![]() The C P1 capacitor blocks the polarization current of the circuit, so that it doesn't flow into the device connected to the input. To complete the information about the system we can compute the input impedance of the whole circuit:Ĭhoosing R 2 = 33 KΩ and keeping in mind the E12 series approximation, we obtain good values: R 1 = 100 KΩ, R z = 22 KΩ, R in = 63 KΩ. Now we can write an equations system based on the V IN e V alim gains: ![]() To find the components values, we can make some brief considerations: we decide that the V IN voltage is reported, unchanged, at the output in order to polarize correctly the signal we must sum half of the power supply voltage to V IN finally, we chose α=2, since this allows us to use R F = R G. The total gain of the non-inverting stage is therefore: The gain of the non inverting amplifier is independent from the resistances which appear in the V IN1 expression, and therefore for simplicity we can put it equal to a constant: While to determine the V 1 IN voltage we can consider V alim = 0V, and therefore we can substitute to the power supply a short circuit (as the superimposition method requires): To find the V 1 alim value, we can consider the capacitor C P1 as an open circuit, since V alim is a direct voltage: The voltage will be the sum of two elements: the V 1 IN component, related to the input voltage V IN, and the V 1 alim, obtained from the V alim power supply voltage: In order to calculate V IN1 we can use the effects superimposition, following a procedure similar to the one commonly used to solve the polarization in traditional BJT transistors circuits. ![]() In this case V IN is the voltage after the resistive network composed by R 1, R 2 and R z. In the traditional non-inverting amplifier V IN is connected directly to the op-amp non-inverting pin in this configuration the gain is: ![]() The first stage of the circuit is a non-inverting amplifier, which takes care of decoupling the filter input voltages and of biasing the signal by summing half of the supply voltage. R z and CP1 must be substituted with two resistors in parallel with the double of the value, together with their decoupling capacitors.Ĥ - The design: decoupling and polarization stage Figura 7: The modification for the filter input to obtain a stereo input. ![]()
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