I need to set the biasing values of an op amp but maybe there is a way without calculate all voltages and currents ....If I want for example a 70 dB gain how can I assign the value of biasing?
thanks
An opamp's input must be biased at half of its total power supply voltage for the highest symmetrical output swing.
Biasing an opamp has nothing to do with its voltage gain.
Its voltage gain is the ratio of its negative feedback resistor to the other resistor (the input resistor if the opamp circuit is inverting or the resistor to ground if the opamp circuit is non-inverting).
70dB is a lot of gain. Most opamps rolloff the high frequencies and with that much gain then the rolloff will begin at about 200hz with most opamps.