3位二进制数B2B1B0的范围为000B~111B, 即为0D~7D, 则Y=2B的范围为0D~14D, 即为0000B~1110B, 所以需要4位二进制数来表示输出. 设四位输出Y=Y3Y2Y1Y0.
根据Y=2B的关系绘制真值表.
| B2 | B1 | B0 | Y3 | Y2 | Y1 | Y0 |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 1 | 0 | 0 | 1 | 0 |
| 0 | 1 | 0 | 0 | 1 | 0 | 0 |
| 0 | 1 | 1 | 0 | 1 | 1 | 0 |
| 1 | 0 | 0 | 1 | 0 | 0 | 0 |
| 1 | 0 | 1 | 1 | 0 | 0 | 1 |
| 1 | 1 | 0 | 1 | 1 | 0 | 0 |
| 1 | 1 | 1 | 1 | 1 | 1 | 0 |
由真值表得到下列逻辑表达式
Y3=B2, Y2=B1, Y1=B2'B0+B1B0, Y0=B2B1'B0.
由上述分析, 绘制出电路的原理图.