JP3120457B2 - Diversity type FM receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multipath interference detection method which is advantageous in terms of malfunction and adjustment in a diversity type FM receiver.

[0002]

2. Description of the Related Art It is difficult for an on-vehicle FM receiver to always receive FM broadcasts in a stable state due to multipath interference or the like. Therefore, in order to improve the reception quality in the on-vehicle FM receiver, the spatial diversity system has been adopted in recent years. This method generally has two circuit blocks such as two antennas, a front end, an IF amplifier and an FM detection circuit, and a signal meter voltage (IF amplifier and FM detection ) indicating an input electric field level obtained by each antenna. (Made of circuit blocks), and a system that selects a receiving circuit system that outputs a higher signal meter voltage is often used. In the above method, multipath interference is generally detected by detecting a ripple component superimposed on a signal meter voltage, or detecting a noise component generated in a high frequency band of an FM detection output. But have the economical problem two front-end in this system, the cost for the IF amplifier · FM detection circuit blocks and each optionally increased.

[0003] In order to improve this point, the antenna only two settings <br/> Keru but the front end, IF amplifier · FM detection circuit blocks are proposed spatial diversity scheme for one use. This is a simple space diversity system that selects another antenna when the signal meter voltage indicating the reception electric field strength of each antenna falls below a predetermined voltage level.

FIG. 4 shows an example of the FM multiplex broadcasting receiver of the simple space diversity system. In FIG. 4, 1A and 1B are antennas, 2 is a switch, 3 is a front end, 4 is an IF amplifier and FM detection circuit, 5 is an antenna switching control circuit, 6 is a stereo demodulation circuit, 7 is a multiplexed signal demodulation circuit, 8A, 8B and 8C are audio amplifiers, respectively, and 9A, 9B and 9C are speakers, respectively.

In the example of FIG. 4, it is assumed that one of the antennas is selected. The input electric field level is obtained from the signal meter voltage generated by the IF amplifier / FM detection circuit 4, and the multipath is obtained from the ripple component superimposed on this voltage. Detect the degree of interference. Since the ripple component is negatively rectified and added to the signal meter voltage (DC), when the input electric field level is low or multipath interference is large, the operation is switched to the other antenna.

The detection of ripple components due to multipath interference, negative rectification, addition with a signal meter voltage, comparison with a predetermined voltage level, judgment, and the like are performed by the antenna control circuit 5 of FIG. Controls the switch 2 for selecting the antenna.

[0007]

The operation of the conventional simple space diversity type FM multiplex broadcasting receiver has been described above. The amplitude level of the ripple component superimposed on the signal meter voltage varies depending on the input electric field strength and is constant. Not.
Therefore, at a certain electric field intensity, the amplitude level becomes large,
At other electric field intensities, the amplitude level becomes small. That is, the ripple component superimposed on the signal meter voltage generally has a peak point or a dip point depending on the electric field intensity. Therefore, when detecting the degree of multipath interference by the ripple component superimposed on the signal meter voltage, it is difficult to adjust the setting of the detection sensitivity. If the input electric field strength is different, a different amount of multipath interference is detected for the same degree of multipath interference, and there is a problem that the antenna switching control may malfunction. Also,
In another conventional multipath interference detection method for detecting a high-frequency component of an FM detection output, in the case of FM multiplex broadcasting, a multiplex signal exists from about 61 kHz to 91 kHz. For this reason, detection must be started at a higher frequency of about 100 kHz or more, and there is a problem in terms of an efficient detection level (a distinction between triangular noise of FM detection output and noise due to multipath interference).

An object of the present invention is to provide a method for detecting multipath interference in the above-mentioned diversity type FM multiplex broadcasting receiver which does not depend on the input electric field strength and does not malfunction due to a multiplex signal.

[0009]

In order to achieve the above object, a first aspect of the present invention provides a diversity type FM receiving apparatus which selects one of a plurality of antennas and receives a signal from the selected antenna. and FM detection means for obtaining a signal selecting means for outputting the detection output signal by FM detecting converts the received signal into a predetermined intermediate frequency, before
From the detection output signal, an integer multiple of the pilot signal frequency
And in the frequency domain where no broadcast signal component exists.
Means for extracting a chippath interference component, means for detecting an interference component level corresponding to the amount of the multipath interference component, and outputting an interference component level signal, and detecting an electric field intensity level from the received signal to generate an electric field intensity level signal. Output means, and selection control means for controlling a selection operation of the signal selection means by a control signal generated based on the interference component level signal and the electric field strength level signal. In a second aspect based on the first aspect, the selection control means negatively rectifies the amplitude level of the disturbance component level signal.
Bei calculating means for adding the signal meter level signal, and a comparator for comparing an output of said calculation means with a predetermined reference level corresponding to the negative rectified signal and the field intensity levels
The control signal is obtained from the comparing unit .

[0010]

The signal meter voltage is obtained from the signal received from any of the antennas, and the FM detection is performed. A signal corresponding to the amount of multipath interference is extracted from the FM detection output signal. The amplitude level is detected from the extracted signal, a predetermined detection signal is calculated from the level and the signal meter voltage, a switching signal is obtained from the output, and one of the antennas is selected by the switching signal.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 2 shows an example of an FM detection output frequency spectrum of a receiver when FM multiplex broadcasting is received. FIG. 3A shows a case without multipath, and FIG. 3B shows a case with multipath. In FIG. 2, for simplification of description, a stereo modulated signal and a multiplexed signal in which a single sine wave fA is added to only Lch or Rch are used.

When there is no multi-path shown in FIG. 2 (a), the FM detection output has a sum signal of fA and a pilot signal of 19 kHz.
z, 38kHz ± fA as difference signal, about 61 as multiplexed signal
Each spectrum from kHz to 91 kHz exists.

When there is a multipath shown in FIG. 2B, an interference spectrum is generated around a frequency which is an integral multiple of 19 kHz due to multipath interference in addition to the spectrum shown in FIG. 2A. The level of the interference spectrum depends on the degree of modulation of the audio signal fA, the amplitude ratio of the multipath direct wave and the reflected wave, the phase difference, the delay time difference, and the like. Since a multiplex signal has a frequency spectrum of about 61 kHz to 91 kHz, a multipath interference causes a problem in that an interference spectrum is generated around 76 kHz at the center. The interference spectrum due to multipath is also 19kHz, 38kHz,
It also occurs at 57 kHz, 95 kHz, etc.

FIG. 1 shows a diversity type FM according to the present invention.
1 shows an embodiment of a multiplex broadcast receiver. In this embodiment, in order to detect a component near 57 kHz in the interference spectrum due to the multipath, a configuration in which a 57 kHz bandpass filter 10 is added to the conventional system of FIG. 1 is used. The same or similar circuits are shown. 57 kHz bandpass filter 10 is an IF amplifier / F
With the FM detection output signal of the M detection circuit 4 as an input, a component near 57 kHz in the multipath interference spectrum is detected and applied to a ripple component input terminal 5a of the antenna switching control circuit 5. A signal meter voltage input terminal 5b of the antenna switching control circuit 5 has an I
A signal meter voltage (DC) is input from the F amplifier / FM detection circuit 4.

FIG. 3 shows a configuration example of the antenna switching control circuit. In the figure, reference numeral 11 denotes a ripple component detection circuit;
Is a negative rectifier circuit, 13 is an adder circuit, 14 is a comparator, and 15 is a reference voltage source. In FIG. 3, a ripple component detection circuit 11 detects a component near 57 kHz due to multipath interference from an FM detection output signal obtained via a band pass filter 10, and a negative rectification circuit 12 negatively rectifies the output to obtain a signal. The addition with the meter voltage is performed by the addition circuit 13. When the added output voltage is higher than the reference voltage level E by the comparator 14, the current receiving antenna is used as it is. A switch signal for switching to the antenna is sent to the switch 2.

[0016]

As described above, according to the present invention,
Multipath interference can be detected and compared without depending on the input electric field strength, and no malfunction due to the FM multiplex signal occurs. Further, the detection sensitivity of the amount of multipath interference can be easily set. That is, as compared with the method of detecting the ripple component included in the signal meter voltage, when the multipath interference does not occur, there is no interference spectrum, so that the sensitivity setting can be easily adjusted. Further, it is possible to detect a multipath disturbance without causing a malfunction due to a multiplex signal even in a conventional FM stereo broadcast signal. Especially for the detection of interfering signals
In the frequency domain that is an integral multiple of the pilot signal frequency,
This makes it possible to detect multipath interference components efficiently.
You. Of course, the present invention is not limited to an FM multiplex broadcast receiver, but can be applied to a conventional FM stereo broadcast receiver.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of an FM detection output frequency spectrum of FM multiplex broadcasting;

FIG. 3 is a block diagram showing a configuration example of an antenna switching control circuit in the embodiment.

FIG. 4 is a block diagram showing a conventional FM multiplex broadcast receiver of a diversity system.

[Explanation of symbols]

 1A, 1B Antenna 2 Switch 4 IF Amplifier / FM Detection Circuit 5 Antenna Switching Control Circuit 10 57 kHz Bandpass Filter 11 Ripple Component Detection Circuit 12 Negative Rectification Circuit 13 Addition Circuit 14 Comparator 15 Reference Voltage Source

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-58-79345 (JP, A) JP-A-57-135533 (JP, A) JP-A-58-70641 (JP, A) JP-A-2- 179129 (JP, A) JP-A-2-159833 (JP, A) JP-A-2-92242 (JP, U) JP-A-1-171139 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04B 1/10-1/14 H04B 15/00-15/06 H04B 7/00 H04B 7/02-7/12 H04L 1/02-1/06

Claims (2)

(57) [Claims] A signal selecting means for selecting one of a plurality of antennas and outputting a received signal from the selected antenna; converting said received signal into a predetermined intermediate frequency;
FM detection means for M detection to obtain a detection output signal, and an integer multiple of a pilot signal frequency from the detection output signal
And in the frequency domain where no broadcast signal component exists.
Means for extracting a chippath interference component, means for detecting an interference component level corresponding to the amount of the multipath interference component, and outputting an interference component level signal, and detecting an electric field intensity level from the received signal to generate an electric field intensity level signal. Output means; and selection control means for controlling a selection operation of the signal selection means by a control signal generated based on the interference component level signal and the electric field strength level signal. Receiver. 2. The calculating means for adding a negative rectified signal obtained by negatively rectifying the amplitude level of the interference component level signal and a signal meter level signal corresponding to the electric field strength level, 2. The diversity type FM receiving apparatus according to claim 1 , further comprising a comparing section for comparing an output with a predetermined reference level, wherein the control signal is obtained from the comparing section .