40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  SUS Lab eLog, Page 36 of 37  Not logged in ELOG logo
ID Date Author Type Categorydown Subject
  197   Tue May 10 16:59:36 2011 tara,ryan, mingyuanThings to BuyBladesblade holding block

We finalized the drawing for blade clamping system. The drawings are posted here and in Crackle ATF Wiki. We will submit the drawings to the machine shop tomorrow.

         For each blade, the clamping system will consist of: 1)Steel base, 2)Steel pillar, 3) Steel top clamp, 4) Al knife edge top piece,5)Al knife edge bottom piece,and 6) Al end piece.

1) Steel base x1:   The steel base is 3"x3"x0.5" . It has 4 counter sunk holes that allow us to mount the steel pillar on it. It has 3" rails on both sides, so we can mount it on the table. Extra clamps can be used to hold the base on the table.

2) Steel pillar x1:   It is 5.5" height with 2"x2" square cross section.  There are 4 tapped 1/4-20 holes , 1" in depth, on the bottom for mounting it on the base. There are 2 tapped 3/8 , 1" in depth, on top for clamping two clamps along with the blade.

3) Steel top clamping piece x1, This will clamp the blade on the pillar.

4) Aluminum knife edge, top piece x1,

5) Aluminum knife edge, bottom piece x1: (4&5) The two knife edge pieces will be used for loading the mass block on the maraging blade tip. The explanation is written in this entry.

6) Aluminum end piece that holds the mirror mount on the blade tip x1: We want to have a steerable mirror for the IFO. So we need a mirror mount. The block will hold the mount and the blade tip together through screws. This piece is uploaded in the above entry.

   

   

 The assembly (without the blade and the mirror mount) is shown below.

clampAssem.PDF

  200   Wed May 11 22:42:28 2011 tara,ryan, mingyuanThings to BuyBladesblade holding block

We submitted the drawing to the machine shop today. The works should be done before May 23rd.

 

   The base/ pillar/ blade clamp will be made from stainless steel. The knife edge pieces and mirror mount at the blade tip will be made from aluminum.

 

  1914   Wed Jul 7 13:05:07 2021 PacoDailyProgress1418 nm AUX ECDLNew aspheric flexures

[Radhika, Paco]

Today we fired up the 1418 nm ECDL and attempted initial adjustment of the aspheric lens. The design follows D2100115 which is a copy of the 2 um ECDL so we just changed the diode, the grating flexure angle, and the aspheric + flexure assembly and we are good to go. Radhika removed the 1900 nm aspheric flexure and we mounted the new collimating assembly which uses a f=3.1 mm (NA = 0.69) lens. At the beginning we had to feed over 300 mA of current to be able to see a beam (which was still diverging) so we had to free the flexure completely and align by hand to find the nominal positioning for a collimated beam. We lost a 2-56 screw in the process, but the final assembly is still in progress. The plan to follow is:

  • Finalize flexure alignment
  • Insert grating
  • Characterize ECDL emission
  1915   Fri Jul 9 11:40:42 2021 PacoDailyProgress1418 nm AUX ECDLNew aspheric flexures

[Radhika, Paco]

We tweaked the flexure alignment until we had a nominally collimated beam (~2 mW @ 250 mA of diode current) through the output aperture in the ECDL housing. We noted that the collimated beam is off-centered on that circular aperture along the horizontal (yaw) angle. After this, Radhika installed the ECDL grating and we hooked up the fiber output onto a InGaAs PD to monitor the power output. We tweaked the alignment of the grating (mostly yaw) to try and see a change in the power output to indicate optical gain in the diode, but saw no changes. We observed a change in the PD photocurrent as a function of the diode current in the absence of the grating (no optical feedback) which is indicative of ASE. We measured this level to be ~ 140 mV at 200 mA of current; with no observed threshold. In conclusion, we still need to refine our grating alignment to provide gain on the diode and observe lasing at the nominal 1450 nm wavelength.

  1916   Wed Jul 14 12:21:08 2021 PacoDailyProgress1418 nm AUX ECDLECDL lases... and MZ locked mid-fringe

[Paco]

Worked for a few hours to get the aspheric properly aligned. The procedure is quite finnicky, as the four 2-56 flexure screws have too much game and the fine thread setscrew that adds tension is too constrained. Anyways, it generally goes like this:

  1. With the grating out of the way, and the 2-56 screws slightly loose, move the aspheric flexure until a collimated beam (as round as possible) exits the centered round aperture in front of the SAF chip.
  2. Very carefully tighten the fine threaded setscrew in place to register the aspheric alignment.
  3. Check that the desired beam hasn't changed
  4. Insert grating careful not to touch the aspheric flexure (again, the mechanical registration is not great!)
  5. Manually rotate the grating while monitoring the power at the fiber output until non-ASE light appears. This is quite sensitive to alignment/angle and the better the mode is matched back into the fiber, the easier it is to find the right position.
  6. Fix the grating flexure.
  7. Slightly tweak the grating mirror knobs by hand to maximize said power (careful to avoid saturating PD)

After this, I installed a second amplified InGaAs detector, hooked up the unbalanced MZ beamsplitter output into the two PDs, adjusted the gains to equalize the output voltages and then hooked the two signals to the A and B inputs of an SR560 in "A-B" mode. The output (gain 1) was good enough to feed back in the HV PZT amplifier input modulation which allowed the MZ to lock mid-fringe. The lock is rough, as the balanced homodyne signal retains a tiny offset due to imperfect balancing... Attachment 1 shows the setup, including a typical scope trace after coarse current tuning (Ch1 and Ch2 in yellow and blue represent the photocurrents in the two MZ ports in the absence of feedback).

Indeed, scanning the nominal PZT voltage broke the lock, potentially after crossing a mode hopping region.

Tasks to be done:

  • Power characterization, including RIN, emission vs current.
  • Emission spectrum characterization; using the homemade spectrograph (grating + lens + camera) as the PZT is scanned
  • MZ feedback loop characterization, including optimizing the balancing stage
  • Self-homodyne phase noise spectrum

Next, as was suggested during yesterday's group meeting, we will transition into a self-heterodyne setup (with an AOM which I have yet to check out in the QIL).

  1917   Wed Aug 4 11:36:30 2021 RadhikaDailyProgress1418 nm AUX ECDL1419 nm ECDL with 2um AOM tests

[Radhika, Paco]

In order to transition the ECDL laser noise characterization to a heterodyne setup, we needed to test the AOM (acousto-optic modulator). We wanted to drive the AOM at 80MHz using the Marconi signal generator. Since the AOM has a max driving power of 600 mW, we determined that if we run the Marconi at max output power (13dBm), we saturate the AOM through a variable attenuator and a 5W amplifier. The detailed setup is in Attachment 1.

As we scanned the AOM RF input power, we monitored the mean of the 0th and 1st order power outputs using 2 amplified photodiodes on the scope. Attachment 2 plots the results of the scan; although we noticed the 0th order dropping, we did not see evidence of diffraction in the 1st order. Our suspected theory is that the lost power from the 0th order is due to thermally-driven attenuation inside the AOM (we do not know what is inside the AOM, so this is purely speculative). The next thing we want to try is to add a DC power level to the AOM RF input, but we will double check with Aidan.

  1918   Tue Aug 10 09:51:44 2021 PacoDailyProgress1418 nm AUX ECDL1419 nm ECDL AOM diffraction at 95 MHz

[radhika, paco]

We changed the setup to use a low power amplifier rather than the 5W amp from last time. The updated schematic is in Attachment 2. This is in part because 5W is an overkill to drive a fiber AOM which is known to saturate at 0.6 mW of RF input, but also because working with lower power active elements is easier and considerably safer. We dropped the 5W amp. in Rana's office last Friday, and got a ZHL-3A-sma. This little guy gives a max power output of 29.5 dBm (~890 mW) which should be more than enough while using the Marconi as our source (max output +13 dBm).

We hooked the amplifier to the load (AOM) without any couplers or attenuators in between, powered it with +24 VDC and quickly repeated a scan of the source power level while to see any sign of diffraction in the PDs. The result is in Attachment 2. We were a little bit disappointed that there appeared to be no diffraction, so next we tried scanning the RF frequency (it was nominally at 80 MHz) around and we finally succeeded in seeing some diffraction at 95 MHz! Paco thinks the internal fiber coupling made for the design wavelength (2004 nm) is suboptimal at 80 MHz and ~1.4 um wavelength. Therefore, to couple the 1st order back into the fiber, we need to shift the RF frequency to restore the diffraction angle at the cost of potentially not driving the optimal efficiency. An interesting observation made at the same time we saw 1st order light was that the power seemed to drift very slowly (-1%/min), which may have to do with some thermal drift inside the crystal... Our plan is to make a complete characterization of the diffraction efficiency at 1.4 um, and also investigate the slow intensity drifts as a function of RF input. The goal is not so much to understand and fix this last one, but to be able to operate the setup at a point where things are stable for a low frequency, frequency noise measurement.

  1920   Thu Aug 12 11:49:59 2021 RadhikaDailyProgress1418 nm AUX ECDL1419 nm ECDL AOM diffraction at 95 MHz

[Paco, Radhika]

When previously trying to characterize the AOM, we had noticed no 1st order diffraction when operating at 80 MHz, but significant diffraction at 95 MHz. This motivated us to take measurements while sweeping across both RF drive frequency and Marconi drive power. For frequency, we swept from 80-120 MHz in steps of 1 MHz. For power, we swept across [3, 0, -3] dBm (3 dBm is max power before saturating AOM). We took our measurements of 0th and 1st order signal using an oscilloscope.

Contour plots of the 0th and 1st order signals can be seen in Attachments 1 and 2, respectively. Peak 1st order diffraction seems to occur at ~106 MHz. Using this AOM for a beat note measurement, the frequency difference would be greater than intended, which could lead to a weaker beat note signal. 

*Bonus: Today we moved the ECDL setup off the cryostat table and onto the other table. These measurements were taken after the move. 

  1921   Tue Aug 17 11:09:29 2021 ranaDailyProgress1418 nm AUX ECDL1419 nm ECDL AOM diffraction at 95 MHz

Should measure the S-matrix using a bi-directional coupler.

  1922   Wed Sep 1 13:12:02 2021 RadhikaDailyProgress1418 nm AUX ECDL1419 nm ECDL AOM diffraction at 95 MHz

[Paco, Radhika]

Today we tried to pick up from [1920] by repeating the sweep measurements across RF frequency, at 3 dBm (max power). We noticed that the 0th order signal would dip around the expected value, consistent with the plot in [1920]. However, there was no signal from the 1st order. Clearly diffraction was occurring as seen by the dip in 0th order, but nothing was coming out of the 1st order port. We spent some time debugging by swapping the photodetector inputs / playing with the PD gains / performing power cycles, but got no insight into the issue. 

We suspected the 1st order fiber coming out of the AOM might be damaged, since it loops around fairly tightly. After giving it more slack, we still saw no signal. We wanted to test the fiber, so we took an unused output of the 50-50 beamsplitter and fed it into the 1st order port, effectively running the AOM in reverse. We hooked up the input and 0th order ports to the photodiodes and did not observe any signal. From here we were more convinced that the 1st order fiber may have seen some damage. 

For next steps, we can still use the existing fiber setup to take measurements of relative intensity noise (RIN), using the 0th order output of the AOM. I plan to do this in the next few days. Meanwhile, Paco is looking into ordering parts for a free space setup. We found a free-space AOM at 1064nm that seems promising, and we will work to transition the setup accordingly. 

  1923   Thu Sep 2 17:31:38 2021 RadhikaDailyProgress1418 nm AUX ECDL1418 nm ECDL Relative Intensity Noise

I took a relative intensity noise (RIN) measurement of the ECDL, by feeding the 0th order output of the AOM to the SR785. The RF power driving the AOM was set to 0 dBm. The RIN at 1 Hz is about 3x10-5, which is consistent with informal measurements we took on 08/13. From my understanding this noise looks pretty low, which is good. I will consult with Paco and add more discussion or conclusions, if any.

  1924   Thu Sep 16 15:21:21 2021 PacoDailyProgress1418 nm AUX ECDLFree space AOM

[Paco,  Radhika]

Uninstalled the fiber AOM and temporarily removed the third fiber 2x2 port beamsplitter. We are now using this free-space AOM. Then, I managed to launch one of the outputs of the second fiber beamsplitter into free space using a F220APC-1550 fixed collimator. The beam clears the  AOM aperture nicely and lands on the other side.

This AOM operates at a RF frequency of 35 MHz, so we set up a sweep on the Marconi to cover a window of 35 MHz +- 15 MHz. Using an IR detector card, we looked for evidence of 1st-order diffraction (from the setup geometry, the 1st order beam should have been visibly discernable). We first scanned the AOM across yaw but did not notice diffraction. Then, Paco lowered the height of the fixed collimator and we repeated scanning across yaw. We eventually saw the beam "jump" - diffraction! We adjusted yaw until we recovered both 0th and 1st order beams, at 50/50 intensity.

In summary, the free-space AOM works and we have managed to see 1st order diffraction. Next steps will be to quantitatively measure this diffraction while sweeping across RF frequency and power.

  1925   Wed Sep 22 16:44:34 2021 RadhikaDailyProgress1418 nm AUX ECDLFree space AOM

[Paco, Radhika]

We had previously noticed that the ECDL laser power seemed weaker compared to when we originally set it up and tested it. Today Paco opened it up and tweaked the grating inside to obtain a max power of 3 mW. This way, we could better resolve the 0th and 1st order beams coming out of the AOM.

Since we don't yet have a lens to send the collimated 1st-order beam to fiber, we connected a power meter to detect the beam and hooked it up to the oscilloscope. We noted peak diffraction at around 38.5 MHz (rough estimate). Using the inverse relationship between laser wavelength and the RF frequency f \lambda = constant, and the fact that the AOM is designed to operate at 1550 nm at 35 MHz, we calculated that the ECDL wavelength should be ~1409 nm. Of course this is a rough estimation, but it is a quick validation that we are indeed operating near 1418 nm. 

  1926   Mon Oct 4 17:44:34 2021 RadhikaDailyProgress1418 nm AUX ECDLFree space AOM

[Paco, Radhika]

Last Friday we received a new lens to direct the AOM 1st-order beam from free space into a fiber cable. We mounted the lens and connected a fiber cable into the photodiode, and tried to align the lens and see a jump in the oscilloscope. We were not able to do so and wrapped up for the day.

Today we continued aligning the lens with the fine adjustment on the mount, and eventually saw signal on the scope! Hooray, done with free space. We then prepared for eventually taking a heterodyne beat note measurement and hooked up the appropriate inputs/outputs to the beamsplitters. We added in the 50-50 beamsplitter that takes in the 1st order diffracted beam along with the beam from the delay line as inputs. We passed one of the outputs to the photodiode and had to retweak the freespace-to-fiber lens until we recovered signal on the scope, and we saw the beatnote signal.

Next, while Paco is out of town I will continue to work towards making a frequency noise measurement. We made a roadmap today:

I will demodulate the beat note using a mixer and a 35 MHz LO sourced from the Marconi. The result will be a 2f cosine term, along with a much lower frequency term which encloses the frequency noise information. This will be passed through a low-pass filter to get rid of the first high-frequency term. The remaining time-domain signal will be passed to the SR785 to obtain a spectra of the frequency noise. Calibration will need to be performed to obtain the right units for the spectra, Hz2/Hz (or Hz/rtHz). 

  1927   Tue Oct 19 13:52:03 2021 RadhikaDailyProgress1418 nm AUX ECDL1418nm ECDL Frequency noise

Attachment 1 is a diagram of the current setup for measuring ECDL frequency noise. Since the last update, I have fed the beat note signal to a mixer, using a 35 MHz LO sourced from the Marconi. The resulting demodulated signal is passed to a low-pass filter, removing the 2f sinusoidal term (any trace of the frequency difference) and leaving behind a low-frequency term containing frequency noise information of the original beam (accumulated over the length of delay line).

I took spectra of the resulting signal using the SR785 (Attachment 2). Note that these units are still in V/rtHz, since the signal has not been calibrated to the appropriate units for frequency noise, Hz/rtHz. Finding the calibration term will involve study of delay line frequency discrimination. 

  1928   Tue Mar 8 09:32:56 2022 PacoDailyProgress1418 nm AUX ECDL1418nm ECDL Frequency noise

[Paco, Radhika]

Beatnote recovery

Restarted ECDL characterization last Friday. After some lab cleanup, and beatnote amplitude optimization we borrowed Moku Lab from Cryo lab to fast-track phase noise measurements. Attachment #1 shows a sketch of our delayed self-heterodyne interferometer. The Marconi 2023A feeds +7 dBm to a  ZHA-3A amplfier which shifts the frequency of the laser in one of the arms using a free space AOM. The first order is coupled back into a fiber beamsplitter to interfere with a 10 m delay line beam.

Improved beatnote detection

The 38.5 MHz beatnote was barely detectable before when using PDA20CS2 because at unity (lowest) gain stage, the bandwidth was only 11 MHz... We instead switched to an FPD310-FC-NIR type which has a more adequate high-frequency response. Attachment #2 shows the beatnote power spectrum taken with Moku Lab spectrum analyzer. The two vertical lines indicate (1) the heterodyne beatnote frequency and (2) the "free spectral range" indicating the actual delay in the MZ arms, which is calibrated to c\tau/n = 9.73 m (using 1.46 for n, the fused silica fiber index).

Phase meter and freq noise calibration

We then tried using the phase meter application on the Moku. The internal PLL automatically detected the 38.499 MHz center frequency and produced an unwrapped RF phase timeseries (e.g. shown in Attachment #3). The MZ interferometer gives an AC signal

I_{\rm AC} = I_0 \cos(\Omega_0t + \phi(t + \tau) - \phi(t))

oscillating at \Omega_0 , i.e. the angular beatnote frequency. The delay (calibrated above) characterizes the response of the MZ relating the RF phase noise spectrum to the optical phase noise spectrum. The RF phase obtained through the phase meter has a fourier transform

\tilde{\phi}_{\rm RF}(\omega) = \tilde{\phi}(\omega) e^{-i \omega \tau} - \tilde{\phi}(\omega)

So the optical phase spectral density is related to the rf phase spectral density by a transfer function H(\omega) = e^{-i \omega \tau} - 1  Then, the RF & optical phase power spectral densities are related by S_{\phi_{\rm RF}}(\omega) = |1 - e^{-i \omega \tau}|^2 S_{\phi}(\omega)  or

S_{\phi}(\omega) = \frac{S_{\phi_{\rm RF}}(\omega) }{ 4 \sin^2(\omega \tau /2) }

Then, because the instantaneous laser frequency is 2 \pi \nu = \dot{\phi},  in fourier domain \tilde{\nu} = \frac{i\omega}{2 \pi} \tilde{\phi} the frequency and phase PSDs are related by the magnitude square of this transfer function like

S_{\nu}(\omega) = f^2 S_{\phi}(\omega)

Following this prescription, we compute an estimate for the frequency noise ASD (square root of the PSD) shown in Attachment #4. The frequency noise estimated by this method has several contributions and *does not* necessarily represent the free-running ECDL frequency noise.


Next steps

  • Noise budgeting (experiment)
  • Control loop (open/closed) models
  654   Fri Jun 28 13:04:27 2013 Edward TaylorLab Infrastructure Experimental Cavity Dimensions

The bottom of the cryostat contains a chamber where the main components of the experiment will be contained. This space is cylindrical in nature with heighth = 5.6cm and diameter = 13cm. In addition, the cylinder has two inner lips which create an inner diamter = 11.4cm. Furthermore, hole spacing for the screws that will attach the apparatus to the cryostat is approximately 1cm.

 

Also, we are working with a square window through which a laser will pass. The opening is an embedded circle with diamter 2.7cm and the square itself having length = 5.5cm.

  657   Mon Jul 1 08:08:22 2013 Edward TaylorLab Infrastructure IR Lab Cryostat Photos
CryoSUS / IR labs Cryostat
  658   Mon Jul 1 08:46:47 2013 Edward TaylorDailyProgress Mechanical Loss of Silicon Flexures (With Comsol Models)

I include comsol models of 6 different eigenfrequencies for a certain silicon flexure. In addition,  the expected graphs of the thermoelastic noise and phonon-phonon loss are also presented for the various mode shapes.

  794   Mon Jun 16 17:52:37 2014 GabrieleDailyProgress Some progress

 I opened the chamber and spent half afternoon tweaking the fiber feed-through. This thing is extremely unreliable. 

At the end I was able to get back a reasonable level of power, even not the maximum.

I also checked that the blades are not rubbing anywhere and that the shadow sensors are close to mid range. Nevertheless, after closing again, I'm still unable to drive at 800 cts.

I started a set of measurements at 600 counts.

 

  975   Wed May 13 17:10:16 2015 GabrieleDailyProgress Some retuning
  • The Michelson fringes looked too fast to me, so I started investigating the reason. The z damping od both test blades was not very efficient: it reduced the motions but noth really overdamping the blades. So I retuned the loop shape, moving the elliptic low pass to a slightly higher frequency and increasing the gain by about a factor 5. The 'notch' filter bank is no more necessary, since it was used to reduce the correction by killing some lines in the optical table motion, which are no more there. 
    With this new configuration of the damping, the 2.2 Hz resonances are overdamped, and fringes are significantly slower
  • The locking filter we designed for the lock on tha table was working, even though with not good performances. I modified it, moving down the roll-off poles to about 10 Hz. I also modified the elliptic low pass, moving it to 20 Hz and adding an additional low pass at 100 Hz. In this way I reduced a lot the high frequency control signal. Still, I'm not able to lock with very good performance: the error signal is sitting around 0, but with a peak to peak variation of the order of half or full fringe. My impression is that we have a lot of motion due to air currents, but this has to be verified.
  1171   Mon Aug 24 13:00:05 2015 GabrieleSummary Plan of the week

The goal is to start crackling noise data taking before the end of the week.

Activities to do

  1. Summarize the findings concerning the seismic coupling investigations (Xiaoyue, Yingtao)
  2. Complete the test and assembly of the new photodiode (Xiaoyue, Yingtao)
  3. Install the new photodiode (all)
  4. Investigate the origin of the bad sensitivity we have right now (Gabriele)
  5. Finish DAC noise measurements, including effect of dithering lines (Gabriele)
  6. Laser intensity noise projection (Gabriele)
  7. Automation of alignment using picomotors (Gabriele)
  8. Move electronic rack far from optical table (Gabriele)

 

  1226   Tue Sep 15 11:39:02 2015 FedericoDailyProgress Local Oscillator board

[Federico, Gabriele]

We decided to downconvert the "broadband" output of the ultrasonic microphones (the ones actually sampled at 64k) using Double Balanced Mixers and a Local Oscillator.

In order to have the cleanest possible L.O. signal, we built a breadboard with a 5MHz TTL xtal oscillator (model MX045-3C-5M0000) followed by two 74LS90, each dividing x10.

The output of the last 74LS90 (=50kHz) is sent to a power buffer (BUF634), then splitted in two 50 ohm signals to drive the L.O. port of the mixers with about +7dBm level.

The next step wiil be to complete the setup adding D.B. mixers on the bench

  1237   Fri Sep 18 15:15:58 2015 GabrieleDailyProgress Analysis of last night data

[Gabriele, Federico]

Last night we left the acoustic emission test bed running, with an excitation that gave us about 210 um peak to peak motion of the blade tip. As before, we collected one-hour-long alternating stretches of data, with drive on and off. The difference with respect to before is that microphone 2 has been moved further up the blade.

Both microphones signals still show wider distribution when the blade is driven with respect to when it's not driven. However, microphone 2 (the one further up the blade) shows a smaller increase in the distribution width. We don't have a good explanation for this just yet. The following plots show the histograms of the microphone signal RMS at 4kHz.

To improve the analysis, we considered only the driven data, and tried to correlate the distribution width with the force we were applying to the blade. The force is estimated using the DAC output, in coils. We haven't calibrated it in netwon. 

The following plot is a bidimensional histogram: the color gives the number of times the microphone was at a given value while the DAC was at given value. For each bin of the DAC value, we normalized the microphone histogram to the total number of points. In this way we can get rid of the different number of points that have given DAC values (in other words, the DAC value, being a sinusoid, stays more at the extreme than at the center, and we have to compensate for this effect in out histogram, otherwise we can't compare the microphone signal distributions at different DAC values).

The colorscale is hihly saturated to show the tails of the distribution, and the colorscale is logarithmic. It's apparent that the wider distribution that we saw in the first plot are there only when the drive is close to the maximum values. So we have an increase of the microphone noise when the absolute value of the oscillating force we are applying is large. We can't conclude that this is crackling noise, but it's a step in the right direction, even though we were expecting to see an increase of noise when the force derivative was larger. 

Next steps:

  • run with different amplitudes and frequencies, to see how the noise changes
  • derive a numerical estimation of the "ditribution width" to have quantitative results
  • repeat the above analysis with the full rate signal which should have a gaussian distribution if it's only sensor noise
  1768   Sat Oct 20 00:38:43 2018 DuoHowTo DAC Noise monitor PCB layers

Background: The design of the DAC noise monitor is in the PCB design stage - I am trying to put the circuit on the PCB board in Altium. We use three power voltages to drive the op amps in the circuit: -15 V. +15 V. We also need power ground and signal ground. This circuit is going to replace a part of a big PCB board with other existing circuits.

Question: What are the layers used by the existing design? The DAC noise monitor needs to fit with other parts, so they have to share the same layers. Is there a PCB layout file for the existing design?

In case of absence, I will start with a signal layer, a -15V power layer, a +15V power layer, a power ground, and a signal ground. I googled a bit and they say the cost will be high and five layers might be more than what we want. Besides, I am not sure about the sequence of the layers either. I will start with this in order to proceed in Altium before we figure out what we need to do:

TOP

Signal layer

+15V power

Power ground

Signal ground

-15V power

BOTTOM

How much sense does it make?

  1769   Tue Oct 23 00:57:13 2018 DuoHowTo DAC Noise monitor PCB layers

I proceeded as described below. The routing is completed. All the signal routing is completed. One thing worries me is that I am afraid the signal ground and power ground is yet separated. I do have two internal planes for signal ground and power ground. Should they be connected to the same power input (so that they are just two planes with the same source)? Altium treats all the ground as one net GND. If the answer to the question is yes, I need to figure out how to get Altium separate them. In Altium, you can specifiy which net you connect to, but I did not figure out how to specify which layer. (Maybe I need to create a separated GND net, like PGND/SGND for that?) 

Here is a summary file with the schematics and PCB design: NoiseMonitor.pdf

Also, this is the link to the Wiki page, with more details about this work: https://wiki-40m.ligo.caltech.edu/Electronics/NoiseMonitor

Quote:

Background: The design of the DAC noise monitor is in the PCB design stage - I am trying to put the circuit on the PCB board in Altium. We use three power voltages to drive the op amps in the circuit: -15 V. +15 V. We also need power ground and signal ground. This circuit is going to replace a part of a big PCB board with other existing circuits.

Question: What are the layers used by the existing design? The DAC noise monitor needs to fit with other parts, so they have to share the same layers. Is there a PCB layout file for the existing design?

In case of absence, I will start with a signal layer, a -15V power layer, a +15V power layer, a power ground, and a signal ground. I googled a bit and they say the cost will be high and five layers might be more than what we want. Besides, I am not sure about the sequence of the layers either. I will start with this in order to proceed in Altium before we figure out what we need to do:

TOP

Signal layer

+15V power

Power ground

Signal ground

-15V power

BOTTOM

How much sense does it make?

 

  1770   Wed Oct 24 15:01:50 2018 DuoHowTo DAC Noise monitor PCB layers

As per Chris's suggestions, I replaced the capacitors with surface mount ceramic capacitors, doubled the trace width to 0.5mm and adjusted the routings accordingly. New PCB layout is attached.

  1771   Wed Oct 24 21:55:45 2018 DuoHowTo DAC Noise monitor PCB layers

I forgot to connect the outputs of U1 and U2. It is fixed. I also run the design rule check and verified that all the connections are made. I separated the power ground and signal ground as well. The summary PDF is updated below.

  1772   Sat Nov 24 20:09:14 2018 DuoMisc Noise monitor PCB assembly completed

Progress: the board and components arrived and assembled. Some obvious mistakes are fixed on the next version in Altium.

Next: how to test the board? i.e. How to connect the test instruments (such as spectrum analyzer, DC power supply) to the board? We need connector converters (from BNC to headers female & from BNC to 9 pin D shape male). Or do we have better ways to test it?

Note: Altium footprints for WIMA capacitors are created. Altium test point component is created. These might be useful in the future.

  1774   Fri Dec 7 18:27:27 2018 DuoMisc Noisemon problem identified and another order placed

Progress: The reason why the board from oshpark did not work is found. The board has 6 layers, but Oshpark only make 2 or 4 layer boards. They just ignored two layers (the two ground layers) so there is no ground at all on the board.

Some known issues is fixed in the new board (capacitor footprint, connector in the wrong direction). The new board will arrive next Wednesday.

Some good quality connectors are made - next board will be ready to test once arrived.

Next: I plan to put other components into Altium by Wednesday. 

  1775   Wed Dec 12 21:50:44 2018 DuoDailyProgress New board arrived and other components on the board placed in Altium

The new board arrived this afternoon. I tried the connections - it has enough layers and is grounded. I will assemble the board tomorrow. 

In the meanwhile, I have put other unchanged components on the board into Altium, not quite finished (put them in schematics but not PCB, gives me error when importing changes). I will prioritize assembling the new board.

A picture of the board is attached.

  1776   Sat Dec 15 15:30:44 2018 DuoDailyProgress Noise in the last Low pass sallen key filter

Progress:

1. Board assembled

2. One design error found and fixed in the instrumental amplifier. Now the instrumental amplifier is working

Issue:

Noise above 100Hz (pass band 20-100Hz), as shown in the transfer function in the picture. 

The noise comes from the last stage of the circuit: the low pass sallen key filter. The first two high pass stages works well.

(structure of the circuit: differential input - passive filter - instrumental amplifier - high pass - high pass - low pass - output)

I have tried

1. Checking the connections - the connections are good

2. Replacing the opamp - did not work

  1778   Thu Jan 3 15:33:40 2019 DuoDailyProgress New, Full noisemon completed

Here is a full version of the noisemon, with four channels and the power regulator. I did the routing again since the previous routing 1) did not leave enough space for connectors/other components; 2) Altium does not transfer properly from the schematics to the PCB layout when expanding to 4 channels.

  1779   Thu Jan 3 16:24:22 2019 DuoDailyProgress Noise in the last Low pass sallen key filter

The reason for this problem was found. The gain of the sallen key filters was too high. There is an intrinsic limit of the sallen key filters - they cannot have a gain more than a certain value. Otherwise, they will be unstable. See this TI document  for details.

Quote:

Progress:

1. Board assembled

2. One design error found and fixed in the instrumental amplifier. Now the instrumental amplifier is working

Issue:

Noise above 100Hz (pass band 20-100Hz), as shown in the transfer function in the picture. 

The noise comes from the last stage of the circuit: the low pass sallen key filter. The first two high pass stages works well.

(structure of the circuit: differential input - passive filter - instrumental amplifier - high pass - high pass - low pass - output)

I have tried

1. Checking the connections - the connections are good

2. Replacing the opamp - did not work

 

  1781   Sun Jan 6 15:37:39 2019 DuoDailyProgress Isolated test of the oscillating op amp

It seems there can be multiple reasons for an op amp to oscillate. I wanted to identify the nature of the oscillation.

I want to isolate one stage and see what is going on. I used the extra empty board and assembled the last stage on it. Putting in nothing at all (the input is GND), I get a signal of 5.792MHz, 321mV at the output.

Now that the problem is even more clear, I will keep looking into this.

  1782   Tue Jan 8 22:47:07 2019 DuoDailyProgress Isolated test of the oscillating op amp

After a few days of struggling (and essential help from Chris), mystery is resolved. Fortunately, the oscillation does not have much to do with my circuit design. It is caused by the RLC resonance formed by 1) the inductance of the parallel wires + 2) capacitance of the signal ground plane and the power ground plane.

As is seen in the picture, I twisted the two grounding wires together (reduce the inductance) and the oscillation is gone.

You can also connect the planes on the board (removing the capacitance) and the oscillation will disappear as well.

Quote:

It seems there can be multiple reasons for an op amp to oscillate. I wanted to identify the nature of the oscillation.

I want to isolate one stage and see what is going on. I used the extra empty board and assembled the last stage on it. Putting in nothing at all (the input is GND), I get a signal of 5.792MHz, 321mV at the output.

Now that the problem is even more clear, I will keep looking into this.

 

  1783   Sun Jan 20 16:00:37 2019 DuoDailyProgress Update on the noisemon board

Two more oscillations problems are resolved, and there is no more oscillations. In the time series (the inputs are terminated), we see only the 60Hz noise.

- Some big bypass capacitors are used to regulate the power.

- A small capacitor is attached to the negative feedback loop in the second HP filter.

New board/components arrived. I will assemble and test them immediately.

  1784   Fri Feb 1 12:35:13 2019 not DuoDailyProgress Update on the noisemon board

Duo's noisemon has been in the EE shop/cryo lab for testing.  It is a drop-in replacement for the existing monitor board, including both noisemon and Vmon/Imon/RMSmon circuits for all four channels.

Duo is still working on a log entry summarizing the performance of the new board vs simulation.  This entry shows some measurements of the performance of the new board vs the old board.

Attachments:

  1. Transfer functions of the new noisemon board, in coil driver state 1.
  2. Noise spectra of the new noisemon board, in coil driver state 1, with and without DAC noise input.
  3. Transfer function of an old noisemon board, in coil driver state 1.
  4. Noise spectra of an old noisemon board, in coil driver state 1, with (REF traces) and without (live traces) DAC noise input.
  1785   Tue Feb 5 20:55:34 2019 DuoSummary Noisemon test results

Based on the test results posted, I did the following analysis:

1. Compared measured transfer function to the LISO calculations. Attachment 4 and 6. The transfer functions match well with LISO.

2. Compared measured noise at the output to the LISO calculations. Attachment 1 and 3. The noise is more than LISO calculations by roughly a factor of 2, but I think it is expected - there is coil driver noises (amplified more than 300 times). Also, LISO uses ideal resistors, considering that the noise here is dominated by resistor noise. We also have plots of the noise spectrum with DAC noises injected. In this case, the noise in the passband (20 - 100Hz) is much more, suggesting that the board noise is dominated by the DAC noise.

3. Compared input-referenced measured noise to DAC noise. Attachment 2 and 5. We divided the noise by the transfer function and compare it directly with the DAC noise model. We can see that, in the passband, the board noise is about a factor of 10 less than the DAC noise (channel 2 and 4 has more noise; the signal is polluted by the ADC). 

4. A simple calculation based on the transfer function comparing the ADC noise and the amplified DAC noise. 

DAC noise > 300nV/rtHz. Passband amplification > 50dB > 300. Amplified DAC noise in the passband > 90uV/rtHz, compared to ADC noise 4uV/rtHz.

FYI: 1. I cannot attachment PDF plots directly since it will stuck the elog server. I put some PNG plots, but PDF plots can still be found in the compressed files.

2. Also, channel 2 is more noisey. It comes from ADC not the noisemon.

  1787   Tue Feb 19 18:11:43 2019 DuoDailyProgress Tuesday report

Some clean up work on the noisemon is done.

1. Added compensate capacitor.

2. Added mounting holes.

3. Added DCC number. https://dcc.ligo.org/LIGO-D1900052

4. Renumbered the components.

5. Added 0 ohm resistor between power ground and signal ground.

6. Added more test points for the voltage monitor and current monitor.

7. Increased schematics font size.

Next I will create the Bill Of Materials. I need to assemble the manufacturer information and put meaningful and consistent descriptions for the components.

  1788   Mon Apr 1 20:25:20 2019 DuoDailyProgress Changes on noisemon being made

Attachment: new PCB schematics with all the changes made.

We (Chris and I) had a conversation with Rich last week and the following work on the noisemon board has been suggested:

1. Name of power nets: +VCC to +15, -VCC to -15. +V to +18; -V to -18, making it clearer what the power is.

2. Fix the off-grid problems of the schematics.

3. Draw the circuits on the schematics in the standard way. (Rich gave me a bunch of snippets that shows the standard way to draw the circuits, like how to draw a sallen key filter)

4. Ground the shells of the D connectors.

5. Add 1 Ohm resistors at the inputs of the power regulators

6. Use polymer tantalum with at least 35V rating. Previously we are not using polymer ones. Rich said the ones (non-polymer ones) we were using burn and explode sometimes.

7. Add "No error checking" for those pins not being used (e.g. unused op amp pins)

8. Disassemble the "repeat()" in the sheet symbol. Making four sheet symbols and connect them directly to the connectors.

9. Change the outputs of the current monitor, noise monitor and the voltage monitor to differential. Previously we had one of the pins of the D connectors pairs grounded. Now we add a differential driver at the end. It doubles the gain and the range.

Rich said my PCB routing was OK, so all the changes can be reflected on the schematics. I have made all the changes on the schematics (I do have the previous version). The current schematics is attached.

However, "#9 change the outputs to differential" requires a lot more space and the current PCB routing does not have enough free space between the components. Thus, this requires routing the whole PCB again, which is what I am working on now.

  1789   Wed Apr 17 16:34:37 2019 DuoDailyProgress Noisemon update

We added differential drivers at the outputs of all the monitors. After that the routing becomes impossible at the output connectors.

I replaced the signal ground with an additional signal layer, and reversed the order of the channels on the layout.

Having exhausted all the possible routing tricks, I finally managed to connect the whole board.

  1790   Sat Jun 8 15:52:48 2019 DuoMisc Arrival date of noisemon

We ordered the board from Screaming Circuits and chose to provide the component ourselves. However, the parcel we ordered from Verical was lost by Fedex on its way to Screaming Circuits. The original delivery date was delay from late May to June 13.

Once the board arrives, we will test the board - TF, noise etc. Any others?

  1795   Wed Jul 17 13:35:02 2019 DuoDailyProgress Unknown issue

I connected the DAC to ADC direclty (picture 1) and send a sine signal into the DAC. However, I did not get the sine signal back from the ADC. I sent the signal in X1:CRY-DITHER_W_MOD_EXC, channel 9 of DAC and expect the signal from X1:CRY-E_REFLDC_IN1, channel 16 of ADC. However, picture 2 shows what I get: a constant signal around 4400 counts.

  1804   Thu Aug 15 17:23:40 2019 DuoDailyProgress L1 noisemon 1-coherence

Noisemon installed in ITMX at L1. I pulled the 1-coherence data. trying to compare with Valery's measurement: https://alog.ligo-la.caltech.edu/aLOG/index.php?callRep=43240.

 

 

  1805   Tue Aug 20 10:31:12 2019 DuoDailyProgress Noisemon test

I calculated the noise based on L1 data. My calculation is

(1-coherence) * drive = noise in DAC counts

noise in volts = noise in DAC counts * 20 / 2^16

Is this correct?

  1806   Tue Aug 20 18:15:11 2019 DuoDailyProgress Noisemon data more avg

Increase avg to 1000. We are going to calculate the DAC noise from this.

  1808   Thu Aug 22 18:13:19 2019 DuoDailyProgress Noisemon Data from all four channels

L1 noisemon data for all four channels.

  1809   Fri Aug 23 13:42:16 2019 DuoDailyProgress Noisemon Data from all four channels

Plotted.

Quote:

L1 noisemon data for all four channels.

 

  1810   Fri Aug 23 15:11:36 2019 DuoDailyProgress ETMY noisemon

Will compare ITMX with ETMY.

ELOG V3.1.3-