I have a sensor which outputs a normally distributed baseband signal with cut-off frequency of 100Hz, whose mean is ~1mV and variance is (0.1mV)2. I want to amplify it about x1000 times by using TL084 opamp (other three opamps the TL084 contains are already occupied for different functions).
simulate this circuit – Schematic created using CircuitLab
I have a practical consideration on this circuit. The input signal is smaller than the input off-set voltage of the opamp which is given to be 3mV. Will this opamp successfully and precisely amplify my signal? If not, how do I increase precision of this circuit?
And how does the input offset voltage appear at the output (suppose that the input offset voltage s 3mV, the input signal is x(t) and the opamp output is y(t))?
a) 1000 times amplified along with the input signal. (i.e.; y(t) = 3V + 1000x(t))
b) Added at the output stage. (i.e.; y(t) = 3mV + 1000x(t))
Best Answer
Other answers have already made the main point: TL084 is not a good op-amp for your application. I'll answer one of your specific questions:
The input offset appears as if it were a voltage source in front of one of the input pins (doesn't really matter which one).
This typically means it appears as an error in your input signal, and sees the same gain as the input signal.
Yes, though it might be more clear to say \$ y(t) = 100 \left( x(t) + V_{os}(t) \right)\$.
If you look you will be able to find an op-amp with Vos in the 10 uV range, which might be acceptable for your application.
You might also consider that 1000x is a very high gain to achieve with a single op-amp stage. You might want to consider doing this with two stages instead of one.