| 摘要 |
A system (10) and method are provided in which a phase modulation generator (12) is used to modulate the output signal of a DDS (18) with a modulation index, h/N. The phase-modulated DDS output drives a PLL (26), which is an upconversion stage for a radio transmitter, with the modulated DDS signal as the PLL's (26) reference. The output of the PLL (26) will have a modulation index of h. Consequently, the frequency band of the DDS (18) output is significantly narrower than the frequency band of upconversion stages used in conventional transmitters, and there are significantly less spurious emissions in the transmitted signal. However, a transmitter employing the present phasemodulated DDS-driven PLL topology can still transmit over a relatively wide frequency band.
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