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ID Date Author Type Categoryup Subject
  3898   Thu Nov 11 17:47:36 2010 kiwamuUpdateGreen Locking80MHz VCO : improve PLL hold-in range and put a boost

In order to enlarge the hold-in range I modified the control filter and increased the gain by factor of 25 in the PLL.

It successfully enlarged the range, however the lock was easily broken by a small frequency change.

So I put a low frequency boost (LFB) and it successfully engaged the PLL stiffer.

Now it can maintain the lock even when the frequency disturbance of about 1MHz/s is applied.

 


(enlargement of the hold-in range)

I modified the control filter by replacing some resistors in the circuit to increase the gain by factor of 25.

        - R18 390 [Ohm]  => 200 [Ohm]

    - R20 1000 [Ohm] => 5000 [Ohm]

    - R41 39 [Ohm] => 10 [Ohm]

 This replacement also changes the location of the pole and the zero

    - pole 1.5 [Hz] => 0.3 [Hz]

    - zero 40 [Hz] => 159 [Hz]

 Note that this replacement doesn't so much change the UGF which was about 20 kHz before.

It becomes able to track the input frequency range of +/- 5MHz if I slowly changes the frequency of the input signal. 

However the PLL is not so strong enough to track ~ 1 kHz / 0.1s frequency step.  

 

(make the PLL stiffer : a low frequency boost)

One of the solution to make the PLL stiffer is to put a boost filter in the loop.

I used another channel to more drive the VCO at low frequency. See the figure below.

 vco_pll.png

The 80MHz VCO box originally has two input channels, one of these inputs was usually disabled by MAX333A.

This time I activated both two input channels and put the input signal to each of them.

Before signals go to the box, one of the signal path is filtered by SR560. The filter has G=20000, pole=0.3Hz. So it gives a big low frequency boost.

VCO_lfb.png

Once the PLL was achieved without the boost, I increased the filter gain of SR560 to 20000 because locking with the boost is difficult as usual.

 

  3908   Fri Nov 12 12:06:11 2010 AidanConfigurationGreen LockingPID script working - now it needs to be tuned

 I've set up a PID script that senses the EX-PSL Green Beat note (from the frequency counter) and actuates on the temperature of the end laser to drive the beat note to a given setpoint.

  • I've added the necessary EPICS channels to c1iscaux and rebooted it so that the channels are live. They are listed in a new database file slow_grnx_pid.db
  • This database was added to the list of those loaded by startup.cmd.  
  • The PID script, GRNXSlowServo, is just a modified version of FSSSlowServo.
  • The version I've been running is currently in /cvs/cds/caltech/users/abrooks/.
  • There's also an MEDM screen in this directoy, C1LSC_EX_GRN_SLOW.adl, there that shows the PID settings.

Right now the script only passes the initial sanities checks, that is:

  1. It runs.
  2. You can enable/disable it without any errors and it starts actuating.

The settings all need to be tuned up - e.g. maximum_increment, hard_stops, time_step, PID constants.

Additionally, the units in the whole thing are pretty useless - some of the channels are in VOLTS, others in WATTS. I'd like to change all these to be in Hz. 


EPICS channels added:

  • grecord(ao,"C1:LSC-EX_GRN_SLOWKD")
  • grecord(ao,"C1:LSC-EX_GRN_SLOWKP")
  • grecord(ao,"C1:LSC-EX_GRN_SLOWKI")
  • grecord(ao,"C1:LSC-EX_GRN_PID_SETPT")
  • grecord(ao,"C1:LSC-EX_GRN_TIMEOUT")
  • grecord(stringin,"C1:LSC-EX_GRN_SLOWVERSION")
  • grecord(bi,"C1:LSC-EX_GRN_SLOWLOOP")
  • grecord(bi,"C1:LSC-EX_GRN_DEBUG")
  • grecord(bi,"C1:LSC-EX_GRN_SLOWBEAT")
 

 

Attachment 1: Screen_shot_2010-11-12_at_12.05.01_PM.png
Screen_shot_2010-11-12_at_12.05.01_PM.png
  3920   Mon Nov 15 11:52:22 2010 kiwamuUpdateGreen LockingPLL with real green signal

 PLL_with_green.png

Stabilizing the beat note frequency using Yuta's temperature servo (see this entry)

I was able to acquire the PLL of 80MHz VCO to the real green signal.

Some more details will be posted later.

  3927   Mon Nov 15 17:10:59 2010 kiwamuUpdateGreen LockingPLL with real green signal

 I checked the slow servo and the PLL of 80MHz VCO using the real green beat note signal.

 The end laser is not locked to the cavity, so basically the beat signal represents just the frequency fluctuation of the two freely running lasers.

 The PLL was happily locked to the green beat note although I haven't fedback the VCO signal to ETMX (or the temperature of the end laser).

 It looks like we still need some more efforts for the frequency counter's slow servo because it increases the frequency fluctuation around 20-30mHz.

 


 (slow servo using frequency counter)

   As Yuta did before (see his entry), I plugged the output of the frequency counter to an ADC and fedback the signal to the end laser temperature via ezcaservo.

The peak height of the beat note is bigger than before due to the improvement of the PMC mode matching.

The peak height shown on the spectrum analyzer 8591E is now about -39dBm which is 9dB improvement. 

 

     The figure below is a spectra of the frequency counter's readout taken by the spectrum analyzer SR785.

 FCnoise.png

When the slow temperature servo is locked, the noise around 20-30 mHz increased.

I think this is true, because I was able to see the peak slowly wobbling for a timescale of ~ 1min. when it's locked.

But this servo is still useful because it drifts by ~5MHz in ~10-20min without the servo.

Next time we will work on this slow servo using Aidan's PID control (see this entry) in order to optimize the performance.

In addition to that, I will take the same spectra by using the phase locked VCO, which provides cleaner signal.

 

(acquisition of the PLL)

 In order to extract a frequency information more precisely than the frequency counter, we are going to employ 80MHz VCO box.

 While the beat note was locked at ~ 79MHz by the slow servo, I successfully acquired the PLL to the beat signal.

 However at the beginning, the PLL was easily broken by a sudden frequency step of about 5MHz/s (!!).

I turned off the low noise amplifier which currently drives the NPRO via a high-voltage amplifier, then the sudden frequency steps disappeared.

After this modification the PLL was able to keep tracking the beat signal for more than 5min.

(I was not patient enough, so I couldn't stand watching the signal more than 5min... I will hook this to an ADC)

Quote: #3920

Some more details will be posted later.

 

  3930   Tue Nov 16 09:02:54 2010 AidanUpdateGreen LockingPID loop - calibration of SR620 output

 [Aidan, Kiwamu]

Kiwamu and I roughly calibrated the analogue output from the SR620 frequency counter yesterday. The input channel, intuitively named C1:PSL-126MOPA_126MON, now reads the measured frequency in MHz with an error of about 0.1MHz - this is, I think, due to the bit noise on the D/A conversion that Kiwamu discovered earlier. That is, the output range of the SR620 corresponds to around 100MHz and is digitized at 10-bit resolution, and ...

100MHz/(10^2) ~= 0.098MHz. [Sad Face]

Calibration:

We set the EPICS range to [-100, 100] (corresponding to [-5V, 5V]), connected a Marconi to the Freq Counter, input a variety of different frequencies and measured the counts on the EPICS channel.

The linear fit to the calibration data was F = 2.006*EPICScount - 0.2942. From this we worked out the maximum and the minimum for the range settings that give the channel in MHz: EGUF = -200.8942 and EGUL = 200.3058. The previous range was [-410, 410]

 

Calibration of SR620 analogue output
Input Frequency (MHz) Measured EPICS Value
10  5.191
20  9.98
30 15.21
40 20.00
50 25.18
60 29.99
70 35.18
71 35.565
72 35.9894
73 36.3861
74 37.17
75 37.576
76 37.9669
77 38.3575
78 39.166
79 39.5691
80 39.978
   

 

  3931   Tue Nov 16 10:47:45 2010 AidanUpdateGreen LockingRebooted c1psl - added new GRNBEAT_FREQ channel

I restored C1:PSL-126MOPA_126MON to its original settings (EGUF = -410, EGUL = 410) and added a new calc channel called C1:LSC-EX_GRNBEAT_FREQ that is derived from C1:PSL-126MOPA_126MON. The calibration in the new channel converts the input to MHz.

grecord(calc, "C1:LSC-EX_GRNBEAT_FREQ")
{
        field(DESC,"EX-PSL Green Beat Note Frequency")
        field(SCAN, ".1 second")
        field(INPA,"C1:PSL-126MOPA_126MON")
        field(PREC,"4")
        field(CALC,"0.4878*A")
        }

I rebooted c1psl and burtrestored.

  3932   Tue Nov 16 12:47:30 2010 AidanUpdateGreen LockingPID loop but no green

The PID loop is ready to be run on the green beat note but, since the tanks are open, there is no green transmission from the end getting to the PSL table. Nevertheless, here's the screen for the PID loop. The loop script is still in my directory /cvs/cds/caltech/users/abrooks/GRNXSlowServo

The medm screen is attached. It shows the current beat note frequency in MHz ()

In c1auxey/ETMYaux.db I added a couple of channels. These are all displayed on the MEDM screen. I added them to autoBurt.req as well.

  • C1:LSC-EX_GRNLSR_TEMP_NOM: the zero-volt setpoint temperature of the end laser (as set on the front panel of the Mephisto controller). This must be entered manually in EPICS as there is no way to read it remotely. [Sad Face]
  • C1:LSC-EX_GRNLSR_TEMP_CALC: the sum of the zero-volt set point temperature and the offset temperature set by the input voltage from C1:LSC-EX_GREENLASER_TEMP

I rebooted c1auxey to get these to work.

Once we get the green beat back again, the PID loop should servo on the end laser temperature to drive the Beat Frequency to the Frequency Setpoint, C1:LSC-EX_GRN_PID_SETPT, which can be set by the pink slider.

RA: All MEDM screens must be in the proper MEDM directory!! Also, all perl scripts must have a .pl extension!!! Also, all scripts must be in the scripts directory even if they are in development!!! And all scripts should use 'env' rather than have absolute pathnames for the location of perl, csh, tcsh, python, etc.

Attachment 1: Screenshot-C1LSC_EX_GRN_SLOW.adl.png
Screenshot-C1LSC_EX_GRN_SLOW.adl.png
  3934   Tue Nov 16 16:00:26 2010 AidanUpdateGreen LockingPID loop but no green

Quote:

RA: All MEDM screens must be in the proper MEDM directory!! Also, all perl scripts must have a .pl extension!!! Also, all scripts must be in the scripts directory even if they are in development!!! And all scripts should use 'env' rather than have absolute pathnames for the location of perl, csh, tcsh, python, etc.

 That's not unreasonable. But if we try 

 grep "perl" /cvs/cds/rtcds/caltech/c1/scripts/*/* 

you can see that we've got a fair amount of housekeeping to attend to. We might want to think about tidying up the scripts directory as part of the cds upgrade.

 

 

 

 

  3970   Mon Nov 22 20:31:58 2010 kiwamuUpdateGreen Lockingsearching for unknown loss in green PD path

 As I said in the past entry (see this entry), there was unknown loss of about 20dB in the beat detection path.

So I started fully characterizing the beat detection path. 

Today I measured the frequency response of the wideband RFPD using the Jenne Laser.

Since all the data were taken by using a 1064nm laser, the absolute magnitudes [V/W] for 532nm are not calibrated yet.  

I will calibrate the absolute values with a green laser which has a known power.


 RFPDresponse.png

The data were taken by changing the bias voltage from -150V to 0V.

The shape of the transfer function looks quite similar to that Hartmut measured before (see the entry).

It has 100MHz bandwidth when the bias voltage is -150V, which is our normal operation point.

 

Theoretically the transfer function must keep flat at lower frequency down to DC.

Therefore for the calibration of this data, we can use the DC signal when a green beam with a known power is illuminating the PD.

 

  3972   Tue Nov 23 01:45:47 2010 kiwamuUpdateGreen Lockingnoise curve of wideband RFPD

Quote: #3970

So I started fully characterizing the beat detection path. 

As a part of the characterization works, I measured the spectra of the RFPD noise as well. 

The noise is totally dominated by that of the RFPD (i.e. not by an RF amplifier).

I am going to check the noise curve by comparing with a LISO model (or a simple analytical model) in order to make sure the noise is reasonable.


 (results) 

 noise_RFPD.png

The red curve represents the dark noise of the RFPD, which is amplified by a low noise amp, ZFL-1000LN.

The blue curve is a noise of only ZFL-1000LN with a 50 Ohm terminator at its input.

The last curve is noise of the network analyzer AG4395A itself.

It is clear that the noise is dominated by that of RFPD. It has a broad hill around 100MHz and a spike at 16MHz.

 

(notes)

Gain of ZFL-1000LN   = 25.5 dB (measured)

Applied voltage to ZFL-1000LN = +15.0 V

Bias voltage on PD = -150 V

  4007   Fri Dec 3 05:21:11 2010 kiwamuUpdateGreen Lockinglocked the laser to the cavity

I succeeded in locking the end green laser to X arm with the new ETM.

Though the lock is still not so stable compared to the previous locking with the old ETM. Also the beam centering is quite bad now.

So I will keep working on the end green lock a little bit more.

Once the lock gets improved and becomes reasonably stiff, we will move onto the corner PLL experiment.

 

(to do)

 - beam centering on ITMX

 - check the mode matching

 - revise the control servo

  4016   Mon Dec 6 22:18:39 2010 kiwamuUpdateGreen Lockingaligned the beam axis

 [Suresh and Kiwamu]

We aligned the green beam to the X arm cavity more carefully.

Now the green beam is hitting the centers of ETMX, ITMX and BS.

Also we confirmed that the green beam successfully comes out from the chamber to the PSL table.

 


(what we did)

- opened the BS, ITMX and ETMX chambers. 

- checked the positions of the beam spots on ITMX, BS and ETMX

   The spot position on ETMX was fine,

   But at BS and ITMX, the spots were off downward.

   We decided to move the beam angle by touching a steering mirror at the end green setup.

- changed the beam axis by touching the steering mirror at the end station.

- checked the spot positions again, they all became good. It looks the errors were within ~ 1mm.

- moved the position of a TT, which is sitting behind the BS, by ~10mm, because it was almost clliping the beam.

- aligned the green optics

- got the beam coming out from the chamber. 

 

 

  4093   Thu Dec 23 12:19:43 2010 kiwamuUpdateGreen Lockinginstalled doubling oven base at PSL table

I gave a christmas present to a doubling oven who has been sitting on the PSL table.

The below is a picture of the present I gave. It's a base plate for the doubling oven, made from a block of aluminum, and black-anodized.

The size and the shape are nicely tailored for the combination of the Newfocus kinematic mount and the Covesion oven.

The design had been done by using Solid Works 2010

 

DSC_2820_ss.jpg

 

Here is a picture before he got the present.

DSC_2814_ss.jpg

 

Now he looks pretty happy.

DSC_2815_ss.jpg

  4095   Thu Dec 23 18:51:37 2010 ranaUpdateGreen Lockinginstalled doubling oven base at PSL table

This is not such a bad base design, but remember that we have to get a couple of parts with the purple anodize to see if there is a difference between black and purple in terms of the 532 nm reflectivity.

  4123   Fri Jan 7 00:49:16 2011 JenneUpdateGreen LockingRecovered Xarm Green Lock, Preparation for Beat Note Measurement

[Kiwamu, Jenne]

We went this evening in search of a beat note signal between the Xarm transmitted green light and the PSL doubled green light. 

First, we removed our new ETMX camera (we left the mount so it should be easy to put back) from the other day.   We left the test masses exactly where they had been while flashing for IR, so even though we can no longer confirm, we expect that the IR beam axis hasn't changed.  We used the steering mirror on the end table to align the green beam to the cavity.  We turned on the loop to lock the end laser to the cavity, and achieved green lock of the arm.

Then we went to the PSL table to overlap the arm transmitted light with the PSL doubled light.  We made a few changes to the optics that take the arm transmitted light over to the PD.  We found that the arm transmitted light was very high, so we changed from having one steering mirror to having 3 (for table space / geometry reasons we needed 3, not just 2) in order to lower the beam axis.  We also found that the spot size of the arm transmitted beam was ~2x too small, so we changed the mode matching telescope from a 4x reducer to a 2x reducer by changing the 2nd lens from f=50mm to f=100mm (the first lens is f=200mm).  We made the arm transmitted beam and the PSL green beam overlap, but we saw no peak on the spectrum analyzer. 

We checked the temperature of the PSL and end lasers, and determined that we needed to adjust the set temp of the end laser.  However, we still didn't find any beat note.

We then tweaked the temperature of the doubling oven at the end station, to maximize the power transmitted, since Kiwamu said that that had worked in the past.  Alas, no success tonight.

We're stopping for the evening, with the success of reacquiring green lock of the Xarm.

  4159   Fri Jan 14 20:37:00 2011 kiwamuHowToGreen Lockingplan for this month

 I summarized how we proceed our green locking in this month on the wiki.

Since step1 and 2 shown on the wiki are mostly done apparently, so we will move on to step 3-D and 3-E.

A short term target in the coming couple of days is to phase lock the VCO to the beat note.

green_plan.png

  4174   Thu Jan 20 04:43:28 2011 kiwamuUpdateGreen Lockingstatus update: PLL connected to ADC

 I connected the PLL signal to the ADC on c1ioo. 

So now we are able to take the data into the digital world, and will be able to feedback signals to the suspensions.

 The output signal from the VCO box goes to a black beakout board on 1X2 rack though a BNC cable.  

Then the signal comes out from the back side of the board with DB39 style, so I put a DB39 to SCSI adapter so that we can take it to the IO chasis.

Now the SCSI is connected to ADC_1 (the second ADC card) on the IO chasis at 1X1. 

 

  Additionally I modified the green locking simulink model, C1GCV, in order to pick the right ADC channels.

A medm screen for green locking is now under the construction. I put a link on the sitemap screen, so anyone can look at the half-baked green locking screen.

Any comments and suggestions are really welcome.

  4176   Thu Jan 20 15:15:39 2011 kiwamuUpdateGreen Lockingstatus update: PLL connected to ADC

I realized that the black AA board I mentioned on the last entry has the same range issue as Valera reported before (see #3911)

Basically our ADC card has +/- 10V input range, but on the other hand the AA board is already limited by approximately +/- 2V.

We have to fix it.

Quote: #4174

  The output signal from the VCO box goes to a black beakout board on 1X2 rack though a BNC cable.  

Then the signal comes out from the back side of the board with DB39 style, so I put a DB39 to SCSI adapter so that we can take it to the IO chasis.

Now the SCSI is connected to ADC_1 (the second ADC card) on the IO chasis at 1X1. 

  4181   Fri Jan 21 02:45:43 2011 kiwamuUpdateGreen Lockinginterface for PLL to ADC

 [Suresh, Kiwamu]

  We did the following things:

     - installed a 1/10 voltage divider such that the signal won't be saturated at the AA board (see here)

     - put a Ithaco preamplifier 1201 as a whitening filter

     - checked the entire beat detection system without using the real beat note

Here are some items to be done before the sun goes down tomorrow:

       - calibration of ADC and the interfaces including the voltage divider and the whitening filter.

     - fine matching of unwhitening filter at the digital side

         - PLL response measurement ( freq to voltage response ) over the frequency range of interest

         - plotting an well calibrated spectrum of the PLL output 


(whitening filter)

The Ithaco 1201 was setup to have a zero at 0 Hz and two poles at 0.1 Hz and 10 Hz in order to emphasize the signal over the frequency range of interest.

Around 1Hz it is supposed to have a gain of 1000. These settings have done by tweaking the knobs on the front panel of the Ithaco 1201.

In addition to that, we made an unwhitening filter in digital filter banks. This filter was designed to cancel the analog whitening filter.

(system check) 

 To check the entire beat detection system, we phase-locked the VCO to a Marconi running at 80 MHz, which is the center frequency of the VCO.

Then we imposed a frequency modulation on the Marconi to see if the signal is acquired to ADC successfully or not. It's quite healthy.

According to the spectra corrected by the unwhitening filter, we confirmed that the noise floor at 1Hz is order of 1Hz/sqrt Hz, which is already quite good.

Then we took several spectra while putting a modulation on the Marconi at a different frequency in each measurement.

The peak due to the artificial modulation essentially works as a calibration peak in the spectra.

So in this way we briefly checked the flatness of the response of the system in the frequency domain.

As a result we found that the response is not perfectly flat in the range of 0.05 - 30Hz, probably due to a mismatch of the combination of the whitening and unwhitening filters.

We will check it tomorrow.

 

  4187   Sat Jan 22 01:56:04 2011 SureshUpdateGreen LockingExamining the stability of VCO PLL at low frequencies

[Kiwamu, Suresh, Rana]

Our goal:

        We wished to determine the performance of the VCO PLL at low frequencies,. 

The procedure we followed:

        The scheme is to use the Marconi (locked to Rb Clock) as an 80MHz reference and lock to it using the PLL. 

        We set up the VCO PLL as in the diagram shown in the attachment and obtained the spectra shown below.

Results:

          We need to figure out the PLL servo gain profile in order to build the Inv PLL filter....

 

   

 

 

VCO_PLL_stability.png

 

 

  4188   Sat Jan 22 02:03:55 2011 KojiUpdateGreen LockingExamining the stability of VCO PLL at low frequencies

Damn. If this figure is true, we were looking at wrong signal. We should look at the feedback signal to the VCO.

  4189   Sat Jan 22 02:11:09 2011 kiwamuUpdateGreen Lockingsome more progress

[Rana, Suresh, Kiwanu]

 We did the following things:

   *  taking the VCO stability data from the error signal instead of the feedback

   *  tried calibrating the signal but confused

   *  increased the modulation depth of the green end PDH.

--

 We found that a cable coming out from the VCO box was quite touchy. This cable was used for taking the feedback signal.

When we touched the cable it made a big noise in the feedback. So we decided to remove the cable and take the signal from the error point (i.e. just after the mixer and the LPF.)

In order to correct that signal to the one in terms of the feedback signal, we put a digital filter which is exactly the same as that of the PLL (pole at 1.5 Hz, zero at 40 Hz, G=1) .

However for some reasons the signal shown in the digital side looked completely mis-calibrated by ~ 100. We have no idea what is going on.

Anyway we are taking the data over tonight because we can correct the signal later. The 2nd round data started from AM1:40

  4190   Sat Jan 22 02:23:26 2011 KojiUpdateGreen Lockingsome more progress

What is the point to use the error instead of the feedback? It does not make sense to me.

If the cable is flaky why we don't solder it on the circuit? Why we don't put a buffer just after the test point?

It does not make sense to obtain the error signal in order to estimate the freeruning noise without the precise loop characterization.
(i.e. THE FEEDBACK LOOP TRINITY: Spectrum, Openloop, Calibration)

RA: I agree that feedback would be better because we could use it without much calibration. But the only difference between the "error signal" and the "feedback signal" in this case is a 1.6:40 pole:zero stage with DC gain of 0 dB. So we can't actually use either one without calibration and the gain between these two places is almost the same so they are both equally bad for the SNR of the measurement. I think that Suresh and Kiwamu are diligently reading about PLLs and will have a more quantitative result on Monday afternoon.

 

  4191   Mon Jan 24 02:58:46 2011 kiwamuUpdateGreen LockingX arm locked !

I succeeded in green-locking the X arm by feeding back the beat signal to ETMX.

Here are some quick reports. Some more details will be posted tomorrow.

 

The below shows a time series data of the PLL feedback signal when the servo was acquiring the lock.

time_series.png

At t = -2 sec. I started feeding back the signal to ETMX with the gain 50 times smaller than its nominal.

Then at t = 0 sec.I switched on a low frequency boost (pole 0.1Hz and zero 1Hz) to make it more robust.

At t = 3 sec. I increased the gain to the nominal.

Finally the UGF became ~ 60 Hz according to my open loop measurement by diaggui.

However I couldn't make the UGF higher than 60Hz because the more gain caused a instability for some reasons.

 

Here is a diagram for the green locking.

I used the same VCO box as we setup on the last Friday (see #4189).

 green_one_arm.png

  4192   Mon Jan 24 09:33:08 2011 ranaUpdateGreen LockingX arm locked !

Very cool.

But the PLL seems very fishy to me. The ZP-3MH needs 13 dBm to operate correctly. You should change the MODLEVEL input of the VCO so as to make the LO input of the mixer go up to 13 dBm. Then the input from the PD should be ~0 dBm.

Also, the PLL diagram seems to show that you have a 1/f^2 loop: 1/f from the SR560 and 1/f from the Hz->rad conversion ??

  4193   Mon Jan 24 10:19:21 2011 KojiUpdateGreen LockingX arm locked !

Well... The ALS loop is engaged and the error was suppressed.
So, how is the IR error signal stabilized when the IR is brought in to the resonance?

I can see the linear trend of 0.1V/s from 5s to 10s.  This corresponds to 100kHz/s and 13nm
for the residual beat drift and the arm length motion, respectively. That sounds huge. The DC gain must be increased.

  4195   Mon Jan 24 13:08:07 2011 kiwamuUpdateGreen LockingRe: X arm locked !

Quote: #4192

Also, the PLL diagram seems to show that you have a 1/f^2 loop: 1/f from the SR560 and 1/f from the Hz->rad conversion ??

Well, the diagram I drew is true. I also have been confused by this 1/f^2 issue in our PLL.

As Rana pointed out, the open-loop TF should become 1/f^2 over most of the frequency range, but it still remains 1/f above 5kHz for some reasons. 

 Need more investigations.

e_pll_oltf.png

 At the beginning I tried phase-locking the VCO to the beat note without any external filters (i.e. SR560 see here), but I never succeeded.

It was because the hold-in range of the PLL was not sufficiently wide, it could stay locked within frequency range of less than +/- 1MHz from the center frequency of 80 MHz.

This is obviously not good, because the beat note typically fluctuates by more than +/- 3MHz in time scale of 1 sec or so.

  So I decided to put an external filter, SR560,  in order to have a larger DC gain and a higher UGF.

Somehow I unconsciously tuned the SR560 to have a pole at 1Hz with the gain of 2000, which shouldn't work in principle because the open-loop will be 1/f^2.

However I found that the PLL became more robust, in fact it can track the input frequency range of +/- 5MHz.

The open-loop TF is shown above. For comparison I plotted also the open-loop TF wehn it's without the SR560.

I checked the frequency of the VCO output when it was phase-locked to a Marconi, it was healthy (i.e. the same frequency as the input signal from Marconi).

  4196   Mon Jan 24 14:27:13 2011 kiwamuUpdateGreen LockingRe: X arm locked !

Quote: #4193

So, how is the IR error signal stabilized when the IR is brought in to the resonance?

I can see the linear trend of 0.1V/s from 5s to 10s.  This corresponds to 100kHz/s and 13nm for the residual beat drift and the arm length motion, respectively. That sounds huge.

 I haven't yet taken any data for the IR fluctuation when the Xarm is locked by the green locking.

You are right, the DC drift was due to a lack of the DC gain. But don't worry about that, because this issue has been solved.

 


(DC gain issue)

  The lack of DC gain was because I put an IIR filter called ''DC block" that I made. It has 1/f shape below 30mHz and becomes flat above it.

The purpose of this filter was to avoid a DC kick when it starts feeding back to ETMX.

Usually the output signal from the PLL has an offset, typically ~5V, then this offset is also acquired into the ADC and eventually kicks ETMX through the feedback.

So when I took the time series data I enabled the 'DC block', that's why it drifts slowly.

 After taking the time series, I found that without this 'DC block' technique, the lock can be achieved by appropriately subtracting the offsets with epics numerical values.

This subtraction technique, of course, gave me more stable lock at DC.

 


(open loop transfer function)

Here is the open-loop TF of the arm locking I measured last night:

masslock_oltf.png

The IIR filter chain has the following poles and zeros:

     pole 0.1Hz, 1000Hz,

   zero 1Hz, 30Hz

For the fitting I assume that the ETMX pendulum has a resonance at 1Hz with Q of 5. Also I put the cavity pole at 24 kHz, assuming the finesse is 80 at 532 nm.

I just fitted the gain and the time delay by my eyes.

If I believe the result of the fitting, whole time delay is 330 usec, which sounds pretty large to me.

  4198   Tue Jan 25 05:26:51 2011 kiwamuUpdateGreen Lockingcavity scan

cavity_scan.png

I scanned the X arm by changing an offset for the feedback to ETMX while the arm stayed locked by the green locking.

But the resultant plot is still far away from a beautiful one.

Changing the offset broke the lock frequently, so eventually I couldn't measure the stability of the IR-PDH signal at the resonance. 

 

 The plot above is a result of the scanning. You can see there is a clear resonance at the center of the plot.

However the lock frequently became unstable when I was changing the offset.

It looked like this unstability came from the end PDH lock. I guess there are two possible reasons:

  (1)  feedback range for the laser PZT is not wide enough. Right now the range is limited by a SR560, which has been used for a summing amplifier.

  (2)  Length to Alignment coupling. Pushing ETMX causes a misalignment.

The issue (1) can be easily solved by engaging the temperature feedback, which helps actuating the laser frequency a lot at DC.

The issue (2) will be also solved by well align the IR beam, the arm cavity and the green beam.

  4199   Tue Jan 25 06:48:55 2011 kiwamuUpdateGreen LockingTo do list

Here are some tasks that I want someone to work on during my absence.

1. Y-arm alignment for IR

 Basically we gradually have to move onto the Y-arm locking at some point.

Prior to it we need to align the Y arm for IR. Probably we have to touch PZT1 and PZT2.

It would be very nice if the X-arm alignment also gets improved together with this work. 

 

2. Temperature feedback with a digital control for X end PDH lock

  Need a temperature feedback not with an analog way but with a digital way because we want to put an offset and the feedback signal at the same time (#4198).

 Right now the temperature control input of the laser is connected to a slow DAC (#3850).

Probably we should plug the feedback signal from the PDH box to the fast ADC (i.e. c1iscex), and then connect a fast DAC to the laser temperature.

This entry maybe helpful.

 

3. Calibration of optical gain for IR arm locking

 In order to evaluate the performance of the green locking, one of the key points is the IR PDH signal.

Because it tells us how much the motion of the X arm is suppressed at IR when the green lock is engaged.

To get this information in m/sqrtHz, we need to know the optical gain.

 

4. MC servo characterization and PSL frequency noise measurement

 SInce the green beat note tells us the frequency difference between the MC and the arm in the current configuration, we should know how the MC servo is.

Along with this work, I need someone to measure the PSL frequency noise, when it is locked to the MC over the frequency range from 0.01Hz to 1kHz.

 

5. PLL characterization 

 Solve this issue (#4195) and make it reliable.

  4201   Tue Jan 25 20:42:46 2011 OsamuUpdateGreen LockingSlow servo for green laser

I implemented a slow servo for green laser thermal control on c1scx.mdl. Ch6,7 of ADC and ch6 of DAC are assigned for this servo as below;

 

Ch6 of ADC: PDH error signal

CH7 of ADC: PZT feedback signal

CH6 of DAC: feedback signal to thermal of green laser

 

Note that old EPICS themal control cable is not hooked anymore.

I made a simple MEDM screen(...medm/c1scx/master/C1SCX_BCX_SLOW.adl) linked from GREEN medm screen (C1GCV.adl) on sitemap.

During this work, I noticed that some of the epics switch is not recovered by autoburt. What I noticed is filter switch of SUSPOS, SUSPIT, SUSYAW, SDSEN, and all coil output for ETMX.

I had no idea to fix them, probably Joe knows. I guess other suspensitons has the same problems.

  4202   Tue Jan 25 21:57:59 2011 KojiUpdateGreen LockingSlow servo for green laser

1. The dewhitening filter CH6 had no output. I disconnected the cable and put it to the monitor out of the AI filter.
So the dewhitening is not in the loop.

2. I have made a thermal control filter

BANK1: pole 0Hz, zero 1mHz / LF boost stage
BANK2: pole 1mHz, zero 30mHz / LPF stage
BANK3: pole 1Hz, zero 0.1Hz / phase compensation stage
Gain: 0.05

It seems working with the gain of 0.05. As the thermal is very strong, the output has less than 10.
This means the we are effectively only using ~4bit. We need external filter.

Note that output of 30000counts were about 3V at  CH6.

3. Measured End PZT feedback with and without the thermal control. The UGF seems to be 0.2Hz.
The suppression at 10mHz is ~100. This is so far OK.

Quote:

I implemented a slow servo for green laser thermal control on c1scx.mdl. Ch6,7 of ADC and ch6 of DAC are assigned for this servo as below;

 

Ch6 of ADC: PDH error signal

CH7 of ADC: PZT feedback signal

CH6 of DAC: feedback signal to thermal of green laser

 

Note that old EPICS themal control cable is not hooked anymore.

I made a simple MEDM screen(...medm/c1scx/master/C1SCX_BCX_SLOW.adl) linked from GREEN medm screen (C1GCV.adl) on sitemap.

During this work, I noticed that some of the epics switch is not recovered by autoburt. What I noticed is filter switch of SUSPOS, SUSPIT, SUSYAW, SDSEN, and all coil output for ETMX.

I had no idea to fix them, probably Joe knows. I guess other suspensitons has the same problems.

 

Attachment 1: 110125_Xend_thermal.pdf
110125_Xend_thermal.pdf
  4205   Wed Jan 26 10:11:47 2011 AidanUpdateGreen Lockingcavity scan

Quote:

cavity_scan.png

 

Whether or not it's as clean as we'd like, it's really nice to see this result with real data.

  4211   Thu Jan 27 11:04:27 2011 KojiUpdateGreen Lockingbeat freq scan

Experiment in the night of Jan 26.

o The arm was locked for the IR beam and was aligned for it.
o The green was aligned to the arm
o The beat freq was observed with the RF analyzer and the webcam.
o Engaged the ALS servo
o Compared the fluctuation of the beat freq with and without ALS
o Scanned the beat freq in order to find an IR resonance

The beat freq was scanned. A resonance for IR was found.
However, the residual motion of the arm was not within the line width of the IR resonance.

 To Do
- Improve the ALS servo (==>Koji)
- VCO noise characterization (==>Suresh is on it)
- Calibrate the PLL feedback (i.e. ALS error) into Hz/rtHz (==>Suresh)
- Calibrate the end green PZT fb into Hz/rtHz (==>Osamu is on it)
- Tuning of the suspension filters to reduce the bounce mode coupling.


DETAILS

o How to lock the arm with IR

  • Coarsely align the arm without lock. Transmittion was ~300 with MCTRANS ~40000
  • REFL11I is the error signal. unWhiten filter (FM1) should be on.
  • Unlock the MC and null the error and the arm trans offset by running the following commands

ezcaservo -g -0.1 -r C1:LSC-REFL11_I_OUTPUT C1:LSC-REFL11_I_OFFSET
ezcaservo -g -0.1 -r C1:LSC-REFL11_Q_OUTPUT C1:LSC-REFL11_Q_OFFSET
ezcaservo -g 0.1 -r C1:LSC-TRX_OUTPUT C1:LSC-TRX_OFFSET

  • Confirm the input matrix to pass REFL11I to MC path (why don't we use XARM path...?)

ezcawrite C1:LSC-MTRX_81 1.0

  • Servo configuration
    • For acquisition: Gain of 2. Only FM1 (1000:10) has to be on.
    • After the acquisition (TRX>200): The gain is to be changed to 1. FM2 and FM3 can be turned on for the LF boost.
  • Actuator matrix: connect MC path to ETMX and MC2

ezcawrite C1:LSC-OM_MTRX_18 1.0
ezcawrite C1:LSC-OM_MTRX_78 1.0

 

o How to align the green beam

  • After the alignment I went the end and aligned the last two steering mirrors.


o The beat freq monitor

  • Put the RF analyzer at the RF splitter of the RFPD output.
  • Used Zonet webcam (http://192.168.113.201:3037) for the remote monitoring

 

o How to engage the ALS servo

  • Preparation:
    • VCO PLL feedback comes to X_FINE path.
    • Put an offset of -850 to cancel too big offset (when the VCO is unlocked)
    • Use Y_FINE channel for the offset addtion. FM1 is 10mHz LPF in order to make the offset smooth.
    • Add X_FINE and Y_FINE by the matrix.
  • Control
    • Turn off X_FINE out. Leave Y_FINE output turned on.
    • Turn on ETMX ALS path.
    • Servo setting: FM1 1000:30 ON, others OFF, gain1
    • Wait for the beat comes in to the locking range at around 80MHz.
    • If the peak is too far, sweep Y_FINE offset in order to . Or change GCV slow thermal offset to let the beat freq jump.
    • You may have ambiguity of the feedback sign depending on which green has higher freq.
    • After the capture of the ALS lock, increse the gain up to 20. Turn on 0.1:boost at FM3.

 

o Comparison of the stability of the beat freq (Attachment3)

  • The spectra of the VCO PLL feedback was measured.
  • First of all, the signal was measured without ALS (blue).
    The PLL lost lock quite frequently, so the careful adjustment of the offset was necessary.Still I think there was slight saturation upconversion.
  • Then, the ALS was turned on (red). The gain was 20. This is an in-loop evaluation of the servo. The suppression was ~1000 at 1Hz.

o Beat freq scanning

  • The following command was used for the beat note scanning 

ezcastep -- "C1:GCV-YARM_FINE_OFFSET" "5,500"

  • Once the IR transmission was found, the scan was stopped.
  • Because the resultant rms stability of the arm was not within the line width of the cavity, the smooth resonant curve was not obtained.
  • From the shape of the error signal the peak-to-peak displacement (f>1Hz) was estimated to be +/-0.7nm. The dominant displacement
    in the period is 16Hz component.

 

Attachment 1: arm_scan.pdf
arm_scan.pdf
Attachment 2: arm_cav_scan3.png
arm_cav_scan3.png
Attachment 3: 110126_ALS_inloop.pdf
110126_ALS_inloop.pdf
  4213   Thu Jan 27 17:12:02 2011 Aidan, JoeSummaryGreen LockingDigital Frequency to Amplitude converter

Joe and I built a very simple digital frequency to amplitude converter using the RCG. The input from an ADC channel goes through a filter bank (INPUT), is rectified and then split in two. One path is delayed by one DAQ cycle (1/16384 s) and then the two paths are multiplied together. Then the output from the mixer goes through a second filter bank (LP) where we can strip off twice the beat frequency. The DC output from the LP filter bank should be proportional to the input frequency.

Input Channel: C1:GFD-INPUT_xxx

Output Channel: C1:GFD-LP_xxx

Joe compiled the code and we tested it by injecting a swept sine [100, 500]Hz in the input filter bank. We confirmed that output of the LP filter bank changed linearly as a function of the input frequency.

The next thing we need to do is add a DAC output. Once that's in place we should inject the output from a 4kHz VCO into the ADC. Then we can measure the transfer function of the loop with an SR785 (driving the VCO input and looking at the output of the DAC) and play around with the LP filter to make sure the loop is fast enough.

The model is to be found here:

/opt/rtcds/caltech/c1/core/advLigoRTS/src/epics/simLink/c1gfd.mdl

The attached figures show the model file in Simulink and a realtime dataviewer session with injecting a swept sine (from 500Hz to 100Hz) into the INPUT EXC channel. We've had some frame builder issues so the excitation was not showing on the green trace and, for some reason, the names of the channels are back to front in dataviewer (WTF?), - the lower red trace in dataviewer is actually displaying C1:GFD-LP_OUT_DAQ, but it says it is displaying C1:GFD-INPUT_OUT_DAQ - which is very screwy.

However, the basic principle (frequency to amplitude) seems to work.

Attachment 1: Screenshot.png
Screenshot.png
Attachment 2: Swept_sine_F_to_A.png
Swept_sine_F_to_A.png
  4215   Thu Jan 27 21:43:37 2011 KojiUpdateGreen Lockingno transmission of ALS signals

No signal is transmitted from C1:GCV-SCX_ETMX_ALS (on c1gcv) to C1:GCV-SCX_ETMX_ALS (on c1scx)

I can't find RFM definition for ALS channels in c1rfm. Where are they???

  4216   Thu Jan 27 23:21:50 2011 ranaSummaryGreen LockingDigital Frequency Discriminator

That's some pretty fast work! I thought we would be taking up to a week to get that happening. I wonder what's the right way to measure the inherent frequency noise of this thing?

Also, should the comparator part have some hysteresis (ala Schmidt trigger) or is it best to just let it twirl as is? Is it sensitive to DC offsets on the input or is there a high pass filter? What's the correct low pass filter to use here so that we can have a low phase lag feedback to the ETM?

  4217   Fri Jan 28 09:03:38 2011 AidanSummaryGreen LockingDigital Frequency Discriminator

Quote:

That's some pretty fast work! I thought we would be taking up to a week to get that happening. I wonder what's the right way to measure the inherent frequency noise of this thing?

Also, should the comparator part have some hysteresis (ala Schmidt trigger) or is it best to just let it twirl as is? Is it sensitive to DC offsets on the input or is there a high pass filter? What's the correct low pass filter to use here so that we can have a low phase lag feedback to the ETM?

 

We could try inputing a 4kHz carrier modulated width a depth of a few Hz at a modulation frequency of F1. Then we could take an FFT of the output of the discriminator and measure the width of the peak at F1 Hz. This seems like an arduous way to measure the frequency noise at a single frequency though.

It'll definitely be sensitive to DC offsets but there is already a filter bank on the INPUT filter so we can shape that as necessary. We could probably band-pass that from [4.5 - 5.3kHz] (which would correspond to a range of [73,87] MHz into a 2^14 frequency divider.

 

  4218   Fri Jan 28 10:27:46 2011 Aidan, JoeSummaryGreen LockingDigital Frequency Discriminator - calibration

 One more thing ... we can calibrate the output of the LP filter to give a result in Hz with the following calibration:

LP_OUT = -1/(2*dt)*(LP_IN -1), where dt is 1/16384, the delay time of the delayed path.

Therefore LP_OUT = -8192*(LP_IN-1).

  4219   Fri Jan 28 11:08:44 2011 josephbUpdateGreen Lockingno transmission of ALS signals

As you've correctly noted, the source of the C1:GCV-SCX_ETMX_ALS channels is in the c1gcv model. The first 3 letters of the channel name indicate this (GCV).

The destination of this channel is c1scx, the 2nd 3 letters indicate this (SCX). If it passed through the c1rfm model, it would be written like C1:GCV-RFM_ETMX_ALS.

This particular channel doesn't pass through the c1rfm model, because the computers these two run on (c1ioo and c1scx) are directly connected via our old VMIC 5565 RFM cards, and don't need to pass through the c1sus computer. This is in contrast to all communications going to or from the c1lsc machine, since that is only connected the c1sus machine by the Dolphin RFM. The c1rfm also handles a bunch of RFM reads from the mode cleaner WFS, since each eats up 3-4 microseconds and I didn't want to slow the c1mcs model by 24 microseconds (and ~50 microseconds before the c1sus/c1scx computer switch).

So basically c1rfm is only used for LSC communications and for some RFM reads for local suspensions on c1sus.

As for the reason we have no transmission, that looks to be a problem on c1ioo's end. I'm also noticing that MCL is not updating on the MC2 suspension screen as well as no changes to MC PIT and YAW channels, which suggests we're not transmitting properly.

I rebooted the c1ioo machine and then did a burt restore of the c1ioo and c1gcv models. These are now up and running, and I'm seeing both MCL and ALS data being transmitted now.

Its possible that when we were working on the c1gfd (green frequency divider model) on c1ioo machine we disturbed the RFM communication somehow. Although what exactly, I'm not sure.

Quote:

No signal is transmitted from C1:GCV-SCX_ETMX_ALS (on c1gcv) to C1:GCV-SCX_ETMX_ALS (on c1scx)

I can't find RFM definition for ALS channels in c1rfm. Where are they???

 

  4227   Sun Jan 30 17:15:09 2011 AidanSummaryGreen LockingDigital Frequency discriminator - frequency noise

I've had a go at trying to estimate the frequency noise of the digital frequency discriminator (DFD). I input a 234.5Hz (0.5Vpp) signal from a 30MHz function generator into the ADC. The LP output of the DFD measured 234.5Hz. However, this signal is clearly modulated by roughly +/- 0.2Hz at harmonics of 234.5Hz (as you can see in the top plot in the dataviewer screenshot below). So the frequency noise can be estimated as rms of approximately 0.2Hz.

This is supported by taking the spectra of the LP output and looking at the RMS. Most of the power in the RMS frequency noise (above the minimum frequency) comes from the harmonics of the input signal and the RMS is approximately 0.2Hz.

I believe this stems from the rather basic LP filter (three or four poles around 10Hz?) that is used in the LP filter to remove the higher frequency components that exist after the mixing stage. (The currently loaded LPF filter is not the same as the saved one in Foton - and that one won't load at the moment, so I'm forced to remember the shape of the current filter).

 The attached screen capture from data viewer shows the LP_OUT hovering around 234.5Hz.

Attachment 1: _Untitled_(modified).png
_Untitled_(modified).png
  4228   Sun Jan 30 19:26:03 2011 KojiSummaryGreen LockingPrototype freq divider

A prototype freq divider has been made which works up to ~40MHz.

74HC4060 (14bit binary ripple counter) divides the freq of the input signal, which is comverted by the comparator LT1016
into the rectangular signal. The division rate is 2^14.

Attachment1: Circuit diagram

Attachment2:
Photo, the prototype bread board

Attachment3:
Photo, the spectrum of the freq divided output. The 40MHz input has been divided into 2.4k.
There are the 3rd and 5th harmonics seen. The peak was pretty sharp but the phase noise was not evaluated yet.


The circuit was made on the prototype bread board which is apparently unsuitable for RF purposes.
Indeed, it was surprising to see its working up to 40MHz...

In order to increase the maximum freq of the system we need the following considerations

  • RF PCB board
  • Input RF buffer (or amplifier) with a 50Ohm input impedance.
  • Faster comparator. LT1016 has the response time of 10ns, which is not enough fast.
  • Faster counter. Faster chip 74HC4020 has already been ordered.
Attachment 1: freq_divider.pdf
freq_divider.pdf
Attachment 2: IMG_3813.jpg
IMG_3813.jpg
Attachment 3: IMG_3814.jpg
IMG_3814.jpg
  4229   Mon Jan 31 07:03:59 2011 AidanSummaryGreen LockingDFD - noise spectra

Quote:

I've had a go at trying to estimate the frequency noise of the digital frequency discriminator (DFD). I input a 234.5Hz (0.5Vpp) signal from a 30MHz function generator into the ADC. The LP output of the DFD measured 234.5Hz. However, this signal is clearly modulated by roughly +/- 0.2Hz at harmonics of 234.5Hz (as you can see in the top plot in the dataviewer screenshot below). So the frequency noise can be estimated as rms of approximately 0.2Hz.

This is supported by taking the spectra of the LP output and looking at the RMS. Most of the power in the RMS frequency noise (above the minimum frequency) comes from the harmonics of the input signal and the RMS is approximately 0.2Hz.

I believe this stems from the rather basic LP filter (three or four poles around 10Hz?) that is used in the LP filter to remove the higher frequency components that exist after the mixing stage. (The currently loaded LPF filter is not the same as the saved one in Foton - and that one won't load at the moment, so I'm forced to remember the shape of the current filter).

 The attached screen capture from data viewer shows the LP_OUT hovering around 234.5Hz.

 Here is the spectrum of the input into the DFD (a 234.5Hz sine wave, 0.5 Vpp) and the spectrum and RMS of the LP output. The linewidth of the input signal is clearly much less than 0.1Hz, where as the RMS noise (above 2mHz) is approximately 0.2Hz and the main contributions are clearly the harmonics of the 234.5Hz signal.

Attachment 1: DFD-bandwidth_noise.pdf
DFD-bandwidth_noise.pdf
  4230   Mon Jan 31 07:41:23 2011 AidanUpdateGreen LockingDFD - medm screen

I added an MEDM screen for the DFD to the GREEN screen. It is displayed in the attached screen shot.

This screen is located in: /cvs/cds/rtcds/caltech/c1/medm/c1gfd/C1GFD_DFD.adl

Attachment 1: Screenshot-3.png
Screenshot-3.png
  4232   Mon Jan 31 12:40:38 2011 rana, joeUpdateGreen LockingDFD - medm screen

This is a plot showing the old filters and the new ones we added this morning.

The new ones have a Cheby for AC coupling below 10 Hz and then a 500 Hz LP after the mixer. The LP frequency has been increased so that we can use this signal in a feedback loop to the ETM with a ~100 Hz UGF.

Attachment 1: a.pdf
a.pdf
  4234   Mon Jan 31 18:25:25 2011 AidanUpdateGreen LockingDFD - results from the new filters (and running with AWG)

Quote:

This is a plot showing the old filters and the new ones we added this morning.

The new ones have a Cheby for AC coupling below 10 Hz and then a 500 Hz LP after the mixer. The LP frequency has been increased so that we can use this signal in a feedback loop to the ETM with a ~100 Hz UGF.

Joe injected a 234.567 etc. Hz sine wave into the excitation channel in the DFD INPUT filter. The spectrum of the output of the LP filter with the new filter is shown below with the RMS calculated from 300Hz down to 1mHz - see first attachment. The RMS is equal to about 2.5Hz. (Incidentally, the RMS is very much higher (slightly less than 400Hz - see second attachment) if you calculate it from 7kHz down to 1mHz). 

Attachment 1: DFD-bandwidth_noise_CLP500_to_300Hz.pdf
DFD-bandwidth_noise_CLP500_to_300Hz.pdf
Attachment 2: DFD-bandwidth_noise_CLP500_to_7000kHz.pdf
DFD-bandwidth_noise_CLP500_to_7000kHz.pdf
  4237   Wed Feb 2 03:27:20 2011 KojiSummaryGreen Locking85MHz Freq divider

The freq divider was built and installed in the beat detection path.

Attachment 1: Circuit diagram

  • Input stage:  Wideband RF amp with DC block at the input and the output. The gain is 10dB typ.
  • 2nd stage: Ultra fast comparator AD9696. Note: AD9696 is an obsolete IC and there are only a few extra at Wilson house.
    The output is TTL/CMOS compatible.
  • 3rd stage: 14bit binary ripple counter (fmax~100MHz.)

Note: I have added 7805/7905 regulators to the circuit as I could not find -5V supply on the 1X1/2 racks.

Attachment 2: Packaging

  • The box is german made Eurocard size box from Techno-Isel Linear Motion http://www.techno-isel.com/lmc/Products/EnclosureProfiles11055.htm
    The box is excellent but I didn't like the fixing bolts as they are self-tapping type. I tapped the thread and used #6-32 screws.
     
  • The prototyping board is BPS's (BusBoard Prototype System http://www.busboard.us/)  SP3UT. The card size is 160mm x 100mm.
    The other side is a ground plane and the small holes on the board are through holes to the ground plane.
    This particular card was not easy to use.
     
  • The input is SMA. Unfortunately, it is not isolated. The output is an isolated BNC.
     
  • The supply voltage of +/-15V is given by the 3pin D-connector. The supply voltages have been obtained from the cross connect of 1X1.

Attachment 3: Input specification

  • The input frequency is 10MHz~85MHz. At lower frequency chattering of the comparator against the multiple zero crossing of the (relatively) slow sinusoidal waves.
  • The input amplitude. There are no apparent degradation of the freq jitter when the input power was larger than -30dBm.

 

Attachment 1: freq_divider.pdf
freq_divider.pdf
Attachment 2: IMG_3816.JPG
IMG_3816.JPG
Attachment 3: IMG_3818.JPG
IMG_3818.JPG
  4238   Wed Feb 2 09:56:55 2011 KojiSummaryGreen LockingInstalled the freq divider and Rana's PFD

- The freq divider and Rana's PFD were hooked up to the ADCs. (Attachment 1)
(I leave the analog PFD not explained in this entry.)
For this purpose, the VCO feedback signal has been disconnected and the beat signal was moved from the VCO loop to the analog PFD.

The output level of the splitter was +12dBm and was too high for the freq divider.
So, I had to stupidly add an attenuator of 10dB before the box.

- Gain of the digital PFD LPF

The LPF of the digital PFD had the gain of -4096 to let the output signal indicate the direct frequency reading.

The gain has been changed to -67.108864
such that the output shows the direct reading of the beat freq in the unit of MHz

-4096*2^14/10^6 = -67.108864

 

- Attachment 2 shows the acquired beat note through the freq divider.
The blue is the beat note between "green locked" and "IR locked only to MC" (i.e. MC vs XARM)
The red is the beat note with the both beam locked to the arm

The freq divider is a bit flaky in some freq region as the divided output sometimes shows freq jumps or the captured at a freq.
I still don't know why it happens. We have to check why this happens.

Attachment 1: freq_divider_installation.pdf
freq_divider_installation.pdf
Attachment 2: 110201_freq_divider_output.pdf
110201_freq_divider_output.pdf
  4239   Wed Feb 2 10:44:26 2011 KojiSummaryGreen LockingFreq fluctuation measured by the freq divider and Rana's analog PFD

The freq fluctuation of the beat note has been measured with the following condition

  • The IR beam only locked to the MC. The green beam locked to the arm
  • Both of the IR and green locked to the x-arm

Calibration
- The output of the freq divider is already calibrated to have the unit of MHz.

- The transfer function between the analog PFD channel and the digital PFD output was measured to be -23dB = 0.7.
  The gain of the XARM-FINE channel was changed to 0.7 such that the output is calibrated in MHz.

Results

- I have not checked the analog noise level of the analog PFD path. We may need more whitening gain (by icreasing the gain of SR560).

- The analog PFD is always better than the digital PFD above 20Hz.

- Both the digital and analog PFD showed good agreement below 20Hz.
  Note the measurement was not simultaneous.

- When the arm is locked with the ETMX being actuated , the fluctuation of the arm length must be stabilized by a huge factor
(~10^5 according to Kiwamu's entry) However, we only could see the stabilization factor of 30.

As this residual is the difference of the freq noise felt by the IR and the green,
this is a real issue to be tackled.

- The RMS fluctuations of the arm with and without the IR beam being locked are 2MHz and 0.1MHz,
which correcponds to the arm length motion of 250nm and 13nm, respectively.
Ed: I had to use 532nm in stead of 1064nm. The correct numbers are 130nm and 7nm.

- Without the IR locked, The typical peak-to-peak fluctuation of the beat freq was 10MHz.

Attachment 1: 110201_green_freq_fluctuation.pdf
110201_green_freq_fluctuation.pdf
  4240   Wed Feb 2 12:55:34 2011 KojiSummaryGreen LockingFreq fluctuation measured by the freq divider and Rana's analog PFD

I found that some flakiness of the beat signals comes from the RF components for the beat detection.
They are touching the racks in an indefinite way. If we move the components the output of the analog PFD
goes crazy.

Once Kiwamu is back I will ask him to clean up all of the green setting in an appropriate way.

 

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