Dual-mode modulation systems and methods including oversampling of narrow bandwidth signals and DC offset compensation

A dual-mode modulation system comprising:

• means for sampling an applied signal;
• means for converting the sampled signal to an analog signal;
• means for low pass filtering the analog signal to produce a filtered analog signal, at least one of the means for converting and the means for low pass filtering introducing DC offset into the filtered analog signal;
• means for modulating the low pass filtered analog signal onto a carrier;
• means for compensating for the DC offset in the filtered analog signal that is introduced by the at least one of the means for converting and the means for low pass filtering;
• means for applying a first signal to the sampling means to thereby modulate the first signal on a carrier using the sampling means, the converting means and the low pass filtering means, and for applying a second signal of narrower bandwidth than the first signal to the sampling means to thereby sample the second signal and modulate the second signal on a carrier using the sampling means, the converting means and the low pass filtering means;
• and
• wherein the means for compensating further comprises:
• means for sensing the DC offset in the filtered analog signal;
• means for converting the sensed DC offset into a digital DC offset signal;
• means for subtracting the digital DC offset signal from the sampled signal, and for applying the sampled signal less the DC offset signal to the means for converting the digital input signal into an analog signal;
• and
• means for intermittently latching the digital DC offset signal, and for applying the latched digital DC offset signal to the means for subtracting, such that the latched digital DC offset signal is subtracted from the sampled signal.

A dual-mode modulation system comprising:

• means for sampling an applied signal;
• means for converting the sampled signal to an analog signal;
• means for low pass filtering the analog signal to produce a filtered analog signal, at least one of the means for converting and the means for low pass filtering introducing DC offset into the filtered analog signal;
• means for modulating the low pass filtered analog signal onto a carrier;
• means for compensating for the DC offset in the filtered analog signal that is introduced by the at least one of the means for converting and the means for low pass filtering;
• means for applying a first signal to the sampling means to thereby modulate the first signal on a carrier using the sampling means, the converting means and the low pass filtering means, and for applying a second signal of narrower bandwidth than the first signal to the sampling means to thereby sample the second signal and modulate the second signal on a carrier using the sampling means, the converting means and the low pass filtering means;
• and
• wherein the means for compensating further comprises:
• means for sensing the DC offset in the filtered analog signal;
• means for converting the sensed DC offset into a digital DC offset signal;
• means for subtracting the digital DC offset signal from the sampled signal, and for applying the sampled signal less the DC offset signal to the means for converting the digital input signal into an analog signal;
• and
• means for periodically inverting the polarity of the sensed DC offset and for applying the polarity inverted sensed DC offset to the means for converting the sensed DC offset in a digital DC offset signal.

A dual-mode radiotelephone comprising:

• means for sampling an applied signal;
• means for converting the sampled signal to an analog signal;
• means for low pass filtering the analog signal to produce a filtered analog signal, at least one of the means for converting and the means for low pass filtering introducing DC offset into the filtered analog signal;
• means for modulating the low pass filtered analog signal onto a radiotelephone carrier;
• means for compensating for the DC offset in the filtered analog signal that is introduced by the at least one of the means for converting and the means for low pass filtering;
• means for generating a first radiotelephone signal and a second radiotelephone signal of narrower bandwidth than the first radiotelephone signal;
• means for applying the first radiotelephone signal to the sampling means to thereby modulate the first radiotelephone signal on a carrier using the sampling means, the converting means and the low pass filtering means, and for applying the second radiotelephone signal of narrower bandwidth than the first radiotelephone signal to the sampling means to thereby sample the second radiotelephone signal and modulate the second radiotelephone signal on a carrier using the sampling means, the converting means and the low pass filtering means;
• and
• wherein the means for compensating further comprises:
• means for sensing the DC offset in the filtered analog signal;
• means for converting the sensed DC offset into a digital DC offset signal;
• means for subtracting the digital DC offset signal from the sampled signal, and for applying the sampled signal less the DC offset signal to the means for converting the digital input signal into an analog signal;
• and
• means for scaling the digital DC offset signal into a scaled digital DC offset signal;
• the means for subtracting being responsive to the means for scaling, to subtract the scaled digital DC offset signal from the sampled signal.

A dual-mode radiotelephone comprising:

• means for sampling an applied signal;
• means for converting the sampled signal to an analog signal;
• means for low pass filtering the analog signal to produce a filtered analog signal, at least one of the means for converting and the means for low pass filtering introducing DC offset into the filtered analog signal;
• means for modulating the low pass filtered analog signal onto a radiotelephone carrier;
• means for compensating for the DC offset in the filtered analog signal that is introduced by the at least one of the means for converting and the means for low pass filtering;
• means for generating a first radiotelephone signal and a second radiotelephone signal of narrower bandwidth than the first radiotelephone signal;
• means for applying the first radiotelephone signal to the sampling means to thereby modulate the first radiotelephone signal on a carrier using the sampling means, the converting means and the low pass filtering means, and for applying the second radiotelephone signal of narrower bandwidth than the first radiotelephone signal to the sampling means to thereby sample the second radiotelephone signal and modulate the second radiotelephone signal on a carrier using the sampling means, the converting means and the low pass filtering means;
• and
• wherein the means for compensating further comprises:
• means for sensing the DC offset in the filtered analog signal;
• means for converting the sensed DC offset into a digital DC offset signal;
• means for subtracting the digital DC offset signal from the sampled signal, and for applying the sampled signal less the DC offset signal to the means for converting the digital input signal into an analog signal;
• and
• means for intermittently latching the digital DC offset signal, and for applying the latched digital DC offset signal to the means for subtracting, such that the latched digital DC offset signal is subtracted from the sampled signal.

A dual-mode radiotelephone comprising:

• means for sampling an applied signal;
• means for converting the sampled signal to an analog signal;
• means for low pass filtering the analog signal to produce a filtered analog signal, at least one of the means for converting and the means for low pass filtering introducing DC offset into the filtered analog signal;
• means for modulating the low pass filtered analog signal onto a radiotelephone carrier;
• means for compensating for the DC offset in the filtered analog signal that is introduced by the at least one of the means for converting and the means for low pass filtering;
• means for generating a first radiotelephone signal and a second radiotelephone signal of narrower bandwidth than the first radiotelephone signal;
• means for applying the first radiotelephone signal to the sampling means to thereby modulate the first radiotelephone signal on a carrier using the sampling means, the converting means and the low pass filtering means, and for applying the second radiotelephone signal of narrower bandwidth than the first radiotelephone signal to the sampling means to thereby sample the second radiotelephone signal and modulate the second radiotelephone signal on a carrier using the sampling means, the converting means and the low pass filtering means;
• and
• wherein the compensating means further comprises:
• means for sensing the DC offset in the filtered analog signal;
• means for converting the sensed DC offset into a digital DC offset signal;
• means for subtracting the digital DC offset signal from the sampled signal, and for applying the sampled signal less the DC offset signal to the means for converting the digital input signal into an analog signal;
• and
• means for periodically inverting the polarity of the sensed DC offset and for applying the polarity inverted sensed DC offset to the means for converting the sensed DC offset in a digital DC offset signal.

A dual-mode radiotelephone comprising:

• a sampler that samples an applied signal;
• a digital-to-analog converter that converts the sampled signal into an analog signal;
• a low pass filter that filters the analog signal to produce a filtered analog signal, at least one of the digital-to-analog converter and the low pass filter introducing DC offset into the filtered analog signal;
• a modulator that modulates the filtered analog signal onto a radiotelephone carrier;
• a DC offset compensator that compensates for the DC offset in the filtered analog signal that is introduced by the at least one of the digital-to-analog converter and the low pass filter;
• a circuit that generates a first radiotelephone signal and a second radiotelephone signal of narrower bandwidth than the first radiotelephone signal, that applies the first radiotelephone signal to the sampler to thereby modulate the first radiotelephone signal on a carrier using the sampler, the digital-to-analog converter and the low pass filter, and that applies the second radiotelephone signal of narrower bandwidth than the first radiotelephone signal to the sampler, to thereby sample the second radiotelephone signal and modulate the second radiotelephone signal on a carrier using the sampler, the digital-to-analog converter and the low pass filter;
• wherein the DC offset compensator comprises:
• a sensor that senses the DC offset in the filtered analog signal;
• an analog-to-digital converter that is responsive to the sensor to convert the sensed DC offset into a digital DC offset signal;
• a subtractor that is responsive to the analog-to-digital converter to subtract the digital DC offset signal from the sampled signal, and to apply the sampled signal less the DC offset signal, to the digital-to-analog converter;
• and
• a scaler that is responsive to the analog-to-digital converter to scale the digital DC offset signal into a scaled digital DC offset signal;
• the subtractor being responsive to the scaler to subtract the scaled digital DC offset signal from the sampled signal.

A dual-mode radiotelephone comprising:

• a sampler that samples an applied signal;
• a digital-to-analog converter that converts the sampled signal into an analog signal;
• a low pass filter that filters the analog signal to produce a filtered analog signal, at least one of the digital-to-analog converter and the low pass filter introducing DC offset into the filtered analog signal;
• a modulator that modulates the filtered analog signal onto a radiotelephone carrier;
• a DC offset compensator that compensates for the DC offset in the filtered analog signal that is introduced by the at least one of the digital-to-analog converter and the low pass filter;
• a circuit that generates a first radiotelephone signal and a second radiotelephone signal of narrower bandwidth than the first radiotelephone signal, that applies the first radiotelephone signal to the sampler to thereby modulate the first radiotelephone signal on a carrier using the sampler, the digital-to-analog converter and the low pass filter, and that applies the second radiotelephone signal of narrower bandwidth than the first radiotelephone signal to the sampler, to thereby sample the second radiotelephone signal and modulate the second radiotelephone signal on a carrier using the sampler, the digital-to-analog converter and the low pass filter;
• wherein the DC offset compensator comprises:
• a sensor that senses the DC offset in the filtered analog signal;
• an analog-to-digital converter that is responsive to the sensor to convert the sensed DC offset into a digital DC offset signal;
• a subtractor that is responsive to the analog-to-digital converter to subtract the digital DC offset signal from the sampled signal, and to apply the sampled signal less the DC offset signal, to the digital-to-analog converter;
• and
• a latch that is responsive to the analog-to-digital converter to intermittently latch the digital DC offset signal, and to apply the latched digital DC offset signal to the subtractor, such that the latched digital DC offset signal is subtracted from the sampled signal.

A dual-mode radiotelephone comprising:

• a sampler that samples an applied signal;
• a digital-to-analog converter that converts the sampled signal into an analog signal;
• a low pass filter that filters the analog signal to produce a filtered analog signal, at least one of the digital-to-analog converter and the low pass filter introducing DC offset into the filtered analog signal;
• a modulator that modulates the filtered analog signal onto a radiotelephone carrier;
• a DC offset compensator that compensates for the DC offset in the filtered analog signal that is introduced by the at least one of the digital-to-analog converter and the low pass filter;
• a circuit that generates a first radiotelephone signal and a second radiotelephone signal of narrower bandwidth than the first radiotelephone signal, that applies the first radiotelephone signal to the sampler to thereby modulate the first radiotelephone signal on a carrier using the sampler, the digital-to-analog converter and the low pass filter, and that applies the second radiotelephone signal of narrower bandwidth than the first radiotelephone signal to the sampler, to thereby sample the second radiotelephone signal and modulate the second radiotelephone signal on a carrier using the sampler, the digital-to-analog converter and the low pass filter;
• wherein the DC offset compensator comprises:
• a sensor that senses the DC offset in the filtered analog signal;
• an analog-to-digital converter that is responsive to the sensor to convert the sensed DC offset into a digital DC offset signal;
• a subtractor that is responsive to the analog-to-digital converter to subtract the digital DC offset signal from the sampled signal, and to apply the sampled signal less the DC offset signal, to the digital-to-analog converter;
• and
• a polarity inverter that is responsive to the sensor to periodically invert the polarity of the sensed DC offset and to apply the polarity inverted sensed DC offset to the analog-to-digital converter, the analog-to-digital converter converting the periodically polarity inverted sensed DC offset signal into the digital offset signal.

A dual-mode modulation method for a first digital input signal and a second digital input signal having narrower bandwidth than the first digital input signal, comprising the steps of:

• oversampling the second digital input signal;
• converting the first digital input signal and the oversampled second digital input signal into an analog signal;
• low pass filtering the analog signal to produce a filtered analog signal, at least one of the converting and low pass filtering steps introducing DC offset into the filtered analog signal;
• modulating the filtered analog signal onto a carrier;
• compensating for the DC offset in the filtered analog signal that is introduced by the at least one of the converting and low pass filtering steps;
• wherein the compensating step comprises the steps of:
• sensing the DC offset in the filtered analog signal;
• converting the sensed DC offset into a digital DC offset signal;
• subtracting the digital DC offset signal from the first and second oversampled digital input signals;
• and
• scaling the digital DC offset signal into a scaled digital DC offset signal.

A dual-mode modulation method for a first digital input signal and a second digital input signal having narrower bandwidth than the first digital input signal, comprising the steps of:

• oversampling the second digital input signal;
• converting the first digital input signal and the oversampled second digital input signal into an analog signal;
• low pass filtering the analog signal to produce a filtered analog signal, at least one of the converting and low pass filtering steps introducing DC offset into the filtered analog signal;
• modulating the filtered analog signal onto a carrier;
• compensating for the DC offset in the filtered analog signal that is introduced by the at least one of the converting and low pass filtering steps;
• wherein the compensating step comprises the steps of:
• sensing the DC offset in the filtered analog signal;
• converting the sensed DC offset into a digital DC offset signal;
• subtracting the digital DC offset signal from the first and second oversampled digital input signals;
• and
• intermittently latching the digital DC offset signal.

A dual-mode modulation method for a first digital input signal and a second digital input signal having narrower bandwidth than the first digital input signal, comprising the steps of:

• oversampling the second digital input signal;
• converting the first digital input signal and the oversampled second digital input signal into an analog signal;
• low pass filtering the analog signal to produce a filtered analog signal, at least one of the converting and low pass filtering steps introducing DC offset into the filtered analog signal;
• modulating the filtered analog signal onto a carrier;
• compensating for the DC offset in the filtered analog signal that is introduced by the at least one of the converting and low pass filtering steps;
• wherein the compensating step comprises the steps of:
• sensing the DC offset in the filtered analog signal;
• converting the sensed DC offset into a digital DC offset signal;
• subtracting the digital DC offset signal from the first and second oversampled digital input signals;
• and
• periodically inverting the polarity of the sensed DC offset.