Forums

lock-in amplifier

Started by scot March 5, 2013
On Thu, 07 Mar 2013 15:51:49 +0000, John Devereux
<john@devereux.me.uk> wrote:

>Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> writes: > >> On Thu, 07 Mar 2013 15:26:59 +0000, John Devereux >> <john@devereux.me.uk> wrote: >> >>>Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> writes: >>> >>>> On 03/07/2013 01:40 AM, John Devereux wrote: >>>>> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> writes: >>> >>>[...] >>> >>>>>> The AD630 is an ancient chip that was never that great to begin >>>>>> with. Nowadays you can do a great deal better with a low charge >>>>>> injection mux, e.g. the ADG1236 dual SPDT. With a bit more work, you >>>>>> can do better still with a couple of dual-gate MOSFETs, which have >>>>>> almost no charge injection at all. >>>>> >>>>> Could you expand on that, or suggest a favorite part? >>>> >>>> Last time I used it, it was a metal-can 3N201. ;) You drive the >>>> source, and come out the drain. Connect G2 to the source, and put the >>>> gate signal on G1. You can do somewhat different things with G2 >>>> depending on the application, but the low charge injection seems to >>>> come from the top half of the cascode cutting off before the bottom >>>> half, so that the gate charge comes back out the source instead of the >>>> drain. >>>> >>>> Unfortunately I no longer have the lab notebook that had the pictures in it. >>> >>>OK, thanks. >>> >>>Looks like something I will have to breadboard some time. >>> >>>I seem to recall someone (John L?) talking about using opto-fets as zero >>>charge injection switches. But I wonder are they really? They have fets >>>inside, with gates that charge and discharge presumably. Hmm, not sure I >>>understand how they work, now I come to think of it. Photovoltaic mode >>>photodiode(s) connected to the gate I guess. >> >> Well? You know how reliable Larkin's advice is >:-} > >Not even sure it was him. > >But do *you* know how they work? Is there charge injection?
It definitely takes a change of charge on the surface of the channel to turn the FET on or off. But I'm unsure of the construction of "opto-fets". Anyone have a part number and I'll look them up. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 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.
Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> writes:

> On Thu, 07 Mar 2013 15:51:49 +0000, John Devereux > <john@devereux.me.uk> wrote: > >>Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> writes: >> >>> On Thu, 07 Mar 2013 15:26:59 +0000, John Devereux >>> <john@devereux.me.uk> wrote: >>> >>>>Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> writes: >>>> >>>>> On 03/07/2013 01:40 AM, John Devereux wrote: >>>>>> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> writes: >>>> >>>>[...] >>>> >>>>>>> The AD630 is an ancient chip that was never that great to begin >>>>>>> with. Nowadays you can do a great deal better with a low charge >>>>>>> injection mux, e.g. the ADG1236 dual SPDT. With a bit more work, you >>>>>>> can do better still with a couple of dual-gate MOSFETs, which have >>>>>>> almost no charge injection at all. >>>>>> >>>>>> Could you expand on that, or suggest a favorite part? >>>>> >>>>> Last time I used it, it was a metal-can 3N201. ;) You drive the >>>>> source, and come out the drain. Connect G2 to the source, and put the >>>>> gate signal on G1. You can do somewhat different things with G2 >>>>> depending on the application, but the low charge injection seems to >>>>> come from the top half of the cascode cutting off before the bottom >>>>> half, so that the gate charge comes back out the source instead of the >>>>> drain. >>>>> >>>>> Unfortunately I no longer have the lab notebook that had the pictures in it. >>>> >>>>OK, thanks. >>>> >>>>Looks like something I will have to breadboard some time. >>>> >>>>I seem to recall someone (John L?) talking about using opto-fets as zero >>>>charge injection switches. But I wonder are they really? They have fets >>>>inside, with gates that charge and discharge presumably. Hmm, not sure I >>>>understand how they work, now I come to think of it. Photovoltaic mode >>>>photodiode(s) connected to the gate I guess. >>> >>> Well? You know how reliable Larkin's advice is >:-} >> >>Not even sure it was him. >> >>But do *you* know how they work? Is there charge injection? > > It definitely takes a change of charge on the surface of the channel > to turn the FET on or off.
Yes, I imagine an isolated little battery connected between source and gate, magically charging itself up. But does that inject charge out the drain, say? Must do I think.
> But I'm unsure of the construction of > "opto-fets". Anyone have a part number and I'll look them up.
The datasheets I have seen don't show anything much. I use a lot of LCA710 (for power switching, so probably not the best choice for this). Actually I think it might have been a Jim Williams app note, not JL. Sorry to be so vague; really can't remember. -- John Devereux
On Wed, 06 Mar 2013 23:27:31 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 3/6/2013 10:31 PM, George Herold wrote: >> On Mar 6, 9:37 pm, Phil Hobbs <pcdhSpamMeSensel...@electrooptical.net> >> wrote: >>> On 3/6/2013 9:30 PM, George Herold wrote: >>> >>> >>> >>> >>> >>>> On Mar 6, 7:18 pm, Phil Hobbs <pcdhSpamMeSensel...@electrooptical.net> >>>> wrote: >>>>> On 3/6/2013 7:00 PM, scot wrote: >>> >>>>>> On Tuesday, March 5, 2013 8:07:59 PM UTC-5, scot wrote: >>>>>>> Anyone have experience with lock-in amplifiers? I am thinking of purchasing a used one but don't know enough about them. I know they are extremely effective at finding small signals buried in lots of noise but what are the downsides to a lock-in besides expense? >>> >>>>>>> Also, this is probably over my head but I have read about the AD630 chip from Analog Devices and supposedly that can be used to make a very low cost lock-in amplifier. Anyone ever try that? Was it worth it for the money? I should mention a friend of mine has a couple of these AD630 IC's so I would be willing to solder something up pretty quick if it's not a waste of time. >>> >>>>>>> Scot >>> >>>>>> Thanks Phil for the suggestion on the ADG1236. I read up on Lock-in's last night and learned a lot. I found this interesting article and it looks like the principles are pretty understandable. >>> >>>>>> http://physlab.lums.edu.pk/images/9/90/LIA.pdf >>> >>>>>> The article specifies a DG303A chip but I think the ADG1236 can be substituted instead. My main goal here is to learn about Lock-in's by building one myself since reading only takes you so far. What do you think? Is this a good starting point? >>> >>>>>> Scot >>> >>>>> Lock-ins are very useful for (slow) measurements in low-SNR >>>>> situations--they can pull signal out of some pretty grimy-looking >>>>> interference. >>> >>>>> Building your own analogue lock-in is an excellent project. I built my >>>>> first one when I was a postdoc (about 1988) for an atomic force >>>>> microscope. More recently, I've built a few just like that for >>>>> customers, as part of the back ends of their measurement systems. They >>>>> really are Good Medicine. (I found the ADG1236 just the other day, when >>>>> I needed parts to make a baby-scale loop.) >>> >>>>> There are two main dangers with lock-ins. The first and more insidious >>>>> one is that they can tempt you to skimp on the front end of the >>>>> measurement, and so lose SNR for no particularly good reason. The other >>>>> is that in the presence of drift or 1/f noise, narrowing the bandwidth >>>>> doesn't help, and may make things worse. >>> >>>>> Cheers >>> >>>>> Phil Hobbs >>> >>>> Re: front ends >>>> With a nice front end I find a DSO with an average function, and sync >>>> trigger is 'good enough' lots of times. (a poor man's lockin.) >>> >>>> George H. >>> >>> That's more of a poor man's signal averager, which is a much better >>> approach in the presence of 1/f noise. >>> >>> Cheers >>> >>> Phil Hobbs >>> > >> >> Well it's not phase sensitive, but it does select frequency, so 128 >> averages is like a band pass with a Q of 128(?) > >Something like that. It is phase-sensitive actually, because you're >triggering on some sync signal, which makes I and Q easy to tell apart. > >The main thing is that if you're sweeping at 1 kHz, with 1000 data >points, anything below 1 kHz can cause only a baseline shift, whereas >the actual data is taken from a forest of comb filters, each centered on >a harmonic of the sweep frequency. Almost all of that sensitive >bandwidth is well outside the 1/f noise of anything except a pHEMT. >> >> Ya know I've never seen a good article on the many ways to use the >> average button on a DSO. >> >> George H. >> > >You just need to get Teachspin to rebadge a Rigol or Owon scope, and >write an app note about it. ;) > >Cheers > >Phil Hobbs > >(Just bought an Owon SDS7102, which should be here tomorrow. It's >mostly for my son to use in his continuing firmware endeavours.)
Make him pull out some scope test points that show checkpoints in the software. It's amazing how many programmers have no clue, not by 10:1, about how long it takes min-max for their subroutines to execute. Or how badly IRQs are chopping up their mainline code. I used to use one cross assembler that added execution times to every line in the listing. On the 68332, I could figure about 1 us execution time per line of assembly code. I often comment execution times into my source code, for reuse guidance. When designing products at the architectural level, one has to guess whether the selected CPU has the horsepower to do what needs to be done. Some accumulated experience with actual code execution times becomes valuable. The recent DDS-on-an-ARM thread is an example: Joerg's entire control algorithm and DDS sine output would easily run at 100 KHz on an LPC17xx, with the CPU clock cranked down to save some power. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
On Thu, 07 Mar 2013 16:24:44 +0000, John Devereux <john@devereux.me.uk> wrote:

>Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> writes: > >> On Thu, 07 Mar 2013 15:51:49 +0000, John Devereux >> <john@devereux.me.uk> wrote: >> >>>Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> writes: >>> >>>> On Thu, 07 Mar 2013 15:26:59 +0000, John Devereux >>>> <john@devereux.me.uk> wrote: >>>> >>>>>Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> writes: >>>>> >>>>>> On 03/07/2013 01:40 AM, John Devereux wrote: >>>>>>> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> writes: >>>>> >>>>>[...] >>>>> >>>>>>>> The AD630 is an ancient chip that was never that great to begin >>>>>>>> with. Nowadays you can do a great deal better with a low charge >>>>>>>> injection mux, e.g. the ADG1236 dual SPDT. With a bit more work, you >>>>>>>> can do better still with a couple of dual-gate MOSFETs, which have >>>>>>>> almost no charge injection at all. >>>>>>> >>>>>>> Could you expand on that, or suggest a favorite part? >>>>>> >>>>>> Last time I used it, it was a metal-can 3N201. ;) You drive the >>>>>> source, and come out the drain. Connect G2 to the source, and put the >>>>>> gate signal on G1. You can do somewhat different things with G2 >>>>>> depending on the application, but the low charge injection seems to >>>>>> come from the top half of the cascode cutting off before the bottom >>>>>> half, so that the gate charge comes back out the source instead of the >>>>>> drain. >>>>>> >>>>>> Unfortunately I no longer have the lab notebook that had the pictures in it. >>>>> >>>>>OK, thanks. >>>>> >>>>>Looks like something I will have to breadboard some time. >>>>> >>>>>I seem to recall someone (John L?) talking about using opto-fets as zero >>>>>charge injection switches. But I wonder are they really? They have fets >>>>>inside, with gates that charge and discharge presumably. Hmm, not sure I >>>>>understand how they work, now I come to think of it. Photovoltaic mode >>>>>photodiode(s) connected to the gate I guess. >>>> >>>> Well? You know how reliable Larkin's advice is >:-} >>> >>>Not even sure it was him. >>> >>>But do *you* know how they work? Is there charge injection? >> >> It definitely takes a change of charge on the surface of the channel >> to turn the FET on or off. > >Yes, I imagine an isolated little battery connected between source and >gate, magically charging itself up. But does that inject charge out the >drain, say? Must do I think. > > >> But I'm unsure of the construction of >> "opto-fets". Anyone have a part number and I'll look them up. > >The datasheets I have seen don't show anything much. I use a lot of >LCA710 (for power switching, so probably not the best choice for this). > >Actually I think it might have been a Jim Williams app note, not >JL. Sorry to be so vague; really can't remember.
Photofets are used to discharge particle detector front-end integrators, but a little charge injection does no harm there. Fairchild says "no charge injection" on the H11F1M data sheet, which is a remarkable claim. A photofet is different from an SSR type structure, which has separate photovoltaic diodes and mosfets and tend to be slow. Thompson is being the usual old biddy, flinging ignorant insults about things he knows nothing about. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
On 03/07/2013 11:26 AM, John Larkin wrote:
> On Wed, 06 Mar 2013 23:27:31 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 3/6/2013 10:31 PM, George Herold wrote: >>> On Mar 6, 9:37 pm, Phil Hobbs <pcdhSpamMeSensel...@electrooptical.net> >>> wrote: >>>> On 3/6/2013 9:30 PM, George Herold wrote: >>>> >>>> >>>> >>>> >>>> >>>>> On Mar 6, 7:18 pm, Phil Hobbs <pcdhSpamMeSensel...@electrooptical.net> >>>>> wrote: >>>>>> On 3/6/2013 7:00 PM, scot wrote: >>>> >>>>>>> On Tuesday, March 5, 2013 8:07:59 PM UTC-5, scot wrote: >>>>>>>> Anyone have experience with lock-in amplifiers? I am thinking of purchasing a used one but don't know enough about them. I know they are extremely effective at finding small signals buried in lots of noise but what are the downsides to a lock-in besides expense? >>>> >>>>>>>> Also, this is probably over my head but I have read about the AD630 chip from Analog Devices and supposedly that can be used to make a very low cost lock-in amplifier. Anyone ever try that? Was it worth it for the money? I should mention a friend of mine has a couple of these AD630 IC's so I would be willing to solder something up pretty quick if it's not a waste of time. >>>> >>>>>>>> Scot >>>> >>>>>>> Thanks Phil for the suggestion on the ADG1236. I read up on Lock-in's last night and learned a lot. I found this interesting article and it looks like the principles are pretty understandable. >>>> >>>>>>> http://physlab.lums.edu.pk/images/9/90/LIA.pdf >>>> >>>>>>> The article specifies a DG303A chip but I think the ADG1236 can be substituted instead. My main goal here is to learn about Lock-in's by building one myself since reading only takes you so far. What do you think? Is this a good starting point? >>>> >>>>>>> Scot >>>> >>>>>> Lock-ins are very useful for (slow) measurements in low-SNR >>>>>> situations--they can pull signal out of some pretty grimy-looking >>>>>> interference. >>>> >>>>>> Building your own analogue lock-in is an excellent project. I built my >>>>>> first one when I was a postdoc (about 1988) for an atomic force >>>>>> microscope. More recently, I've built a few just like that for >>>>>> customers, as part of the back ends of their measurement systems. They >>>>>> really are Good Medicine. (I found the ADG1236 just the other day, when >>>>>> I needed parts to make a baby-scale loop.) >>>> >>>>>> There are two main dangers with lock-ins. The first and more insidious >>>>>> one is that they can tempt you to skimp on the front end of the >>>>>> measurement, and so lose SNR for no particularly good reason. The other >>>>>> is that in the presence of drift or 1/f noise, narrowing the bandwidth >>>>>> doesn't help, and may make things worse. >>>> >>>>>> Cheers >>>> >>>>>> Phil Hobbs >>>> >>>>> Re: front ends >>>>> With a nice front end I find a DSO with an average function, and sync >>>>> trigger is 'good enough' lots of times. (a poor man's lockin.) >>>> >>>>> George H. >>>> >>>> That's more of a poor man's signal averager, which is a much better >>>> approach in the presence of 1/f noise. >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>>> >> >>> >>> Well it's not phase sensitive, but it does select frequency, so 128 >>> averages is like a band pass with a Q of 128(?) >> >> Something like that. It is phase-sensitive actually, because you're >> triggering on some sync signal, which makes I and Q easy to tell apart. >> >> The main thing is that if you're sweeping at 1 kHz, with 1000 data >> points, anything below 1 kHz can cause only a baseline shift, whereas >> the actual data is taken from a forest of comb filters, each centered on >> a harmonic of the sweep frequency. Almost all of that sensitive >> bandwidth is well outside the 1/f noise of anything except a pHEMT. >>> >>> Ya know I've never seen a good article on the many ways to use the >>> average button on a DSO. >>> >>> George H. >>> >> >> You just need to get Teachspin to rebadge a Rigol or Owon scope, and >> write an app note about it. ;) >> >> Cheers >> >> Phil Hobbs >> >> (Just bought an Owon SDS7102, which should be here tomorrow. It's >> mostly for my son to use in his continuing firmware endeavours.) > > Make him pull out some scope test points that show checkpoints in the software. > It's amazing how many programmers have no clue, not by 10:1, about how long it > takes min-max for their subroutines to execute. Or how badly IRQs are chopping > up their mainline code. > > I used to use one cross assembler that added execution times to every line in > the listing. On the 68332, I could figure about 1 us execution time per line of > assembly code. I often comment execution times into my source code, for reuse > guidance. > > When designing products at the architectural level, one has to guess whether the > selected CPU has the horsepower to do what needs to be done. Some accumulated > experience with actual code execution times becomes valuable. The recent > DDS-on-an-ARM thread is an example: Joerg's entire control algorithm and DDS > sine output would easily run at 100 KHz on an LPC17xx, with the CPU clock > cranked down to save some power. > >
Good idea. I'll do that. 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
On 3/7/2013 10:26 AM, John Devereux wrote:
> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> writes: > >> On 03/07/2013 01:40 AM, John Devereux wrote: >>> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> writes: > > [...] > >>>> The AD630 is an ancient chip that was never that great to begin >>>> with. Nowadays you can do a great deal better with a low charge >>>> injection mux, e.g. the ADG1236 dual SPDT. With a bit more work, you >>>> can do better still with a couple of dual-gate MOSFETs, which have >>>> almost no charge injection at all. >>> >>> Could you expand on that, or suggest a favorite part? >> >> Last time I used it, it was a metal-can 3N201. ;) You drive the >> source, and come out the drain. Connect G2 to the source, and put the >> gate signal on G1. You can do somewhat different things with G2 >> depending on the application, but the low charge injection seems to >> come from the top half of the cascode cutting off before the bottom >> half, so that the gate charge comes back out the source instead of the >> drain. >> >> Unfortunately I no longer have the lab notebook that had the pictures in it. > > OK, thanks. > > Looks like something I will have to breadboard some time. > > I seem to recall someone (John L?) talking about using opto-fets as zero > charge injection switches. But I wonder are they really? They have fets > inside, with gates that charge and discharge presumably. Hmm, not sure I > understand how they work, now I come to think of it. Photovoltaic mode > photodiode(s) connected to the gate I guess. >
I did a bit of digging. NXP has discontinued all of their enhancement-mode dual gate FETs, including the cute ones like the BF1100, which had an interesting feedback FET mechanism to improve the linearity of AGC. The best-looking one for sampling appears to be the BF998, which has reasonable I_D with V_G2S = 0. 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 USA +1 845 480 2058 hobbs at electrooptical dot net http://electrooptical.net
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> writes:

> On 3/7/2013 10:26 AM, John Devereux wrote: >> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> writes: >> >>> On 03/07/2013 01:40 AM, John Devereux wrote: >>>> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> writes: >> >> [...] >> >>>>> The AD630 is an ancient chip that was never that great to begin >>>>> with. Nowadays you can do a great deal better with a low charge >>>>> injection mux, e.g. the ADG1236 dual SPDT. With a bit more work, you >>>>> can do better still with a couple of dual-gate MOSFETs, which have >>>>> almost no charge injection at all. >>>> >>>> Could you expand on that, or suggest a favorite part? >>> >>> Last time I used it, it was a metal-can 3N201. ;) You drive the >>> source, and come out the drain. Connect G2 to the source, and put the >>> gate signal on G1. You can do somewhat different things with G2 >>> depending on the application, but the low charge injection seems to >>> come from the top half of the cascode cutting off before the bottom >>> half, so that the gate charge comes back out the source instead of the >>> drain. >>> >>> Unfortunately I no longer have the lab notebook that had the pictures in it. >> >> OK, thanks. >> >> Looks like something I will have to breadboard some time. >> >> I seem to recall someone (John L?) talking about using opto-fets as zero >> charge injection switches. But I wonder are they really? They have fets >> inside, with gates that charge and discharge presumably. Hmm, not sure I >> understand how they work, now I come to think of it. Photovoltaic mode >> photodiode(s) connected to the gate I guess. >> > > I did a bit of digging. NXP has discontinued all of their > enhancement-mode dual gate FETs, including the cute ones like the > BF1100, which had an interesting feedback FET mechanism to improve the > linearity of AGC. > > The best-looking one for sampling appears to be the BF998, which has > reasonable I_D with V_G2S = 0.
OK, nice, thank you. I just went on digikey and I see that is the same one I already clicked on, when I idly looked one up after you mentioned them! Ordered some for a rainy day. Thanks, -- John Devereux
Hi John & Jim,

>>>>> I seem to recall someone (John L?) talking about using opto-fets as zero >>>>> charge injection switches. But I wonder are they really? They have fets >>>>> inside, with gates that charge and discharge presumably. Hmm, not sure I >>>>> understand how they work, now I come to think of it. Photovoltaic mode >>>>> photodiode(s) connected to the gate I guess.
Just think a little before flaming someone else, please. opto-fets can never have a charge injection, because the charge they use to load the gate comes from the chanel that the charge flows in. so the sum will allways be zero. I would say, this is as obvious as Kirchhoffs law can be. Regards Marte
On Sat, 09 Mar 2013 18:55:23 +0100, Marte Schwarz
<marte.schwarz@gmx.de> wrote:

>Hi John & Jim, > >>>>>> I seem to recall someone (John L?) talking about using opto-fets as zero >>>>>> charge injection switches. But I wonder are they really? They have fets >>>>>> inside, with gates that charge and discharge presumably. Hmm, not sure I >>>>>> understand how they work, now I come to think of it. Photovoltaic mode >>>>>> photodiode(s) connected to the gate I guess. > >Just think a little before flaming someone else, please. > >opto-fets can never have a charge injection, because the charge they use >to load the gate comes from the chanel that the charge flows in. so the >sum will allways be zero. I would say, this is as obvious as Kirchhoffs >law can be. > >Regards > >Marte
Izzat so ?:-} ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 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.
On Tue, 5 Mar 2013 20:05:33 -0800 (PST), George Herold <gherold@teachspin.com>
wrote:

>On Mar 5, 8:07&#2013266080;pm, scot <bonesisal...@gmail.com> wrote: >> Anyone have experience with lock-in amplifiers? &#2013266080;I am thinking of purchasing a used one but don't know enough about them. &#2013266080;I know they are extremely effective at finding small signals buried in lots of noise but what are the downsides to a lock-in besides expense? >> >> Also, this is probably over my head but I have read about the AD630 chip from Analog Devices and supposedly that can be used to make a very low cost lock-in amplifier. &#2013266080;Anyone ever try that? &#2013266080;Was it worth it for the money? &#2013266080;I should mention a friend of mine has a couple of these AD630 IC's so I would be willing to solder something up pretty quick if it's not a waste of time. >> >> Scot > > >As Phil said, there are better IC's these days, > >But for learning how a lockin works the AD630 will be fine. >There's at least two kinds of lockin's (all analog techniques can be >done in digital.) Multiplying and switched gain. (gain = +1/-1) The >AD630 is a switched gain lockin. > >George H.
Digital makes more sense these days, in most cases. A 16 bit ADC with a little noise dithering would be really good. Many tricks become possible. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators