The Differential Input and Differential Output

For getting balanced differential output  we use this circuit. In this circuit  two source is present, so the superposition theory is applied to get the output. In this circuit both the inverting and non-inverting terminal is working.It rejects the common-mode voltages, so  it is very useful in noisy environments.

A  differential input and differential output amplifier using two identical Op amp. It is     most commonly used as a preamplifier and driving push-pull  arrangement. The differential input and output  are inphase or the same polarity provided  V_in  =V_x – V_y and

V_o  =V_ox – V_oy

When we want to find out the 1^st op-amps output V_OX , we will use the  superposition theory.

When we get  V_X  is active , V_Y  is  inactive then ,

In non inverting terminal 

V₁= (1+ )V_X

When we get  V_y   is  active,  V_x   is  inactive then,

In  inverting terminal,

V₁ = - V_y

 So, V_ox = V₁+V₁

                =(1+ )V_X  -  V_y

 

Fig: The circuit diagram of the differential input and output amplifier. 

When we want to find out the 2^nd  op-amps output V_Oy ,we will use superposition theory.

                      When we get  V_X  is active , V_Y  is  inactive then

                      In  inverting terminal ,

                      V₂= - V_x

        

      Again, when  we get  V_y  is  active ,  V_x  is  inactive then

        In non inverting terminal we get, 

V₂= (1+ )V_y

So, V_oy = V₂+V₂

                                      =(1+ )V_y - V_x

So the output result   

V_o = V_ox  –  V_oy 

= (1+ )V_X  -  V_y  –[(1+ )V_y - V_x ]

                                      = (1+ ) ( V_X - V_y ) +( V_X - V_y )

                                       = ( V_X - V_y ) (1+ )

Design

To design a input and differential output amplifier,  taking a  differential output of at least 3.7V and the  differential  input V_in  =10V.

                        We know,

 V_o = ( V_X - V_y ) (1+ )

            Or, 3.7 = (0.1) (1+ )

 Or, 37 = (1+ )

            Or, 36 = 

            Or, R_f  = 18 R₁

                                    Let, R₁ = 100Ώ, then R_f  = 1.8 KΏ . 

                   Fig: The designing circuit diagram of the differential input and output amplifier.