| 摘要 |
It is described a broad band digital radio receiver for multicarrier signals, such as for instance TACS or GSM, employing a quadrature demodulator (DEMI/Q) to directly shift in base band the radiofrequency signal. To this purpose, a local oscillator is used, having frequency f0 placed at the centre of the radiofrequency BW band, in order that pairs of channels, symmetric versus f0 are superimposed in the lower base half-band. The equivocation originated in the base band is then solved by second orthogonal demodulators (DEMx/y), of numeric type, which supply pairs of twice demodulated signals that can be grouped in four-equation systems in the four unknown values consisting of the components, in phase and in quadrature, of the two channels of each pair. Subsequent reconstruction networks (RSCOR) solve the relevant systems and give the two components of each single channel for each pair. One (RSBIL) network is foreseen in the receiver, measuring the amplitude and phase dissymmetries in the two branches of the analogue demodulator and supplying four corresponding digital coefficients (a, b, c, d) to the reconstruction network, which is thus able to conunterbalance at output the effect due to dissymmetries.
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