10 Differential Amplifier

Figure 10-1 displays two op amps connected in an differential amplifier configuration. As seen in the figure the differential amplifier has two input signals V1 and V2 and two output signals OP1OUT and V2. The difference between the two output signals is proportional to the difference between the input signals. The ratio or the gain between the two differential signals is set by the ratio between R2 and R1. This way the differential amplifier can amplify a differential signal.

The output voltage OP1OUT is given by the formula:

$V_{O P 1 O U T} = V_{2} - (V_{1} - V_{2}) \frac{R_{2}}{R_{1}}$

The differential signal is given by the formula:

$V_{D I F F} = O P 1 O U T - V_{2} = (V_{2} - V_{1}) \frac{R_{2}}{R_{1}}$

The gain is:

$G a i n = \frac{R_{2}}{R_{1}}$

The differential amplifier is suitable for amplifying a small differential signal before it is converted to a digital signal by a differential ADC.