Modulation systems and methods that compensate for DC offset introduced by the digital-to-analog converter and/or the low pass filter thereof
First Claim
1. A modulation system for a digital input signal, comprising:
- a digital-to-analog converter that converts the digital input 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 carrier; and
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 by subtracting from the digital input signal, a digital value representing 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.
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Accused Products
Abstract
Modulation systems and methods compensate for the DC offset that is introduced by the digital-to-analog converter and/or the low pass filter thereof. Compensation is preferably provided in the digital domain, to thereby reduce DC offset within acceptable limits for the modulation that is being used. More preferably, compensation is provided by subtracting from the digital input signal, a digital value representing the DC offset in the filtered analog signal that is introduced by the digital-to-analog converter and/or the low pass filter. A sensor senses the DC offset in the filtered analog signal. An analog-to-digital converter is responsive to the sensor to convert the sensed DC offset into a digital offset signal. A subtractor is responsive to the analog-to-digital converter to subtract the digital DC offset signal from the digital input signal and to apply the digital input signal minus the DC offset signal, to the digital-to-analog converter.
50 Citations
39 Claims
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1. A modulation system for a digital input signal, comprising:
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a digital-to-analog converter that converts the digital input 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 carrier; and 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 by subtracting from the digital input signal, a digital value representing 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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A modulation system for a digital input signal, comprising:
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means for converting the digital input signal into 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 filtered analog signal onto a carrier; and 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 by subtracting from the digital input signal, a digital value representing 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. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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27. A modulation method for a digital input signal, comprising the steps of:
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converting the 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; and 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 by subtracting from the digital input signal, a digital value representing the DC offset in the filtered analog signal that is introduced by the at least one of the converting and low pass filtering steps. - View Dependent Claims (28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39)
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Specification