JPH0141252Y2 - - Google Patents

Description

[Detailed description of the invention] <Industrial field of application> The present invention relates to a diversity receiving device that selects and receives reception from among two or more receiving antennas with the lowest multipath noise, and is particularly useful in weak electric fields. The present invention relates to a diversity receiving device that automatically selects a receiving antenna with a high gain and automatically stops switching operation of receiving antennas in the case of a weak electric field.

<Prior Art> There is a diversity receiving device that selects a receiving antenna that causes less multipath noise among two or more receiving antennas to receive signals. FIG. 1 is a block diagram of such a conventional diversity receiving device, in which two receiving antennas 11a and 11a, each having different directivity, are used.
11b is input to a switching circuit 12, which switches the receiving antenna so that multipath noise is reduced, and inputs a predetermined receiving antenna output to the front end 13.
The front end 13 performs high frequency amplification and frequency conversion to generate an intermediate frequency signal, and the IF amplifier 1
4 performs intermediate frequency amplification and inputs the output to the FM detector 15. The FM detection output of the FM detector 15 is applied to a stereo demodulation circuit 16 and also to a multipath noise detection circuit 17. The high pass filter 17a inputs multipath noise components of approximately 100 KHz or higher to the variable gain amplifier 17b, and the output of the variable gain amplifier 17b is input to the level converter 17c.
is applied to the Schmitt circuit 17d via. The Schmitt circuit 17d generates a signal to switch the state of the bistable circuit 17e when the level converter output becomes higher than a threshold level, in other words, when the noise signal level becomes higher than a predetermined threshold level. This causes the switching circuit 12 to select another receiving antenna and input the output of the receiving antenna to the front end 13 . On the other hand, the automatic gain control circuit (AGC circuit) 17f constantly monitors the level converter output, in other words, the noise signal level, and controls the gain of the variable gain amplifier 17b according to the noise signal level. That is, AGC circuit 17
If the reception condition worsens and the noise signal level increases (when the electric field is weak), f automatically switches to the variable gain amplifier 17.
The gain of the variable gain amplifier 17b is lowered, and if the reception condition is good and the noise signal level is small (at the time of a medium to strong electric field), the gain of the variable gain amplifier 17b is automatically increased. Note that since the threshold level of the Schmitt circuit 17d is maintained constant, the weaker the electric field becomes, the lower the multipath noise detection sensitivity of the multipath noise detection circuit 17 becomes. Therefore, in the case of a medium to strong electric field, the multipath noise detection circuit 17 reacts sensitively even to small multipath noise, and a receiving antenna that reduces multipath noise is selected. Furthermore, since the detection sensitivity becomes low when the electric field is weak, the receiving antenna is not switched unless the noise signal level becomes considerably large.

<Disadvantages of the Prior Art> Now, in the conventional device described above, the threshold level of the Schmitt circuit 17d is not changed, but the gain of the variable gain amplifier 17b is changed according to the noise signal level, so the essential point is Generally speaking, it can be considered that the threshold level changes depending on the noise signal level. And A.G.C.
Assuming that the circuit 17f operates for all levels of the noise signal, the relationship between the noise signal level and the threshold level is as shown in FIG. 2, where the threshold level (dotted line) is equal to the noise signal level. (solid line) is always set at several dB or more. or,
When the noise signal level exceeds the specified level
Assuming that the AGC circuit 17f is saturated, the relationship between the noise signal level and the threshold level is as shown in Figure 3, and the electric field strength E of the antenna is
Below Ea, the noise signal level (solid line) is always higher than the threshold level (dotted line).

Now, when the noise signal level and the threshold level have the relationship shown in Figure 2, if the electric field strengths of the two receiving antennas are both less than Ea, the noise signal will not be generated even if the input signal is worse than the current level. The level will not rise above the threshold level and therefore no antenna switching will occur. That is,
If the electric field strength of the antenna is less than Ea, only one of the antennas is selected, and it is uncertain which antenna is selected, and it is not possible to use the antennas properly. When receiving with one antenna, when the electric field strength becomes less than Ea,
A situation occurs in which the side to which the antenna is not connected is selected by the switching circuit 12, and since the noise signal level is always at the maximum point at this time, the side to which the antenna is not connected continues to be selected thereafter.

On the other hand, when the noise signal level and the threshold level have the relationship shown in FIG. 3, when the electric field strength of the two receiving antennas becomes less than Ea, the noise signal level always becomes more than the threshold level. Therefore, the switching operation by the switching circuit 12 is always performed, and if the electric field strengths of the two receiving antennas are different, abnormal noise may occur. FIG. 4 is a waveform diagram showing abnormal sound generation when the receiving antenna 11a has a power of about 10 dBμ and the receiving antenna 11b has a power of 0 dBμ or less.
B is the output waveform of the receiving antenna 11b, C is the receiving antenna switching pulse waveform (switching frequency is 2 to 5 KHz), and D is the output of the switching circuit 12, resulting in abnormal noise.

<Purpose of the invention> An object of the invention is to provide a diversity receiving device that selects a predetermined main antenna when the electric field strength of all receiving antennas falls below a predetermined value.

Another purpose of the present invention is to select the main antenna when the electric field strength of all receiving antennas falls below a predetermined value, and to stop the antenna switching operation to prevent abnormal noise from occurring due to the switching operation. An object of the present invention is to provide a diversity receiving device that can improve the S/N ratio in a weak electric field.

Yet another purpose of the present invention is to create diversity by making the high-gain antenna the main antenna and the low-gain antenna the sub, and by selecting the main antenna when the electric field is weak. An object of the present invention is to provide a receiving device.

<Summary of the invention> The invention comprises at least two receiving antennas, a switching circuit for selecting one of the receiving antennas,
FM receiver and determines whether a noise signal included in the output signal of the FM receiver has exceeded a predetermined first threshold level; and a multipath noise detection circuit that causes the switching circuit to select another receiving antenna.
a detection circuit that detects whether the noise signal has exceeded the second threshold level, and a detection circuit that detects whether the noise signal has exceeded the second threshold level regardless of which receiving antenna is used; and a control circuit that controls the switching circuit so that the switching circuit is selected. According to this diversity receiving device, when the electric field strength of all receiving antennas is less than a predetermined value, a predetermined antenna with a high gain is selected, and since the switching operation of the receiving antennas is stopped, abnormal noise is generated due to switching. stops occurring,
The S/N ratio in a weak electric field is improved.

<Example> Fig. 5 is a block diagram showing an embodiment of the diversity receiving device of the present invention, Fig. 6 is a circuit diagram of the diversity receiving device of the present invention, and Fig. 7 is a circuit diagram of the diversity receiving device of the present invention. FIG. 3 is a relationship diagram between a noise signal level and a threshold level of a receiving device. still,
In FIG. 5, the same parts as those of the conventional device shown in FIG. 1 are given the same reference numerals.

The AGC circuit 17f monitors the noise signal level output from the variable gain amplifier 17b, and controls the gain of the variable gain amplifier 17b in accordance with the noise signal level, similar to the conventional device shown in FIG. Therefore, the seventh
As shown in the figure, the threshold level (first threshold level) FSL of the Schmitt circuit 17d changes substantially as shown by the dotted line in accordance with the level of the noise signal NS. When the average noise signal level is low during a medium to strong electric field (E≧Ea), when the noise signal level exceeds the first threshold level, the Schmitt circuit 17d
A multipath noise detection signal MNS is generated from
The set/reset state of bistable circuit 17e is reversed. Thereby, the switching circuit 12 selects another receiving antenna and inputs the output of the receiving antenna to the front end 13. From then on, when the electric field is medium to strong, the first threshold level is changed, multipath noise is detected, and the receiving antenna is switched depending on the noise signal level, so that the multipath noise is always kept small. A receiving antenna selection operation is performed.

On the other hand, when the received electric field strength by the receiving antenna becomes a weak electric field (E<Ea) and the noise signal level exceeds the second threshold level (the level indicated by the dashed line in FIG. 7) SSL, the detection circuit 21 generates a detection signal DS. As long as the detection signal DS is generated, the gate circuit 22 locks the set/reset state of the bistable circuit 17e to a predetermined state. As a result, the switching circuit 12 continues to input only one receiving antenna output determined by the state of the locked bistable circuit 17e to the front end 13.

Therefore, the gain of the receiving antenna 11a selected when the bistable circuit 17e is locked is determined by considering the antenna shape, mounting position, etc.
By setting the gain to be larger than the gain of , it is possible to always select the antenna side with a high gain even in a weak electric field. When only one receiving antenna is used, by connecting the receiving antenna to the side that is selected when the bistable circuit 17e is locked, the side to which no receiving antenna is connected is selected and no reception occurs. It never becomes a state.

In addition, when the electric field becomes weak, the set/reset state of the bistable circuit 17e is locked, so the switching operation of the receiving antenna is not performed during the weak electric field, and the generation of abnormal noise accompanying the switching operation is eliminated, and the S/N ratio is improved. Leads to improvement.

FIG. 6 is a circuit diagram of the diversity receiving device of the present invention, and the same parts as in FIG. 5 are given the same reference numerals. A noise signal of approximately 100 KHz or more outputted from the high-pass filter 17a is input to a variable gain amplifier 17b having a differential amplifier configuration via a capacitor _C1 , and the differential amplifier of the variable gain amplifier 17b is
The output signal of the DAMP is charged to the capacitor C ₂ via the transistors Tr ₁ to Tr ₃ and the diode D ₁ with a time constant determined by the resistor R ₁ and the capacitor C ₂ .
The charging voltage of the capacitor is applied to the variable resistance circuit VRC of the AGC circuit 17f. variable resistance circuit
Resistance value seen from the variable gain amplifier 17b side of VRC
Since R ₀ is configured to decrease as the charging voltage of the capacitor C _{2 increases} , the gain of the variable gain amplifier 17b with respect to the noise signal decreases as the noise signal increases.

The output (noise signal) of the variable gain amplifier 17b is level-shifted and half-wave rectified by the level converter 17c, and its peak value is stored in the capacitor _C3 . When the output of the level converter 17c (the terminal voltage of the capacitor _C3 ) exceeds a predetermined threshold level (first threshold level), the Schmitt circuit 17d switches the transistor _Tr4.
is turned on, the multipath noise detection signal MNS is input to the bistable circuit 17e, and the transistors Tr ₅ ,
The on/off states of transistors Tr ₇ and Tr ₈ are reversed via Tr ₆ . Further, the multipath noise detection signal MNS generated from the Schmitt reset circuit 17d is applied to the Schmitt reset circuit 17d'. The transistor Tr ₉ of the Schmitt reset circuit 17d' is turned on by the multipath noise detection signal, the charge stored in the capacitor _C3 is discharged, and the Schmitt reset circuit 17d is reset to the initial state.

Now, if we predetermine the transistor Tr ₈ of the bistable circuit 17e to select the main receiving antenna 11a and the transistor Tr ₇ to select the sub receiving antenna 11b, then when the transistor Tr ₈ is on, the transistor Tr ₁₀ will be on. , transistor
Tr ₁₁ is turned off, a high level signal is output to the output line _n , and a low level signal is output to the output line _s , causing the switching circuit 12 (see FIG. 5) to select the main receiving antenna 11a. In addition, the multipath noise detection signal MNS turns on the transistor Tr ₇ of the bistable circuit 17e.
When Tr ₈ is turned off, transistor Tr ₁₀ is turned off, transistor Tr ₁₁ is turned on, a low level signal is output to the output line _n , and a high level signal is output to the output line _s . to select the receiving antenna 11b.

From the above, when the noise signal level exceeds the first threshold level of the Schmitt circuit 17d during a medium to strong electric field (E≧Ea), the receiving antenna is switched. If the reception condition of this switched antenna is the same or worse than that of the previous antenna, the noise voltage of the output stage transistor Tr ₃ of the variable gain amplifier 17b will be equal to or larger than the voltage before switching, so the signal is switched again. circuit 17
d operates and inverts the bistable circuit 17e. Thereafter, during the repetition of such operations, the AGC circuit 17f decreases the gain of the variable gain amplifier 17b with the time constant of the resistor R ₁ and the capacitor C ₂ , so that the apparent Schmitt circuit 17d's gain decreases. 1 threshold level gradually increases, so that the better of the two antennas is finally selected. In addition, the repetition period of the above operation should be set to about 0.2 to 0.4 msec,
Furthermore, by setting the operating time constant of the AGC circuit 17 to about 1 to 2 msec, a good antenna can be selected instantaneously.

On the other hand, when the receiving electric field strength of the receiving antenna becomes weaker (E<Ea) and the noise signal level becomes higher than the second threshold level, the transistor _Tr12 of the detection circuit 21 becomes conductive. As a result, the capacitor C ₄ of the gate circuit 22 is charged with the time constant R ₂ ·C ₄ . Now, the transistor of bistable circuit 17e
When Tr ₇ is off and transistor Tr ₈ is on to select the main receiving antenna, when capacitor C ₄ is charged, transistor Tr ₁₃ of gate circuit 22 is turned on. Then, when the transistor Tr ₁₃ is turned on, the noise signal becomes higher than the first threshold level and the multipath noise detection signal MNS is output from the Schmitt circuit 17d.
Even if this occurs, the bistable circuit 17e does not invert and the main receiving antenna 11a continues to be selected.
Note that even when the transistor Tr ₇ of the bistable circuit 17e is on and the transistor Tr ₈ is off and the sub reception antenna 11b is selected, when the capacitor C ₄ is charged, the transistor Tr ₁₃ of the gate circuit 22 is turned on. turns on, transistor Tr ₇ turns off,
The transistor Tr ₈ is turned on, and the main receiving antenna 11a continues to be selected until the noise signal becomes below the second threshold level.
Then, when the noise signal becomes lower than the second threshold level, the transistor of the detection circuit 21 is activated.
Tr ₁₂ is turned off, and as a result, the charge accumulated in the capacitor C ₄ is discharged with the time constant of R ₄ ·C ₄ , and the transistor Tr ₁₃ is turned off. Thereafter, each time the noise signal level becomes equal to or higher than the first threshold level, the above-mentioned receiving antenna selection switching operation in the case of a medium to strong electric field is executed.

Although the present invention has been described above in detail with reference to embodiments, the present invention is not limited to the embodiments. For example, although a case has been described in which there are two receiving antennas, the number does not necessarily have to be limited to two and may be three or more. Furthermore, although the case has been described in which an AGC circuit is provided to change the apparent first threshold level, the first threshold level may also be changed directly in accordance with the noise level. Furthermore, although the case has been described in which the first threshold level is changed, the first threshold level may be fixed.

<Effects of the invention> As explained above, when the electric field strength of the receiving antenna becomes a weak electric field below a predetermined value, the antenna with higher gain is selected, and the antenna switching operation is stopped when the electric field is weak. , it was possible to select the most suitable receiving antenna in a weak electric field, prevent abnormal noise from occurring due to the switching operation of the receiving antenna, and improve the S/N ratio in a weak electric field. Naturally, when only one receiving antenna is used, by predetermining that antenna to be selected in a weak electric field, the side to which no antenna is connected will be selected in the weak electric field. The situation can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional diversity receiver, Figs. 2 and 3 are relational diagrams between the conventional noise signal level and threshold level, Fig. 4 is an illustration of the conventional drawbacks, and Fig. 5 6 is a block diagram showing an embodiment of the diversity receiving device of the present invention, FIG. 6 is a circuit diagram of the diversity receiving device of the present invention, and FIG. 7 is a diagram showing the noise signal level of the diversity receiving device of the present invention. This is a relationship diagram of threshold levels. 11a, 11b... Reception antenna, 12... Switching circuit, 13... Front end, 17... Multipath noise detection circuit, 17a... High pass filter, 17b... Variable gain amplifier, 17c... Level conversion circuit, 17d ... Schmitt circuit, 17
e...Bistable circuit, 17f...AGC circuit, 21
...Detection circuit, 22...Gate circuit.

Claims (1)

[Claims for Utility Model Registration] (1) At least two receiving antennas, a switching circuit for selecting one of the receiving antennas, an FM receiving device, and a noise signal included in the output signal of the FM receiving device is A multipath device that determines whether or not the threshold level has exceeded a predetermined first threshold level, and causes the switching circuit to select another receiving antenna when the threshold level has exceeded the first threshold level. A diversity receiving device having a noise detection circuit includes a detection circuit that detects whether a noise signal has exceeded a predetermined second threshold level, and a diversity receiving device that detects whether a noise signal is detected by using any receiving antenna. and a control circuit that controls the switching circuit so that a predetermined receiving antenna is selected when the reception antenna is equal to or higher than the second threshold level. (2) The multipath noise detection circuit includes a variable gain amplifier to which a noise signal is applied, an automatic gain control circuit that automatically controls the gain of the variable gain amplifier according to the output level of the variable gain amplifier, and a variable gain amplifier. Utility model registration claim (1), characterized in that it has a detection circuit that detects whether the output level of the antenna becomes equal to or higher than the first threshold level and generates a receiving antenna switching signal. diversity receiver.