On Wednesday, February 12, 2014 1:34:57 PM UTC-5, Xunchen Liu wrote:> Hi sorry for cross posting from sci.optics. I just summarize what I want =to do:>=20 >=20 >=20 > I am trying to use a quartz crystal tuning fork at 32768 Hz, 12.5 pF, 35 =kOhm as a sensitive sound detector at its resonance frequency from its piez= oelectric signal.=20>=20 >=20 >=20 > So I need a transimpedance amplifier to convert its current to voltage wh=en it is mechanically driven by the sound.=20>=20 >=20 >=20 > I read article by Phil Hobbs' get-all-done about the front end design.=20 >=20 > http://www.electrooptical.net/www/frontends/frontends.pdf=20 >=20 >=20 >=20 > Just wondering in my case if the commercial SRS570 current amplifier is g=ood enough?=20>=20 > From literature, the noise level I need is under 0.1 uV/Hz^-2 after the T=IA.=20>=20 > The SRS570 spec says at 32 KHz noise is around 10E-12 A/Hz^-2 with 10E-6 =A/V. Hmm 0.1 uV/(sqrt Hz)? I'm not quite sure what the TIA gain is, but if it's= anything over 1 meg ohm then that blows your noise budget right there. =20 (Unless you're a TIA guru like Phil H who makes TIA's w/o room temperature = resistors as feedback.) =20 Hey speaking of no R's in the feedback path. I've been reading Mark Johnso= n's "Photodetection and Measurement" book. And he shows a circuit I've nev= er seen before. It uses optical feedback. The output of the TIA opamp dri= ves a resistor/ LED, the light of which goes to a second photodiode that is= in series with the "signal" photodiode.=20 George H. =20>=20 >=20 >=20 > If the SRS570 cannot do the job and I have to build the circuit, what TIA=I should choose? Like the programmable-gain TIA from Analog-Device?=20>=20 > http://www.analog.com/library/analogdialogue/archives/47-05/pgtia.html=20 >=20 >=20 >=20 > and last question, would a 6 pF, 35 kOHm tuning fork has smaller noise?
current amplifier or current to voltage op-amp
Started by ●February 11, 2014
Reply by ●February 12, 20142014-02-12
Reply by ●February 12, 20142014-02-12
On Thursday, 13 February 2014 05:15:36 UTC+11, Xunchen Liu wrote:> Thanks all for insightful discussion, with my insufficient information. > > The tuning fork I am using is standard 12.5 pF and 35 kOhm 32768 Hz quartz crystal tuning fork. The bandwidth I need is at its fundamental frequency 32 kHz.The electrical equivalent circuit of the watch crystal is going to include a significant inductance http://www.cypress.com/?docID=38894 For actual values, here's an example Spice subcircuit model I googled. .SUBCKT XT32768K 1 2 CP 1 2 1.5000P RS 1 3 30.000K L 3 4 10.200K C 4 2 2.3129F .ENDS Plug that into a Spice circuit for a transimpedance amplifier and see what happens. I've not done it, but I suspect that the results won't be all that pleasing. <snip> -- Bill Sloman
Reply by ●February 12, 20142014-02-12
On Tuesday, February 11, 2014 9:04:24 PM UTC-8, Xunchen Liu wrote:> Thanks. > > I think the circuit should be something similar to the front end circuit design such as the one by Philip Hobbs > > http://www.osa-opn.org/abstract.cfm?URI=opn-12-4-44 > > > > but I am just intimidated to build the circuit myself. > > If the commercial one such as SRS 570 will do the job, I tent to buy it.That's a bad plan, generally. You would have to put the piezo and its fixture into some kind of model, including the cable that connects to that big box of a 'preamp'. Putting an op amp and a feedback resistor into the fixture, is no big deal. It doesn't save any of the really intimidating parts of measuring your device, just a few probably-don't-care items. Do you need an RS-232 interface, and is it a benefit to have adjustable bias voltage, and just how low does the noise HAVE to be, anyhow?
Reply by ●February 12, 20142014-02-12
On Wednesday, February 12, 2014 7:00:49 AM UTC-8, Jim Thompson wrote:> Off on a tangent, if I wanted a detector to tell me that the sodium > > something-or-other street lamp across the street is on, what would be > > the best detector to use?If you can clamp things, an old camera with telephoto lens (hey, the 35mm optics are kinda... cheap... at thrift stores!) onto a screen, with a silicon photocell behind that. Either use a venetian-blinds arrangement in front of the lens, or focus carefully and mask the light by scribbling with magic marker on the screen... Or, lens and pinhole. mounted in a cardboard tube with the inside painted black. Either way, you're sculpting the active solid angle acceptance of the detector. For extra points, find the lamp's ballast power frequency (probably 120 Hz or 5 kHz) with an NE567 tone decoder.
Reply by ●February 12, 20142014-02-12
On Wed, 12 Feb 2014 10:15:36 -0800 (PST), Xunchen Liu <xunchen@ualberta.ca> wrote:>Thanks all for insightful discussion, with my insufficient information. > >The tuning fork I am using is standard 12.5 pF and 35 kOhm 32768 Hz quartz crystal tuning fork. The bandwidth I need is at its fundamental frequency 32 kHz. > >I find these prgrammable-gain TIA: >http://www.analog.com/library/analogdialogue/archives/47-05/pgtia.html > >The SRS current amplifier 570 spec says the noise at 32 KHz is around 10E-12 A/Hz^-2 with 10E-6 A/V. >This is good enough, I can use another SRS560 to amplify the voltage. >http://www.thinksrs.com/products/SR570.htm > >Now I really worried is as Spehro Pefhany says, the SRS570 cannot do the job. >The noise level after the TIA should be lower than 0.1 uV/Hz^-2. > >Also, I noticed that the link to Phil Hobbs's circuit is down. It's chapter 18 of his get-all-done book. >http://www.electrooptical.net/www/frontends/frontends.pdfWhy not just amplify the voltage across the tuning fork, with a good opamp or a jfet? Since a crystal looks inductive one side of resonance, you might even resonate it with a capacitor and get more voltage into a hi-z amp. You'd need to gat an approximate motional-equivalent Spice model for the crystal, and play with that in simulation maybe. I wanted to use a vacuum-sealed 32K tuning-fork crystal as a cryogenic temperature sensor, for the CEBAF/Jefferson Labs accelerator, but we couldn't get them interested. -- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●February 12, 20142014-02-12
On Thursday, 13 February 2014 11:33:05 UTC+11, John Larkin wrote:> On Wed, 12 Feb 2014 10:15:36 -0800 (PST), Xunchen Liu > <xunchen@ualberta.ca> wrote: > > >Thanks all for insightful discussion, with my insufficient information. > > > >The tuning fork I am using is standard 12.5 pF and 35 kOhm 32768 Hz quartz crystal tuning fork. The bandwidth I need is at its fundamental frequency 32 kHz. > > > >I find these programmable-gain TIA: > > >http://www.analog.com/library/analogdialogue/archives/47-05/pgtia.html > > > > >The SRS current amplifier 570 spec says the noise at 32 KHz is around 10E-12 A/Hz^-2 with 10E-6 A/V. > > >This is good enough, I can use another SRS560 to amplify the voltage. > > >http://www.thinksrs.com/products/SR570.htm > > > > >Now I really worried is as Spehro Pefhany says, the SRS570 cannot do the job. > >The noise level after the TIA should be lower than 0.1 uV/Hz^-2. > > > >Also, I noticed that the link to Phil Hobbs's circuit is down. It's chapter 18 of his get-all-done book. > > >http://www.electrooptical.net/www/frontends/frontends.pdf > > Why not just amplify the voltage across the tuning fork, with a good > opamp or a jfet?Sounds like the safe way to go.> Since a crystal looks inductive one side of resonance, you might even > resonate it with a capacitor and get more voltage into a hi-z amp. > You'd need to get an approximate motional-equivalent Spice model for > the crystal, and play with that in simulation maybe.Have you looked at the electrical model I dug out, and the L and C values in the Spice sub-circuit that I found? If might be difficult to find real components big enough to be useful, and even more difficult to get them to couple to any useful part of the tuning fork. Electronic reactive components - made with gyrators or whatever - might do better, but you may be stretching the OP's competence.> I wanted to use a vacuum-sealed 32K tuning-fork crystal as a cryogenic > temperature sensor, for the CEBAF/Jefferson Labs accelerator, but we > couldn't get them interested.If you didn't know what the electrical Spice model of the part looked like, that might explain their indifference. How well did the vacuum seal cope with cryogenic temperatures? The trouble with physicists is that while they can be shaky on electronic details, they tend to have a reasonable gasp of physical reality. -- Bill Sloman, Sydney
Reply by ●February 12, 20142014-02-12
"Bill Sloman"> > The trouble with physicists is that while they can be > shaky on electronic details, they tend to have a reasonable > gasp of physical reality. >** Thinking a tiny clock crystal makes a good ultrasonic microphone is not very realistic. Quote from the OP: " I am using the quartz tuning fork as a very sensitive force detector to pick up sound wave at its resonance frequency. " ... Phil
Reply by ●February 13, 20142014-02-13
On a sunny day (Thu, 13 Feb 2014 14:24:38 +1100) it happened "Phil Allison" <phil_a@tpg.com.au> wrote in <bm2s7fF81dkU1@mid.individual.net>:> >"Bill Sloman" >> >> The trouble with physicists is that while they can be >> shaky on electronic details, they tend to have a reasonable >> gasp of physical reality. >> > > >** Thinking a tiny clock crystal makes a good ultrasonic microphone is not >very realistic. > >Quote from the OP: > >" I am using the quartz tuning fork as a very sensitive force detector to >pick up sound wave at its resonance frequency. "Long time agao I did read about acoustic coupling between xrystals. Selectivity should be great.
Reply by ●February 13, 20142014-02-13
On Tue, 11 Feb 2014 15:04:30 -0800 (PST), xunchen@ualberta.ca wrote:>I want to measure very weak piezoelectric signal from a quartz crystal detector that mechanically vibrate.Is this crystal operated close to a resonant frequency ? If so, you would need quite different circuits, if you are interested at frequencies near the series or parallel resonance frequency.
Reply by ●February 13, 20142014-02-13
On 2014-02-13 07:29, Jan Panteltje wrote:> On a sunny day (Thu, 13 Feb 2014 14:24:38 +1100) it happened "Phil Allison" > <phil_a@tpg.com.au> wrote in <bm2s7fF81dkU1@mid.individual.net>: > >> >> "Bill Sloman" >>> >>> The trouble with physicists is that while they can be >>> shaky on electronic details, they tend to have a reasonable >>> gasp of physical reality. >>> >> >> >> ** Thinking a tiny clock crystal makes a good ultrasonic microphone is not >> very realistic. >> >> Quote from the OP: >> >> " I am using the quartz tuning fork as a very sensitive force detector to >> pick up sound wave at its resonance frequency. " > > Long time agao I did read about acoustic coupling between xrystals. > Selectivity should be great. >I'd think these crystals would be designed to minimize acoustic coupling. Jeroen Belleman
