| 摘要 |
An RF tuner and tuning method employs analog quadrature mixing with a coarse-stepwise tunable local oscillator to a near-baseband passband region, followed by A/D conversion of the I and Q signals, correction of phase, group delay, and amplitude errors, image rejection, and translation to baseband by (1) fixed frequency translation, (2) stepwise channelized translation, or (3) essentially continuously variable tuning over a given digital tuning range. The near-baseband passband region is sized and located such that alternating image rejection provides non-redundant and complete tuning coverage of a desired high frequency spectrum with a local oscillator step size equal to about twice the digital tuning range or about twice the number of channels digitally stepwise tunable times the channel width, effectively doubling the typical local oscillator step size. The digital tuning is preferably performed by a continuously variable bandpass decimating filter with aliasing to within RD of baseband, where RD is the filter's out put sampling rate, followed by fine-shifting to baseband by digital complex mixing. Demodulation is then accomplished according to signal type. Image rejection and phase error and gain correction are preferably performed with a modified type III Hilbert transform pair with 90 DEG +/-CF phase change and variable gain. The near-baseband passband is preferably centered at R/4 where R is the sampling rate entering the Hilbert transform.
|
