Istituto Nazionale di Fisica Nucleare
Sezione di Pisa
Largo Bruno Pontecorvo, 56127 Pisa – Italy. http://www.pi.infn.it
VIRGO Collaboration
Actuation Noise in Virgo+ and Advanced Virgo
Document Number: VIR-0146A-10
Issue: 1.0
Date: 05/02/2010
Author: Alberto Gennai
Actuation Noise in Virgo+ and
Advanced Virgo
Doc Nr: VIR-0146A-10 Issue: 1.0 Date: 05/02/2010 Page 2 of 15
Change Record
Issue Date Affected Paragraphs Reason/Remarks Author
1.0 05/02/2010 All First issue A. Gennai
Table Of Contents
1. INTRODUCTION ................................................................................................................. 3
1.1 PURPOSE & SCOPE ............................................................................................................ 3 1.2 ACRONYMS ...................................................................................................................... 3 1.3 REFERENCES .................................................................................................................... 3
2. VIRGO COIL DRIVER ........................................................................................................ 4
2.1 OVERVIEW ....................................................................................................................... 4 2.2 COIL DRIVER NOISE ......................................................................................................... 4
2.3 DAC NOISE ...................................................................................................................... 7 2.3.1 Old Coil Driver ............................................................................................................ 8
3. SIGNALS DYNAMIC ........................................................................................................... 9
3.1 REFERENCE MASS – MIRROR ACTUATORS ........................................................................ 9 3.2 FILTER #7 - MARIONETTE ............................................................................................... 11
4. PAYLOAD TRANSFER FUNCTIONS ............................................................................. 12
4.1 REFERENCE MASS – MIRROR .......................................................................................... 12
4.2 FILTER #7 – MARIONETTE ............................................................................................... 13
5. NOISE BUDGET ................................................................................................................ 13
5.1 VSR2 NOISE BUDGET ..................................................................................................... 13
5.2 VIRGO+ MS NOISE BUDGET ........................................................................................... 14
5.3 ADVANCED VIRGO ......................................................................................................... 14
Actuation Noise in Virgo+ and
Advanced Virgo
Doc Nr: VIR-0146A-10 Issue: 1.0 Date: 05/02/2010 Page 3 of 15
1. INTRODUCTION
1.1 Purpose & Scope This document presents the noise budget for lower stage actuators for Virgo Science Run no. 2
(VSR2), Virgo+ with monolithic payloads (Virgo+MS) and Advanced Virgo (AdvV) . Main
purpose is the preparation of the Virgo+MS total noise budget.
The content of this document was presented to the Virgo Collaboration at the Advanced Virgo
meeting held in Cascina on February 4th, 2010 and at the Commissioning/Detector Meeting on
February 8th, 2010.
1.2 Acronyms This document contains several abbreviations and acronyms to refer concisely to an item after it has
been introduced. The following list is aimed to help the reader in recalling the extended meaning of
each short expression.
AdvV Advanced Virgo
CD Coil Driver
DAC Digital to Analog Converter
DSP Digital Signal Processor
RD Reference Document
Virgo+MS Virgo+ with Monolithic payloads
VSR2 Virgo Science Run No. 2
1.3 References This report refers to the following documents containing background or detailed information that
can be useful for the reader.
[RD1] A.Gennai, Actuators Noise in AdvV, VIR-0093A-10 Presentation to the AdvV Meeting,
February 4th, 2010
[RD2] M.Bitossi, A.Gennai, D. Passuello, Low Noise DAC Selection for Advanced Virgo, VIR-
0078A-10, January 20th, 2010
A. Gennai, DAC Noise Effect on Virgo Sensitivity, VIR-0006B-09, October 2nd, 2009
[RD3] Gennai, DAC Noise Contribution to Virgo Sensitivity, VIR-0072A-08, June 6th, 2008
[RD4] Gennai, New Coil Driver Measurements, VIR-0010C-08, March 23rd, 2008
[RD5] Gennai, Coil Driver Final Design Document, VIR-SPE-PIS-4900-121, September 30th, 2004
Actuation Noise in Virgo+ and Advanced Virgo
2. VIRGO COIL DRIVER
2.1 Overview In Virgo, mirrors actuation along laser beam direction is performed using 6 electromagnetic
actuators. Two horizontal actuators ac
Filter#7) while 4 actuators act directly on mirror from recoil mass (also known as ‘reference’ mass).
Starting from position error, the Suspension Control System computes forces
Processors (DSP).
In a magnet-coil actuator, force is proportional to the current flowing in the coil. The Coil Driver
(CD) is the electronic device that converts the voltage at the output of the Digital to Analog
Converter (DAC) into a current flowing int
Figure
New Coil Drivers, currently installed at terminal north and west suspensions, have a voltage to
current conversion factor that is remotely selectable with a smooth transition from one operation
mode to the next one. Five are the available operational modes: HIGHPOWER, used during cavities
lock acquisition phase, and LOWNOISE1 to LOWNOISE4 used during linear regime. Fur
details on coil drivers and their operational modes can be found in
2.2 Coil Driver Noise Coil Driver noise can be evaluated using an accurate PSPICE simulation and
measured values (see [RD4]). The f
simulation. Three distinct blocks put in evidence the input differential stage, the noise shaping filter
and the series resistor. Changing operating mode we simply change the value of the series resi
Monitoring network is reported only to keep into account of its noise contribution.
shown corresponds to the second order filter (two poles
coil driver. Actual design foresees the possibility
filter) to 5th.
Actuation Noise in Virgo+ and
Advanced Virgo
Doc Nr: VIR-0146AIssue: 1.0 Date: 05/02/2010 Page 4 of 15
VIRGO COIL DRIVER
In Virgo, mirrors actuation along laser beam direction is performed using 6 electromagnetic
actuators. Two horizontal actuators act on Marionette from the Steering Filter (also known as
Filter#7) while 4 actuators act directly on mirror from recoil mass (also known as ‘reference’ mass).
Starting from position error, the Suspension Control System computes forces using Digital Signal
coil actuator, force is proportional to the current flowing in the coil. The Coil Driver
(CD) is the electronic device that converts the voltage at the output of the Digital to Analog
Converter (DAC) into a current flowing into the coil.
Figure 1 Sketch of the control chain
New Coil Drivers, currently installed at terminal north and west suspensions, have a voltage to
factor that is remotely selectable with a smooth transition from one operation
mode to the next one. Five are the available operational modes: HIGHPOWER, used during cavities
lock acquisition phase, and LOWNOISE1 to LOWNOISE4 used during linear regime. Fur
details on coil drivers and their operational modes can be found in [RD4] and [RD5]
Coil Driver noise can be evaluated using an accurate PSPICE simulation and a comparison
. The following picture shows the coil driver schematic used in
simulation. Three distinct blocks put in evidence the input differential stage, the noise shaping filter
and the series resistor. Changing operating mode we simply change the value of the series resi
Monitoring network is reported only to keep into account of its noise contribution.
shown corresponds to the second order filter (two poles – two zeros) we are using in the installed
coil driver. Actual design foresees the possibility to implement filter with order ranging from 0 (no
0146A-10
In Virgo, mirrors actuation along laser beam direction is performed using 6 electromagnetic
t on Marionette from the Steering Filter (also known as
Filter#7) while 4 actuators act directly on mirror from recoil mass (also known as ‘reference’ mass).
using Digital Signal
coil actuator, force is proportional to the current flowing in the coil. The Coil Driver
(CD) is the electronic device that converts the voltage at the output of the Digital to Analog
New Coil Drivers, currently installed at terminal north and west suspensions, have a voltage to
factor that is remotely selectable with a smooth transition from one operation
mode to the next one. Five are the available operational modes: HIGHPOWER, used during cavities
lock acquisition phase, and LOWNOISE1 to LOWNOISE4 used during linear regime. Further
[RD5].
a comparison with
ollowing picture shows the coil driver schematic used in
simulation. Three distinct blocks put in evidence the input differential stage, the noise shaping filter
and the series resistor. Changing operating mode we simply change the value of the series resistor.
Monitoring network is reported only to keep into account of its noise contribution. Shaping filter
two zeros) we are using in the installed
to implement filter with order ranging from 0 (no
Actuation Noise in Virgo+ and Advanced Virgo
Noise refereed to the output of the coil driver, expressed in Ampere/sqrt(Hz) is of course a function
of the operating mode since changing operating mode we change the voltage to current conversion
factor.
Figure
Due to the second order low pass filter, referring the Coil Driver noise to its input, we obtain the
following picture where at frequencies bigger than about 10 Hz noise is ‘amplified’ by the filter
C10
1n
0
R2122k
C7
1n
U3B
OPA2604E/BB
+5
-6
V+8
V-4
OUT7
+15
ilnmoni
-15
R20
47k
R17
47k
U12
AD8671
+1
-2
V+3
V-4
OUT5
U13
AD8671
+1
-2
V+3
V-4
OUT5
DIFFERENTIAL INPUT STAGE
-15
R1
1k
R10
1k
R2
560
0
R11
560R13100k
OP-27A/AD
+3
-2
C110n
C510n
C410n
0
R14100k
VIN11Vac0Vdc
+15
+15
-15
V115Vdc
0V2
15Vdc
+15
-15
U11A
OPA2604E/BB
OUT1
-15
ihpmoni
R35
47k
0
R2322k
C8
1n
U7A
OPA2604E/BB
+3
-2
V+8
V-4
OUT1
+15
-15
R22
47k
R19
1.6k
C6
5u
Actuation Noise in Virgo+ and
Advanced Virgo
Doc Nr: VIR-0146AIssue: 1.0 Date: 05/02/2010 Page 5 of 15
Figure 2 Coil Driver Schematic
Noise refereed to the output of the coil driver, expressed in Ampere/sqrt(Hz) is of course a function
changing operating mode we change the voltage to current conversion
Figure 3 Coil Driver Output Noise
Due to the second order low pass filter, referring the Coil Driver noise to its input, we obtain the
following picture where at frequencies bigger than about 10 Hz noise is ‘amplified’ by the filter
R9
{rval}
R3622k
0
U14
AD8671
+1
-2
V+3
V-4
OUT5
R26
100k
R27100k
U15
AD8671
+1
-2
V+3
V-4
OUT5
0
U10
AD743J/AD
+3
-2
V+7
V-4
OUT6
N11
N25
+15
-15
vmoni
R300.1
0
R12
560
R3
560
0
U7B
OPA2604E/BB
+5
-6
V+8
V-4
OUT7
R4
33k
+15
R53.6k
-15
0
C24.7u
+15
-15
U2
OP-27A/AD
V+7
V-4
OUT6
N11
N28
-15
R16
560
R25
560
R24
560
R15
560
0
+15
-15
U8
OP-27A/AD
+3
-2
V+7
V-4
OUT6
N11
N28
+15
+15
-15
R28
1k
R31
1k
R3250k
0
R34
50k
U3A
OPA2604E/BB
+3
-2
V+8
V-4
OUT1
U11A
OPA2604E/BB
+3
-2
V+8
V-4
OUT
+15
-15
+15
R35
47k
-15
SHAPING FILTER
R29
47k
R6
33k R73.6k
0
C34.7u
VOLTAGE AND CURRENT MONITORING
R33
1.6k
U4
AD743J/AD
+3
-2
V+7
V-4
OUT6
N11
N25
C9
5u
+15
-15
SERIES RESISTOR
R18
47kR19
1.6k
R8
{rval}
PARAMETERS:rval = 150
LN1 --> rval = 150LN2 --> rval = 600
LN3 --> rval = 1200LN4 --> rval = 2400
0146A-10
Noise refereed to the output of the coil driver, expressed in Ampere/sqrt(Hz) is of course a function
changing operating mode we change the voltage to current conversion
Due to the second order low pass filter, referring the Coil Driver noise to its input, we obtain the
following picture where at frequencies bigger than about 10 Hz noise is ‘amplified’ by the filter
RCOIL110
+-
H1
H
LCOIL13mH
1
2
icoil
Rdummy11
0
COIL (cabling included)
VOLTAGE AND CURRENT MONITORING
Actuation Noise in Virgo+ and Advanced Virgo
itself. We should in fact notice that voltage gain (from
output) is lower or equal to one and therefore input stage noise is not dominant in respect with
shaping filter noise.
For better understanding, we can comp
order filter.
Figure 5 Low Noise 1 Output Noise: Comparison between
Actuation Noise in Virgo+ and
Advanced Virgo
Doc Nr: VIR-0146AIssue: 1.0 Date: 05/02/2010 Page 6 of 15
itself. We should in fact notice that voltage gain (from differential stage input to shaping filter
and therefore input stage noise is not dominant in respect with
Figure 4 Input Referred Noise
For better understanding, we can compare output and input noise using a first order and a second
Low Noise 1 Output Noise: Comparison between 1st order and 2nd order shaping filter
0146A-10
differential stage input to shaping filter
and therefore input stage noise is not dominant in respect with
are output and input noise using a first order and a second
1st order and 2nd order shaping filter
Actuation Noise in Virgo+ and Advanced Virgo
Figure 6 Low Noise 1 Input Referred Noise: Comparison between 1st order and 2nd order shaping filter. High frequency (1 kHz) value is about 270 nV/sqrt(Hz). Completely removing shaping filters that value drops down to
about 12 nV/sqrt(Hz) while low frequency (below 1 Hz)
2.3 DAC Noise Once coil driver noise is known we can evaluate the contribution of DAC noise both at CD input
and output. In the following two plots we used the DAC noise measured as described in
and [RD3]. With filters in use during VSR2 (where only LOWNOISE1 was used) DAC
contribution equals CD contribution betw
Figure 7 Input Referred Noise superposed to DAC noise estimate
1 Removing the shaping filter block, we gain a factor ~10 due to filter transfer function. Total noise is furthermore reduced by the amount of noise introduced by the shaping filter operational amplifiers and resistors.
Actuation Noise in Virgo+ and
Advanced Virgo
Doc Nr: VIR-0146AIssue: 1.0 Date: 05/02/2010 Page 7 of 15
Noise: Comparison between 1st order and 2nd order shaping filter. High
frequency (1 kHz) value is about 270 nV/sqrt(Hz). Completely removing shaping filters that value drops down to about 12 nV/sqrt(Hz) while low frequency (below 1 Hz) behaviour remains unchanged
Once coil driver noise is known we can evaluate the contribution of DAC noise both at CD input
and output. In the following two plots we used the DAC noise measured as described in
. With filters in use during VSR2 (where only LOWNOISE1 was used) DAC
contribution equals CD contribution between 20 and 30 Hz.
Input Referred Noise superposed to DAC noise estimate
Removing the shaping filter block, we gain a factor ~10 due to filter transfer function. Total noise is furthermore reduced by the amount of noise introduced by the shaping filter operational amplifiers and resistors.
0146A-10
Noise: Comparison between 1st order and 2nd order shaping filter. High frequency (1 kHz) value is about 270 nV/sqrt(Hz). Completely removing shaping filters that value drops down to
nchanged1.
Once coil driver noise is known we can evaluate the contribution of DAC noise both at CD input
and output. In the following two plots we used the DAC noise measured as described in [RD2]A
. With filters in use during VSR2 (where only LOWNOISE1 was used) DAC
Removing the shaping filter block, we gain a factor ~10 due to filter transfer function. Total noise is furthermore
Actuation Noise in Virgo+ and Advanced Virgo
Figure 8 Output Noise: Coil Driver and DAC Contribution
2.3.1 Old Coil Driver It is worth reminding here that during VSR2 we used old coil drivers for Filter #7
actuators. Behaviour is different from the one described up to now and applicable to new coil
drivers (acting in VSR2 on mirror only).
nV/sqrt(Hz), almost flat above 1 Hz. At its input there is a first order shaping filter (pole at 0.9 Hz,
zero at 9 Hz). Output noise, including DAC noise contribution,
Figure 9 Old Coil Driver Output Noise (DAC contribution included)
Actuation Noise in Virgo+ and
Advanced Virgo
Doc Nr: VIR-0146AIssue: 1.0 Date: 05/02/2010 Page 8 of 15
Output Noise: Coil Driver and DAC Contribution
during VSR2 we used old coil drivers for Filter #7
Behaviour is different from the one described up to now and applicable to new coil
drivers (acting in VSR2 on mirror only). Voltage gain is 2 while input referred noise is about 10
nV/sqrt(Hz), almost flat above 1 Hz. At its input there is a first order shaping filter (pole at 0.9 Hz,
, including DAC noise contribution, is shown in the following picture.
Old Coil Driver Output Noise (DAC contribution included)
0146A-10
during VSR2 we used old coil drivers for Filter #7 – Marionette
Behaviour is different from the one described up to now and applicable to new coil
Voltage gain is 2 while input referred noise is about 100
nV/sqrt(Hz), almost flat above 1 Hz. At its input there is a first order shaping filter (pole at 0.9 Hz,
is shown in the following picture.
Actuation Noise in Virgo+ and
Advanced Virgo
Doc Nr: VIR-0146A-10 Issue: 1.0 Date: 05/02/2010 Page 9 of 15
3. SIGNALS DYNAMIC Once the noise is known we have to decide what should be the equivalent displacement. Adding a
series resistor to the coil we can reduce the noise equivalent displacement but of course in this way
we also limit the maximum displacement we can achieve. A correct evaluation of required
dynamical range is therefore important for selecting a proper operational mode. For this purpose we
analyzed the first 231 science mode segments during VSR2 (almost all segments). A Science Mode
segment is the time interval in which Virgo interferometer is acquiring scientific data and
corresponds to more than 80% of the total time. Each Science Mode segment was than split into 30
minutes sub-segments and for each segment we computed mean value, standard deviation and
absolute maximum. Analysis was performed only for end mirrors since input mirrors are not driven
along the beam direction and other mirrors have a negligible contribution to total noise.
3.1 Reference Mass – Mirror Actuators
Actuation Noise in Virgo+ and
Advanced Virgo
Doc Nr: VIR-0146A-10 Issue: 1.0 Date: 05/02/2010 Page 10 of 15
As we can clearly see from last two plots, we used only a small fraction of available dynamical
range. We could in fact operate in LOWNOISE2 mode (4x series resistor) for about 95% of science
mode time and in LOWNOISE3 mode (8x series resistor) for more than 80% of science mode time.
Figure 10 Reference Mass - Mirror Actuators. The two plotted lines correspond to two different period of time
Actuation Noise in Virgo+ and
Advanced Virgo
Doc Nr: VIR-0146A-10 Issue: 1.0 Date: 05/02/2010 Page 11 of 15
3.2 Filter #7 - Marionette
In this case we can see that we could operate for 99% of science mode time inserting a 5x series
resistor.
Actuation Noise in Virgo+ and
Advanced Virgo
Doc Nr: VIR-0146A-10 Issue: 1.0 Date: 05/02/2010 Page 12 of 15
Figure 11 Filter#7-Marionette Actuators
Looking at DAC output spectra and comparing with the spectra of reference mass coils (Figure 10)
we notice that at F7 coils we can have a further improvement increasing low pass filter order (from
1st to 2nd)
4. PAYLOAD TRANSFER FUNCTIONS For a correct evaluation of actuation noise contribution we use a model of the payload transfer
function.
4.1 Reference Mass – Mirror DC displacement is about 5.5 um/A per coil. For example, using two coils as we did in VSR1 and
VSR2 we have 11 um/A DC displacement. Mechanical transfer function is the classical single
pendulum response with 0.6 Hz as resonant factor and a quality factor large enough to be assumed
equal to infinity.
Above resonant frequency (0.6 Hz), mechanical transfer function is therefore
|����� � ��| 5.5 10�� ���
��
� ����
�� � �⁄ (acting with 1 coil)
Actuation Noise in Virgo+ and
Advanced Virgo
Doc Nr: VIR-0146A-10 Issue: 1.0 Date: 05/02/2010 Page 13 of 15
4.2 Filter #7 – Marionette Acting from filter #7 onto Marionette, DC displacement is about 1.7 um/VDAC (using a single coil
and old coil drivers) corresponding to 0.85 um/Vcoil or, assuming the coil impedance to have a real
part equal to 16 Ohm, 7 um/A. Mechanical transfer function is equivalent to a double pendulum
response having f1=0.46 Hz and f2=0.98 Hz as resonant frequencies:
|���� � ��| 0.85 10�� �����
�
��
�. ! ���"
�� m/V (with 1 horizontal coil)
or, equivalently
|���� � ��| 7 10�� �����
�
��
�.$ ����
�� m/A (with 1 horizontal coil)
5. NOISE BUDGET
5.1 VSR2 Noise Budget In VSR2 we used the following configuration: new coil drivers in LOWNOISE1 mode acting on
two coils at NE and WE. NI and WI mirrors, due to the extremely large value used for series
resistors (6 kOhm), give a negligible contribution to long arms actuator noise.
Coil driver used for Filter #7-Marionette actuators is the old one with a first order shaping filter.
Figure 12 VSR2 Actuators Noise Budget (Long Arms only)
101
102
10-24
10-23
10-22
10-21
10-20
10-19
10-18
VSR2 Actuators Noise Budget
Frequency (Hz)
h [1
/sqr
t(H
z)]
F7-Mar Actuation NoiseRM-Mirr Actuation Noise
Virgo Design
VSR2 Sensitivity
Virgo+MS DesignAdvanced Virgo Design
Actuation Noise in Virgo+ and
Advanced Virgo
Doc Nr: VIR-0146A-10 Issue: 1.0 Date: 05/02/2010 Page 14 of 15
5.2 Virgo+ MS Noise Budget After monolithic payloads installation, thermal noise contribution to Virgo sensitivity will drop
down. Meeting requirement for actuation noise is possible using the LOWNOISE2 mode at
reference mass level and adding a 5x series resistor to marionette actuators.
Figure 13 Virgo+ Monolithic Payloads Actuators Noise (Long Arms only)
To be noticed that further improvements are possible implanting second order filter at Filter#7-
Marionette level and switching to LOWNOISE3 mode at reference mass – marionette level.
Furthermore acting on more coils (at present we use only 2 of the 4 coils available) and/or more
mirrors (at present we act only on end mirrors and we do not use input mirrors for cavities
longitudinal lock).
5.3 Advanced Virgo With Advanced Virgo we will be able to take advantage from new DAC. Recent measurements on
evaluation boards show that new DAC performances are much better than old converters (see
[RD2]) with a gain of a factor about 20 at 10 Hz.
101
102
10-24
10-23
10-22
10-21
10-20
10-19
10-18
V+MS Actuators Noise Budget
Frequency (Hz)
h [1
/sqr
t(H
z)]
F7-Mar Actuation NoiseRM-Mirr Actuation Noise
Virgo Design
VSR2 Sensitivity
Virgo+MS DesignAdvanced Virgo Design
Actuation Noise in Virgo+ and
Advanced Virgo
Doc Nr: VIR-0146A-10 Issue: 1.0 Date: 05/02/2010 Page 15 of 15
Figure 14 Advanced Virgo Actuators Noise (Long Arms only)
Moving from old DAC to new one we will reduce DAC noise by about a factor 20 at 10 Hz. As it
can be noticed comparing Figure 13 and Figure 14, sensitivity will not improve by the same amount
since DAC noise is not the limiting noise (see Chapter 2.3). The actual gain is at low-pass filter
level where we could guarantee the same performances using a 1st order filter
Increased linearity will allow achieving required performances without dithering (either ‘natural’ or
‘artificial’)
oOo
101
102
10-24
10-23
10-22
10-21
10-20
10-19
10-18
AdV Actuators Noise Budget
Frequency (Hz)
h [1
/sqr
t(H
z)]
F7-Mar Actuation NoiseRM-Mirr Actuation Noise
Virgo Design
VSR2 Sensitivity
Virgo+MS DesignAdvanced Virgo Design