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.
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?
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.
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
asing a used one but don't know enough about them. I 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?
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 mon ey? I 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.
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.
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?
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.
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.
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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?
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?
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.
night and learned a lot. I found this interesting article and it looks like the principles are pretty understandable.
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?
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
rchasing a used one but don't know enough about them. I 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?
ip from Analog Devices and supposedly that can be used to make a very low c ost 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 w aste of time.
s last night and learned a lot. I found this interesting article and it looks like the principles are pretty understandable.
tituted instead. My main goal here is to learn about Lock-in's by buildi ng one myself since reading only takes you so far. What do you think? Is this a good starting point?
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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.
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 wh at are the downsides to a lock-in besides expense?
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 th e money? I 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.
n's last night and learned a lot. I found this interesting article and i t looks like the principles are pretty understandable.
bstituted instead. My main goal here is to learn about Lock-in's by buil ding one myself since reading only takes you so far. What do you think? Is this a good starting point?
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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 :^)
rchasing a used one but don't know enough about them. I 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?
ip from Analog Devices and supposedly that can be used to make a very low c ost 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 w aste of time.
s last night and learned a lot. I found this interesting article and it looks like the principles are pretty understandable.
tituted instead. My main goal here is to learn about Lock-in's by buildi ng one myself since reading only takes you so far. What do you think? Is this a good starting point?
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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.)
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?
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.
night and learned a lot. I found this interesting article and it looks like the principles are pretty understandable.
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?
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
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 wh at are the downsides to a lock-in besides expense?
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 th e money? I 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.
n's last night and learned a lot. I found this interesting article and i t looks like the principles are pretty understandable.
bstituted instead. My main goal here is to learn about Lock-in's by buil ding one myself since reading only takes you so far. What do you think? Is this a good starting point?
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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.
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?
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.
last night and learned a lot. I found this interesting article and it looks like the principles are pretty understandable.
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?
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.
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.)
--
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
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?
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.
Could you expand on that, or suggest a favorite part?
I found the ADG1236 too for low charge injection. Also DG636.
Same here. Unfortunately the DG1236 does not work at cryogening temperatures, unlike e.g. the TS5 series from Texas Instruments. I have been looking for a low-injecting switch to operate in LHe, and Phil's suggestion of using dual-gste MOSFETs is good. At least such devices as the 2N7000 (from some manufacturers) and the FDV301P do work, so I might try throwing in eg. the BF998.
f purchasing a used one but don't know enough about them. I know they ar e extremely effective at finding small signals buried in lots of noise but what are the downsides to a lock-in besides expense?
0 chip from Analog Devices and supposedly that can be used to make a very l ow 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.
-in's last night and learned a lot. I found this interesting article and it looks like the principles are pretty understandable.
substituted instead. My main goal here is to learn about Lock-in's by bu ilding one myself since reading only takes you so far. What do you think ? Is this a good starting point?
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Well let us know what you think of the Owon. We bought one (probably a different model) years ago, but it now lives in Europe for trade shows over there. I didn't like the screen, it had a very restricted viewing angle. (It seemed a bit noisier than a low end tek too... but no real data.)
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?
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.
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.
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
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?
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.
last night and learned a lot. I found this interesting article and it looks like the principles are pretty understandable.
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?
Will do. This one has an 800x600 display, and otherwise similar specs to the Rigol DS1102E, for just about the same price ($400). Saelig was out of stock of the Rigol, so I switched my order.
It's probably going to spend most of its time looking at SPI busses and so on, at least for the first while.
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
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 >:-} ...Jim Thompson
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I love to cook with wine. Sometimes I even put it in the food.
I'd be interested to know what you think of it. The display is a lot bigger and higher resolution than my Tek, and some of the models have an interesting 16-channel LA function at an interesting price point ( < $1K ).
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