Question

In a differential connection, the signals that are opposite at the inputs are ---- amplified, and those that are common to the two inputs are ------
amplified.
A) slightly, slightly
B) slightly, highly
C) highly, highly
D) highly, slightly

Answer 1

Hint: The differential amplifiers are used to amplify the difference in the voltage of two input signals. It acts as a subtractor circuit. Hence, whatever the value of the voltage applied at the inputs, we get an amplified output. Therefore, to get a non-zero output, the input signals should not be equal.

Complete step-by-step solution:
Differential amplifiers are devices that are used to amplify the difference in the voltage of two input signals. It has three terminals: two high impedance input terminals, and one output terminal. The two input terminals are the inverting input terminal and the non-inverting input terminal. When two inputs are applied at the two terminals, the voltage produced at the output will be proportional to the difference of the applied inputs. It acts as a subtractor circuit because it basically subtracts the two inputs. When the applied input signals are equal, i.e., no difference between the two applied signals, the output will be zero. But practically its value is not exactly zero.
The output voltage of differential amplifier is given by,
\[{{V}_{0}}={{A}_{d}}\left( {{V}_{1}}-{{V}_{2}} \right)\]
Where,
\[{{\text{V}}_{\text{1}}}\text{ and }{{\text{V}}_{\text{2}}}\]represents the voltages applied at the inverting and non inverting terminals.
\[{{A}_{d}}\]represents the differential gain.
Hence, from the above equation, we can see that, if the two input voltages are equal, the output voltage becomes zero.
Therefore, in a differential connection, the signals that are opposite at the inputs are highly amplified, and those that are common to the two inputs are slightly amplified.
The answer is option D.

Note: The main applications of differential amplifiers are, they produce amplified versions of the input. And these amplifiers eliminate noise present in the input signals and are linear in nature. Its main disadvantage is, it rejects the common-mode signal.