Methods for the transfer function design of multiple narrow-band bandpass sigma-delta modulators

This paper presents the design analysis of novel tunable narrow-band bandpass sigma-delta modulators, which can achieve concurrent multiple noise-shaping for multi-tone input signals. Four different design methodologies based on the noise transfer functions of comb filters, slink filters, multi-notch filters and fractional delay comb filters are applied for the design of these multiple-band sigma-delta modulators. The latter approach utilises conventional comb filters in conjunction with FIR, or allpass IIR fractional delay filters, to deliver the desired nulls for the quantisation noise transfer function. Detailed simulation results show that FIR fractional delay comb filter-based sigma-delta modulators tune accurately to most centre frequencies, but suffer from degraded resolution at frequencies close to Nyquist. However, superior accuracies are obtained from their allpass IIR fractional delay counterpart at the expense of a slight shift in noise-shaping bands at very high frequencies. The merits and drawbacks of each technique for the various sigma-delta topologies are assessed in terms of in-band signal-to-noise ratios, accuracy of tunability and coefficient complexity for ease of implementation.

Machiavelli’s Walls: The Legacy of Realism in International Relations Theory

In this paper we argue that Niccolò Machiavelli has little to do with Realism in International Relations theory. By concentrating, as Machaivelli did, on the walls that define political relations—both inside and outside the polity—we find his insights deeply rooted in the specific political contexts of Sixteenth century Italy. Others may wish to generalize from them, but Machiavelli did not. In fact, as we show, Machiavelli was mindful of the difficulties of generalizing about walls and acknowledged the dangers political actors faced in navigating between the internal and external walls of the polity. We examine the geopolitical contours of Machiavelli’s walls and seek to demonstrate how morality is present in these historical spaces. In contrast to Realists, Machiavelli was ready and willing to make ethical judgments. We argue that theorists of international politics should exercise care in reaching for Machiavelli as the iconic thinker for making sense of anarchy in world politics. This article concludes by suggesting that the ideology of Machiavellianism has obscured deeper understanding of the particular contexts of Machiavelli’s own world.