There is no such rule that you need equal concentrations of base and salt of conjugate acid to make a buffer. A buffer solution is one which resists changes in pH when small quantities of an acid or an alkali are added to it. e.g.
NaOH
Base
⟶Na++
OH⊖
Conjugateacid
pOH=−log[OH−] . . . (i) pH+pOH=14 We know that, pKb=−log[Kb]. . . (ii) Comparing Eq. (i) and (ii), we get [pOH=pKb] So, pOH of the buffer solution is same as p Kb of acid.