A COMPARISON OF ANALOG AND DIGITAL CIRCUIT IMPLEMENTATIONS OF LOW-POWER MATCHED-FILTERS FOR USE IN PORTABLE WIRELESS COMMUNICATION TERMINALS

The types of circuits in which analog design techniques are employed t ypically differ from those in which digital design methods are used, w ith analog circuits being commonly applied to high speed, low precisio n functional blocks such as mixers and RF modulators, while digital ci rcuits are chosen for high precision, high complexity blocks that oper ate at frequencies well below the f(T) of the transistors from which t he circuits are comprised. Yet there still exist applications for whic h the superior circuit implementation-analog or digital-is unclear, Th e recent birth of commercial interest in spread-spectrum communication s provides the motivation for investigating one such application, that of the parallel programmable matched filter, In this paper, analog an d digital circuit realizations of a parallel programmable matched filt er are examined, Through wide variations of the design spare parameter s, the general trend that is observed is that short, fast circuits ten d to favor an analog implementation, while longer, slower circuits mak e a digital implementation more appropriate, A methodology is provided for choosing the preferable circuit-implementing technology when powe r consumption-as a function of data precision, filter length, operatin g frequency, technology scaling, and the maturity of the fabrication p rocess-is used as the primary metric of comparison, It is shown that n either the analog nor the digital matched filter implementation is uni versally more power efficient than the other, Rather, a surface is map ped in the multidimensional design space where, on one side of this su rface, a digital solution is preferable, while on the other side of th e surface, an analog circuit is appropriate, Equations are given which delineate the position of this transitional surface in terms of the d esign space parameters, and example calculations and plots depicting t he regions of dominance for the digital and analog matched filters for specific process and system parameters are presented.