Browse Prior Art Database

Phase Correction for Dual Modulation of a Phase Locked Loop Oscillator

IP.com Disclosure Number: IPCOM000117912D
Original Publication Date: 1996-Jul-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 41K

Publishing Venue

IBM

Related People

Camp Jr, WO: AUTHOR [+2]

Abstract

It is a well known problem that any attempt to frequency modulate an oscillator that is embedded in a phase locked loop, will lose the modulation frequency components from the modulated spectrum that are lower in frequency than the cutoff frequency of the loop lowpass filter. It is also a well known solution to this problem to simultaneously modulate the reference oscillator of the phase locked loop system with just those modulation frequency components that would ordinarily be removed by the loop.

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Phase Correction for Dual Modulation of a Phase Locked Loop Oscillator

      It is a well known problem that any attempt to frequency
modulate an oscillator that is embedded in a phase locked loop, will
lose the modulation frequency components from the modulated spectrum
that are lower in frequency than the cutoff frequency of the loop
lowpass filter.  It is also a well known solution to this problem to
simultaneously modulate the reference oscillator of the phase locked
loop system with just those modulation frequency components that
would ordinarily be removed by the loop.  Schematically the prior art
solution looks like:
  MODULATION ----+----> Voltage-controlled ------+---> OUTPUT
                 |           Oscillator           |
                 |               |                |
                 |        Phase-locked Loop <------
             Amplitude           |
              Adjust             |
                 |-----> Reference Oscillator

      This disclosure addresses the problem that the modulation
signal can be slightly out of phase between the points that it is
injected into the system.  Ordinarily, this does not cause any
problem as in a voice system of a digital system with only two levels
of data.  However, for digital systems with more bits per baud and/or
more intersymbol i...