Waveform modulation and demodulation methods and apparatus

An apparatus for modulating a reference signal having a frequency with a modulation signal comprising:

• means for receiving the reference signal to the apparatus;
• means for receiving the modulation signal to the apparatus, wherein the means for receiving the modulation signal includes means for limiting the peak to peak voltage of the modulation signal to less than the peak to peak voltage of the reference signal;
• and
• a waveform modulator cell receiving both the reference signal and the modulation signal and generating a waveform modulated output signal centered at a frequency twice that of said reference frequency, the modulator cell having a voltage to current transfer curve that is linear in a first region and non-linear in at least a second region.

A circuit for modulating a subcarrier with a modulation signal, the circuit comprising a cell including

• a resistive branch;
• and
• a second and third branch both coupled in parallel to the first branch, wherein current flow in the second and third branches being substantially antiparallel and the current voltage transfer characteristics in the second and third branches being non-linear beyond a certain magnitude range and
• a differential amplifier coupled across the branches to provide a single ended output.

A method for modulating a subcarrier having a frequency with a modulation signal to thereby provide an output at a different carrier frequency, the method comprising:

• supplying a modulator cell, having two nodes and a non-linear characteristic current voltage transfer curve that is symmetric about the current axis and circuit elements having a conduction threshold voltage and the subcarrier has a peak to peak amplitude;
• coupling the subcarrier to a first node wherein the step of coupling the subcarrier to the first node includes limiting the peak to peak voltage to a range between 1.5 to 5 times the magnitude of the threshold voltage;
• coupling the modulation signal to the second node;
• and
• coupling the second node to the output.

A communications method for transmitting an output signal bearing a frequency relationship to a supplied subcarrier with information based upon a modulation signal, the method comprising:

• adding a signal proportional to the modulation signal to the subcarrier signal to produce a sum;
• multiplying the sum by a signal proportional to the square of the subcarrier signal;
• bandpass filtering to obtain the output signal in a frequency band selected based upon the frequency relationship;
• transmitting the output of the bandpass filter over a medium;
• receiving the transmitted output;
• and
• demodulating the transmitted output.