Direct conversion FM receiver

• US 5,003,621 A
• Filed: 11/02/1989
• Issued: 03/26/1991
• Est. Priority Date: 11/02/1989
• Status: Expired due to Term

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Gailus, Paul H.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): CHAROUEL, LISA
• Application Number:
  US07/430,467
• Time in Patent Office: 509 Days
• Field of Search: 455/207, 455/208, 455/209, 455/214, 455/265, 455/263, 455/316, 455/324, 375/77, 375/97
• US Class Current: 455/209
• CPC Class Codes: H03J 7/065 the counter or frequency divider being used in a phase locked loop
• CPC Class Codes: H04B 1/30 for homodyne or synchrodyne receivers demodulator circuits H03D1/22

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.

Claims

1. 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.

2. The FM receiver of claim 1 further comprises at least one digitally implemented notch filter at DC, operably associated with the demodulation means and the A/D means, for substantially eliminating DC offset components with negligible effects on the digital in-phase baseband signal and the digital quadrature baseband signal.

3. A method for receiving frequency modulated (FM) signals to produce received FM signals and recovering modulation information comprising the steps of:

(a) mixing the received FM signals with at least one local osciallator signal to produce, at baseband, an analog in-phase baseband signal and an analog quadrature baseband signal;

(b) converting the analog in-phase baseband into a digitally in-phase baseband signal and converting the analog quadrature baseband signal into a digital quadrature baseband signal;

(c) demodulating the digital in-phase baseband and the digital quadrature baseband signal to produce digital modulation information;

(d) locking frequency of the at least one local oscillator signal with, at least in part, frequency of the digital modulation information; and

(e) offsetting the at least one local oscillator signal by a predetermined offset frequency such that a need for tight component tolerance of DC desensing components or manufacturing adjustments of the DC desensing components are substantially eliminated.

4. The method of claim 3 further comprises converting the digital modulation information into analog modulation information.