A/B)

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Log Conformance Error

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-0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5-0.05

-0.04

-0.03

-0.02

-0.01

0.00

0.01

0.02

0.03

0.04

Log_error1.5Log_errorLog_linearised1.5Log_linearised

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Button BPM Response

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-20 -15 -10 -5 0 5 10 15 20-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

A+BA-B(A-B)/(A+B)Log(A/B)Si

gnal

a=25mm, =00, =300

AB

2/

2/

22

22

)(

)cos(22)(

djaI

arrara

aIj

imim

beamim

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Button BPM Linearity Error

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-15 -12 -9 -6 -3 0 3 6 9 12 15-0.05

-0.04

-0.03

-0.02

-0.01

0.00

0.01

0.02

0.03

0.04

0.05

D/S_Lin-errorLog_Lin-error

a=25mm, =00, =300AB

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Commercial Log-Amp

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From Bergoz (sales@bergoz.com)

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CERN Transfer Lines Log-Amps

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From Thierry Bogey (CERN)

BPM Front-end

AD8306

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Log-Amp performance

AD8306100 dB Dynamic Range (±3dB) : –91 to +9 dBV Input Frequency Range: 5-400MHz±0.4 dB Log Linearity: -67 to +13dBmStable Log Scaling: 20 mV/dB Slope Input noise: < 1.5 nV/√HzDITANET-BPM Jan2012

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Front-End Characteristics

• Position and Intensity available• Large dynamic range without requiring gain switching• Two integration times are implemented (200 ns and 1 µs)

• Auto-triggered• No requirement for external timing in the tunnel

• Calibrator• Remotely triggered• Single or 40 MHz LHC bunch simulation• It offers 0 dB (center) and ± 5 dB ratio (slope)

• Analog to digital conversion• Serial transmission of ADC data to surface buildings

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CNGS Beam Acquisition Example10 s Batch (2.2E13 protons), 2000 bunches spaced by 5 ns

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Log A

Integrator Out

Integrator Gate

Pos ≈ Log A- Log B

2µS

1µS

Pos turn 1 Pos turn 2

Pos turn 3Pos turn 4

Pos turn 5

2µS 2µS 2µS 2µS

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Dual Log-Amp Chips

• Analog Devices AD8302 (Gain & Phase Det.)

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Dynamic Range (60dB): -60 to 0dBm

Input Frequency Range: 0 to 2.7GHz

Scaling: 30 mV/dB Small Signal Envelope Bandwidth:

DC to 30 MHz Rise/Fall time (10%–90%):

20 dB change: 60 ns Settling time to 1%:

60 dB change: 300 ns

Typical Nonlinearity (100MHz)• < 0.5 dB over 55 dB• < 0.2dB over 42 dB

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Dual Log-Amp Chips

• Analog Devices ADL5519 (Dual Log Detector)

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Dynamic Range (60dB): -55 to 5dBm

Input Frequency Range: 0.1-10GHz Scaling: 22 mV/dB Small Signal Envelope Bandwidth:

DC to 50 MHz Rise/Fall time (20%–80%):

40 dB change: 16 ns Output noise: 10 nV/√Hz

Typical Nonlinearity• < 0.5 dB over 47 dB• < 0.2dB over 40 dB

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Dual Log-Amp Chips

• Maxim MAX2016 (Dual Log Detector)

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Dynamic Range (80dB): -70 to 10dBm

Input Frequency Range: 0.1-2.5GHz Scaling: 20 mV/dB Small Signal Envelope Bandwidth:

DC to 22 MHz Rise/Fall time (20%–80%):

• Log-output (8dB): 15ns• Diff-output (30 dB): 35 ns

Settling time to ±0.5dB:• Log-output (60dB): 100ns• Diff-output (30 dB): 300 ns

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SPS Beams

• Protons (14 or 26-450GeV/c)charge dynamic range 54 dB (1e9 – 5e11)– RF swing: 199.94 or 200.26MHz 200.39MHz– Frev swing: 43.278 or 43.347kHz 43.375kHz

• LHC-Ions Pb82+ (17.1-450GeV/c)charge dynamic range 46 dB (1e8 – 2e10)– RF swing: 199.93MHz 200.39MHz– Frev swing: 42.967kHz 43.375kHz

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SPS BPM Front-End

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Summary

• Irradiation of a set of these components is on going to select the most robust

• Front-end prototypes are under development• Log Amps are very powerful– Simple implementation– Wide dynamic range

• Limitations– Don’t allow direct single bunch measurement yet

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THANKS FOR YOUR ATTENTION!

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Spare slides

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Lead Ion Beam Acquisition

2 Ion Bunches (2x1.3E10 charges) spaced by 200 ns

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200nS

Integrator Gate

Log A

Pb54 Ion Beam

Pos ≈ Log A- Log B

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SPS Beam Position Monitors

Total = 216 BPMs: 6 x 36 slots

• Current MOPOS acquisition channels: 240 [6 x 40 slots]• Future needs [2-plane BPMs] ≥ 432 channels

Monitor Type Physical BeamAperture (mm)

Quantity MechanicalSection

Comments

BPH 44V x 154H 103 rectangular Electrostatic shoe-box

BPV 83 x 83 94 square Electrostatic shoe-box

BPA 269 4 circular Resonant cavity [LSS2]

BPD 269 2 circular BPA emulation [LSS1]

BPCN 76 7 circular Strip-linedirectional couplers BPCE 206 6 circular

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SPS BPM Resolution & AccuracyResolution of the BPM system

over ±15 mm aperture

• Resolution for large intensity beams (>2.1010 p/b)– Orbit mode (averaging over 40 turns): 0.1 mm

BPH [Na=77mm]: 0.1% BPV [Na=41.5mm]: 0.2%– Trajectory mode (single turn): 0.4 mm (should be much better in the center)

BPH: 0.5%BPV: 1%

• Resolution for single bunches [low/very low intensity](LHC pilot [2.109 p], Pb ions [1…5.108 charges])– Orbit mode (averaging over 40 turns): 0.4 mm

BPH: 0.5%BPV: 1%– Trajectory mode (single turn): 1 mm

BPH: 1.3%BPV: 2.4%