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Digital modulators for use with sub-nyquist sampling of raster- scanned samples of image intensity
Digital modulators for use with sub-nyquist sampling of raster- scanned samples of image intensity
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机译:数字调制器,用于对图像强度的光栅扫描样本进行亚奈奎斯特采样
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摘要
Apparatus useful in electronics for the tape recording of a video signal, which is a baseband signal of a prescribed bandwidth extending up to a prescribed maximum frequency, processes the video signal to generate a folded-spectrum video signal. The video signal is digitized and supplied to a digital band-splitting filter with a cross- over frequency at one-half said prescribed maximum frequency, for separating the digitized video signal into samples of a lower-frequency- band component and into samples of a higher-frequency-band component. A balanced modulator is connected for modulating a folding carrier wave of the prescribed maximum frequency, which modulation is done in accordance with the higher-frequency-band component to generate a balanced modulation signal; and the balanced modulation signal is linearly combined with the lower-frequency-band component to generate the folded- spectrum video signal. Preferably, the sampling rate of the digitized video signal is exactly the Nyquist rate of the prescribed maximum frequency, reduces the balanced modulation of a suitably phased folding carrier wave to multiplication of successive samples of the modulating signal alternately by plus one and by minus one. Such multiplications are done without having to use a digital multiplier.
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