US 5,003,621 A · Direct conversion FM receiver

Abstract

A direct conversion FM receiver that comprises a quadrature mixer, an A to D converter, a digital demodulator, a digital phase lock loop, and frequency offset setting means is disclosed. The quadrature mixer receives FM signals and mixes them with a local oscillator signal to produce an analog in-phase baseband signal and an analog quadrature baseband signal. The analog in-phase baseband signal and the analog quadrature baseband signal are converted into digital signals by the A to D converter. The digitally converted baseband and quadrature signals are digitally demodulated and filtered by the digital demodulator such that modulation information is produced. The modulation information is used, at least in part, to control the phase lock loop means. In addition, the phase lock loop is offset by the frequency offsetting means such that the desensing components of the analog devices are minimized, thus, substantially reducing the need for tight component tolerance of DC sensing components and the need for manufacturing adjustments of DC desensing components.

Claims4

Dependent claims

A direct conversion frequency modulated (FM) receiver for recorvering modulation information from received FM signals comprising:

quadrature mixing means for mixing the received FM signals with at least one local oscillator signal to produce, at baseband, an analog in-phase baseband signal and an analog quadrature base band signal;
analog-to-digital (A/D) means, coupled to the quadrature mixing means, for converting the analog in-phase baseband signal into a digital baseband signal and for converting the analog quadrature baseband signal into a digital quadrature baseband signal;
demodulation means, coupled to the A/D means, for digitally demodulating and digitally filtering the digital in-phase baseband signal and the digital quadrature baseband signal to produce digital modulation information;
phase lock loop means, coupled to the demodulation means and the quadrature mixing means, for digitally generating the at least one local oscillator signal, such that at least one local osciallator signal is at least partially dependent on the digital modulation information;
and
frequency offset means, coupled to the demodulation means and the phase lock loop means, for digitally offsetting the at least one local oscillator signal such that a need for tight component tolerance of DC desensing components or manufacturing adjustments of the DC desensing components are substantially eliminated.

3 more elements

Dependencies are inferred from the claim text.

Direct conversion FM receiver

Life of this patent

Direct conversion FM receiver

Life of this patent

Abstract

Claims4