Method and system for reducing the sampling rate of a signal for use in demodulating high modulation index frequency modulated signals

• US 6,085,073 A
• Filed: 03/02/1998
• Issued: 07/04/2000
• Est. Priority Date: 03/02/1998
• Status: Expired due to Fees

• Current Assignee: General Dynamics C4 Systems Incorporated (General Dynamics Corporation)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Palermo, Keith Charles, Kallman, Kurt Albert
• Primary Examiner(s): Nguyen, Lee
• Application Number:
  US09/033,047
• Time in Patent Office: 855 Days
• Field of Search: 455/205, 455/209, 455/214, 455/21, 455/23, 455/226.2, 455/226.3, 455/38.3, 455/343, 375/322, 375/324, 375/340, 329/341, 329/343, 329/361
• US Class Current: 455/205
• CPC Class Codes: H04L 27/1525 using quadrature demodulation

Abstract

A method and system for reducing the sampling rate of a signal for use with high modulation index frequency modulated signals reduces the power consumption and processing requirements of the digital signal processing equipment which performs the demodulation. In a preferred embodiment, a high modulation index FM signal is divided into in-phase and quadrature phase components by a downconverter (FIG. 1, 10). These components are sampled by analog to digital converters (20, 21) and input to a delay element (40, 41). The resulting delayed and undelayed samples are conveyed to downsamplers (60-63) where the sampling rate is reduced. The undelayed in-phase and delayed quadrature phase components are multiplied together by a first multiplier (70) while the undelayed quadrature phase and delayed in-phase components are multiplied together by a second multiplier (71). The output of the second multiplier (71) is then subtracted from the output of the first multiplier (70) by a subtractor (80) which outputs baseband audio or data.

Claims

1. A method for reducing a sampling rate of a signal for use in a communications receiver, comprising:

a) receiving an in-phase component and a quadrature phase component of a signal;

b) sampling said in-phase component and said quadrature phase component of said signal to create a sampled in-phase component and a quadrature phase component of said signal;

c) delaying said sampled in-phase component and said quadrature phase component of said signal to create a delayed in-phase component and a delayed quadrature phase component of said signal; and

d) downsampling said sampled in-phase and quadrature phase components and said delayed in-phase and quadrature phase components of said signal to create a downsampled in-phase component, a downsampled quadrature phase component, a downsampled delayed in-phase component, and a downsampled delayed quadrature phase component.

2. The method recited in claim 1, wherein the method additionally comprises the steps of:

e) multiplying said downsampled delayed in-phase component with said downsampled quadrature phase component to create an in-phase product; and

f) multiplying said downsampled delayed quadrature phase component with said downsampled in-phase component to create a quadrature phase product.

3. The method recited in claim 2, wherein the method additionally comprises the steps of:

g) subtracting said quadrature phase product from said in-phase product.

4. The method of claim 1 wherein said signal conveys information through frequency modulation of said signal.

5. The method of claim 4 wherein said information is baseband audio.

6. The method of claim 4 wherein said information is baseband data.

7. A system for reducing a sampling rate of a signal for use in a communication system, comprising:

a downconverter which downconverts a signal into in-phase and quadrature phase components;

an analog to digital converter which samples said in-phase and quadrature phase components of said signal to create sampled in-phase and quadrature phase components;

a delay element which delays said in-phase and quadrature phase components of said signal to create delayed sampled in-phase and quadrature phase components; and

a downsampler which downsamples said sampled in-phase and quadrature phase components and said delayed in-phase and quadrature phase components of said signal to create a downsampled in-phase component, a downsampled quadrature phase component, a downsampled delayed in-phase component, and a downsampled delayed quadrature phase component.

8. The system of claim 7 wherein the system additionally comprises:

a first multiplier which multiplies said downsampled delayed in-phase component with said downsampled quadrature phase component to create an in-phase product; and

a second multiplier which multiplies said downsampled delayed quadrature phase component with said downsampled in-phase component to create a quadrature phase product.

9. The system of claim 8 wherein the system additionally comprises:

a subtractor which subtracts said quadrature phase product from said in-phase product.

10. The system of claim 7, wherein the system comprises a portable FM receiver.