Closed loop gain of an amplifier

In the following design pattern, Vin, input voltage is applied to the non-inverting input terminal that means we get “Positive” value of amplifier’s output gain as compared to the "Inverting Amplifier" where we got the “Negative” value of output gain as per our pervious discussion.

As an outcome of this, the input signal is “in-phase” with the output signal. By applying a minor portion of output voltage signal through voltage divider network Rf - R2 to the inverting input i.e. by creating negative feedback, a feedback control system is accomplished.As illustrated the in figure, this closed-loop configuration generates a non-inverting amplifier circuit with very high input impedance,  Rin approaching infinity, low output impedance, Rout ,very good stability as under ideally no current is flowing in the positive input terminal.

The same potential ( V1 ) is applied at the intersection of feedback and input signal. That means at summing point junction is a "virtual earth".  Resisters Rf and R2  are used to develop a simple potential divider network in the non-inverting amplifier. As illustrated below the ratio of resisters Rf  and R2, decides the output voltage gain of the circuit. Let’s calculate the Closed-loop voltage gain ( A V ) by applying the method to find out the output voltage of a potential divider network of Non-inverting Amplifier.

Fig. Equivalent Potential Divider Network
 For a Non-inverting Amplifier, closed loop voltage gain is given as:

For a Non-inverting Amplifier, closed loop voltage gain is a positive value which is always greater than unity (1) and is dependent on the ratio of Rf and R2. The gain of the amplifier will be right equal to unity (1) only if the Rf=0 i.e. value of the feedback resistor is zero. The gain of the amplifier will approaching infinity if the R2=0 . i.e. value of the feedback resistor is zero.   If resistor R2 is zero the gain will approach infinity, but usually it is restricted to the ( Ao ), open-loop differential gain of an Op-Amp. If we change input connections as illustrated below then we can translate the system configuration from operational amplifier into a non-inverting amplifier. 

1 comment: