JPH04328916A - Receiver for mobile body - Google Patents

Abstract

PURPOSE:To prevent saturation of the receiver in a strong electric field region in which electric field fluctuation is large by automating on/off of a high frequency amplifier of the receiver used to enhance the absolute sensitivity in a weak electric field region. CONSTITUTION:High frequency amplifier circuits 2a-2d for improving the sensitivity of a weak electric field region are provided between an antenna changeover circuit 3 and plural antennas 1a-1d of the diversity system D for each antenna. An AGC circuit 10 feeds back an IF.IGC to an intermediate frequency amplifier circuit 6 and an RF.IGC to a tuner 5 based on an output of a video amplifier circuit 8. A digital conversion circuit 9 checks the strength of the electric field strength of a mobile body reception place based on a discrimination level for the IF.IGC and turns on the high frequency amplifier circuit 2 when the electric field is strong and turns off the high frequency amplifier circuit 2 when the electric field is weak.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to mobile receivers for diversity systems such as in-vehicle televisions, in-vehicle radios, and road-to-vehicle information systems, and more particularly to techniques for improving the absolute sensitivity of receivers. .

0002

2. Description of the Related Art Conventionally, some moving objects such as automobiles are equipped with a receiving device equipped with a diversity system equipped with a large number of antennas, as disclosed in Japanese Patent Publication No. 63-22650.

[0003] This type of receiving device generally employs a system in which a tuner section (high frequency amplification circuit) and an intermediate frequency amplification circuit are connected in two stages, similar to fixed (non-mobile) type receiving devices. In the case of the body, the electric field strength varies regionally, and there is a problem with the absolute sensitivity in regions where the electric field strength is 20 dBμV or less.

[0004] Therefore, in receiving apparatuses for mobile objects such as in-vehicle televisions, external high-frequency amplifiers that enable three-stage amplification in addition to the two-stage amplification described above are commercially available. This external amplifier must also be designed to prevent saturation of the receiver in areas with strong electric fields, so it is equipped with a switch to manually turn the amplifier on and off as necessary.

[0005]

[Problems to be Solved by the Invention] Manually operating an external high-frequency amplifier as described above is extremely inconvenient in a moving body, and electric field fluctuations in strong electric fields are extremely large. It was difficult to follow the switch and turn it on and off.

[0006] Furthermore, when external high-frequency amplifiers are connected to a plurality of antennas, the wiring becomes extremely complicated.

Furthermore, the high frequency amplifier is installed externally and is a separate unit from the diversity system, but this is because the external amplifier has a switch for manual operation, making the circuit complicated and extremely large. This was because it would no longer be possible to attach it under a chair. In order to reduce the size, it is also possible to provide only one high-frequency amplifier at the rear stage of the antenna switching circuit of the diversity system instead of at the front stage to make it common. However, in this method, the NF (noise figure) deteriorates in the antenna switching circuit of the diversity system, so the efficiency is much lower than that provided in the front stage of the antenna switching circuit.

The present invention has been made in view of the above points, and its purpose is to move the automation of turning on and off the high frequency amplifier in a receiver equipped with a high frequency amplifier used to increase the absolute sensitivity in weak electric field areas. The purpose is to make it possible to respond to the strength of the electric field at the receiving site, and to achieve both good sensitivity in weak electric field areas and prevention of saturation in strong electric field areas. Another objective is to miniaturize the high-frequency amplifier, which was conventionally attached externally, and equip it inside the diversity system, and to provide a receiver that can achieve high gain amplification without cross-modulation interference even in this way. It's about doing.

[0009]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a diversity system having a plurality of antennas and an antenna switching circuit for selectively controlling these antennas, and a diversity system that amplifies and receives a received signal from the selected antenna. In a mobile receiving device comprising a demodulating receiver, etc., a high frequency amplification circuit for each antenna is disposed between each antenna and the antenna switching circuit, and a high frequency amplification circuit is provided for each antenna, and Equipped with a digital conversion circuit that determines whether the electric field at the mobile reception site is above a predetermined level based on the AGC voltage and generates an on/off digital signal,
The high frequency amplifier circuit was set to be on/off controlled by a signal from this digital conversion circuit.

0010

[Operation] According to the above configuration, a high frequency amplification circuit compatible with weak electric fields is provided for each antenna in the front stage of the antenna switching circuit in the diversity system (this is referred to as a high frequency amplification circuit in the diversity system to distinguish it from other amplification circuits). is provided. When the high frequency amplification circuit in this diversity system is turned on, the number of stages of the receiver's amplification circuit increases accordingly. For example, if the existing reception amplifier circuit is equipped with a high frequency amplifier circuit with a built-in tuner and an intermediate amplifier circuit at the latter stage of the diversity system, the addition of the high frequency amplifier circuit in the diversity system will create a three-stage amplifier circuit. Configure.

[0011] The AGC voltage is used to control the gain of the above-mentioned existing amplifiers in the receiver (for example, high frequency amplification and intermediate frequency amplification on the tuner side), but in order to capture fluctuations in the receiver input level from its output. , this can be used as discrimination data to know the fluctuation of the external electric field strength. for example,
If the AGC voltage (analog voltage) is above a certain level, it is assumed that there is a weak electric field (the electric field strength is below a certain level), and the digital conversion circuit generates an on signal. On the other hand, if the AGC voltage is below a certain level (the electric field is If the intensity is above a predetermined level) or a strong electric field, an off signal is generated.

Under the above setting conditions, when a mobile object is in a weak electric field area, a signal (on signal) that operates the high frequency amplification circuit in the diversity system is always output, and the amplifier circuit of the receiver is The number of stages increases and good reception sensitivity can be obtained.

On the other hand, in areas with strong electric fields, the electric field fluctuates very rapidly, but the time in the strong electric field is long, and when the strong electric field is present, there is a signal (off signal) that stops the operation of the high frequency amplifier circuit in the diversity system. output, and the number of amplification stages in the receiver is reduced accordingly to prevent saturation of the mobile receiver.

[0014] As described above, in this problem solving means, the AGC
The voltage is converted into a digital signal using a discrimination level, and the high frequency amplifier circuit in the diversity system is automatically turned on and off using this digital signal. Since the control signal uses a digital signal with good response, it cannot be covered by AGC control (analog waveform) (in other words,
(GC control does not have the sharpness of response to follow very severe fluctuations in electric field strength) It is possible to eliminate saturation phenomena in response to electric field fluctuations in strong electric field regions.

[0015]

Embodiment An embodiment of the present invention will be explained with reference to FIGS. 1 to 3.

FIG. 1 is a block diagram of a mobile receiver according to an embodiment of the present invention.

1a to 1d are a plurality of antennas in the diversity system D, and high frequency amplification circuits 2a to 2d compatible with weak electric fields are arranged between each antenna 1a to 1d and the antenna switching circuit 3 at the subsequent stage. . 4 is a switching control circuit that sends a switching command to the antenna switching circuit 3; Among these elements, the high frequency amplification circuits 2a to 2d are integrated into a unit together with the antenna switching circuit 3 and the switching control circuit 4.

A conventional tuner 5 with a high frequency amplification circuit (RF amplifier) is provided after the diversity system D.
, a video intermediate frequency amplification circuit 6, a video detection circuit 7, a video amplification circuit 8, etc. are connected, and a video amplification signal is output to the receiver.

The output of the video amplification circuit 8 is monitored by an AGC circuit 10, and the RF/AGC and IF/A circuits are used to keep the output level approximately constant even if the input level fluctuates.
The analog voltage of the GC is fed back to each of the high frequency amplification circuit and the video intermediate frequency amplification circuit 6 of the tuner 5.

Further, the AGC voltage (here, IF/AGC) of the AGC circuit 10 is sent to the digital conversion circuit 9. The digital conversion circuit 9 is composed of an A/D converter, etc., and when the AGC voltage (analog waveform) is higher than the set discrimination level, it assumes that the electric field strength is weak (small) and generates an ON signal, and when the AGC voltage (analog waveform) is lower than the discrimination level. The setting is such that when the electric field strength is strong (large), an off signal is generated.

[0021] The conventional receiving apparatus for a mobile body does not include the digital conversion circuit 9 as described above, and instead, an on/off switch manually operated by the user is provided in the high frequency amplification circuit.

[0022] Figure 2(a) shows a speed of 60 km/h in a weak electric field area.
Figure 2(b) shows the electric field fluctuations when traveling at 60 km/h in a strong electric field area. It is clear from this that the electric field fluctuations are much more severe in strong electric field areas than in weak electric field areas. Current AGC
It is impossible to keep up with these fluctuations using technology alone. Another possibility is to improve the saturation level by increasing the dynamic range of the amplifier, but this is difficult to put into practical use due to the power supply voltage limit for on-vehicle equipment.
(Using a booster circuit is costly). In these strong electric field areas, it is necessary to turn off the amplifier circuits 2a to 2d in the diversity system D for a relatively long time and with good response (the level of waveform shaping of IF/AGC and RF/AGC using CR cannot keep up). .

Therefore, in this embodiment, one of the high frequency amplification circuits 2a to 2b (selected from 2a to 2d, and designated by reference numeral 2) in the diversity system is turned on and off in the following manner. Control.

The digital conversion circuit 9 monitors the AGC voltage (IF/AGC voltage in this case) and determines whether it is above a predetermined level. In this case, if the mobile receiver is located in a weak electric field area, the AGC voltage will only fluctuate above the level (where the electric field is below the level), so the on signal will always be emitted and the high frequency amplifier circuit 2 will be in the operating state. . As a result, in areas with weak electric fields, a three-stage amplification circuit structure is formed in combination with the high frequency amplification circuit of the tuner 5 and the video intermediate frequency amplification circuit 6 to ensure good reception.

Furthermore, when the mobile receiver is located in a strong electric field area, the electric field fluctuates drastically. FIG. 3 shows an IF/AGC analog waveform (2) corresponding to the electric field strength in this situation, and a digital waveform (2) generated by applying this to the discrimination level (2).

The broken line (a) in FIG. 3 is the electric field strength discrimination level, and the IF/AGC analog waveform (b) corresponds to this. When the IF/AGC voltage is below the discrimination level (b), it is determined that the electric field strength is above the level (a), and at this time an off signal is generated for the amplifier (high frequency amplification circuit 2), otherwise an on signal is generated. becomes. As a result, the mobile receiver has a two-stage amplification structure including the tuner 5 and the video intermediate frequency amplification circuit 6. Since the high-frequency amplification circuit 2 is turned off with good responsiveness using a digital signal even in severe electric field fluctuations, the drawback that AGC alone cannot cope with severe electric field fluctuations is eliminated and saturation phenomenon is effectively prevented.

According to this embodiment, the following effects are achieved.

(1) In a receiving device for a mobile object, the number of stages of the receiving amplifier circuit is automatically and responsively increased or decreased in response to fluctuations in electric field strength, thereby improving absolute sensitivity in weak electric field areas and Saturation in electric field areas can be prevented.

(2) By locating the high frequency amplifier circuit 2 in the diversity system before the antenna switching circuit 3, it is possible to realize a mobile receiver having a high gain amplifier without cross-modulation interference or beat interference.

(3) By eliminating the on/off switch in the high frequency amplification circuit in the diversity system,
Multiple high-frequency amplification circuits can be incorporated inside the diversity system unit while reducing the size, and wiring can be simplified compared to an external system.

[0031]

As described above, according to the present invention, in a receiver equipped with a high frequency amplifier built into a diversity system to increase the absolute sensitivity to weak electric fields, this high frequency amplifier can be used to adjust the electric field strength of a moving reception site. By automatically and responsively controlling on and off in accordance with the current situation, the sensitivity of the receiver in weak electric field areas can be increased, while also eliminating saturation of the receiver and achieving good sensitivity even in strong electric field areas with large electric field fluctuations. Can be done.

Furthermore, the high frequency amplifier, which has conventionally been attached externally, can be installed inside the diversity system while reducing its size, and even in this way, cross-modulation interference can be eliminated and high gain amplification can be achieved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a mobile wireless device according to an embodiment of the present invention.

FIG. 2 is a waveform diagram showing electric field fluctuation states in weak electric field and strong electric field regions.

FIG. 3 is an explanatory diagram showing an analog waveform of the AGC voltage in response to electric field fluctuations in a strong electric field region and a state in which this is converted into a digital waveform for turning on and off the amplifier circuit.

[Explanation of symbols]

D...Diversity system, 1a to 1d...Antenna,
2a to 2d...high frequency amplification circuit, 3...antenna switching circuit,
4...Switching control circuit, 5...Tuner (with high frequency amplification circuit), 6...Video intermediate frequency amplification circuit, 7...Video detection circuit, 8
...Video amplification circuit, 9...Digital conversion circuit, 10...AGC
circuit.

Claims (2)

[Claims] Claim 1: A mobile receiving device comprising a diversity system having a plurality of antennas, an antenna switching circuit for selectively controlling these antennas, a receiver for amplifying and demodulating a received signal from a selected antenna, and the like. , a high frequency amplification circuit for each antenna is disposed between each of the antennas and the antenna switching circuit, and whether the electric field at the mobile reception site is higher than a predetermined level than the AGC voltage output from the AGC circuit of the receiver. Turn it on after determining whether
1. A receiving device for a mobile body, comprising a digital conversion circuit that generates an OFF digital signal, and configured to control on/off of the high frequency amplification circuit by a signal from the digital conversion circuit. 2. The receiving device for a mobile body according to claim 1, wherein the high frequency amplification circuit is installed inside a diversity system.