Zero intermediate frequency receiver
First Claim
1. A zero intermediate frequency radio receiver for recovering modulation information from received frequency or phase modulated signals, comprising:
- mixing means which mix the received signals with at least one local oscillator to produce in-phase and quadrature analogue baseband signals,analogue to digitial (A/D) means coupled to the mixing means, which convert the analogue baseband signals into digital baseband signals.demodulation means coupled to the A/D means, which digitally demodulate and filter the digital baseband signals to produce digital modulation information,carrier tracking means, which adjusts the mixing means to maintain the analogue baseband signals at a centre frequency of substantially zero hertz, andcarrier nulling means, which adjusts the mixing means to substantially minimise signal strength at the centre frequency of the analogue baseband signals.
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Accused Products
Abstract
A zero intermediate frequency radio receiver that comprises mixing stages, an A to D converter, a digital demodulator, a carrier tracking system and a carrier nulling system is disclosed. The mixing stages receive FM or PM signals and produce analogue in-phase and quadrature baseband signal which are in turn converted to digital baseband signals by the A to D convertor. DC offsets in the baseband signals are removed by high pass filtering prior to demodulation. Tracking enables the baseband signals to be maintained at a centre frequency of substantially zero hertz, while signal strength at this frequency is minimized or mulled before the DC offset filtering. Information which might otherwise be removed by the filtering is thereby retained in the baseband signals, which are relatively less distorted.
206 Citations
12 Claims
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1. A zero intermediate frequency radio receiver for recovering modulation information from received frequency or phase modulated signals, comprising:
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mixing means which mix the received signals with at least one local oscillator to produce in-phase and quadrature analogue baseband signals, analogue to digitial (A/D) means coupled to the mixing means, which convert the analogue baseband signals into digital baseband signals. demodulation means coupled to the A/D means, which digitally demodulate and filter the digital baseband signals to produce digital modulation information, carrier tracking means, which adjusts the mixing means to maintain the analogue baseband signals at a centre frequency of substantially zero hertz, and carrier nulling means, which adjusts the mixing means to substantially minimise signal strength at the centre frequency of the analogue baseband signals. - View Dependent Claims (2, 3, 4, 5)
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6. A method for receiving frequency or phase modulated signals and recovering modulation information, comprising;
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mixing the received signals with at least one local oscillator to produce in-phase and quadrature baseband signals, converting the analogue baseband signals into digital baseband signals, demodulating the digital baseband signals to produce digital modulation information, adjusting the mixing means to maintain the analogue baseband signals at a centre frequency of substantially zero hertz, and adjusting the mixing means to substantially minimise signal strength at the centre frequency of the analougue baseband signals. - View Dependent Claims (7, 8, 9)
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10. A method for receiving frequency or phase modulated signals and recovering modulation information, the method comprising the steps of:
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mixing the received signals with at least one local oscillator to produce in-phase and quadrature baseband analog signals; converting the analog baseband signals into digital baseband signals; adjusting the mixed signals to maintain the analog baseband signals at a center frequency of substantially zero Hertz; adjusting the mixed signals to substantially minimize signal strength at the center frequency of the analog baseband signals; generating an additional signal which modulates the mixed signals and thereby minimizes signal strength at the center frequency; demodulating the digital baseband signals to produce digital modulation information; and removing the additional signal following demodulation of the digital baseband signals. - View Dependent Claims (11, 12)
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Specification