V

O) +

V

I)

2

) VOCM

V

O– +

–V

I)

2

) VOCM

_

+

_

+

a

b

+1

0

+1

0

THS4150

THS4151

If each output is measured independently, each output is one-half of the input signal when the gain is 1. The

following equations express the transfer function for each output:

The second output is equal and opposite in sign:

Fully differential amplifiers may be viewed as two inverting amplifiers. In this case, the equation of an inverting

amplifier holds true for gain calculations. One advantage of fully differential amplifiers is that they offer twice as

with opposite signs and feed them into the differential input nodes of the ADC. In practice, the designer has been

able to feed a 2-V peak-to-peak signal into a 1-V differential ADC with the help of a fully differential amplifier. The

final result indicates twice as much dynamic range.

Figure 40 illustrates the increase in dynamic range. The gain factor should be considered in this scenario. The

THS415x fully differential amplifier offers an improved CMRR and PSRR due to its symmetrical input and output.

Furthermore, second harmonic distortion is improved. Second harmonics tend to cancel because of the

symmetrical output.

Similar to the standard inverting amplifier configuration, input impedance of a fully differential amplifier is selected

differential amplifier as an instrumentation amplifier. This configuration improves the input impedance of the fully

differential amplifier. The following schematic depicts the general format of instrumentation amplifiers.

18

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