Figure 1.  A Dual Operational Amplifier IC Configured for Differential Amplification

Figure 1 shows how a dual op-amp IC such as the LM358 or 1458 may be configured to serve as a differential amplifier, which is a circuit that only amplifies the difference between two potentials. Note that both the input and output of this amplifier circuit are 'differential' in nature. All common-mode signals are rejected by this circuit, which makes this circuit very useful in amplifying signals in noisy environments or in applications that require high sensitivity.

In this circuit, a differential input voltage is applied across the non-inverting inputs of the two op-amps (pins 3 and 5).  The output is taken from across the two outputs of the two op-amps (pins 1 and 7). 

The gain G of this circuit is given by: G = 1 + (2Rf / Rin).  Thus, Vout = Vin (1 + (2Rf / Rin)).

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