Fast work indeed! It would be nice if we could have the following details filled in as well
a) A short title and caption for the table, saying what we are measuring
b) the units in which this physical quantity is being measured.
It is good to keep in mind that people from other parts of the group, who are not directly involved in this work, may also read this elog.
I measured the transfer function, shot noise, and dark spectrum of AS55.
From the shot noise measurement, the RF transimpedance is (556.3 +- 0.8) Ohms and the dark current is (2.39 +- 0.01) mA. The dark noise agrees with the approximate value calculated from the circuit components.
There are no anomalous oscillations when there is no light on the photodiode. I am working on fitting the transfer function in LISO but the other plots are on the wiki at http://blue.ligo-wa.caltech.edu:8000/40m/Electronics/AS55
We want to increase gain in the lower frequencies, so a circuit must be designed (a passive low pass filter).
First, measurements were taken at the X arm for impedance and capacitance, which were 104.5kOhms and 84.7pF respectively. Kiwamu decided to make the circuit resemble a voltage divider for ease of calculation, such that Vout/Vin would be a ratio of some values of the equivalent circuit reactance values. After a few algebra mistakes, this Vout/Vin value was simplified in terms of the R, C measured and the R', C' that would be needed to complete the circuit.
Since the measured C was very small and the measure R was fairly high, the simplified form allowed us to pick values of R' and C' that would make the critical frequency occur at 0.1Hz: set the R' resistance to 1MOhm and C' capacitance to 10uF, which would yield a gain ~1.
With these values a circuit we can start actually making the circuit.
[Steve, Suresh, Larisa]
The following cables were laid today: ETMYT, ETMY, IFOPO, MC1, OMCR, AS Spare, and MC2T.
Though the paper suggested 135' for the MC2T, we used a 110'. This is too short: need at least another 15' for the MC2T.
The RCR cable wasn't crossed off on the list, but a cable exists at the RCR cable which is black and is labeled (old label, 75 ohms)
There was no indication of which length was needed for MC1, so a 95' cable was used.
This is the continuation of http://nodus.ligo.caltech.edu:8080/40m/4402
The first picture is of the actual component, where the resistor is 1M and capacitor is 10uF.
But before the component can be put into place, its transfer function had to be checked to make sure it was doing what we calculated it would do. The results of these are in the graphs generated: frequency vs. gain, and frequency vs. phase.
According to these graphs, we are not achieving the targeted cutoff frequency: need to recalculate and compensate for the extra 100k resistance being encountered.
For bode plot:
USE LOG-LOG plot for the amplitude
USE LOG-LINEAR plot for the phase
Search "Bode Plot" on web
I have prepared several diagrams outlining the current state of the RF System.
These are uploaded into the svn40m here and will be kept uptodate as we complete various parts of the task. These plans have taken into account
the new priorities of the LSC (set out by Koji here )
We (Koji, Kiwamu and I) took stock of the RF cables which we have inherited from the earlier RF system and have made new plans for them.
I took stock of the filters purchased for the modifying the demod boards. We have pretty much everything we need so I will start modifying the boards right away. The following table summarises the modifications
LP Filter (U5)
We seem to have a spare SHP-175. I was wondering where that is supposed to go.
This is the status and tentative schedule for completing the various tasks. I have put the dates based on priority and state of the hardware.
The RF Cable layout plans are drawn on top of a Lab Layout. The various subsystems are drawn (not to scale) on separate layers. The graffle files are located here . I thought they might come in handy for others as well.
[Steve, Kiwamu, Larisa]
Having finished laying new cable last week, we moved on to connecting those on PSL table and AP table.
--RCR, RCT, PMCR (all three are blue)
--OMCR (blue cable, ***now has a camera***), PMCT, IMCR, REFL, AS (white cable), OMCT (***now has camera***)
Unless otherwise noted, the cables are black on the AP table. Also on the AP table: cables were connected directly to the power source.
The wiki has been updated accordingly.
Steve noted that MC2T and POP cameras are not there.
Ooh. Can you explain the purpose of the resistors which are connected to the (+) inputs? It looks like some real electronics ninjitsu.
51 Ohm for CLC409
The datasheet of CLC409 uses 25Ohm there. This is to cancel the input bias current of the two inputs of the opamp.
The source impedance (series) of SGD444 is 50Ohm. So I used 50Ohm for the + input shunting.
However, I could probably use anything between 0-50Ohm as the datasheet itself tells that the bias currents are
not related between the two inputs. In addition, I am not sure how much the real series resistance of the PD is.
1kOhm for OP27
This resister is to ensure the (+) input to have a high impedance at high frequencies.
As far as OP27 is behaving as an ideal opamp, the (+) input has a high impedance.
Also if the inductor behaves as the ideal inductor, no photocurrent comes to the AF path.
However, if both of the op27 and the inductor show similar impedances to the RF transimpedance of 240Ohm,
the AF path absorbs some photocurrent and affects the RF transimpedance of the RF output.
We know that the inductor has a self resonance where the shunt capacitance take over the impedance of the coil.
Above that frequency, the inductor is no longer the inductor. The self resonant freq of this inductor is ~300MHz. It is OK, but not
too far from the freq of interest if we like to see clear cut off at around f>100MHz.
Also OP27 is an AF amplifier and I had no confidence about the input impedance of the OP27 at 100~300MHz.
If I put 1k in the (+) input of the OP27, I can ensure the entire AF path has the impedance of ~1k (at least 500Ohm even when L and OP27 are shorted).
I think the chip resister easily works as a resister up to 1GHz.
I brought TTFSS set #7 to 40m and kept it in the electronic cabinet.
note that Q4 transistor has not been replaced back to PZT2907A yet. It's still GE82.
Q3 is now pzt3904, not PZT2222A.
The (-) input has been decoupled by the capacitor. So the series resistance of the PD is not the matter.
In this sense, we should use 0Ohm for the (+) input shunting.
However, I could probably use anything between 0-50Ohm as the datasheet itself tells that the bias currents are
not related between the two inputs. In addition, I am not sure how much the real series resistance of the PD is.
The following Video MUX inputs(cameras) and outputs(monitors) have been checked:
MC2F, FI, AS Spare, ITMYF, ITMXF, ETMYF, ETMXF, PSL Spare, ETMXT, MC2T, POP, MC1F/MC3F, SRMF, ETMYT, PRM/BS, CRT1(MON1), ETMY Monitor, CRT2(MON2), CRT4(MON4), MC1 Monitor, CRT3(MON3), PSL1 Monitor, PSL2 Monitor, CRT6(MON6), CRT5(MON5), ETMX Monitor, MC2 Monitor, CRT9, CRT7(MON7), CRT10, and Projector.
Their respective statuses have been updated on the wiki: (wiki is down at the moment, I will come back and add the link when it's back up)
Plotting the data points yielded by the spec analyzer of my first LPF yielded a result that was not expected: the desired cutoff frequency wasn't achieved because of some extra 100k resistance that wasn't taken into consideration. (see here ). I have redrawn the Bode graphs for this configuration so that it is easier to see that it is wrong (first attachment)
After some calculation adjustments, it was found that the capacitor value could remain at 10uF, but the resistance needed to be changed to 100k to maintain a gain of 0.5 and critical frequency at 0.1Hz. Second attachment is the Bode graph that results from this configuration.
Note: Bode graphs are both in Log-Linear scales (Wikipedia said so)
The performance plots for POX_11 in the wiki are horrendous and the schematic is missing.
I opened up the box and found all kinds of horrors. There were multiple tunable parts and a flurry of excess nonsense.
The top 2 worst offenders:
1) The main tunable inductor was busted. I removed it and found that the coil was open. Too much indelicate soldering in its vicinity had melted the wire. Someone had put extra inductors and capacitors around it to make it seem as if the PD was working fine, but the noise performance was off by a factor of ~100.
2) The MAX4107 had a 1.4k series resistor. This make the output go through a 1450/50 voltage division which is not nice for the SNR. I removed it.
I then struggled for awhile to get a sensible response. It turned out that the TEST IN input was not giving me a sensible TF. Jenne and I fired the Jenne laser at it and found that the 11 MHz main resonance is there. In the morning I'll finish this off and post more results. I think its going to end up being fine.
I used the Jenne AM laser to tune up the PD (used to be POX_11 but now is called REFL_11). In addition to the notch at 22 MHz, I have also put in a LC notch at 5*f = 55.3 MHz. The transfer function below shows the RF OUT of the PD v. the drive to the laser. I didn't divide out by the 1811 because its not on the EE bench.
A new 90 deg splitter, PSCQ-2-51W, has been installed on another demod board called AS55.
It shows a reasonably close 90 degree separation between the I and Q signals at 55 MHz with various LO and RF power.
So far we have ordered only three PSCQ-2-51Ws for test. Now we will order some more for the other demodulators.
Some plots will be posted later.
Figure.1 I-Q relative phase measurement as a function of LO power.
Blue curve : relative phase of AS55 that I have modified today (#4572).
Red curve : relative phase of AS11 that I had modified a week ago (#4554). Just for comparison.
The relative phase of AS55 agrees approximately what we expected according to the datasheet of PSCQ-2-51W. We expected 85 degree.
Figure.1 I-Q amplitude imbalance as a function of LO power.
From - 5 dBm to 5 dBm in LO power the imbalance is within 3 %.
But the precision of the measurement is also about 2 % (because I used an oscilloscope). Even so the imbalance is still good.
Some plots will be posted later.
I found that all the Heliax cables landing on the bottom of 1Y2 were too loose.
Due to this loose connection the RF power at 55 MHz varies from -34 dBm to 3 dBm, depending on the angle of the Heliax's head.
The looseness basically comes from the fact the black plate is too thick for the Heliax cable to go all the way. It permits the Heliax's heads to rotate freely.
What we should do is to make countersinks on the black plate like this:
The countersink gives rise to another problem when we mount the N-type-to-SMA bulkhead adaptor. As we are making a circular hole in the plastic strip (instead of a hole with two flat sections) the adaptor is free to turn when we tighten it with a wrench. We currently hold the smooth circular part on the other side with a gripping pliers and while tightening. If that part disappears into the countersink (as seen in the pics) we will not be able to tighten the adaptor sufficiently and consequently we will also not be able to get the heliax connector to be tight.
A better solution would be to use the 1/4-inch plastic L-angle beam which Steve has used on the AS table. In addition to solving this loose connector problem, the beam is also more rigid than the plastic strip.
I was charge with making a Non-Inverting Op Amp Low Pass Feedback circuit for Jenne, which may somehow be integrated into a seismometer project she's working on.
Circuit diagram is attached. Calculations show that R1, R2 and C have the following relationship: if R1=10^n, R2=10^(n+1), C=10^(-n-4). For the particular circuit being modeled by the transfer function, R1=100 Ohm, R2=1k Ohm, and C=1uF.
Attached also is the circuit's Bode plot, showing frequency versus gain and phase, respectively. The frequency versus gain graph is true to what the circuit was calculated to generate: a gain of +20 and a cutoff frequency at 200Hz. Not sure what's going on with the frequency verus phase plot.
This is a continuation of this
The low pass filter is finally acceptable, and its Bode graph is below (on a ~3Hz frequency span that shows the cutoff frequency is at 0.1Hz)
My observation wasn't accurate enough.
The looseness came from the fact that the N-SMA bulk heads were slipping on the black plate.
This is actually what Suresh pointed out (see here). So the thickness of the black plate doesn't matter in this case.
Somehow I was able to tighten the bulk heads using two wrenches and I think they are now tight enough so that the heliax's heads don't move any more.
Building on what was posted previously
The configuration has now evolved into an Inverting Op Amp Feedback Low Pass Filter circuit.
Had to change out some components to satisfy conditions: R1=1k Ohm, R2=10k Ohm, C=0.1uF. These were changed in order to decrease the magnitude of the current passing through the op amp by a factor of 10 (10V supplied through the R1 resistor yields about 10mA). The configuration itself was changed from non-inverting to inverting in order to get the frequency vs. gain part of the Bode plot to continue to decrease across higher frequencies instead of leveling off around 4kHz.
Having finished the bulk of the work for the LPF itself ( see here ), I have begun trying to design the seismometer box to Jenne's specifications.
Currently looking into what the voltage buffer amplifier might look like for this.
Suggestions/corrections would be much appreciated!
Yesterday we found that MC3 OSEM LL PD did not have a sensible signal - the readback was close to zero and it was making MC move around. I disabled the PD LL so that the damping is done with just three face plus side PDs. There still no signal from MC3 LL PD today. It needs debugging.
The schematic for the seismometer box from this last time has been updated...
Koji was helpful for coming up with a general diagram for the voltage buffer amplifier, which has now been added to the configuration pictured below.
The only thing that remains now before I try to plot it with Eagle/LISO is to pick an op amp to use for the voltage buffer itself. Someone suggested THS4131 for that (upon Googling, it hit as a "high speed, low noise, fully-differential I/O amplifier"). It looks good, but is it the best option?
[Valera / Kiwamu]
It was because of a loose connection. Pushing the connector solved the issue.
We really have to think about making reliable connections and strain reliefs.
1X1 is strain relieved in the back. I will use similar approach on the rest of the racks .
[Haixing / Kiwamu]
As a part of the Wednesday's cabling work, we spent some times for identifying the RFPD interface cables.
The RFPD interface cables are made of a 15 pin flat cable, containing DC power conductors for the RFPDs and the DC signal path.
The list below is the status of the interface cables.
- - - - RFPD name, (cable status) - - - -
- REFL11 (identified and labeling done)
- REFL33 (identified and labeling done)
- REFL55 (identified and labeling done)
- REFL165 (no cable found)
- AS55 (identified and labeling done)
- AS165 (identified and labeling done)
- POP22/110 (identified and labeling done)
- POX11 (identified and labeling done)
- POY11 (identified and labeling done)
- POY55 (identified and labeling done)
We still have two cables which are not yet identified. Their heads are around the LSC rack and labeled 'unidentified'
I took REFL11 out from the AS table for a health check because it wasn't working properly.
The symptoms were :
- a big offset of ~ -3 V on the RF output. No RF signals.
- The DC output seemed to be okay. It's been sensitive to light.
I did a quick check and confirmed that +/- 5V were correctly supplied to the op-amps.
It looks that the last stage (MAX4107) is saturated for some reasons. Need more inspections.
At the moment the REFL11 RFPD is on the bench of the Jenne laser.
- Found the inductor which shunts the positive input of MAX4107 was not touching the ground.
This left the positive input level undetermined at DC. This was why MAX had been saturated.
The PCB has a cut, so it was surprising once the circuit worked.
- Resoldered the inductor to the ground. This made the circuit responding to the intensity-modulated beam.
- But the resonances and the notches were totally off, and the 200MHz oscillation has resurrected.
- Attached 40Ohm+22pF network between the neg-input of MAX and the gnd. This solved the oscillation.
- Made the tuning and the characterizations. The PD is on Kiwamu's desk and ready to go.
More to come later
- Resonant at 55MHz. The transimpedance is 258Ohm. That is about half of REFL55 (don't know why).
- 11MHz&110MHz notch
- The 200MHz oscillation of MAX4106 was damped by the same recipe as REFL11.
(Continuation of this)
I plugged the circuit into the LISO program to generate the graphs below....the first graph is a plot of frequency (f, in Hz) versus gain (in dB), and frequency (f, Hz) versus phase (in degrees). Also included is the second graph, which is a noise plot of all circuit parts which contribute to the total noise of the circuit.
The only issue I had was that two of the op amps I'd picked (see third attachment for the original circuit diagram) for the circuit were not in LISO's op amp library. So I replaced THS4131 (from the voltage buffer part) and AD826 (from the ADC driver part) with AD797 and LT1037, respectively in order to generate the plots below....
There are notes calling the AD797 "ultra low noise, low distortion", whose data sheet can be found here: AD797
Notes also call LT1037 "low noise, high speed precision op amp", whose data sheet can be found here: LT1037
I've put these in temporarily only, as I don't know if they are appropriate choices for the job or even if we have them. Suggestions?
We replaced GE81 by PZT2907A (PNP transistor) in TTFSS #7, it's working fine.
Last time I broke Q4 transistor, which is used in the low noise power module for TTFSS, (see the schematic) and could not find another PZT2907A, so GE81 was used temporarily. Now we changed it back to PZT2907A as designed. I tested it by checking the voltage outputs of the board. It works fine, all voltage outputs are correct. I labeled one of the slot on the blue cabinet tower and kept the rest of the transistors there.
The full characterization of REFL11 is found in the PDF.
Resonance at 11.062MHz
Q of 15.5, transimpedance 4.1kOhm
shotnoise intercept current = 0.12mA (i.e. current noise of 6pA/rtHz)
Notch at 22.181MHz
Q of 28.0, transimpedance 23 Ohm
Notch at 55.589MHz
Q of 38.3, transimpedance 56 Ohm
The full characterization of POP55 is found in the PDF.
Resonance at 54.49MHz
Q of 2.5, transimpedance 241Ohm
shotnoise intercept current = 4.2mA (i.e. current noise of 37pA/rtHz)
Notch at 11.23MHz
Q of 2.4, transimpedance 6.2 Ohm
Notch at 110.80MHz
Q of 53.8, transimpedance 13.03 Ohm
(continuation of this)
Here are the transfer function and noise plots of the seismometer box, using the op amps that are actually indicated on the original plan (THS4131, AD826). I added them to the LISO op amp library (can be found in /cvs/cds/caltech/apps/linux64/liso/filter/opamp.lib)
Next step is to compare the noise graph below to the seismic noise curve of the interferometer to verify that the seismometer box configuration won't affect the curve...
I've finished tuning POY11 and it is now sitting on top of the analyzer waiting for Koji to test its noise.
The full characterization of POY11 is found in the PDF.
Resonance at 11.03MHz
Q of 7.6, transimpedance 1.98kOhm
shotnoise intercept current = 0.17mA (i.e. current noise of 7pA/rtHz)
Notch at 21.99MHz
Q of 56.2, transimpedance 35.51 Ohm
Notch at 55.20MHz
Q of 48.5, transimpedance 37.5 Ohm
The noise graphs relating total noise of the Seismometer circuit (GURALP stuff) to the LIGO seismic noise curve have been completed started.
I apparently harbor hate towards Matlab (you may have notice I do everything in Mathematica)....I will try to change my ways DX
What Larisa meant to post (I'm sure) is something more like this (sorry it's a little squished...I put too many words in the legend):
I've only included the 2 noise contributions from the LISO model that seem to dominate the sum noise. The plot gets a little crazy if you include all of the non-important sources.
So, what's the point??
First, the new box design doesn't have any crazy-special op-amps in it, so the noise of the new box is probably comparable to the old box. So, if that's true, the old box may not have been limiting the differential seismic noise. This definitely needs to be checked out. I'll make a quickie LISO model of the old Guralp breakout box, to see what its noise actually looks like, according to LISO. If it wasn't ever the breakout box that was limiting us, what the heck was it??
Second, the current box design seems to be better than the Guralp Spec sheet noise by ~a factor of 10. It would be nice if that number were more like a factor of 100. Or at least 30. So some work needs to be done to find a lower-noise op amp for the voltage buffer (the first op amp in the circuit).
Since Larisa is now starting her SURF project with Tara and Mingyuan, I'll look into improving the design of this box by a factor of 3 or 10.
Then I'll need to make a mock-up of it, and test it out.
If successful, then I'll draw it up in Altium and have it made. Recall that there should be 2 outputs per seismometer channel, one with high gain, one with low gain. Then 3 seismometer channels per seismometer (X, Y, Z), and perhaps multiple seismometer inputs per box. So lots and lots of stuff all in the same box. It's going to be pretty cool.
Koji and I found 2 RFPD boxes to send to LLO. We've put them onto Steve's desk to be overnighted to Valera.
One of them is our old 21.5 MHz gold box RFPD from the FSS (which we don't use). The other one is a 2mm gold box one which was previously tuned for 66 MHz.
They shipped out on Friday
Our design kits are full again. They are waiting for a new brilliant PD design.
We fixed the anti-aliasing board in its aluminum black box, the box couldn't be covered entirely because of the outgoing wires of the BNC connectors, so we drilled additional holes on the top cover to slide it backwards by 1cm and then screw it.
We had to fix the AA board box in rack 1X7, but there wasn't enough space, so we tried to move the blue chassis (ligo electro-optical fanout chassis 1X7) up with the help of a jack. We removed the blue chassis' screws but we couldn't move it up because of a piece of metal screwed above the blue chassis, then we weren't able to screw the two bottom screws again anymore because it had slided a bit down. Thus, the blue chassis (LIGO ELECTRO-OPTICAL FANOUT CHASSIS 1X7) is still not fixed properly and is sitting on the jack.
To accommodate the AA board (along with the panel-mounted BNC connectors) in rack 1X7 we removed the sliding tray (which was above the CPU) and fixed it there. Now the sliding tray is under the drill press.
We laid the cable along the cable keeper from the BACARDI seismometer to the rack 1X6, the excess cable has been coiled under the X arm.
We plugged the cable to the seismometer and to the seismometer electronics box in rack 1X6. We also plugged the AC power cable from the box to an outlet in rack 1X7 (because the 1X6 outlets are full)
With the help of a function generator we tested the following labeled channels of AA board...
2, 3, 11, 12, 14, 15, 16, 18, 19, 20 and 24
that are the channels that can be viewed by the dataviewer, also the channel 10 can be viewed but it's labeld BAD so we cannot use it.
We leveled the seismometer and unlocked it, and saw his X,Y,Z velocity signals with an oscilloscope.
Koji and Haixing,
We did a tolerance analysis to specify the conner frequency for passive low-pass filtering in the AA filter of Cymac. The
link to the wiki page for the AA filter goes as follows (one can have a look at the simple schematics):
Basically, we want to add the following passive low-pass filter (boxed) before connecting to the instrumentation amplifier:
Suppose (i) we have 10% error in the capacitor value and (ii) we want to have common-mode rejection
error to be smaller than 0.1% at low frequencies (up to the sampling frequency 64kHz), what would be
conner frequency, or equivalently the values for the capacitor and resistor, for the low-pass filter?
Given the transfer function for this low-pass filter:
and the error propagation equation for its magnitude:
we found that the conner frequency needs to be around 640kHz in order to have
This is sort of OK, except the capacitor connects across the (+) terminals of the two input opamps, and does not connect to ground.
Also, we don't care about the CMRR at 64 kHz. We care about it at up to 10 kHz, but not above. The sample frequency of the ADC is 64 kHz, but all of the models run at 16 kHz or less, so the Nyquist frequency is 8 kHz.
And doesn't the value depend on the resistors?
>> This sort of OK, except the capacitor connects across the (+) terminals of the two input opamps, and does not connect to ground:
>> Also, we don't care about the CMRR at 64 kHz. We care about it at up to 10 kHz, but not above.
In this case, the conner frequency for the low-pass filter would be around 100kHz in order to satisfy the requirement.
>>And doesn't the value depend on the resistors?
Yes, it does. The error in the resistor (typically 0.1%) is much smaller than that of the capacitor (10%). Since the resistor error propagates in the same as the capacitor,
we can ignore it.
Note that we only specify the conner frequency (=1/RC) instead of R and C specifically from the tolerance analysis, we still need to choose appropriate
values for R and C with the conner frequency fixed to be around 100kHz, for which we need to consider the output impedance of port 1 and port 2.
I found the manual for the Low Noise Preamplifier Model 1201 at this link and I attached it.
The one we have in the lab (S/N 48332) miss the battery packs and miss also the remote programming options input/output. Its inside battery compartment is empty and I found 2 unscrewed screws with washers and nuts inside the preamplifier box. The battery cable are disconnected and they have 2 green tape labels (-) and 2 red tape label (+).