Choosing the correct single supply OP-AMP

Thread Starter

Saviour Muscat

Joined Sep 19, 2014
161
Hello,
Trust this thread finds you in good health.
I need to choose a single supply op-amp with very low noise for signal conditioning of a current sensor . The input signal is a full sinewave(Vmax=3V, Vmin=0V @1Hz) and supply of +12V. Please could someone suggest a suitable part number of an op-amp or which parameters values should I look for?
Thank you for your kind support,
SM
 
Last edited:

crutschow

Joined Mar 14, 2008
28,215
Does the output need to go to the positive voltage rail?
That would mean a rail-rail type op amp.

For lowest noise you probably want a J-FET or bipolar amp, not CMOS.
Compare the noise specs on the devices you look at.
 

neonstrobe

Joined May 15, 2009
180
You have options.
Have you tried looking up distributor's op-amp sections?
Op amps usually run from dual rails but can be wired to run from a single. You would need an op amp that can run from +/-6V (min) and often several work at +/-15V which would suffice.
You could check for rail to rail operation on input so that it works from zero, but do you know how you might adjust the signal to be centered nearer 6V which would be where most op amps would like to work when running from a single 12V supply?
 

Ian0

Joined Aug 7, 2020
3,773
The noise depends on your source impedance, and your bandwidth.
Noise = √((vn^2+(R.in)^2)*B)
where vn = voltage noise in V/√Hz
in = current noise in A/√Hz
and B = bandwidth in Hz
As you are working at a low frequency, also look at the 1/f noise corner.
There is usually a graph on the datasheet showing how the voltage noise increase as the frequency decreases, and sometimes a spec for the output noise at 10Hz.

(But if the signal is 3V, I'm not quite sure why you might be worried about the op-amp noise)
Generally, op-amps that don't have to do anything clever like working from rail to rail can perform better at noise. There's not one op-amp that's good at everything, so if you want precision (low offset voltage) you can't have high speed or low noise.

One of the biggest ranges of op-amps is at Texas Instruments.
https://www.ti.com/amplifier-circuit/op-amps/overview.html
 

Ian0

Joined Aug 7, 2020
3,773
For lowest noise you probably want a J-FET or bipolar amp, not CMOS.
Compare the noise specs on the devices you look at.
A bipolar will be best at low source impedances, a JFET will be best at high source impendances, and a CMOS (as you rightly say) will never be best. Beware of manufacturers that don't quote current noise (New Japan Radio is a repeat offender!) - they are probably bragging about a bipolar op-amp which won't perform well on high source impedances.
 

Thread Starter

Saviour Muscat

Joined Sep 19, 2014
161
Dear members,
Thank you for your precious advice.
Sorry for my late reply because I was at work. I am going to choose a Bipolar op-amp type as suggested by you.
Thank you and best regards
SM
 
Top