Pulse or digital communications – Receivers – Automatic frequency control
Patent
1998-03-17
1999-11-09
Pham, Chi H.
Pulse or digital communications
Receivers
Automatic frequency control
4551823, 375316, H04L 2706
Patent
active
059828234
ABSTRACT:
A method and a coarse tuning circuit for performing direct frequency selection and down-conversion on a received analog bandpass signal for a digital receiver having C channels are disclosed. Each of the C channels has a bandwidth B. The analog bandpass signal in a channel of interest has a center frequency f.sub.c and a two-sided bandwidth not greater than B. The method comprises the following steps: (a) sampling the bandpass signal at a sampling frequency f.sub.s greater than twice the product of B and C, to produce a digital sampled signal which has an intermediate frequency much closer to the baseband frequency of zero kilohertz than the sampling frequency f.sub.s ; (b) computing, from f.sub.c and f.sub.s, a non-negative integer value m to determine the selection of a channel from the C channels of the digital receiver; and (c) forming directly from the digital sampled signal two digital signals I.sub.1 and Q.sub.1 such that they correspond to a digital in-phase component and a quadrature component, respectively, of a complex signal which is approximately centered at a frequency .DELTA.f proximate of the baseband frequency, and which has a frequency spectrum approximately equal to that of the analog bandpass signal.
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Anderson Terry J.
Bayard Emmanuel
Hoch Jr. Karl J.
Pham Chi H.
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