A 7 segment display uses 7 LEDs to display decimal numbers from 0 to 9. It has either a common anode or common cathode configuration. A 7 segment decoder takes a 4-bit binary coded decimal input and outputs a 7-bit code that illuminates the correct LED segments to display that decimal number. For example, the input 0000 would output 1111110 to display the number 0. The decoder operates based on a truth table to map each input to the proper 7-bit segment output.

1. 7 Segment Decoder

2. Seven Segment Display

3. Seven Segment Display
• 7 LEDs (light emitting diodes), each one
controlled by an input
• Two types
– Common Anode
– Common Cathode

6. Seven Segment Decoder
• Input is a 4-bit BCD code  4 inputs (A, B, C,
D)
• Output is a 7-bit code (a,b,c,d,e,f,g) that
allows for the decimal equivalent to be
displayed
• Example:
– Input: 0000BCD
– Output: 1111110
(a=b=c=d=e=f=1, g=0)
d
a
b
ce
f g

7. Truth Table for 7 Segment Decoder

8. Expression for segment g

9. Classworks
• Find expression for segments a,b,c,d,e and f

13. Classworks
• Design seven segment decoder circuit to
display 1
• Design seven segment decoder circuit to
display 7