On Wednesday, February 12, 2014 12:04:24 AM UTC-5, 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>=20 > http://www.osa-opn.org/abstract.cfm?URI=3Dopn-12-4-44 >=20 > 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. > In my breadboard test with a ordinary op-amp tl082cp, the noise level is =very high.=20 Making you own transimpedance amp is a lot of fun... if you like that sort = of thing. But if you've got more money than time, and the srs preamp works= then go that way. =20 If you do want to make your own, then you need to know things like the capa= citance of you piezo detector, the bandwidth of the signal, and how much cu= rrent you are detecting. The TL082 looks to have about 15nV/rtHz of voltag= e noise... (strangely enoguh it's often the voltage noise of the opamp that= causes the most noise in a TIA.) I like the OPA134 for (audio freq.) TIA'= s. =20 If you wanted you could post a schematic of your TIA and we could comment. = =20 (you may just need a bit of capacitance across the feedback R to roll off t= he HF gain.) =20 George H.=20>=20 >=20 > On Tuesday, February 11, 2014 8:22:49 PM UTC-7, Bill Sloman wrote: >=20 > > On Wednesday, 12 February 2014 10:04:30 UTC+11, xun...@ualberta.ca wro=te: <snipping comments from Bill S. you can read them up post.>
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 Wed, 12 Feb 2014 06:55:07 -0800 (PST), George Herold <gherold@teachspin.com> wrote:>On Wednesday, February 12, 2014 12:04:24 AM UTC-5, 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. >> In my breadboard test with a ordinary op-amp tl082cp, the noise level is very high. > >Making you own transimpedance amp is a lot of fun... if you like that sort of thing. But if you've got more money than time, and the srs preamp works then go that way. >If you do want to make your own, then you need to know things like the capacitance of you piezo detector, the bandwidth of the signal, and how much current you are detecting. The TL082 looks to have about 15nV/rtHz of voltage noise... (strangely enoguh it's often the voltage noise of the opamp that causes the most noise in a TIA.) I like the OPA134 for (audio freq.) TIA's. > >If you wanted you could post a schematic of your TIA and we could comment. >(you may just need a bit of capacitance across the feedback R to roll off the HF gain.) > >George H. >> >> >> On Tuesday, February 11, 2014 8:22:49 PM UTC-7, Bill Sloman wrote: >> >> > On Wednesday, 12 February 2014 10:04:30 UTC+11, xun...@ualberta.ca wrote: ><snipping comments from Bill S. you can read them up post.>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? (Keeping in mind that it's to the west and the sun tends to be quite _blazing_ around here :) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●February 12, 20142014-02-12
On Wednesday, February 12, 2014 8:14:07 AM UTC-5, Spehro Pefhany wrote:> On Wed, 12 Feb 2014 18:18:03 +1100, the renowned "Phil Allison" > > <phil_a@tpg.com.au> wrote> > > > > >Doubt he needs to go for fancy lab pre-amp units. > > > > > >... Phil > > > > The fancy lab pre-amp units are not much more than a JFET front end on > a low-noise op-amp.Pretty much... I couldn't find a spec for the voltage noise of the SRS thing. The other issue (of course) is connecting the detector to the preamp.... there's always increased capacitance in the cable and that may (or may not) be an issue. George H.> > > > > Best regards, > > Spehro Pefhany > > -- > > "it's the network..." "The Journey is the reward" > > speff@interlog.com Info for manufacturers: http://www.trexon.com > > Embedded software/hardware/analog Info for designers: http://www.speff.com
Reply by ●February 12, 20142014-02-12
On Wednesday, February 12, 2014 10:00:49 AM UTC-5, Jim Thompson wrote:> On Wed, 12 Feb 2014 06:55:07 -0800 (PST), George Herold >=20 > <gherold@teachspin.com> wrote: >=20 >=20 >=20 > >On Wednesday, February 12, 2014 12:04:24 AM UTC-5, Xunchen Liu wrote: >=20 > >> Thanks. >=20 > >> I think the circuit should be something similar to the front end circu=it design such as the one by Philip Hobbs>=20 > >>=20 >=20 > >> http://www.osa-opn.org/abstract.cfm?URI=3Dopn-12-4-44 >=20 > >>=20 >=20 > >> but I am just intimidated to build the circuit myself. >=20 > >> If the commercial one such as SRS 570 will do the job, I tent to buy i=t.>=20 > >> In my breadboard test with a ordinary op-amp tl082cp, the noise level =is very high.=20>=20 > > >=20 > >Making you own transimpedance amp is a lot of fun... if you like that so=rt of thing. But if you've got more money than time, and the srs preamp wo= rks then go that way. =20>=20 > >If you do want to make your own, then you need to know things like the c=apacitance of you piezo detector, the bandwidth of the signal, and how much= current you are detecting. The TL082 looks to have about 15nV/rtHz of vol= tage noise... (strangely enoguh it's often the voltage noise of the opamp t= hat causes the most noise in a TIA.) I like the OPA134 for (audio freq.) T= IA's. =20>=20 > > >=20 > >If you wanted you could post a schematic of your TIA and we could commen=t. =20>=20 > >(you may just need a bit of capacitance across the feedback R to roll of=f the HF gain.) =20>=20 > > >=20 > >George H.=20 >=20 > >>=20 >=20 > >>=20 >=20 > >> On Tuesday, February 11, 2014 8:22:49 PM UTC-7, Bill Sloman wrote: >=20 > >>=20 >=20 > >> > On Wednesday, 12 February 2014 10:04:30 UTC+11, xun...@ualberta.ca =wrote:>=20 > ><snipping comments from Bill S. you can read them up post. >=20 > 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? =20Hmm well you could maybe put an interference filter in front of a photodiod= e to just see the sodium lines... (well and the sunlight that falls in the = same bandwidth.) Interference filters are spendy though... ~$50-100 Hey maybe the street lights are modulated at 120 Hz? (or some other freque= ncy?) You'd still want to somehow try and filter out as much sunlight as p= ossible. =20 George H.>=20 > (Keeping in mind that it's to the west and the sun tends to be quite > _blazing_ around here :) > ...Jim Thompson >=20 > --=20 >=20 > | James E.Thompson | mens | >=20 > | Analog Innovations | et | >=20 > | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | >=20 > | San Tan Valley, AZ 85142 Skype: Contacts Only | | >=20 > | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | >=20 > | E-mail Icon at http://www.analog-innovations.com | 1962 | >=20 > =20 >=20 > I love to cook with wine. Sometimes I even put it in the food.
Reply by ●February 12, 20142014-02-12
On Wed, 12 Feb 2014 07:01:10 -0800 (PST), George Herold <gherold@teachspin.com> wrote:> >> The fancy lab pre-amp units are not much more than a JFET front end on >> a low-noise op-amp. > >Pretty much... I couldn't find a spec for the voltage noise of the SRS thing. > >The other issue (of course) is connecting the detector to the preamp.... there's always increased capacitance in the cable and that may (or may not) be an issue. > >George H. >>I was referring to the voltage preamp (560), should have made that clear.
Reply by ●February 12, 20142014-02-12
On Tue, 11 Feb 2014 21:04:24 -0800 (PST), xunchen@ualberta.ca 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. >In my breadboard test with a ordinary op-amp tl082cp, the noise level is very high. >If you connect a substantially capacitive transducer to the input of a TIA, you'll get a huge noise peak, and maybe oscillation. What kind of transducer is it? What's the capacitance? How much bandwidth do you need? -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation
Reply by ●February 12, 20142014-02-12
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.pdf
Reply by ●February 12, 20142014-02-12
Hi sorry for cross posting from sci.optics. I just summarize what I want to do: 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 piezoelectric signal. So I need a transimpedance amplifier to convert its current to voltage when it is mechanically driven by the sound. I read article by Phil Hobbs' get-all-done about the front end design. http://www.electrooptical.net/www/frontends/frontends.pdf Just wondering in my case if the commercial SRS570 current amplifier is good enough? From literature, the noise level I need is under 0.1 uV/Hz^-2 after the TIA. The SRS570 spec says at 32 KHz noise is around 10E-12 A/Hz^-2 with 10E-6 A/V. 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? http://www.analog.com/library/analogdialogue/archives/47-05/pgtia.html and last question, would a 6 pF, 35 kOHm tuning fork has smaller noise?
Reply by ●February 12, 20142014-02-12
On 02/12/2014 01:15 PM, 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. > > 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.pdf >Putting a higher frequency crystal on a TIA by itself is a pretty good way to make an oscillator. Your a tuning fork has a pretty large equivalent resistance, so it might work fine. You should be able to see the Johnson noise of the crystal resistance. The Johnson noise is going to be about sqrt(35k/60.4 ohms) = 24 nV/sqrt(Hz), so you don't need a terribly low noise amplifier if you have a second filter in cascade. 32 kHz is out of the 1/f noise of most op amps, fortunately. You might try something like an OPA140 or even a TL084, with about a 10 M feedback resistor. You'll want to roll the feedback off at about 60 kHz or so, which requires about 0.4 pF across the 10M resistor. With a through-hole resistor, that's probably pretty close to the board strays, but if you need a bit more, use a piece of solid wire laid next to the resistor, soldered to the output end, and wiggle it around till you get a result you like. Oh, and use split supplies (+-15V) if you can--it'll make your life easier. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●February 12, 20142014-02-12
On 2/12/2014 9:08 AM, George Herold wrote:> On Wednesday, February 12, 2014 10:00:49 AM UTC-5, Jim Thompson wrote: >> On Wed, 12 Feb 2014 06:55:07 -0800 (PST), George Herold >> >> <gherold@teachspin.com> wrote: >> >> >> >>> On Wednesday, February 12, 2014 12:04:24 AM UTC-5, 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. >> >>>> In my breadboard test with a ordinary op-amp tl082cp, the noise level is very high. >> >>> >> >>> Making you own transimpedance amp is a lot of fun... if you like that sort of thing. But if you've got more money than time, and the srs preamp works then go that way. >> >>> If you do want to make your own, then you need to know things like the capacitance of you piezo detector, the bandwidth of the signal, and how much current you are detecting. The TL082 looks to have about 15nV/rtHz of voltage noise... (strangely enoguh it's often the voltage noise of the opamp that causes the most noise in a TIA.) I like the OPA134 for (audio freq.) TIA's. >> >>> >> >>> If you wanted you could post a schematic of your TIA and we could comment. >> >>> (you may just need a bit of capacitance across the feedback R to roll off the HF gain.) >> >>> >> >>> George H. >> >>>> >> >>>> >> >>>> On Tuesday, February 11, 2014 8:22:49 PM UTC-7, Bill Sloman wrote: >> >>>> >> >>>>> On Wednesday, 12 February 2014 10:04:30 UTC+11, xun...@ualberta.ca wrote: >> >>> <snipping comments from Bill S. you can read them up post. >> >> 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? > Hmm well you could maybe put an interference filter in front of a photodiode to just see the sodium lines... (well and the sunlight that falls in the same bandwidth.) Interference filters are spendy though... ~$50-100 > Hey maybe the street lights are modulated at 120 Hz? (or some other frequency?) You'd still want to somehow try and filter out as much sunlight as possible. > > George H. >> >> (Keeping in mind that it's to the west and the sun tends to be quite >> _blazing_ around here :) >> ...Jim Thompson >> >> -- >> >> | James E.Thompson | mens | >> >> | Analog Innovations | et | >> >> | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | >> >> | San Tan Valley, AZ 85142 Skype: Contacts Only | | >> >> | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | >> >> | E-mail Icon at http://www.analog-innovations.com | 1962 | >> >> >> >> I love to cook with wine. Sometimes I even put it in the food. >ISTM that a 60Hz synchronous detector might do.
