Differential configuration

AN4586

4/19

DocID026915 Rev 1

2

Differential configuration

The differential configuration needs only one op amp and is easily set-up. Consequently, it is

widely used.

Figure 2 shows the differential configuration schematic.

Figure 2. Differential configuration schematic

If we do not consider the inaccuracies, we have Equation 1 at the output.

Equation 1

Considering Rf1 = Rf2 = Rf and Rg1 = Rg2 = Rg, we get Equation 2

Equation 2

Note that the op amp must be used in dual supply if V1 > V2. An alternative option is to use

a reference voltage on Rf2 rather than ground and use the op amp in single supply.

Considering the op amp and resistor inaccuracies and with Rf1 = Rf2 = Rf and

Rg1 = Rg2 = Rg, we get Equation 3

Equation 3

Vout

V2

Rf2

Rg2

-----------

1

Rf1

Rg1

-----------

+

1

Rf2

Rg2

-----------

+

---------------------

V1

Rf1

Rg1

-----------

–

=

Vout

V2 V1

–

()

Rf

Rg

--------

=

Vout

V2 V1

–

()

Rf

Rg

--------

1

Rf

Rg

2

--------

+

⎝⎠

⎛⎞ ε

Rf1

–

()

Rg

2

--------

–

()

+

Rf Rg

+

---------------------------------------------------------------------------------------------------------------

+

⎝⎠

⎜⎟

⎜⎟

⎜⎟

⎛⎞

=

+

V1 V2

+

2

---------------------

Rf

Rg Rf

+

--------------------

–

–

+

() Vio 1

Rf

Rg

--------

1

–

+

()

+

⎝⎠

⎛⎞

–