INVERTING OPERATIONAL AMPLIFIER

 INVERTING OPERATION AMPLIFIER

                                                  

To understanding Inverting operational amplifier , then you have to first understand the concept of Virtual Ground .

Now in this blog article we will go to learn about virtual ground in simple and precisely. This virtual ground concept is only , applicable when we are providing the negative feedback to this operational amplifier (Op-amp) , or we can say in other words this virtual ground concept is only valid when we providing negative feedback to this operational amplifier .

              Now , here for a given (op-amp) the open loop gain of this (op-amp) is 10 raise to the power 6 . And we know the output (o/p) voltage (Vout) of (op-amp) is given as A multiply with differential input voltage .

                                              

             This is the input voltage between these inverting and the non-inverting input terminals . Now , here let's we consider that through this negative feedback , we are controlling the output (o/p) voltage of this (op-amp) in a such a way that , the output voltage is always less than the saturation voltage. Or in other words we can say that we are operating this (op-amp) in a linear region . 

           So , let consider that the output (o/p) voltage is ten volt (10 v) . So, we can say that 10 v is equals to the 10 raise to the power 6 multiply with this differential input voltage . Or we can say that in other words that the differential input voltage is equal to 10 micro volts . 

           Now , here this differential input voltage is nothing , but the differential between this inverting and the non-inverting input terminals . So , we can write this differential input voltage as a (V plus minus V minus) ( V+ -V- ) this is equals to 10 micro volt . 

          Now , here this 10 micro volt is very very small signal and we can almost neglect it . So , we can write this (V plus minus V minus) (V+ - V-) as approximately equal to zero volts or we can say that in other words that Vplus , that is equal to Vminus .

           It means that the inverting and the Non-inverting input (I/P) terminals are at the same potential or we can say that in other words that there is virtually short between this inverting and non-inverting input (I/P) terminals .

             Now here , the term we use virtual it means that , these two terminals are not actually short circuited , but they are virtually short circuited . So, whatever voltage that appear at one terminal , the exact and same voltage will appear at another terminal . 

            So , now in this configuration , this Non-inverting input terminal is grounded . So, we can say that Vplus that is equals to zero (0) . So, accordingly to this result , Vminus should be equals to zero (0) . It means that this terminal is not actually grounded , but it will act like as a virtual ground . 

            So , this negative feedback will ensure that the difference between this inverting and the Non-inverting input (I/P) is very very small or we can say that in another words that it is almost negligible .

           And because of that , we can consider these both input (I/P) terminal at the same potential . So , this concept is known as the virtual ground concept .

          So , now let use this concept , if virtual ground and let's derive the expression between this Vout and Vin .

           And let's say that node is , node X . And let's say that the current , that is flowing through this resistor Rf is If . We had seen that the (Op-amp) has very high input (I/P) impedance or if we assume the ideal (Op-amp) is infinite . It means that no current is entering into this (Op-amp) or we can say that in other words that current ( I ) that is equal to zero (0) .

                                                  

So , as you can see here , just by changing the value of this ( Rf ) and ( R1 ) we can control the gain of this (Op-amp) . And we can use this (Op-amp) as a amplifier .

         Now , here the negative sign indicates that the output voltage is 180 degree out of phase with respect to input voltage .

          So , let's say that , if we have applied the sinusoidal signal at the input , then at the output we will get the amplified sinusoidal signal , which is having a 180 degree phase with respect to the input signal .

           And that is why this configuration of the (Op-amp) is known as the inverting configuration . Because the output (O/P) will be get inverted with respect to input (I/P) voltage .