FM analog demodulator compatible with IBOC signals

Patent metadata

Field	Value
Publication number	US-9634704-B2
Application number	US-201514920720-A
Country	US
Kind code	B2
Filing date	Oct 22, 2015
Priority date	Jul 25, 2011
Publication date	Apr 25, 2017
Grant date	Apr 25, 2017

Abstract

A method includes: receiving an FM radio signal including an analog-modulated portion; digitally sampling an analog-modulated portion of the radio signal to produce a plurality of samples; using a ratio between an average magnitude and an RMS magnitude of a block of the samples to compute a signal quality metric; detecting sum and difference components of the baseband multiplex signal content; using the baseband content to produce an output signal; and blending the output signal from stereo to monaural as the signal quality metric falls below a threshold value.

First claim

What is claimed is:

1. A method comprising:
receiving an FM radio signal including an analog-modulated portion;
digitally sampling an analog-modulated portion of the radio signal to produce a plurality of samples;
using a ratio between an average magnitude and an RMS magnitude of a block of the samples to compute a signal quality metric;
detecting sum and difference components of a baseband multiplex signal content;
using the baseband content to produce an output signal; and
blending the output signal from stereo to monaural as the signal quality metric falls below a threshold value.

2. The method of claim 1 , wherein blending the output signal to monaural is performed through reduction or elimination of a stereo difference signal.

3. The method of claim 2 , wherein a stereo blend control signal weights the stereo difference signal by a value ranging from 0 to 1.

4. The method of claim 3 , wherein a stereo metric value is determined using a pilot power signal and the signal quality metric.

5. The method of claim 4 , wherein an in-phase component of the pilot signal is filtered, the power of the filtered pilot signal is measured, and then the pilot signal is filtered again to provide a measure of the pilot power, having a normalized range from zero to approximately 1.

6. The method of claim 3 , wherein the stereo blend control signal is formed as a function of both a filtered and unfiltered stereo metric signal.

7. An apparatus comprising:
an input for receiving an FM radio signal including an analog-modulated portion; and
processing circuitry for digitally sampling an analog-modulated portion of the radio signal to produce a plurality of samples,
using a ratio between an average magnitude and an RMS magnitude of a block of the samples to compute a signal quality metric,
detecting sum and difference components of a baseband content, using the baseband content to produce an output signal, and
blending the output signal from stereo to monaural as the signal quality metric falls below a threshold value.

8. The apparatus of claim 7 , wherein blending the output signal to monaural is performed through reduction or elimination of a stereo difference signal.

9. The apparatus of claim 8 , wherein a stereo blend control signal weights the stereo difference signal by a value ranging from 0 to 1.

10. The apparatus of claim 9 , wherein a stereo metric value is determined using a pilot power signal and the signal quality metric.

11. The apparatus of claim 10 , wherein an in-phase component of the pilot signal is filtered, the power of the filtered pilot signal is measured, and then the pilot signal is filtered again to provide a measure of the pilot power, having a normalized range from zero to approximately 1.

12. The apparatus of claim 9 , wherein the stereo blend control signal is formed as a function of both a filtered and unfiltered stereo metric signal.

Assignees

• Ibiquity Digital Corp

Inventors

• Kroeger Brian W
• Peyla Paul J

Classifications

• H04B1/123 Primary

  using adaptive balancing or compensation means (adaptive filter circuits and algorithms H03H) · CPC title

• H04B2001/1045

  Adjacent-channel interference · CPC title

• H04L27/156 Primary

  with demodulation using temporal properties of the received signal, e.g. detecting pulse width · CPC title

• H04B1/1036

  with automatic suppression of narrow band noise or interference, e.g. by using tuneable notch filters (H04B1/123 takes precedence; filter circuits H03H) · CPC title

• H04L27/14

  Demodulator circuits; Receiver circuits · CPC title