In Binary Coded Decimal $($BCD$)$ encoding scheme each of the decimal numbers $(0-9)$ is represented by its equivalent binary pattern $($which is generally of $4-$bits$).$ Whereas, Seven segment display is an electronic device which consists of seven Light Emitting Diodes $($LEDs$)$ arranged in a some definite pattern $($common cathode or common anode type$),$ which is used to display Hexadecimal numerals $($in this case decimal numbers, as input is BCD i$.$e$.,0-9).$

This BCD to seven segment decoder has four input lines $($A$,$ B$,$ C and D$)$ and $7$ output lines $(a,b,c,d,$ e$,$ f and g $),$ this output is given to seven segment LED display which displays the decimal number depending upon inputs.