I want to design a voltage divider circuit to bias an op amp, this circuit will be a part in another circuit to measure a biomedical signal. Is there a noise issue arises from using voltage divider to provide biasing? if I choose R1 = 10K and R2 = 10K, then will it make any difference if I choose R1 = 10M and R2 = 10M?
In a paper I read the following:
Using a simple resistive bias network is impractical from a
reliability and noise standpoint.Although a biasing resistor can be
bootstrapped to the required resistance, minimizing its current noise
contribution requires an impossibly high value
I don't know if they mean a voltage divider by "simple resistive bias network", but I assumed that.
Best Answer
It is unlikely that Johnson (thermal) noise is what is being referred to. However high impedance resistor dividers are more susceptible to picking up noise from external sources, and are less stable (because they are more susceptible to leakages).
Use 10k's and add a decoupling capacitor (say 1-100 uF) to reduce noise to insignificant levels.