The logic operations performed by the given digital circuit is equivalent to:

As shown in the figure the various logic gates have been mentioned.

Let the output before the $NOT$ gate be $Z$.

Using the expression for the logic gates, it can be written

$Z=\overline{\left(A+B\right)·(A·B)}$

Hence, the output $Y$ is 

$$\begin{gathered} Y=\overline{Z}=\left(A+B\right)·(A·B) \\ \Rightarrow Y=A·B \end{gathered}$$

Hence the digital circuit is equivalent to an $AND$ gate.