Sigma-Delta Modulator with Tunable Signal Passband
Patent, Filed 31 Jan 95, patented 7 Apr 98
DEPARTMENT OF THE NAVY WASHINGTON DC
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A band-pass sigma-delta modulator includes a translator for tuning to a selected signal passband within the tuning range of the modulator. In a network implementation, the translator is integral with each integrator associated with the sigma-delta modulators. The translator can comprise a network having a transfer function defined in the Z-domain as Zalpha-1Z-alpha, where -1 less than or equal alpha less than or equal 1 defines the tuning. The value of alpha is defined as alpha equivalent cos2pifgmfs, where fgm is the geometric mean frequency of the passband and fs is the input sample frequency of the sigma-delta modulators. The invention can benefit many signal processing applications such as, for example. AD, DA and DD converters and digital communication systems including digital radio and digital TV. In digital communications e.g., radio, TV, etc., the invention can be used where it is desirable to digitize the full tuning range or bandwidth of a receiver at an intermediate frequency early in the processing chain, thus allowing digital tuning or mixing of the desired signal. Such digital mixing or tuning overcomes the limitations of analog mixersreceivers, for example limited linearity in dynamic range as well as the problems associated with aliasing, artifacts, ghosts, harmonics, distortion, gain and phase mismatch, etc. The sigma-delta modulator of the invention also provides variable bandwidth, is operationally stable and is easily and inexpensively realized.
- Electrical and Electronic Equipment