A new low roundoff noise second order digital filter section which is free of constant-input limit cycles

Some second-order digital filter sections which are free of zero-input and constant-input limit cycles have been proposed. In their synthesis, a free parameter is used to equalize the L/sub p/ norms of the transfer functions from the network input to the state variables, thus guaranteeing low output roundoff noise. In this paper, one of those structures is revisited: it is shown how the output roundoff noise varies with the free parameter, suggesting that the norm equalization used is not always the best way to guarantee low roundoff noise. As a result, two new strategies for synthesizing that structure are proposed.