Channel selector for a radio frequency receiver

Abstract

A channel selector for a frequency modulation radio frequency receiver, including a band-pass filter, of which the frequency band is centered on the central frequency of the channel to be selected, and has a width that is automatically variable between a minimum value and a maximum value, the minimum value being determined dynamically proportional to a weighted sum of the field level and the modulation level of the channel, according to a formula MinBW=k1C+k2M, in which MinBW is the minimum value, C the field level, k1 the weight associated with the field level, M the modulation level, and k2 the weight associated with the modulation level. The weight associated with the field level is less than the weight associated with the modulation level, preferably in a ratio of 1:3.

Claims

1. A channel (C.sub.0) selector (1) for a frequency-modulation radiofrequency receiver, comprising a bandpass filter (2), the frequency band (BPF) of which is centered on the center frequency (F.sub.0) of the channel (C.sub.0) to be selected and has a width that is variable automatically between a minimum value (MinBP) and a maximum value (MaxBP), the minimum value (MinBP) being determined dynamically in proportion to a weighted sum of the field level (C) and the modulation level (M) of the channel (C.sub.0), in accordance with a formula MinBW=k1C+k2M, where MinBW is the minimum value, C is the field level, k1 is the weight associated with the field level (C), M is the modulation level, and k2 is the weight associated with the modulation level (M), wherein the weight (k1) associated with the field level (C) is lower than the weight (k2) associated with the modulation level (M).

2. The selector (1) as claimed in claim 1, wherein the field level (C) and/or the modulation level (M) are measured on a measurement frequency band (BPM) equal to the frequency band of the filter (BPF).

3. The selector (1) as claimed in claim 2, wherein the maximum value (MaxBP) is constant and equal to the total modulation range (EMT) of the channel (C.sub.0).

4. The selector of claim 3, wherein the maximum value (MaxBP) is also equal to the useful modulation range (EMU) of the channel (C0).

5. The selector (1) as claimed in claim 2, wherein the minimum value (MinBP) is increased by way of a maximum boundary (Bmax) equal to the maximum value (MaxBP) and decreased by way of a minimum boundary (Bmin).

6. A radiofrequency receiver comprising the channel selector (1) as claimed in claim 2.

7. The selector (1) as claimed in claim 1, wherein the maximum value (MaxBP) is constant and equal to the total modulation range (EMT) of the channel (C.sub.0).

8. The selector of claim 7, wherein the maximum value (MaxBP) is also equal to the useful modulation range (EMU) of the channel (C.sub.0).

9. The selector (1) as claimed in claim 7, wherein the minimum value (MinBP) is increased by way of a maximum boundary (Bmax) equal to the maximum value (MaxBP) and decreased by way of a minimum boundary (Bmin).

10. The selector of claim 9, wherein the maximum value (MaxBP) is also equal to the useful modulation range (EMU) of the channel (C0).

11. A radiofrequency receiver comprising the channel selector (1) as claimed in claim 7.

12. The selector (1) as claimed in claim 1, wherein the minimum value (MinBP) is increased by way of a maximum boundary (Bmax) equal to the maximum value (MaxBP) and decreased by way of a minimum boundary (Bmin).

13. The selector of claim 12, wherein the minimum boundary (Bmin) is between half and double a minimum value (MinBP0) of between 30 and 50 kHz.

14. The selector of claim 12, wherein the minimum boundary (Bmin) is equal to a minimum value (MinBP0) of between 30 and 50 kHz.

15. A radiofrequency receiver comprising the channel selector (1) as claimed in claim 12.

16. A radiofrequency receiver comprising the channel selector (1) as claimed in claim 1.

17. The selector of claim 1, wherein a ratio of the weight (k1) associated with the field level (C) to the weight (k2) associated with the modulation level (M) is 1:3.

18. The selector (1) as claimed in claim 17, wherein the field level (C) and/or the modulation level (M) are measured on a measurement frequency band (BPM) equal to the frequency band of the filter (BPF).

19. The selector (1) as claimed in claim 17, wherein the maximum value (MaxBP) is constant and equal to the total modulation range (EMT) of the channel (C0).

20. The selector (1) as claimed in claim 17, wherein the minimum value (MinBP) is decreased by way of a maximum boundary (Bmax) equal to the maximum value (MaxBP) and increased by way of a minimum boundary (Bmin).

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) Other features, details and advantages of the invention will emerge more clearly from the detailed description given hereinafter by way of indication in relation to the drawings, in which:

(2) FIG. 1, already described, illustrates, in a frequency diagram, the division of the radio band into channels,

(3) FIG. 2, already described, illustrates, in a frequency diagram, a channel that is distorted by an interference signal,

(4) FIG. 3, already described, illustrates two close signals,

(5) FIG. 4, already described, illustrates the signal resulting from the two close signals from FIG. 3 following selection by a frequency band filter of excessive width,

(6) FIG. 5, already described, illustrates a selector equipped with a device that ensures an automatic variation in the width of the frequency band of the selector filter, from the prior art,

(7) FIG. 6 illustrates a selector equipped with a device that ensures an automatic variation in the width of the frequency band of the selector filter, and a means for dynamically determining the minimum value of the width, according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(8) As illustrated in FIG. 6, in comparison with FIG. 5, a channel C.sub.0 selector 1 for a frequency-modulation radiofrequency receiver, according to the invention, comprises a bandpass filter 2 or selector filter 2.

(9) The selector 1 receives, as input, an initial signal 8, which may be a base-frequency signal, originating directly from the antenna, or a signal whose frequency has been lowered beforehand, such as an intermediate-frequency signal. It produces, as output, a signal 9 that is homologous, but confined in terms of frequency only to the channel C.sub.0, as filtered by the selector filter 2, in the frequency band BPF. The signal 9 is able to be processed by a demodulator.

(10) The bandpass filter 2 is characterized by a filter frequency band BPF, which is centered on a center frequency F.sub.0 characteristic of the channel C.sub.0 to be selected and has a variable width. In accordance with this variability, the width of the frequency band BPF is typically controlled depending on reception quality characteristics of the channel C.sub.0. This variability is however advantageously restricted between a minimum value MinBP and a maximum value MaxBP. This is achieved, for example, by a device 4 such as described previously.

(11) Until now, both the maximum value MaxBP and the minimum value MinBP were constant. The result of this is that, as soon as the conditions of the channel C.sub.0 are impaired, this being detected through the field level C or the noise level B, controlling the width of the frequency band BPF has a tendency to reduce the width until saturating said width at the minimum value MinBP.

(12) This may have consequences, in terms of variation in the sound level, which are highly unpleasant to the listener. Therefore, in order to minimize these unpleasant effects, while profiting from the benefits of the automatic variation in the frequency bandwidth, also termed dynamic selectivity, the invention proposes removing the constancy of the minimum value MinBP, and replacing it with a value that is determined dynamically, depending on the characteristics of the signal.

(13) One important characteristic consists in taking into consideration the dynamic range of the signal received via the channel C.sub.0. One known indicator of this dynamic range is the modulation level M. This modulation level M is indicative of the richness of the signal, in that it is indicative of the frequency bandwidth that is effectively used by the signal. The modulation level M is conventionally determined on the basis of the received signal, by a modulation sensor 6. The modulation sensor 6 typically comprises a low-pass filter. The filtered signal is then processed by a modulation detector, which determines the modulation level M of the signal.

(14) As illustrated in FIG. 6, the components 10,11 determining the minimum value MinBP comprise a summer 10. The minimum value MinBP is an increasing function of the modulation level M. Thus, the larger the dynamic range of the signal, the more the minimum value MinBP increases.

(15) According to one additional optional feature, a field level C is also taken into account. This field level C is indicative of the reception quality of the channel C.sub.0. The field level C is conventionally determined on the basis of the envelope of the received signal, by a field level detector 5.

(16) As illustrated in FIG. 6, the components 10,11 determining the minimum value MinBP comprise a summer 10. The minimum value MinBP is an increasing function of the field level C. Thus, the greater the field level of the signal, the more the minimum value MinBP increases.

(17) According to one preferred embodiment, the minimum value MinBP is determined by a linear combination, in the form of a weighted sum of the field level C and the modulation level M, in accordance with a formula MinBW=k1C+k2M, where MinBW is the minimum value of the width of the frequency band BPF, C is the field level, k1 is the weight associated with the field level C, M is the modulation level, and k2 is the weight associated with the modulation level M, k1 and k2 being positive.

(18) According to one embodiment, the contribution comes primarily from the modulation level M and secondarily from the field level C. Therefore, in the previous formula, the weight k1 associated with the field level C is lower than the weight k2 associated with the modulation level M. A ratio k2:k1 preferably equal to 3 has shown advantageous results.

(19) Both the modulation level M and the field level C that were used previously are advantageously indicative of the signal received via the channel C.sub.0. Therefore, as indicated in FIG. 6, the modulation sensor 6 is arranged downstream of the filter 2 and processes the signal 9 originating from the channel C.sub.0, as selected by the filter 2. Likewise, the field sensor 5 is arranged downstream of the filter 2 and processes the signal 9 originating from the channel C.sub.0, as selected by the filter 2. The field level C and/or the modulation level M are thus measured on a measurement frequency band BPM equal to the frequency band of the filter BPF, i.e. a measurement frequency band BPM centered on the center frequency F.sub.0 of the channel C.sub.0 to be selected and with a width equal to the controlled width and that is variable automatically.

(20) In a manner comparable with the prior art, the maximum value MaxBP is constant and equal to the total modulation range EMT of the channel C.sub.0. Advantageously, this maximum width may be confined to the useful modulation range EMU of the channel C.sub.0. The maximum value MaxBP may thus be taken to be equal to the maximum value from the prior art MaxBP0. Thus, in the values of the example, the maximum value MaxBP may be equal to a total modulation range EMT of 200 kHz, or preferably equal to a useful modulation range EMU of 150 kHz.

(21) As was described previously, the minimum value MinPB is variable. Since it is derived from an algorithm that is not necessarily convergent, it is desirable to limit its variation domain through a maximum boundary Bmax and through a minimum boundary Bmin. This is performed by the saturator component 11.

(22) According to one embodiment, the maximum boundary Bmax is advantageously equal to the maximum value MaxBP.

(23) According to one embodiment, the minimum boundary Bmin is advantageously equal to the minimum value MinBP0 that is used, as a constant value, in the prior art.

(24) However, the fact that the minimum value MinBP is determined dynamically guarantees an optimized value of this minimum value MinBP depending on the characteristics of the signal. It is therefore possible to extend downward, or, by contrast, to restrict, the interval of variation [Bmin,Bmax] of the minimum width MinBP by taking a minimum boundary value Bmin that may be as low as half MinBP0/2 of the minimum value MinBP0 used in the prior art or, in contrast, as high as double 2*MinBP0 the minimum value MinBP0 used in the prior art.

(25) Thus, in the example, for a value MinBP0 from the prior art of 40 kHz, it is possible to adopt a minimum boundary Bmin of any value between 20 kHz and 80 kHz.

(26) According to one feature of the invention, the repetition frequency of the dynamic determination of the minimum value MinBP is less than or equal to the repetition frequency of the automatic variation of the frequency bandwidth, such as employed by the device 4. The dynamic determination frequency is advantageously a submultiple, with a ratio of between 1000 and 100000.

(27) The invention also relates to a radiofrequency receiver comprising such a selector 1.