JPS5917740A - Space diversity receiver - Google Patents

Abstract

PURPOSE:To prevent the noise due to antenna switching from being mixed with a receiving signal and to eliminate completely the noise, by generating a signal, which operates a noise eliminating circuit, on the basis of the control signal for antenna selective switching. CONSTITUTION:A noise eliminating circuit 10 is provided in the succeeding stage of an IF amplifier 5 of the space diversity receiver which switches plural antennas 1a and 1b by a switching circuit 2 to receive the antenna input of a good reception state. This circuit 10 is constituted with an LPF10a, an HPF10b, a noise detecting circuit 10c, and a gate circuit 10f. Meanwhile, a latch circuit 8 and a waveform shaping circuit 14 are connected to the output side of a change detecting circuit 7 which detects the change of the reception state. A pulse signal (d) having a prescribed width is outputted from this circuit 14 and is inputted to an OR gate 15. When an output signal (e) of the gate 15 is in the level H, the gate circuit 10f of the circuit 10 is controlled to the operate the circuit 10, thus preventing the noise due to antenna switching from being mixed with the receiving signal.

Description

[Detailed Description of the Invention] The present invention relates to a space and diversity receiver in which a plurality of antennas are disassembled and the antenna input with a better reception condition is selected for listening, and in particular, it eliminates or reduces noise generated when switching antennas. Space 1 that allows you to
・Regarding the diapersity receiver.

FIG. 1 shows a conventional example of a so-called space or diversity receiver that selects and listens to an antenna input with a better reception condition. Space and diversity receivers are generally used in vehicles in many cases.

The switching circuit 2 selects between the two antennas 1a and 1b. The antenna input selected by the switching circuit 2 is input to the frequency conversion circuit 4 through a high frequency amplification circuit. The frequency conversion circuit 4 outputs an IF multiplied signal, and the IF multiplied signal is amplified by the intermediate frequency amplifier 5. Amplified IF times signal, A
It is input to the M detector 6 and the FM demodulator 9.

The AM detector 6 outputs an IF multiplied signal envelope component. This envelope component includes information regarding a signal that changes depending on the strength of antenna input and a signal that changes due to multipath or the like. The change detection circuit 7 detects whether the output of the AM detector 6 has deteriorated from the current reception state, and if the output has deteriorated, outputs a signal to switch the latch circuit 8. The latch circuit 8 outputs a switching control signal to the switching circuit 2, which causes the switching circuit 2 to switch from the currently receiving antenna to the other antenna.

On the other hand, the IF multiplied signal input to the FM demodulator 9 is demodulated here and noise removed by the noise removal circuit 10. The noise-removed signal is sent to a speaker 13 via a stereo demodulator 11, a low frequency amplification/power amplifier 12, and a speaker 13.

FIG. 2 shows a specific example of the switching circuit 2 shown in FIG. Terminal A
A switching control signal is input to the latch 8. Now, if this switching control signal is at the %L" level, the transistor 2a
l, 2a2 is turned off, transistor 2a3 is turned on, and antenna 1a is selected. The signal received by the antenna 1a is sent to the high frequency amplifier circuit 5 via the diode 2bll capacitor 2c1. On the other hand, when the switching control signal is at the HI level, the transistor 2a12a
2 is turned on, transistor 2a3 is turned off, and antenna 1b is selected. The signal received by antenna 1b is
Diode 2b2. The signal is sent to the high frequency amplifier circuit 6 via the capacitor 2c2.

Next, noise removal in the conventional diversity receiver as described above will be explained. Now, assume that the output signal a of the FM demodulator 9 includes pulse noise aIta3 such as vehicle ignition system noise and noise a2+a4 due to antenna switching as shown in FIG. 3(a). The noise removal circuit 10 can remove or reduce noise above a certain threshold level, but cannot remove noise below the threshold level. Therefore, noise that does not reach the threshold level, such as noise a4 caused by antenna switching in FIG. 6(a), cannot be removed.

As described above, the conventional space and diversity receiver has the drawback that it cannot remove noise caused by antenna switching that is lower than the threshold level of the noise removal circuit.

It is an object of the present invention to eliminate the drawbacks of the prior art described above and to almost completely eliminate or reduce the noise that occurs due to antenna switching.

A feature of the present invention is that a signal for activating a noise removal circuit is generated based on a control signal for switching antenna selection, and that the signal is used to activate the noise removal circuit.

The present invention will be explained below by way of examples.

FIG. 4 shows an embodiment of the present invention. In the figure, 14 indicates a waveform shaping circuit, 15 indicates an OR gate, and other symbols are the same as in FIG. 1. Note that the noise removal circuit 10 includes a low-pass filter 10a, a bypass filter 10b,
It consists of a noise detection circuit 10c and a gate circuit 10d. Figure 5 shows the main parts of the signals in Figure 4.
Figures (a) to (e) show signals a to e in Figure 4, respectively.

Now, assume that the FM demodulator 9 in FIG. 4 outputs noise as shown in FIG. 5(a).

This noise is the same as that in FIG. 6(a), and al.

a3 is pulse noise such as vehicle ignition system noise, a2+a4
It is assumed that is the noise due to antenna switching.

Such noise a1-a4 is the bypass filter 1
When the signal passes through 0b and is input to the noise detection circuit 10c, the noise detection circuit 10c outputs a pulse signal with a constant pulse width in response to noise exceeding a predetermined threshold level.

On the other hand, the change detection circuit 7 detects that the reception condition of the antenna 1a or 1b has deteriorated, and outputs the change detection signal C at a slightly earlier time than the noise a2+a4, as shown in FIG. 5(c). do.

This change detection signal C is input to the latch circuit 8, and the output of the latch circuit 8 is inverted. Therefore, the switching circuit 2 operates to switch the antenna. Additionally, this generates noises a2 and a4. Now, the change detection signal C is input to the waveform shaping circuit 14, and this circuit 1
4 outputs a pulse signal d having a predetermined pulse width.

The pulse signals S and d are input to the OR gate 15. Therefore, from the OR gate 15, as shown in FIG.
The signal shown in is output. When the signal e is input to the gate 10d of the noise removal circuit 10, the gate HOd closes and no signal passes during the period when the signal e is 1H level. Therefore, according to this embodiment, not only the noise al+a2+a3 above the threshold level can be removed, but also the noise a4 caused by antenna switching K which is smaller than the threshold level t.

In this embodiment, if it takes time for the noise caused by antenna switching to reach the noise removal circuit 10, the waveform shaping circuit 5 may delay the pulse generation point by an amount matching the delay time. Alternatively, consideration must be given to increasing the pulse width.

FIG. 6 shows a second embodiment of the invention. Reference numeral 16 in the figure is a gate circuit, and the other symbols are the same as in FIG. 4. In this embodiment, a pulse signal output from a waveform shaping circuit 14 controls a gate circuit 16 inserted between an FM demodulator 9 and a stereo demodulator 11. That is, each time the receiving antenna is switched from the waveform shaping circuit 14.

Then, a pulse signal with a constant pulse width as shown in FIG. 5(d) is output. When this pulse signal enters the gate circuit 16, the gate circuit 16 closes and becomes non-conductive while the pulse signal is at the high level. Therefore, noise caused by antenna switching can be removed.

FIG. 7 shows a sixth embodiment of the invention. In the figure, the first
The second gate circuits 17 and 18 are gate circuits that do not pass the output signals of the waveform shaping circuit 14 and the noise detection circuit 10c when the output signal level of the AM detector B is low, but allow them to pass when the output signal level is high.

Therefore, when the received radio wave is weak and the output of the AM detector 6 is reduced, the gates 17 and 18 will not pass the output signals of the waveform shaping circuit 14 and the noise detection circuit 10c, respectively. Therefore, the OR gate 15 does not output a signal that makes the gates 1-10d non-conductive, and the L
The output of P F 10a passes through this gate 10d. That is, even if the received signal contains noise or antenna switching noise is mixed in, these noises are sent to the stereo demodulation circuit 11 without being removed.

According to this embodiment, when the received radio waves are weak and noisy, and the antennas are frequently switched, it is possible to prevent the noise from being removed too many times and making listening difficult. There are benefits.

In this embodiment, when the output signal level of the AM detector 6 is low, the gates 17 and 18 are connected to the waveform shaping circuit 14.
By passing the output signal of the noise detection circuit 10c so that it does not occur when the level is high, it is possible to stop the noise removal operation when the received radio waves are strong. Further, an amplifier included in either or both of the change detection circuit 7 and the noise detection circuit 10c may be provided with an AGC function to provide an AM
This may be controlled by the output of the wave detector 6.

In each of the above embodiments, the AM detector 6 was used.

However, instead of this, the signal and meter drive output of the IF amplifier integrated circuit may be used.

As described above, according to the present invention, when noise caused by antenna switching is mixed into a received signal, it can be reliably removed no matter how small the noise is.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional space and diversity receiver, Figure 2 is a circuit diagram showing a specific example of a switching circuit, Figure 6 is a waveform diagram of the output signal of the FM demodulator in Figure 1, 4.
6th. FIG. 7 shows the first embodiment of the present invention. Second. FIG. 5 is a block diagram showing the sixth embodiment. FIG. 5 shows a waveform diagram of the main signals of FIG. 4. 2...Switching circuit, 6...High frequency amplification circuit,
4... Frequency conversion circuit, 5... Intermediate frequency amplifier, 6
...A iVI detector, 7... Change detection circuit, 8... Latch circuit, 9... FM demodulator, 1
0... Noise removal circuit, 11... Stereo demodulator, 12... Low frequency amplification and power amplifier, 14...
Waveform shaping circuit, 15...OR gate,
Zuzai 2 Zuga 3 Zuzai Yuzu omzuzai Thousand zu? 7 Figure

Claims (1)

[Claims] 1. In a diversity receiver, which has a plurality of antennas and selects and listens to an antenna input with a good reception condition, a noise removal circuit provided after the intermediate frequency amplifier, The present invention includes means for generating a selection switching control signal, and means for generating a signal for activating the noise removal circuit based on the control signal, thereby eliminating noise caused by antenna switching. Featured space. Diapersity receiver. 2. A patent space characterized in that the noise removal circuit is a gate circuit. Diapersity receiver. 6. The space according to claim 1, wherein the noise removal circuit comprises a noise detection circuit and a gate circuit controlled by a noise detection signal detected by the circuit. Diapersity receiver. 4. A space with multiple antennas where you can select and listen to the antenna input with good reception. In the diversity receiver, a noise elimination circuit provided after the intermediate frequency amplifier, a means for generating a control signal for switching antenna selection, and a signal for operating the noise elimination circuit based on the control signal. and means for controlling the supply of a signal to the noise elimination circuit to activate the noise elimination circuit by at least one of a change in the electric field strength of the received signal and a distortion generated in the received signal, A space characterized by added restrictions. Diapersity receiver.