# US 6,725,023 B2 · Radio FM receiver

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- Number: US 6,725,023 B2
- Document ID: US6725023B2
- Status: Granted
- Kind: B2
- Application number: 09/775,848
- Filed: 2001-02-02
- Published: 2001-10-11
- Granted: 2004-04-20
- Earliest claimed: 2000-02-04
- Assignees: Koninklijke Philips Electronics N.V.
- Inventors: Wolfdietrich Georg Kasperkovitz
- Web page: https://patentgrep.com/patent/US6725023B2

## CPC

- H03D 3/245: {using at least twophase detectors in the loop (H03D3/244 takes precedence; in general H03L7/087)}
- H03J 7/04: where the frequency control is accomplished by varying the electrical characteristics of a non-mechanically adjustable element or where the nature of the frequency controlling element is not significant
- H04B 1/28: the receiver comprising at least one semiconductor device having three or more electrodes
- H04B 1/123: {using adaptive balancing or compensation means (adaptive filter circuits and algorithms H03H)}
- H04B 1/30: for homodyne or synchrodyne receivers (demodulator circuits H03D1/22)
- H03D: DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER (masers, lasers H01S; circuits capable of acting both as modulator and demodulator H03C; details applicable to both modulators and frequency-changers H03C; demodulating pulses H03K9/00; transforming types of pulse modulation H03K11/00; coding, decoding or code conversion, in general H03M; repeater stations H04B7/14; demodulators adapted for AC systems of digital information transmission H04L27/00; synchronous demodulators adapted for colour television H04N9/66)
- H03J: TUNING RESONANT CIRCUITS; SELECTING RESONANT CIRCUITS
- H04B: TRANSMISSION

## Abstract

A radio FM receiver is provided with a receiver portion with quadrature channels for converting received radio frequency signals into center frequency quadrature signals, a center frequency filter circuit connected to the former for suppressing undesirable image frequencies, and a first quadrature PLL demodulator for demodulating the obtained center frequency quadrature signals, said PLL being tuned to the carrier frequency within the selected frequency band. An error detector is furthermore present for detecting amplitude and phase errors in the quadrature channels, which error detector in response to the quadrature components of the center frequency signals, the quadrature signals of a VCO in the quadrature PLL demodulator, and the filtered difference said quadrature components of the center frequency signal, supplies amplitude and phase correction signals to a quadrature channel correction network which is provided between the filter circuit and the quadrature PLL demodulator.

## Claims

### Claim 1

A radio FM receiver comprising:
a receiver portion for converting received radio frequency signals into center frequency quadrature signals;
a center frequency filter circuit connected to said receiver portion for suppressing undesirable image frequencies; and
a quadrature PLL (phase-locked loop) demodulator having a VCO (voltage-controlled oscillator) for demodulating the obtained center frequency quadrature signals, said PLL being attuned to the carrier frequency within the selected frequency band, characterized in that said radio FM receiver further comprises:
an error detector for detecting amplitude and phase errors in the quadrature channels; and
a quadrature channel correction network coupled between said filter circuit and the quadrature PLL demodulator, said error detector, in response to the quadrature components of the center frequency signals, the quadrature signals of the VCO in the quadrature PLL demodulator, and the filtered difference of said quadrature components of the center frequency signals, supplying amplitude and phase correction signals to said quadrature channel correction network.

### Claim 2 (depends on 1)

The radio FM receiver as claimed in claim 1, characterized in that the error detector comprises:
a second quadrature PLL demodulator having a VCO (voltage-controlled oscillator) for demodulating the obtained center frequency quadrature signals, wherein the PLL is attuned to the carrier frequency of the image signals within the selected frequency band;
a non-linear processing unit for generating mixing signals in the first and second PLL demodulators after being supplied with the quadrature signals from the two VCOs; and
two mixing stages for mixing a respective one of the mixing signals with the filtered difference of the quadrature signals from the first quadrature PLL demodulator, said mixing stages supplying said correction signals after filtering.

### Claim 3 (depends on 2)

The radio FM receiver as claimed in claim 2, characterized in that the filtered difference of the quadrature signals from the first quadrature PLL are represented by the relation:
ST=A{ΔA sin δωt+ΔΦcos δωt},
in which A is the amplitude of the undesirable carrier wave frequency ωC′, ΔA is the relative amplitude error between the quadrature channels, and ΔΦ is the phase error between the quadrature channels, while the output signals of the non-linear processing unit are directly proportional to the value sin δωt and cos δωt, the mixing stages providing signals proportional to ΔA and ΔΦ after filtering.