Universal digital biquads which are free of limit cycles

Two second-order, multiple-output digital-filter structures are described which realize simultaneously a low-pass, a high-pass, a bandpass, a notch, and an all-pass transfer function. The two structures can be stabilized with respect to limit-cycle oscillations by employing the techniques of magnitude truncation and controlled rounding, and each uses four multipliers and two unit delays. The two structures are attractive for VLSI implementation since each can serve as the basis of a versatile, universal digital-filter chip which can be used for the implementation of Butterworth, Chebyshev, and elliptic digital filters and also for the design of digital equalizers.