| 摘要 |
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. |
