JPH01236738A - Diversity receiver - Google Patents

Abstract

PURPOSE:To improve the quality of communication by detecting an average level of the reception electric field intensity and giving a maximum hysteresis for the high average level and reducing the hysteresis in accordance with reduction of the average level. CONSTITUTION:An electric field intensity discriminating part 21 consists of plural comparators, and they have second inputs (+) of level references Vgamma1, Vgamma2-Vgamman different from one another. The addition output of LPFs 137-1 and 137-2, namely, the average reception electric field intensity is received by the first input (-) of each comparator to change the output of the comparator in the discriminating part 21. According as the electric field intensity is increased, the feedback resistance value of a hysteresis giving part 22 built in a comparator 14 as a feedback resistance group Rf of an operational amplifier is reduced because it is necessary to increase the hysteresis. According as the electric field intensity is reduced, the feedback resistance value is increased and the hysteresis is reduced as prescribed. Thus, the degradation in S/N of the output is improved.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a diversity receiver suitable for reception in situations where strong and weak electric fields frequently appear, such as an on-vehicle FM receiver. The purpose is to provide a diversity receiver that can suppress as much as possible the deterioration of the S/N of the demodulated output caused by switching to the grid or vice versa. It has a detection unit and a switch that compares the level of each of the received electric field strengths, selects the higher side, and sends out a demodulated output, and detects the average level of each of the received electric field strengths and compares the level with respect to a plurality of reference levels. and a hysteresis providing section that provides hysteresis to the comparison level when comparing the received field strength, and provides maximum hysteresis when the average level is high, and determines the average level. The configuration is such that the smaller the hysteresis becomes, the smaller the hysteresis becomes.

[Industrial application field]

The present invention relates to a diversity receiver suitable for reception in situations where strong and weak electric fields frequently appear, such as a vehicle-mounted FM receiver.

Diversity, especially spatial diversity type receivers can quickly respond to changes in the electric field and can always maintain high quality reception. However, responding too quickly to changes in the electric field will actually degrade reception quality. The present invention refers to how to follow such electric field fluctuations.

[Conventional technology]

FIG. 5 is a schematic block diagram showing a general diversity receiver. In this figure, ATl and Ar1 are first and second antennas spaced apart from each other, which supply radio frequency signals RF1 and RF2 to the first and second receivers 11 and 12, respectively.

Since it is a diversity receiver, it first detects which of the first and second receivers 11 and 12 has a higher reception level, and selectively selects the higher demodulated signal (Sl or 32) by switching the switch 15. demodulated output S. Get it as ut. First, the electric field strength detection unit 13 determines which reception level is higher.
receives the intermediate frequency signals IFI and IF2 from the receivers 11 and 12 and detects each electric field strength, and the electric field strength comparison unit 14 compares the magnitude of each detection result. Assuming that the system of the first receiver 11 has a high electric field strength, the detection result from the comparator 14 is “
H", the first switch 16 is turned on, and the first demodulated signal S1 becomes the demodulated output S.ut. In the opposite case, the detection result of the comparator 14 becomes "L", and the first demodulated signal S. The second switch 17 is turned on, and the second demodulated signal S2 becomes the demodulated output S out .

[Problem to be solved by the invention]

In the general diversity receiver described above, the switches 16 and 170 are turned on and off every time the electric field strengths of the first and second systems (11, 12) are switched.

However, this on/off switching is first caused by a shift in the phase characteristics of the receivers 11 and 12, and also because the switch 15 switches from the first system to the second system or vice versa. Due to the crosstalk at the time, the demodulated output S. There is a problem in that it causes deterioration of the S/N of UT.

SUMMARY OF THE INVENTION An object of the present invention is to provide a diversity receiver that can suppress as much as possible the deterioration of the S/N of demodulated output caused by switching from a first system to a second system or vice versa.

[Means to solve the problem]

FIG. 1 is a block diagram showing the basic configuration of the present invention. However, components similar to those described above are designated with the same reference numbers or symbols. Therefore, compared to the block diagram of FIG. 5, the present invention is characterized by the addition of blocks 21 and 22.

The block 21 is an electric field strength determination section, which is a first system (a system belonging to the first antenna ATL) and a second system (a system belonging to the first antenna ATL).
The received electric field strength of the system belonging to the second antenna AT2 is determined. This determination is not a determination as to whether the electric field strength is higher in the first system or the second system, but rather, the absolute value under the current reception situation is Also, it is determined which level corresponds to a plurality of predetermined reference values of different levels. Therefore, the first and second systems are judged at a rough level so that they appear to have approximately the same received field strength (average level). According to this level determination, the hysteresis applying section of block 22 is controlled. That is, the comparison operation of the electric field strength comparator 14 is given a large hysteresis or a small hysteresis.

[For production]

The present invention focuses on the empirical fact that as long as the electric field strength is high, even if there is some fading, the deterioration of the S/N of the demodulated output S out is not a concern. In other words, when the received electric field strength is high, system switching between the first system and the second system should not be performed frequently. Therefore, deterioration in S/N due to switching by the switch 15 is significantly improved.

When the received electric field strength becomes low overall, the deterioration of S/N due to fading becomes noticeable, so the hysteresis is reduced or eliminated. No hysteresis means:
This means that the original diversity receiver operation has returned.

FIG. 2 is a graph schematically showing the operating principle of the present invention, in which the horizontal axis represents the received electric field strength E, and the vertical axis represents the comparison level C of the electric field strength comparator 14 (FIG. 1). show. As long as the electric field strength E is low, as before, system switching is performed immediately (without hysteresis) depending on whether the difference in received field strength between the first system and the second system is positive or negative. When the intensity E becomes medium, a little hysteresis is added to the comparison level C,
Even if there is a slight difference in the received electric field strength between the two systems, it does not react, and only when the difference exceeds a predetermined value Δe does the switch 15
(Figure 1). When the strength E becomes considerably high, there is no reaction at all to some fading, and the switching device 5 does not perform switching unless the received field strength difference between the two systems exceeds a predetermined maximum value ΔE. . This results in [41 output S. S/N deterioration of ut is improved.

〔Example〕

FIG. 3 is a block diagram representing one embodiment of the present invention. Description of the same components as those shown in FIG. 1 will be omitted. Also, for the sake of simplicity, the switch 15 is completely redrawn schematically.

The electric field strength determining section 21 and the hysteresis applying section (indicated by H) 22, which are characteristics of the present invention, will be shown in detail later, so they are simply shown as small blocks here. What is specifically shown in comparison with FIG. 1 is the electric field strength detection section 13, which forms a so-called sample-and-hold type envelope detection. Its components include a switch 131 for system switching, a logarithmic amplifier 132 that amplifies the intermediate frequency signal (IF) of one of the systems selected by the switch 131, and an envelope detector that performs envelope line detection of the amplified output. 133, a sampling clock generator 134 that generates a sampling clock for sample and hold; a switch 136 that switches the aforementioned switch 131 in synchronization with the sampling clock; and a switch 136 that is switched in synchronization therewith and selects the envelope detection output; A low-pass filter 137-1.137-2 that low-pass filters the output of the switch 136, and a DC amplifier 138-1.138-2 that amplifies the low-pass filtered output.
The DC amplified outputs of the first and second systems are compared in level by the electric field strength comparator 14, and whichever has the higher level is the demodulated output S. Select with the switch 15 as uL.

Note that the sampling clock has a duty of 5, for example.
It is a pulse of about 10kHz at 0. 1st at 10kHz
and the second system is switched, but at the input stage of the comparator 14, the low-pass filter 137-1.137-2
The current is smoothed to a DC level.

FIG. 4 is a circuit diagram showing a detailed example of the main parts of the present invention. The comparison section 14 is shown. Electric field strength determination section 21
is composed of a plurality of comparators 211, 212, .
Vr□...Vrn each have a second human power (+). Each first manual power (-) has a low pass filter 137 to 1.1.
37-2, that is, the average received electric field strength (average level). As a result, as the electric field strength E in Fig. 2 changes, L-LL→LLL→ or H
→HH-11) l) The output of the electric field strength determining section 21 changes as shown in l). Since it is necessary to increase the hysteresis as the electric field strength E becomes higher, the feedback resistance value of the hysteresis applying section 22 incorporated in the comparator 14 as the feedback resistance group Rr of the operational amplifier (OP) is made smaller as a whole. In the figure, transistor switches (SL, S2°...Sn) connected in series with each resistor Rt are turned on.

As the electric field strength decreases, it is necessary to reduce the hysteresis, but in this case, the number of transistor switches that are turned off gradually increases, and the feedback resistance value increases as a whole, so the hysteresis is reduced as expected. It's getting smaller.

When the electric field strength falls below a predetermined low level, all transistor switches are turned off (feedback resistance is at its maximum) and hysteresis is minimal or no hysteresis.

〔Effect of the invention〕

As described above, according to the present invention, by changing the hysteresis, the switch 15 is switched in a manner appropriate to the received field strength, and the quality of communication can be improved without impairing diversity characteristics.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the principle configuration of the present invention, Fig. 2 is a graph schematically showing the operating principle of the present invention, Fig. 3 is a block diagram showing an embodiment of the invention, and Fig. 4 is the main FIG. 5 is a circuit diagram showing a detailed example of the main part of the invention. FIG. 5 is a schematic block diagram showing a general diversity receiver. In the figure, 10... diversity receiver, 11... first receiver, 12... second receiver,
13... Electric field strength detection section, 14... Electric field strength comparison section, 15... Switch, 21... Electric field strength determination section, 22... Hysteresis adding section, OP... Operational amplifier, R2. ...Return resistance.

Claims (1)

[Claims] 1. First receiver (11) and second receiver (12)
and a field strength detection unit (13) that detects each received field strength of the first and second receivers (11, 12), and compares the level of each received field strength, selects the higher side, and demodulates the received field strength. output(
In a diversity receiver having a switch (15) for transmitting a signal S_o_u_t), the average level of each received electric field strength is detected and a plurality of reference levels (V_r_1, V_r_1,
V_r_2...V_r_n), and a hysteresis applying unit (22) that applies hysteresis to the comparison level when comparing the received field strengths. A diversity receiver characterized by providing maximum hysteresis when the average level is high, and decreasing the hysteresis as the average level decreases.