Modulation Shaping in a Phase Shift Oscillator
Original Publication Date: 1996-Jul-01
Included in the Prior Art Database: 2005-Mar-31
This invention applies to the particular spectrum requirements imposed by the FCC in 2.400-2.483 GHz ISM band. They require that the spectrum of the transmitted signal be greater than 20 dB down (relative to the power at the carrier frequency) for frequency components greater than plus or minus 0.5 MHz from the carrier frequency. This is currently achieved by a variety of means. If a vector modulator is used to modulate the carrier, one way to meet this spectral requirement is to lowpass filter the baseband modulation signals going to the I and Q modulation ports of the modulator. The lowpass filtered baseband spectrum, with its rapid rolloff in frequency response, then is upconverted by the vector modulator and the resulting spectrum mirrors that of the baseband spectrum but now on both sides of the carrier.