| 摘要 |
<p>The present invention provides a digital radio frequency (RF) modulator for providing modulation for base-band TV signals. The RF modulator provides direct conversion of digital base-band audio and video signals to a desired RF channel frequency, without any analogue up conversion. The RF modulator in the present invention includes an audio module, a video module, and a RF converter. The audio module includes a pre-emphasis filter, a multi-stage audio interpolator and a complex frequency modulator to generate frequency modulated (FM) audio signals. The video module includes a complex VSB filter, a group-delay compensation filter and some processing logic to generate a filtered output video signal. The RF converter includes a complex adder, a complex multiplier and a RF interpolator to construct the base band TV signals and to shift the base band TV signals in a frequency domain to the desired RF channel frequency. The exponential video carrier is generated at baseband and has a frequency whose value is in the range of +/-13.5MHz. The RF interpolator includes a zero pad logic followed by a quadrature band pass filter (BPF), and an optional second stage of another zero-pad logic followed by a real band pass filter (BPF). The second stage is optional in the sense that it is required only if the desired RF channel is in the higher VHF band.
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