US 5,715,281 A · Zero intermediate frequency receiver

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.

Claims12

Dependent claims

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, and
carrier nulling means, which adjusts the mixing means to substantially minimise signal strength at the centre frequency of the analogue baseband signals.

2 more elements

Dependencies are inferred from the claim text.

Zero intermediate frequency receiver

Life of this patent

Zero intermediate frequency receiver

Life of this patent

Abstract

Claims12