WANTED: Precision current source/sink - Page 1
Forum section: electronics / general

author: Unknown
author_rank: Unknown
timestamp: June 24, 2011, 04:16:23 pm
content: I am looking for a precision current source that can cover the nA and uA range. Sink capability would be ideal but not necessary. Output compliance can be as low as 10V in the first instance. Bandwidth is not important but if it can cover the audio range, that would be great.I live in the UK and I don't want to break the bank. Please let me know if you have something suitable, all countries open.Regards,Alex

author: Bored@Work
author_rank: Super Contributor
timestamp: June 24, 2011, 05:21:32 pm
content: Quote from: Alex on June 24, 2011, 04:16:23 pmDoes that mean you want to have an AC, not a DC current source? There aren't many, e.g. Keithley 6221.QuoteIf you want AC, consider robbing a bank.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: July 06, 2011, 01:00:53 am
content: Quote from: BoredAtWork on June 24, 2011, 05:21:32 pmWell even for DC powered one, without nA range,you will have to crack down your credit card for good.The word precision, is a very bad word in relation with cost.And the point is that you are aware of it.

author: Zero999
author_rank: Super Contributor
timestamp: July 06, 2011, 05:46:07 pm
content: Alex,You've not given a detailed specification. It might be possible to build this yourself.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: July 07, 2011, 12:52:04 am
content: Quote from: Hero999 on July 06, 2011, 05:46:07 pmBuilt what ?An calibrator ?I will bring the national TV and the press, if he did build something like that.

author: ejeffrey
author_rank: Super Contributor
timestamp: July 07, 2011, 07:10:16 am
content: In addition to accuracy and modulation bandwidth, you probably need to specify the noise and the output impedance, both at DC and AC. Getting high source impedance at high frequency is particularly difficult, especially in conjuction with accuracy.

author: Zero999
author_rank: Super Contributor
timestamp: July 07, 2011, 04:02:34 pm
content: He didn't mention the accuracy and bandwidth.If it's just 1% accuracy over the audio spectrum, I don't see how it's going to break the bank.

author: Unknown
author_rank: Unknown
timestamp: July 07, 2011, 06:37:05 pm
content: Thanks all for your replies.A few clarifications. The need came about because of a log amp in a loudness level indicator, part of an after hours project. The requirements are very relaxed, sourcing (no sinking, amplitude modulated DC current) 100nA +/- 1nA to 1mA +/-10uA at approx 1mV pk-pk, sawtooth at 20kHz , 2Mohm impedance at 20kHz and those currents. The log amp is bandwidth-limited to about 23kHz. The Keithley 6221 on the 200nA range has 0.5nA RMS noise over 100kHz bandwidth. Really, this application is not noise limited, I would expect other effects like offset voltage drift to dominate errors in the log amp.So you will agree with me there is nothing 'precision' about the specs above, but I am not aware of a product you can 'dial-in' such currents apart from 'precision current sources' and 'precision voltage/current source/monitors' (?). Depending on the marketing department they might drop the word 'precision'; you get the idea.This is indeed very easy to DIY, however I wanted to seize the opportunity and ask if you are aware of any second or third hand deals for a current source instrument (which should easily meet the above specs) that I can also use as a general purpose piece of equipment as it will most likely exceed the above specs. The Keithley 225 will not modulate above 500Hz, the 228 doesnt cover the nA range, the LDX-3412 is a laser diode driver (10s of mA). I am under the impression the Keithley 224 can do a slow ramp, but no external modulation. The Keithley 236 doesnt have external modulation, only some internal ramps. These are most of the items on ebay.The Keithley 6221 is a fine piece of equipment, but it seems it is sold via the 'sales rep' channel, which suggests its price range. Joy could possibly confirm this?