JPS60148235A - Antenna switching device - Google Patents

Abstract

PURPOSE:To prevent the reception of a signal with an antenna inferior in sensitivity at a weak input even if plural antennas is different in sensitivity by selecting a pprescribed antenna when the level of a reception signal reaches a prescribed value or below. CONSTITUTION:An on-vehicle receiver provided with a switching means 8 selecting one of plural antennas runs during reception while switching the antennas through the operation of a variable threshold comparator 8b when the antenna input is a certain level or over. In this case, an output of a fixed threshold comparator 8d is constant and an FF8c generates a switching signal selecting alternately the plural antennas based on the output of the comparator 8b in this state. When the antenna input is low and the comparator 8b is not operative at an output voltage of a level detector 7, an output of the comparator 8d stops the operation of the FF8c and sets it so that the antenna having the good sensitivity decided in advance is selected. In this case, a hysteresis circuit 8e increases a fixed voltage vased on the output of the comparator 8d and inhibits the operation of the comparator 8b uless the output voltage of a level detector detector 7 reaches to a certain level.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an antenna switching device for an antenna diversity system suitable for mobile reception, for example.

For example, receivers mounted on vehicles move as the vehicle moves, so they are susceptible to fading and multipath effects, which generate noise.

There is the inconvenience of doing so. In order to improve this problem, there has conventionally been a device shown in FIGS. 1 and 2 in which a plurality of antennas are provided and the one with the best reception condition is selected to reduce the noise.

Figure 1 is a block diagram of the antenna diversity system.
FIG. 2 is a detailed block diagram of the switching signal generator in FIG. 1. In Fig. 1, 1 and 2 are antennas, 3 is a switch circuit for selecting antennas 1 and 2, 4 is a front end, 5 is an intermediate frequency amplifier (IF AMP), and 6 is a detector (DET), whose output AF Send audio signal to OUT. 7 is a level detector for detecting the antenna input level, and 8 is a switching signal generator, which selects antennas 1 and 2 based on its output.

In FIG. 2, 8a is a level shift time constant circuit, 8b
is a variable dark value comparator, 8C is a flip-flop (FF)
The output of the FF 8c is sent to the switch circuit 3 as an antenna switching signal.

The operation of the above configuration will be explained below with reference to FIGS. 3 and 4. In addition, Fig. 3 shows antenna 1,
2 shows the relationship between the voltage across the variable dark value comparator 10 and the input level from 2, where A is the instantaneous value voltage and B is the level-shifted average value voltage. FIG. 4 shows the relationship between the voltage across the variable dark value comparator 10 and the moving distance during mobile reception, where C is the multipath noise spot, D is the antenna switching signal generation point, and E is the output of the FF 8c.

By the way, one of the antennas 1 and 2 is selected by the switch circuit 3, and the high frequency (RF) signal thereof is input to the front end 4, where it is amplified, and the IF AMP
5 to a detector 6, where an audio signal is obtained. In addition, level detector 7 is connected from IF AMP5.
A signal is applied to the antenna 1 and the signal level from the antennas 1 and 2 is detected here.

The output of the level detector 7 is connected to one input of the variable dark value comparator 8b, and the level shift time constant circuit 8a.
is connected to the other input of the variable dark value comparator 8b via
The signal applied to this other input is averaged with a level shift time constant.

The variable darkness value comparator 8b compares the above average value with the instantaneous unification, outputs the result, and inputs the result to the FF 8c. The switch circuit 3 is operated by the output of the FF 8c at this time.

During mobile reception, the level detector 7 sends out an output waveform having an envelope component as shown in A in FIG.
In response to this, the level shift time constant circuit 8a outputs an average value voltage waveform as shown by B, which is obtained by level shifting the waveform A. Waveforms A and B are applied to the comparator 8b and compared, and when A≦, antenna switching is performed □′. The FF 8C operates to alternately switch the antennas 1 and 2 at the point where the antenna □ switching signal corresponding to the multipath noise spot C is generated.

As mentioned above, the conventional device operates by comparing the instantaneous value with the level-shifted average value to alternately use the antenna 1.2, but as shown in FIG. If the condition is below, it will no longer be possible to generate a switching signal, and one of the antennas 1 and 2 will be fixed to the antenna eave. For this reason, especially when using antennas □ with different antenna sensitivities, the antenna with the lower sensitivity will be fixed. There were drawbacks such as reception sensitivity being affected by insensitive antennas.

The present invention was made in order to eliminate the drawbacks of the conventional ones as described above, and improves the reception situation by switching to a more sensitive antenna when the level detection output falls below a certain level. An object of the present invention is to provide an antenna switching device for an antenna diversity system.

An embodiment of the present invention will be described below with reference to FIG. In FIG. 5, the level detector 7, level shift time constant circuit 8as, variable threshold comparator 8b, and FF 8c may be the same as the conventional ones shown in FIG. In addition to these, the present invention provides a fixed dark value comparator 8d, which compares the output voltage of the droplet detector 7 with the fixed voltage from the DC voltage source 8f, and uses the output from the FF 8c and the hysteresis circuit 8e. The output of the hysteresis circuit 8e is connected to the fixed voltage input of the fixed dark value comparator 8d.

In the above configuration, the operation will be explained below. As shown in FIG. It is set to a value close to the level detection output voltage at the time of the antenna input level, at which antenna switching becomes impossible due to the low level.

Now, if the antenna input is above the level, the variable dark value comparator 8b operates to perform reception while switching the antenna. At this time, the output of the fixed dark value comparator 8d is constant, and in this state, the FF 8c generates a switching signal for alternately selecting antennas 1 and 2 based on the output of the variable dark value comparator 8b.

When the antenna input becomes low and the output voltage of the level detector 7 does not allow the variable dark value comparator 8b to operate, the output of the fixed dark value comparator 8d changes, and the FF 8c
operation is stopped and its output is set to select a predetermined sensitive antenna.

When shifting to such an operation, unless the fixed voltage of the fixed dark value comparator 8d becomes a voltage considerably higher than the output voltage of the level detector 7, the operation of the variable dark value comparator 8b is not shifted. A hysteresis circuit 8e increases the fixed voltage based on the output of the fixed dark value comparator 8d to prevent malfunction.

As explained above, according to the present invention, when the level of the received signal becomes less than a predetermined value, a predetermined antenna is selected with priority over a normal switching signal, so that the sensitivity of multiple antennas is reduced. Even if the signals are different, reception is no longer performed using an antenna with poor sensitivity when receiving a weak input, and the drawbacks of conventional antenna diversity systems are eliminated.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional antenna diversity system, Figure 2 is a detailed block diagram of a portion of Figure 1, Figure 3 is a graph showing the relationship between the comparator input voltage and the antenna input level, and Figure 4. 5 is a graph showing an example of a comparator input voltage and a flip-flop output waveform during mobile reception, and FIG. 5 is a block diagram showing an embodiment of the apparatus of the present invention. 1.2... Antenna, 3... Switch circuit, 7...
・Level detector, 8...Switching signal generation circuit, 8d...
・Fixed darkness value comparator, 8e...Hysteresis circuit, 8f
...DC voltage source. Patent applicant: Pioneer Co., Ltd.

Claims (1)

[Claims] +11 A plurality of antennas, a switching means for selecting one of the antennas, and comparing the average level and instantaneous change of the received signal from the antennas, and controlling the switching means based on the comparison result. In the antenna diversity system, the antenna diversity system is equipped with a switching signal generating means that generates a switching signal that operates, and selects an antenna according to reception conditions. An antenna switching device comprising priority selection signal generation means for generating a selection signal for activating the switching means to select a predetermined antenna in preference to a switching signal from the signal generation means. (2) The priority selection signal generating means has a hysteresis characteristic and maintains the selected state of the predetermined antenna until the level of the received signal becomes higher than the predetermined value by a certain value or more. An antenna switching device according to claim (1).