Direct digital synthesis of FM signals
AssigneeGeneral Instrument Corporation
InventorQin Zhang
Life of this patent
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Abstract
A digital FM signal generator allows the generation of a modulated FM signal for broadcasting without the need for an analog modulator. The signal generator includes a digital signal processor which receives left and right signals from left and right signal channels and interpolates the signals to create a composite base band signal. The composite base band signal is then used by a numerically controlled oscillator to modulate a digital carrier signal. The result is a digital modulated FM RF signal which is then converted to an analog signal for broadcasting.
Claims5
A digital modulated signal generator comprising:
- a digital signal processor for receiving and processing left and right signal channels to produce a composite base band signal, wherein said digital signal processor comprises a first digital signal processing unit which receives and samples said left and right signals, said first digital processing unit having:
- a base band filter to eliminate cross talk between said left and right signals;
- a pre-emphasis filter receiving an output of said base band filter;
- a sampling speed-up converter receiving an output of said pre-emphasis filter;
- and
- an anti-aliasing filter receiving an output of said sampling speed-up converter, said anti-aliasing filter outputting an interpolated signal;
- and
- a numerically controlled oscillator for receiving said composite base band signal and generating a modulated digitial carrier signal which is modulated in accordance with said composite base band signal.
A method of generating a modulated digital signal comprising the steps of:
- digitally modulating a digitial carrier signal with a numerically controlled oscillator in accordance with a composite base band signal produced by a digital signal processor from left and right signals received from left and right signal channels;
- controlling an SCA error with an SCA error control circuit having:
- a Reed-Solomon encoder;
- an inter-leaver connected to said Reed-Solomon encoder;
- a convolution and differential encoder connected to said inter-leaver;
- a base band shaping unit connected to said convolution and differential encoder;
- an RF unit connected to said base band shaping unit;
- a convolution and differential decoder connected to said RF unit;
- a de-inter-leaver connected to said convolution and differential decoder;
- and
- a Reed-Solomon decoder connected to said de-inter-leaver;
- and
- modulating a sub-carrier with SCA data with said digital signal processor which receives an input signal containing said SCA data.
Dependencies are inferred from the claim text.