Need working I to V converter

[ex4]

i to v converter

hello,
can anybody got circuit current to voltage converter that can convert 0-2,5uA current to 0-5V output using regular op amp such as LM324, and single supply. i've design it but got no luck at single supply

 

[kender]

i to v converter using op amp

... 0-5V output using regular op amp such as LM324, and single supply. i've design it but got no luck at single supply

If you have only one +5V supply, you can not acheive a 0-5V output with a regular supply. You can acheive, may be +0.7V to +4.3V. You heed a rail-to-rail op amp.

 

[ex4]

op-amp i-to-v converter

ok then, i know the boundary, but what about the I to V converter using single supply opamp?? i nee to convert current of 5nA - 2,5uA to voltage level that can be read using AVR ADC

 

[jourval]

transimpedance amplifier lm324

Where is actually the problem ?
Simple transimpedance with offset will work fine...
See attached

 

[ex4]

na current to voltage converter

been doing that kind of schematic using LM324 but got no luck.
any suggestion about the op amp? AD opamp is hard to find here :|

 

[kender]

+i to v +schematic

been doing that kind of schematic using LM324 but got no luck.

If you tell us what you've measured and what you've expected, we can help you with your op amp design. Unfortunately, we can't help you get your luck back. We are not psychiatrists, we’re mere engineers. :|

any suggestion about the op amp? AD opamp is hard to find here

Whose opamps can you buy? You've mentioned LM342 earlier; it's a National Semiconductor part. Can you buy National parts? Who is you supplier? Do they have a web site? If you are limited on parts supply, may be you consider the other route and make a negative power supply (out of TC7660 or 555 for example).

 

[jourval]

transimpedance amplifier with lm324

With LM324 you never can not get output swing close to your VCC
It is "strong" not rail-to-rail.
If you can not obtain any rail-to-rail amplifier - the only way is or add negative supply or try to add push-pull transistor stage to output amp in the schematic
above. In this case your output voltage will only 0.4V less then Vcc
but your minimum measurable current will be only 50-100 nA not more.
There is a lot of other options (log-amp etc) but you'll need access to "modern"
elements

 

[ex4]

convert lm324 to rail to rail op amp

ok, got OP07 in hand and ready to test the schematic from jourval
so, any estimation how small the current i can measure using OP07?

 

[kender]

lm324 transimpedance

The minimum current depends on the accuracy that you want to achieve. The input bias current OP07 is Ib=1nA. (This is a pretty big current. Opamps that have Ib=10pA are not uncommon nowadays.) You should be able to measure current down to 100nA without much distortion. You could go even lower, if you correct the distortion with a calibration table.

 

[jourval]

my estimation that with op07 you can get 20-30 nA resolution
I made simulation with op07 model it gave something like 15 nA current
noise floor, but it is 'ideal" condition...
Op07 much-much better then LM324 but still....
When you begin to build this circuit beware about very low noise Vcc,
bypass all Vcc dividers with big capacitors, sheld with grounded foil all, what you can, because the pick-up of external noise is the main problem for such
circuits... to get the real noise floor of amplifier is not so straitforward...
Good luck

 

[Asadkh21]

Re: i to v converter

hello,
can anybody got circuit current to voltage converter that can convert 0-2,5uA current to 0-5V output using regular op amp such as LM324, and single supply. i've design it but got no luck at single supply

Try Using LTC1050 package which works on single supply and has a very fine response with a wide bandwidth and Photodiode typical application circuit present in the data sheet. Hope thats ready made.

 

[priyanksalot]

Re: i to v converter

Hello!

Even I am working on a similar design and haven't landed to any final design. So if possible can u post your circuit diagram?

 

[dick_freebird]

Sounds like a 2Mohm resistor to me, if the source has
more than 5V worth of voltage compliance range and is
linear over it.

If not then you use the same resistor as feedback and
sum the op amp output and the current input to the
amplifier virtual ground.

One issue being, if the current is that low, you can't
afford to be wasting much of it against op amp input
bias current - which in the case of LM324, can be
substantial and prone to environmental drift big time.
You should look at an amplifier whose worst case Iib
is less than 2.5uA/2^bits_of_desired_accuracy.

 

[priyanksalot]

As per my requirements, I need to convert current (range 0-5uA) to a voltage (0-5V)
I dont think as per my input, lm324 would work. What about op 07?