Forums

lock-in amplifier

Started by scot March 5, 2013
Anyone have experience with lock-in amplifiers?  I am thinking of purchasin=
g a used one but don't know enough about them.  I know they are extremely e=
ffective 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 fr=
om Analog Devices and supposedly that can be used to make a very low cost l=
ock-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 woul=
d be willing to solder something up pretty quick if it's not a waste of tim=
e.

Scot
On 3/5/2013 8:07 PM, 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 >
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. The key is to not let the poorly-controlled channel resistance of the FETs cause too large an error. 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
On Mar 5, 8:07=A0pm, scot <bonesisal...@gmail.com> wrote:
> Anyone have experience with lock-in amplifiers? =A0I am thinking of purch=
asing a used one but don't know enough about them. =A0I know they are extre= mely effective at finding small signals buried in lots of noise but what ar= e 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. =A0Anyone ever try that? =A0Was it worth it for the mon= ey? =A0I should mention a friend of mine has a couple of these AD630 IC's s= o I would be willing to solder something up pretty quick if it's not a wast= e 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 =3D +1/-1) The AD630 is a switched gain lockin. George H.
On Tuesday, March 5, 2013 8:07:59 PM UTC-5, scot wrote:
> Anyone have experience with lock-in amplifiers? I am thinking of purchas=
ing 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 th= e downsides to a lock-in besides expense?
>=20 >=20 >=20 > 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 wo= uld be willing to solder something up pretty quick if it's not a waste of t= ime.
>=20 >=20 >=20 > 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 li= ke 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 substitu= ted 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
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 -- 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
On Mar 7, 1:18=A0pm, 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? =A0I am thinking of pu=
rchasing a used one but don't know enough about them. =A0I know they are ex= tremely 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 ch=
ip from Analog Devices and supposedly that can be used to make a very low c= ost lock-in amplifier. =A0Anyone ever try that? =A0Was it worth it for the = money? =A0I 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 w= aste of time.
> > >> Scot > > > Thanks Phil for the suggestion on the ADG1236. =A0I read up on Lock-in'=
s last night and learned a lot. =A0I 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 subs=
tituted instead. =A0My main goal here is to learn about Lock-in's by buildi= ng one myself since reading only takes you so far. =A0What do you think? = =A0Is 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. =A0I built my > first one when I was a postdoc (about 1988) for an atomic force > microscope. =A0More recently, I've built a few just like that for > customers, as part of the back ends of their measurement systems. =A0They > really are Good Medicine. =A0(I found the ADG1236 just the other day, whe=
n
> I needed parts to make a baby-scale loop.) > > There are two main dangers with lock-ins. =A0The 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. =A0The othe=
r
> is that in the presence of drift or 1/f noise, narrowing the bandwidth > doesn't help, and may make things worse.
The last sentence should be wrong, if you are using lock-in right. The basic idea is that you start off by modulating whatever it is you are measuring at some convenient frequency, and the detect only the modulation frequency in the output that you are looking at (usually after amplification and a certain amount of filtering). For added extra credit you can detect just some of the higher harmonics of the modulation frequency, but it takes sophisitcated experimental design to make this a useful approach. One of the great virtues of this approach is that you can stay well away from the frequencies where 1/f noise (and drift can be seen as a form of 1/f noise) is a problem. -- Bill Sloman, Sydney
On Mar 6, 7:38=A0pm, Bill Sloman <bill.slo...@ieee.org> wrote:
> On Mar 7, 1:18=A0pm, 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? =A0I am thinking of =
purchasing a used one but don't know enough about them. =A0I know they are = extremely effective at finding small signals buried in lots of noise but wh= at 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. =A0Anyone ever try that? =A0Was it worth it for th= e money? =A0I should mention a friend of mine has a couple of these AD630 I= C'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. =A0I read up on Lock-i=
n's last night and learned a lot. =A0I found this interesting article and i= t 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 su=
bstituted instead. =A0My main goal here is to learn about Lock-in's by buil= ding one myself since reading only takes you so far. =A0What do you think? = =A0Is 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. =A0I built =
my
> > first one when I was a postdoc (about 1988) for an atomic force > > microscope. =A0More recently, I've built a few just like that for > > customers, as part of the back ends of their measurement systems. =A0Th=
ey
> > really are Good Medicine. =A0(I found the ADG1236 just the other day, w=
hen
> > I needed parts to make a baby-scale loop.) > > > There are two main dangers with lock-ins. =A0The first and more insidio=
us
> > 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. =A0The ot=
her
> > is that in the presence of drift or 1/f noise, narrowing the bandwidth > > doesn't help, and may make things worse. > > The last sentence should be wrong, if you are using lock-in right. The > basic idea is that you start off by modulating whatever it is you are > measuring at some convenient frequency, and the detect only the > modulation frequency in the output that you are looking at (usually > after amplification and a certain amount of filtering). > > For added extra credit you can detect just some of the higher > harmonics of the modulation frequency, but it takes sophisitcated > experimental design to make this a useful approach. > > One of the great virtues of this approach is that you can stay well > away from the frequencies where 1/f noise (and drift can be seen as a > form of 1/f noise) is a problem. > > -- > Bill Sloman, Sydney- Hide quoted text - > > - Show quoted text -
I think Phil was talking about 1/f noise elsewhere in the signal chain. (I assume he knows how to pick a modulation frequency.) But in answering for someone else I've likely stuck my foot in my mouth. (again :^) George H.
On Mar 6, 7:18=A0pm, 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? =A0I am thinking of pu=
rchasing a used one but don't know enough about them. =A0I know they are ex= tremely 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 ch=
ip from Analog Devices and supposedly that can be used to make a very low c= ost lock-in amplifier. =A0Anyone ever try that? =A0Was it worth it for the = money? =A0I 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 w= aste of time.
> > >> Scot > > > Thanks Phil for the suggestion on the ADG1236. =A0I read up on Lock-in'=
s last night and learned a lot. =A0I 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 subs=
tituted instead. =A0My main goal here is to learn about Lock-in's by buildi= ng one myself since reading only takes you so far. =A0What do you think? = =A0Is 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. =A0I built my > first one when I was a postdoc (about 1988) for an atomic force > microscope. =A0More recently, I've built a few just like that for > customers, as part of the back ends of their measurement systems. =A0They > really are Good Medicine. =A0(I found the ADG1236 just the other day, whe=
n
> I needed parts to make a baby-scale loop.) > > There are two main dangers with lock-ins. =A0The 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. =A0The othe=
r
> 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 > > -- > 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 nethttp://electrooptical.net- Hide quoted tex=
t -
> > - Show quoted text -
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.
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 -- 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
On Mar 6, 9:37=A0pm, 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? =A0I am thinking of =
purchasing a used one but don't know enough about them. =A0I know they are = extremely effective at finding small signals buried in lots of noise but wh= at 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. =A0Anyone ever try that? =A0Was it worth it for th= e money? =A0I should mention a friend of mine has a couple of these AD630 I= C'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. =A0I read up on Lock-i=
n's last night and learned a lot. =A0I found this interesting article and i= t 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 su=
bstituted instead. =A0My main goal here is to learn about Lock-in's by buil= ding one myself since reading only takes you so far. =A0What do you think? = =A0Is 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. =A0I built=
my
> >> first one when I was a postdoc (about 1988) for an atomic force > >> microscope. =A0More recently, I've built a few just like that for > >> customers, as part of the back ends of their measurement systems. =A0T=
hey
> >> really are Good Medicine. =A0(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. =A0The first and more insidi=
ous
> >> 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. =A0The o=
ther
> >> 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. =A0(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 > > -- > 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 nethttp://electrooptical.net- Hide quoted tex=
t -
> > - Show quoted text -
Well it's not phase sensitive, but it does select frequency, so 128 averages is like a band pass with a Q of 128(?) Ya know I've never seen a good article on the many ways to use the average button on a DSO. George H.