A universal, second-order, digital-filter structure is proposed, which realises simultaneously a lowpass, a highpass, a bandpass, a notch and allpass transfer function. The structure uses two unit-delays and four multipliers, and is quite attractive for VLSI implementation since a versatile universal chip can be fabricated, which can be used for the implementation of Butterworth, Cheby̅shev and elliptic digital filters as well as digital equalisers.