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Current oscillator

by 0xDEADBEEF
Tags: current, oscillator
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0xDEADBEEF
#1
Jan19-10, 03:46 PM
P: 824
Are there sine wave generators for current? I need something like .1Hz, 30uA_rms, to a target of about 1kOhm.

If you would try to convert a normal function generator for this purpose, would you go for a large resistance like 1MOhm in series or a current mirror design? Where would the noise be larger?
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f95toli
#2
Jan19-10, 04:09 PM
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Use a resistor in series, something like 100kOhm. There is no need to make anything more complicated than that (I've used functions generators to current-bias samples for many years).
Just watch out for the 50 ohm output impedance of you use a function generator (set it to high-Z if that is an option), or it can get a bit confusing.
Also, you should definitely measure the current (at 0.1 Hz you can just let the current pass through a 10 ohm resistor and measure it using a multimeter), don't trust the function generator if you need accurate values.

Btw, there ARE generator that can give you the current directly. Most people I know use an old (well, pre-Agilent) HP generator, unfortunately I can't remember the designation. We have a couple of them at work (you can still buy them used from variour companies, they are not more expensive than when they were new...).
That said, I would NEVER bias a sensitive sample directly from a generator without putting a large resistor in series, doing so will inevitable destroy the the sample.
waht
#3
Jan19-10, 05:20 PM
P: 1,636
Quote Quote by f95toli View Post
Btw, there ARE generator that can give you the current directly. Most people I know use an old (well, pre-Agilent) HP generator, unfortunately I can't remember the designation. We have a couple of them at work (you can still buy them used from variour companies, they are not more expensive than when they were new...).
Was it the HP 3325A or B?

f95toli
#4
Jan19-10, 06:07 PM
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Current oscillator

No, not quite that old (although I think we have one or two of those as well).
I'll have a look when I get to work tomorrow morning.
f95toli
#5
Jan20-10, 09:08 AM
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The generator I was referring to is called HP 3245A, the model is about 20 years old. You can buy a refurbished one for about $4000.
waht
#6
Jan20-10, 11:46 AM
P: 1,636
Didn't get to play around with it yet. It's truly remarkable though, it has dc output with 6 1/2 digits of resolution.
0xDEADBEEF
#7
Jan20-10, 01:56 PM
P: 824
We have some old HP I`ll try to get it to work, but I think it speaks an ancient GPIB dialect.
f95toli
#8
Jan20-10, 03:01 PM
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Well, GPIB (and/or HP-IB) hasn't changed much over the past 25 years or so (probably longer), so I doubt you'll have any problems with that. Although on some old equipment you might have to set the GPIB address using DIP switches, you should also try to put it last in the chain if you are daisy-chaining devices.


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