Modulator having direct digital synthesis for broadband RF transmission
First Claim
1. An RF modulator for reverse channel baseband to RF frequency translation in a CATV cable data transmission system comprisingmeans;
- for receiving and digitally sampling an input data stream and providing a sampled digital data stream,digital mixer means including a digitally tunable oscillator for receiving said sampled digital data stream and providing a digital RF data stream in selected frequency bands, said mixer means including in-phase and quadrature phase mixers and a numerically controlled oscillator driven by a 100 MHz clock for modulating said in-phase and quadrature phase digital data stream to a selected RF frequency band in the range of 5-40 MHz, and an adder for combining said in-phase and quadrature phase digital data streams.
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Abstract
A modulator for data transmitted in a reverse channel or upstream spectrum in a cable transmission system requires a single frequency translation from baseband to a selected RF channel, thus eliminating conventional intermediate frequency (IF) translation. The modulator requires fewer components than the conventional modulator while eliminating nonlinearity, noise, and delay introduced by the IF upconversion. In a preferred embodiment, the modulator includes a serial to parallel differential quadrature phase shift keying encoder with transversal FIR filters and interpolation filters connecting the phase shift keyed data to a single mixer stage for directly translating the baseband signal to an RF (e.g., 5-40 MHz) channel spectrum.
176 Citations
5 Claims
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1. An RF modulator for reverse channel baseband to RF frequency translation in a CATV cable data transmission system comprising
means; - for receiving and digitally sampling an input data stream and providing a sampled digital data stream,
digital mixer means including a digitally tunable oscillator for receiving said sampled digital data stream and providing a digital RF data stream in selected frequency bands, said mixer means including in-phase and quadrature phase mixers and a numerically controlled oscillator driven by a 100 MHz clock for modulating said in-phase and quadrature phase digital data stream to a selected RF frequency band in the range of 5-40 MHz, and an adder for combining said in-phase and quadrature phase digital data streams. - View Dependent Claims (2, 3, 4, 5)
- for receiving and digitally sampling an input data stream and providing a sampled digital data stream,
Specification