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Browse Prior Art Database

Modulation Shaping in a Phase Shift Oscillator

IP.com Disclosure Number: IPCOM000117906D
Original Publication Date: 1996-Jul-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Camp Jr, WO: AUTHOR

Abstract

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.

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This is the abbreviated version, containing approximately 61% of the total text.

Modulation Shaping in a Phase Shift Oscillator

      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.

      However, there can be cases when the baseband spectrum cannot
be filtered as much as necessary to achieve a prescribed spectral
mask.  For the cases where this is true and the spectral mask is
being exceeded only by a single sidelobe, the following circuit can
be used to reduce the single sidelobe level only and not affect the
rest of the baseband response.  The example is for the case of a BPSK
modulation where the Q port has a DC level on it and the I port has a
single ended modulation signal.
  Modulation --> Lowpass ---------------------> I port vector
modulator
   (0,1)        ...