| 摘要 |
Out-of-channel intermodulation distortion in a combined analog and digital television (DTV) signal is corrected using a circuit preferably operating at intermediate frequency (IF). The circuit provides out-of DTV-channel suppression of DTV intermodulation components in a way that better protects an analog (for example, NTSC) signal in an immediately-adjacent channel at radio frequency (RF). When adjacent-channel DTV and analog television signals are amplified by a single, high-power amplifier, the intermodulation corrector circuit suppresses the out-of-DTV-channel DTV intermodulation products to below the threshold of visibility (TOV) of the analog channel viewer. In particular, an exemplary circuit has a first mixer receiving the input DTV signal at both inputs. A second mixer receives the first mixer's output and the input DTV signal, and provides a broadband intermodulation cancellation signal. Finally, the input DTV signal is delayed in time so that it is aligned with a phase-and amplitude-adjusted cancellation signal, and then is combined with it (such as by summing) so as to provide a corrected DTV signal that provides for substantial elimination of the out-of-band intermodulation distortion at the RF output of the transmitter.
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