Low Noise Voltage Source
Low Noise Voltage Source
(OP)
Hi, All:
I am monitoring the change in resistance of a load (~50 Ohms) with respect to a varying applied magnetic field (changes R_load by fractions of an Ohm). I would like to bias a constant voltage across this load to monitor these changes.
I am having difficulty maintaining a low-noise DC voltage bias across the load. Previously, I tried designing the circuit based on a noninverting opamp configuration, with the load at the inverting input and grounded. However the voltage noise across the load was near 100mV. Which is an issue since I will need to monitor changes in voltage of less than an ohm.
Any circuit ideas?
Thanks,
Paul





RE: Low Noise Voltage Source
RE: Low Noise Voltage Source
RE: Low Noise Voltage Source
pick-up? 100 mV noise is a lot, you can do much better
you just must know what really do you need.
<nbucska@pcperipherals.com>
RE: Low Noise Voltage Source
RE: Low Noise Voltage Source
The idea is to retrieve an M-R transfer curve by monitoring the load.
RE: Low Noise Voltage Source
RE: Low Noise Voltage Source
it for integer periodes of this.
<nbucska@pcperipherals.com>
RE: Low Noise Voltage Source
RE: Low Noise Voltage Source
Widely used in strain measurements and such.
RE: Low Noise Voltage Source
This technique is very old and very good. See equipment from Signal Recovery (Princeton Applied Research), Boston Electronics, Stanford Research:
http://www.signalrecovery.com/lockinde.htm
http://www.boselec.com/products/siglimwhat.shtml
http://www.srsys.com/html/sr830.html
TTFN
RE: Low Noise Voltage Source
http://www.analog.com/Analog_Root/productPage/productHome/0,2121,generic%253DADR280%2526level4%253D%25252D1%2526level1%253D117%2526level2%253D%25252D1%2526level3%253D%25252D1%2526resourceWebLawID%253D0,00.html
see the other voltage references by Analog Devices:
http://search1.analog.com/searchProxy.asp?queryText=voltage+reference
You should be able to achieve noise in the low microvolt range for relatively low frequency bandwidths. For high frequencies, you'll have to use a lock-in amplifier
TTFN
RE: Low Noise Voltage Source
RE: Low Noise Voltage Source
jtdsamuels, do you have any links to these sites that you mention? How about any circuit schematics of an instrumentation amplifier?
Thanks.
RE: Low Noise Voltage Source
However, I would not bother with the notion of trying to build your own instrumentation amp. It can't be done without low leakage, high-performance transistors, which are integral to the design.
TTFN
RE: Low Noise Voltage Source
For clean and stable DC bias use a battery and precision voltage reference (ex.:REF02 from Burr-Brown). This best way for low noise DC bias. Burr-Brown and Analog devices have a instrumentation amplifier (Ex.: INA101, INA102,INA105, AD628, AD620, etc).
Regards,
M3
RE: Low Noise Voltage Source
First of all if your sensor is not in a bridge configuration, PUT it in a bidge format; it is not a professional idea to use a precision sensor in a potentiometric format. Secondly, pick up the out of balance voltage and then amplify it, say 20 or 50 times with a good FET input op-amp like CA3140. Then add your dc signal to that. Now your measured signal is 20 or 50 (the more you amplify the better) times more and the error coming from the power supply will be 20 or 50 times less, as it is constant but your signal is more powerful!! then you can monitor your signal, however I also think you can acieve some 2mv ripple in your power supply.
If you have very much digital (computer or processor) stuff in the lab and really intended to have a virtually zero error, then do some DSP and filter out your signal with digital filters; very silly though!!!!
Battery as a power supply was a very nice idea; consider it.
I hope it would help
Zimbali
RE: Low Noise Voltage Source
Could someone elaborate on "bridge configuration"? Links?
Thanks everyone,
Paul