QPSK and 16 QAM self-generating synchronous direct downconversion demodulator

A system for recovering and demodulating a carrier, comprising:

• a carrier recovery loop receiving the carrier as an input, said carrier recovery loop producing a recovered carrier at a frequency approximately equal to that of the carrier;
• wherein said carrier recovery loop comprises a downconverting mixer, a ×5 multiplier, a ×4 multiplier, and a phase locked loop, and wherein said downconverting mixer receives the carrier as an input, said phase locked loop provides a VCO reference frequency through said ×5 multiplier to said downconverting mixer, said downconverting mixer provides a frequency shifted signal, and said frequency shifted signal is passed through said ×4 multiplier to said phase locked loop;
• and
• a data detector, said data detector receiving the carrier and said recovered carrier as inputs and using said recovered carrier to demodulate the carrier and detect I channel data and Q channel data.

A system for recovering and demodulating a carrier, comprising:

• a carrier recovery loop receiving the carrier as an input, said carrier recovery loop producing a recovered carrier at a frequency approximately equal to that of the carrier;
• wherein said carrier recovery loop comprises a downconverting mixer, a ×5 multiplier, a first ×4 multiplier, and a phase locked loop, and wherein said downconverting mixer receives the carrier as an input, said phase locked loop provides a VCO reference frequency through said ×5 multiplier to said downconverting mixer, said downconverting mixer provides a frequency shifted signal, and said frequency shifted signal is passed through said first ×4 multiplier to said phase locked loop,
• wherein said phase locked loop comprises a phase detector, a loop filter, a VCO, and a second ×4 multiplier, and wherein said VCO provides said VCO reference frequency to said second ×4 multiplier, said second ×4 multiplier produces an upconverted VCO reference frequency to provide said recovered carrier, said phase detector compares an upconverted frequency shifted signal to said upconverted VCO reference frequency and drives said loop filter, and said loop filter provides a control voltage to said VCO, and
• wherein the carrier has a carrier frequency and said frequency shifted signal has a frequency, said frequency of said frequency shifted signal is approximately one quarter said carrier frequency, and said first ×4 multiplier upconverts said frequency shifted signal by a factor of four;
• and said VCO reference frequency is approximately one quarter said carrier frequency, and said ×5 multiplier upconverts said VCO reference frequency by a factor of five;
• a phase adjuster, wherein said recovered carrier is passed through said phase adjuster to provide a phase adjusted recovered carrier, and wherein the carrier and said phase adjusted recovered carrier each have a phase and said phase adjuster matches the phase of said phase adjusted recovered carrier to the phase of the carrier;
• and
• a data detector, said data detector receiving the carrier and said phase adjusted recovered carrier as inputs and using said phase adjusted recovered carrier to demodulate the carrier and detect I channel data and Q channel data,
• wherein said data detector comprises a first mixer, said first mixer using the carrier and said phase adjusted recovered carrier to detect said I channel data, said data detector comprises a second mixer and a phase shifter, said phase adjusted recovered carrier feeding to said second mixer via said phase shifter, and said second mixer using the carrier and said phase adjusted recovered carrier to detect said Q channel data, said data detector comprises a first post detection filter, an output of said first mixer being passed through said first post detection filter to reproduce said I channel data, and said data detector comprises a second post detection filter, an output of said second mixer being passed through said second post detection filter to reproduce said Q channel data.

A method for demodulating a carrier having a carrier frequency, comprising steps of:

• upconverting a VCO reference frequency by a factor of 5 to produce a signal at a frequency of approximately 5/4 times the carrier frequency;
• mixing said signal at a frequency of approximately 5/4 times said carrier frequency with the carrier to down converting the carrier to produce a frequency shifted signal;
• feeding said frequency shifted signal through a multiplier, said muliplier upconverting said frequency shifted signal by a factor of 4, to a phase locked loop;
• using said phase locked loop to produce a recovered carrier, said recovered carrier having a frequency approximately equal to the carrier frequency, and said recovered carrier having a phase;
• adjusting said phase of said recovered carrier to produce a phase adjusted recovered carrier;
• providing the carrier and said phase adjusted recovered carrier to a data detector;
• and
• demodulating the carrier and detecting I channel data and Q channel data using said data detector.

A method for demodulating a carrier having a carrier frequency, comprising steps of:

• downconverting the carrier to produce a frequency shifted signal;
• feeding said frequency shifted signal to a phase locked loop;
• using said phase locked loop to produce a recovered carrier, said recovered carrier having a frequency approximately equal to the carrier frequency, and said recovered carrier having a phase, including steps of:
• detecting a phase of said frequency shifted signal relative to a VCO reference frequency to drive a loop filter to provide a control voltage to a VCO;
• and
• controlling said VCO with said control voltage to provide said VCO reference frequency;
• wherein:
• said frequency shifted signal has a frequency and the carrier has the carrier frequency,
• said frequency of said frequency shifted signal is approximately one quarter the carrier frequency,
• said VCO reference frequency is approximately one quarter the carrier frequency,
• said frequency shifted signal is upconverted to approximately the carrier frequency and said VCO reference frequency is upconverted to approximately the carrier frequency before said step of detecting a phase;
• and wherein said step of downconverting the carrier further comprises steps of:
• upconverting said VCO reference frequency by a factor of five to produce a signal at a frequency of approximately 5/4 times said carrier frequency;
• and
• mixing said signal at a frequency of approximately 5/4 times said carrier frequency with the carrier;
• adjusting said phase of said recovered carrier to produce a phase adjusted recovered carrier;
• providing the carrier and said phase adjusted recovered carrier to a data detector;
• and
• demodulating the carrier and detecting I channel data and Q channel data using said data detector.