JPS6231864B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a receiving system, and more particularly to a receiving system that suppresses multipath interference in a vehicle-mounted FM receiver.

In conventional receiving systems, in order to reduce noise due to multipath interference, basic antenna elements are appropriately arranged and combined to have different directivity characteristics of the antennas, and these are changed as appropriate.

To switch the antenna, a circuit is used that detects multipath noise components in the detected output and generates a switching control signal. In such a circuit, it is necessary to detect switching noise during antenna switching to prevent the antenna from switching again.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a receiving system that does not malfunction due to detection of switching noise during antenna switching.

The present invention will be explained below using the drawings.

FIG. 1 is a schematic block diagram of one embodiment of the present invention, in which 1 is a switch circuit for switching between two antennas 8 and 9 with different directivity, 2 is a front end, 3 is an intermediate frequency amplifier, 4 is an FM detector,
Reference numeral 5 indicates an MPX decoder, from which left and right channel signals are derived.

Noise due to multipath interference is detected from the detection output of the FM detector 4, and a multipath detection circuit 10 is used. In this circuit 10, 101 is a high-pass filter for detecting multipath noise components of 100 KHz or more from the detection output, 102 is an amplifier, and 103 is a noise detector that sends the noise detection output that can be taken into the Schmitts circuit and bistable multi, which will be described later. 104 is a Schmitt circuit that generates pulses simultaneously with multipath detection, and 105 is a bistable multicircuit that alternately generates two types of antenna control signals using the pulses of the Schmitt circuit 104.

Figure 2 shows a partial circuit diagram of the antenna switching circuit 1 and front end 2, in which the received signals A and A' from antennas 8 and 9 are transferred to transformers.
The voltage is applied to the respective first gate electrodes of dual-gate MOS transistors Q ₃ and Q ₄ via a first tuning circuit consisting of T ₁ and capacitor C ₃ and a second tuning circuit consisting of transformer T ₂ and capacitor C ₄ . ing. The drain outputs of both transistors Q ₃ and Q ₄ become a selection output B through a third tuning circuit consisting of an output transformer T ₃ and a capacitor C ₅ . The sources of both transistors Q ₃ and Q ₄ are grounded via resistors R ₃ and R ₄ and provided with a reference potential.

A reference bias V ₁ is applied to the second gate electrodes of both transistors Q ₃ and Q ₄ via resistors R ₁ and R ₂ to give a predetermined amplification to the transistors Q ₃ and Q ₄ . There is. Switching transistors Q ₁ and Q ₂ are connected to each second gate electrode and are controlled to be turned on or off by a control signal Q applied to their bases. Incidentally, capacitors C ₁ and C ₂ are respectively provided between each second gate electrode and ground, and together with resistors R ₁ and R ₂ respectively constitute a switching time constant.

FIG. 3 shows the waveforms of various parts in the block of FIG. The output waveform of E
is the output waveform of the noise detector 103, F is the switching signal to the switch circuit 1, and
One of the mutually complementary outputs Q, signals of the pair is shown.

When receiving with the antenna 8, if the influence of multipath appears on the output waveform A due to inappropriate directivity, and a multipath noise component (100KHz or more) appears on the detection output C, the HPF 101, amplifier 102, and noise The output is transmitted via the detector 103 and the multi-channel 105, and each output converted from B→C→D→E→F is transmitted to the switch circuit 1 as an antenna switching signal F. Switch circuit 1 (second
In Figure), when transistor Q ₁ becomes conductive, transistor Q ₃ turns off, and transistor
Since Q ₂ is in the cut-off state, transistor Q ₄
turns on. Therefore, the output B of the third tuned circuit
becomes the signal A' of the antenna 9.

When the antenna 9 detects multipath noise again and the output waveform is disturbed as shown in A', the antenna is switched to the antenna 8 again according to the above procedure. Therefore, the reception antennas 8 and 9 are switched instantaneously upon detection of multipath noise, maintaining appropriate directivity and maintaining good reception conditions.

Now, using the waveforms shown in Figure 4, switch circuit 1
The operation during the transient period will be explained in detail. In addition, B, C, D, E and F in Fig. 4 are B, C, D, E in Fig. 3.
and F waveforms, respectively. For example, as described in FIG. 3, when the received signal of antenna A is affected by multipath as shown in B, waveforms C, D, E, and F are generated correspondingly in sequence. And in switch circuit 1, the time constant
A switching operation is performed using C ₁ R ₁ and C ₂ R ₂ . In this case, if the above time constant is selected to be a short value of several microseconds, switching will occur almost instantaneously, but as shown in B, a momentary no-signal period will inevitably occur, and the no-signal during this switching will cause detection. Switching noise a will occur in the audio output C that has passed through the device 4.

If the detection time constant of the noise detector 103 is selected to be larger than the switching time constant of the switch circuit 1, the noise detection output will not be sensitive to the switching noise a, as shown in E, and malfunction will occur. There's nothing to do. In other words, the switching time constant is selected to be sufficiently smaller than the noise detection time constant (for example, 1/10 or less) to shorten the switching time and prevent the noise detector from responding to the noise during switching. .

As described above, according to the present invention, since there is no sensitivity to switching noise, malfunctions can be prevented and effective multipath countermeasures can be taken. It is particularly suitable for in-vehicle receivers.

Note that the illustrated circuit merely shows an example, and the present invention is not limited thereto. Similar effects can also be obtained by using two or more antennas.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a specific example of a part of FIG. 1, FIG. 3 is a waveform diagram of each part of the block in FIG. FIG. 3 is a waveform diagram illustrating the effects of the invention. Explanation of symbols of main parts: 1...Antenna switching circuit, 8, 9...Antenna, 10...Multipath noise detection circuit, 103...Noise detector.

Claims (1)

[Claims] 1 At least two receiving antennas with mutually different directivity distributions, and multipath noise that generates a noise detection signal by detecting multipath noise in a received signal by one of the receiving antennas with a predetermined detection time constant. It is characterized by comprising a detection means and a switching means which operates in response to the detection signal and switches one of the antennas to another, and the switching time of the switching means is selected to be smaller than the detection time constant. receiving system.