JPS6014542B2 - fm radio receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an FM radio receiver, particularly an in-vehicle FM radio receiver, which is equipped with at least two sets of antennas and receiving paths, and is configured to switch between the antennas and receiving paths depending on the received radio wave condition. This invention relates to improvements in FM radio receivers.

A normal car-mounted FM radio receiver, which is equipped with just one antenna and receiving path, always has an average electric field strength because the antenna directivity, radio wave propagation characteristics, etc. change from moment to moment as the car moves. Difficult to receive radio waves
Particularly in areas with weak electric fields, receiving high-quality FM broadcast waves is a waste of time.

In order to eliminate such difficulties, an FM radio for car training is provided with at least two sets of antennas and receiving paths, and is configured to automatically switch to the antenna side that is in good condition depending on the reception radio wave condition. Conventional receivers, for example,
14327, etc.

FIG. 1 shows an example of a conventional FM stereo receiver of this type.

In the figure, 1 and 2 are antennas, 3 and 4 are receiving paths, and in the receiving paths 3 and 4, 5 and 6 are high frequency amplification stages,
7 is a commonly used oscillator, 8 and 9 are intermediate frequency amplification stages, 10 and 11 are detection stages, and 12 is the intermediate frequency amplification stage 8,
The signal voltages V, , V2 from 9 are connected to interference prevention diodes D.
．． , D2, 13 and 14 are switching circuits connected to the detection stages 10 and 11 and commonly connected to the comparator 12, 15 is an inverter, and 16 is commonly connected to the switching circuits 13 and 14. 17 and 18 are low frequency amplification stages, and 19 and 20 are speakers. It is assumed that the antennas 1 and 2 are placed at the front and rear of the vehicle to receive a common broadcast wave, and that the reception channels 3 and 4 have the same characteristics. In the above configuration, the signal voltages V, , V2 from the intermediate frequency amplification stages 8 and 9
is relative to the field strength of the received radio wave, and the diodes D,...
Applied to comparator 12 via D2.

In the comparison of signal voltages in the comparator 12, V,>V
In the case of 2, the output of the comparator 12 becomes high level, and the switching circuit 13 is turned on by this high level output.
On the other hand, as a result of the high level output being applied to the switching circuit 14 via the inverter 15, its input becomes low level and is turned off. V. If <V2, comparator 1
The output of 2 becomes low level, and the switching circuit i3 is turned off by this low level output, but the switching circuit 14 is turned on because the low level output is given as a high level via the inverter 15. .

In this way, whichever of the two switching circuits 13 and 14 has a better reception radio wave condition is always turned on, so that the turned-on switching circuit 13 or 14 outputs the output of the preceding detection stage 10 or 11. is transmitted to the multiplex circuit 16 at the subsequent stage. Therefore, in the above-mentioned conventional FM radio receiver, a new problem has arisen that the audio signal is momentarily interrupted and noise is generated due to the switch time delay of the switching circuits 13 and 14.

As a result, the switching circuit 14 has a switching time delay compared to the switching circuit 13 by the required inversion time Δt in the inverter 15.

Therefore, as shown in FIG. 2, even if the switching circuit 13 is turned off at time t, the switching circuit 14 is turned on with a delay of △, so the switching output (
(input of the multiplex circuit 16) is interrupted.
An interruption in the output due to a mismatch in the switch timings of the two switching circuits feels like noise to the mind. The present invention has been made to improve the drawbacks of such conventional technology, and prevents the audio signal from being interrupted instantaneously and deteriorating the sound quality due to the response delay of the switching circuit connected to each receiving path. Therefore, instead of the inverter, a set of comparators is used, and the signal voltage is commonly applied to the positive and negative inputs of one comparator and the negative and positive inputs of the other comparator, respectively. The present invention is characterized in that the output of the switch is used to turn on and off the respective switching circuits, thereby preventing the generation of noise due to mismatch in the switch timing. The present invention will be described below with reference to the embodiment shown in the drawings. FIG. 3 shows the main part of one embodiment of the present invention, and the parts common to FIG. 1 are omitted from illustration.

In FIG. 3, 12' is a comparator used in place of the inverter 15, and the positive and negative inputs of the comparator 12 and the negative and positive inputs of the comparator 12' each have the aforementioned signal in common. Voltages V, , V2 are given. switching circuit 13,
14 are respectively connected to the outputs of the comparators 12 and 12', and in response to each comparison result, the switching circuit 13 or 14 is turned on or off, and the output of the detection stage 10 or 11 is sent to the multiplex circuit 16. Given.

When configured as described above, the switching circuit 1
4 is a direct comparator 12 similar to the switching circuit 13.
Since the trigger is triggered by the output of It can be prevented. It is desirable to use both comparators with the same characteristics, and it is possible that the output timing may be slightly different in reality, but this is ignored compared to the time delay caused by the time required for inversion of the inverter. This is as much as possible, and there is no practical problem.

As explained above, according to the present invention, the receiving characteristics are improved by using two sets of switching circuits that are equipped with two sets of antennas and tuners and automatically switch to the antenna side that is always in a good state according to the received radio wave state. In an FM radio receiver intended for improvement, since there is no time delay caused by the outside of the inverter as in the prior art, the switch timings of both of the switching circuits match, making it possible to prevent the generation of noise.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a conventional FM radio receiver, FIG. 2 is a diagram showing the characteristics of its switching circuit, and FIG. 3 is a block diagram showing the main part of an embodiment of the present invention. 1, 2... Antenna, 3, 4... Tuner, 8, 9.
...Intermediate frequency amplification stage, 10, 11...Detection stage, 12, 12'...Comparator, 16...Multiplex circuit, V,, V2... signal voltage. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. In a receiver that compares the electric field strength of the received waves received by each of the two antennas, switches to the receiving path with the higher electric field strength, and reproduces the audio, input a signal corresponding to the electric field strength of each of the above received waves. An FM radio receiver characterized in that the receiving path is switched according to the outputs of comparators having mutually different polarities.