JPH0314849Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Field of Application> The present invention relates to a diversity receiving device that selects a receiving antenna with which multipath noise is reduced from among two or more receiving antennas to receive signals.

<Prior Art> FIG. 5 is a block diagram of a conventional diversity receiver, in which signals received by two receiving antennas 11a and 11b with different directivities are transferred to a switching circuit 12.
The switching circuit switches the receiving antenna so that the multipath noise is reduced.
A predetermined receiving antenna output is input to the front end 13. The front end 13 performs high frequency amplification and frequency conversion to generate an intermediate frequency signal, and the intermediate frequency amplifier 14 performs intermediate frequency amplification and outputs the output.
Input to FM detector 15. The detection output of the FM detector 15 is input to the noise removal circuit 16, where the pilot signal and pulse noise are removed and sent to the next stage stereo demodulation circuit (multiplex circuit) 1.
8 and is input to the multipath noise detection circuit 17. The multipath noise detection circuit 17 extracts multipath noise components of 100 KHz or more, and when the multipath noise level exceeds a predetermined threshold level, the switching circuit 12 selects another receiving antenna. The receiving antenna output is applied to the front end 13.

The stereo demodulation circuit 16 reproduces an L-channel signal and an R-channel signal using the input stereo composite signal, and inputs each channel signal to a speaker via a low frequency amplifier (not shown) to output audio.

<Problem that the invention aims to solve> However, in conventional diversity receivers, antenna switching is performed based on multipath noise even when the received field strength is below a predetermined level, so switching operations are frequently performed. However, the problem was that the difference in reception levels between the two antennas made it difficult to hear, and the frequent switching caused switching noise.

Additionally, since the noise detection sensitivity of the noise removal circuit is kept constant regardless of the strength of the received electric field, there will be many signal cuts in weak electric fields, lowering the fidelity and making the sound distorted, making it difficult to hear well. There is also the problem.

From the above, it is an object of the present invention to provide a diversity receiving device that allows good listening even in a weak electric field.

<Means for Solving the Problems> FIG. 1 is a circuit diagram of a diversity receiving device according to the present invention.

In the figure, 1a and 1b are two receiving antennas, 2 is a front end, 3 is a level detection circuit that detects and outputs received electric field strength (received electric field level) EL,
4 is a comparison unit that compares the magnitude of the received electric field level EL and the first threshold level _SL1 , and 4a
4b is a threshold level setting circuit, and 4c is a comparator. Also, 4'
is a switching transistor circuit that turns on and outputs a high-level signal BL when the received electric field level EL exceeds the second threshold level SL ₂ (>SL ₁ ), 5 is a noise removal circuit, and 6 is a noise detection sensitivity 7 is a circuit unit having a multipath noise detector 7a and a part of a switching circuit 7b; 8 is a channel separation/high cut circuit; 9 is a separation/high cut drive circuit; and 10 is a stereo demodulation circuit.

<Operation> The switching circuit 7b is configured so that the received electric field level EL is equal to or higher than the first threshold level SL ₁ (comparator 4
c output AL is low level), the receiving antennas 1a and 1b are switched and selected based on multipath noise, and the receiving electric field level EL is below the first threshold level SL ₁ (AL is high level). In this case, a predetermined main antenna 1a is selected. Further, the switching circuit 7b outputs a switching frequency signal ACF corresponding to the antenna switching frequency.

The transistor TR1 of the noise detection sensitivity control unit 6 is activated when the received electric field level EL is below the first threshold level _SL1 (output AL is at high level), and when the received electric field level EL is at the first and second threshold level SL1. When the switching frequency signal ACF is at a predetermined level or higher between the shoring level SL ₁ and SL ₂ , it is turned off to lower the noise detection sensitivity of the noise removal circuit 5, and the received electric field level is switched between SL ₁ and SL ₂ . When the frequency signal ACF is below a predetermined level and when the second threshold level _SL2 is above, it is turned on to increase the noise detection sensitivity.

<Embodiment> FIG. 1 is a circuit diagram of a diversity receiving device according to the present invention.

In the figure, 1a and 1b are two receiving antennas with different directivity, 2 is a front end, 3 is a level detection circuit connected to an intermediate frequency amplifier (not shown) and detects received electric field strength (received electric field level) EL, 4
4 is a comparison unit that compares the received electric field level EL with a predetermined first threshold level _SL1 , 4a is a signal input circuit, 4b is a threshold level setting circuit, and 4c is a comparator.
The threshold level setting circuit 4b generates the first threshold level _SL1 by dividing the bias voltage _Vcc by a resistor R and a variable resistor VR, and by adjusting the variable resistor VR. The optimum level can be set for each set or specification.

4' is a switching transistor circuit that turns on and outputs a high-level signal BL when the received electric field level EL exceeds the second threshold level SL ₂ (>SL ₁ ).

Reference numeral 5 designates a noise removal circuit that removes a pilot signal and pulse noise contained in the detected output from an FM detector (not shown), and 6 a noise detection sensitivity control unit that controls the noise detection sensitivity of the noise removal circuit 5.
FIG. 2 is a block diagram of the noise removal circuit, and FIG. 3 is a waveform diagram of each part. The noise removal circuit 5 has a detection output
A high-pass filter 5a that receives S _DT and outputs a noise signal NSS, and a noise detection circuit 5 that detects pulsed noise NS included in the noise signal NSS.
b, a monostable multi 5c that generates a gate control pulse S _G of a predetermined time width by noise detection, gate circuits 5 d and 5 e that are normally open but are closed by the gate control pulse S _G , and a subtraction circuit that subtracts the anawag signal. 5f, and a storage circuit 5g made up of a capacitor that stores the immediately previous detection output level.

Since the output signal (stereo decoded signal) CPS of the noise removal circuit 5 is the difference voltage between the addition input and the subtraction input of the subtractor 5f, it is equal to the voltage between the terminals of the capacitor of the storage circuit 5g. Now, when no noise occurs and both gates 5d and 5e are open, the detection output _SDT is applied to the addition terminal of the subtractor 5f, and the pilot cancel signal PC is applied to the subtraction terminal, so the pilot signal is output. is canceled and only a low frequency signal appears (output signal CPS in Figure 3)
). In addition, the terminal voltage of the capacitor of the memory circuit 5g is also the detection output _SDT and the pilot cancel signal.
This becomes a differential voltage across the PC, and this differential voltage is stored in the capacitor.

In such a state, when noise NS occurs, the noise NS appears at the subtraction terminal of the subtracter 5f via the capacitor of the memory circuit 5g, and the output signal CPS from which the noise has been removed is output from the output terminal of the subtracter 5f.
is output. The reason why the noise NS appears at the subtraction terminal is that the input impedance of the subtractor 5f is so large that the capacitor becomes short-circuited in terms of alternating current.

Returning to FIG. 1, 7 is a circuit unit (for example, an IC "LA1060" manufactured by Tokyo Sanyo Electric) that includes a multipath noise detection section 7a and a part of a switching circuit 7b that performs antenna switching based on multipath noise.
FIG. 4 is a block diagram of this IC circuit "LA1060", and shows the part surrounded by the dotted line DTL in FIG. 1 in an enlarged manner.

In FIG. 4, multipath noise detection section 7a
is the noise signal output from the noise removal circuit 5
It has a noise amplifier AMP that amplifies NSS, an automatic gain control circuit AGC, and a counter MPNC that counts noise above a predetermined level that occurs within a certain period of time as multipath noise. That is,
If the count number N is greater than or equal to the predetermined number S, it is determined that the reception condition has deteriorated due to multipath noise.

The switching circuit 7b has an antenna switching control section ACC, a flip-flop FF, and an antenna switching section AST. The antenna switching control unit ACC sets the multipath noise count number N to the set value when the received electric field level EL is equal to or higher than the threshold level SL, in other words, when the signal AL input to pin 6 is at a low level. Flip-flop every time S is exceeded
In addition to changing the state of FF and using the antenna switching unit AST to select a receiving antenna different from the current receiving antenna, if the receiving electric field level EL is below the threshold level SL (signal AL is high level), Set the flip-flop FF to a predetermined state (Q=“1”)
, and causes the antenna switching section AST to select a predetermined main antenna 1a.
Further, the antenna switching control unit ACC outputs a switching frequency signal ACF corresponding to the antenna switching frequency from the terminal 6 (pin 6).

Returning to Fig. 1, 8 is a separation/high cut circuit that makes the output of the stereo demodulation circuit monaural and attenuates the high frequency components of the audio signal, and 9 is a separation/high cut circuit that makes the output of the stereo demodulation circuit monaural and _attenuates the high frequency components of the audio signal. (EL≦SL ₁ ), or when the first threshold level SL ₁ or more (SL ₁ <EL), and the switching frequency signal ACF is above a predetermined level, the separation/high-cut drive signal DS is output. The circuit 10 is a stereo demodulation circuit. The overall operation of the diversity device according to the present invention will be described below with reference to FIG.

At the time of weak electric field (EL≦SL ₁ ) When the received electric field strength is weak (for example, 20 dBμ or less), the received electric field level EL is smaller than the set first threshold level SL ₁ .
The output of the comparator 4c becomes high level.

As a result, a high level signal AL is input to the 6th pin of the IC circuit 7. When a high level signal is input to pin 6, the antenna switching control section ACC (see Figure 4) in the switching circuit 7b sets the flip-flop FF (when the Q terminal is high) regardless of the multipath noise generation situation. level). As a result, the antenna switching unit AST selects the main antenna 1a and inputs the antenna output to the front end 2.

The high-level comparator output AL is also applied to the separation/high-cut drive circuit 9 (FIG. 1), and channel separation control and high-cut control are performed. In addition, by using channel separation control to make it monaural, the S/N ratio in weak electric fields is improved compared to stereo.
Also, by removing (high-cut) high-frequency components of 7KHz or higher from each channel signal, the audible S/
The N ratio is improved.

On the other hand, in the case of a weak electric field, of course EL<SL ₂ , so
The transistor TR2 of the switching transistor circuit 4' is turned off, and the comparator 4c output
Since AL is at a high level (above the set level E _S ), the comparator CMP output of the noise detection sensitivity control section 6 becomes a low level, and as a result, the transistor TR1 of the noise detection sensitivity control section 6 is turned off and the noise detection sensitivity decreases. .

During medium electric field (SL ₁ <EL≦SL ₂ ) When the received electric field strength is at medium level (for example, 20 dBμV ~
40dBμV), the received electric field level EL becomes higher than the set first threshold level SL ₁ (however, below the second threshold level SL ₂ ), so the output signal AL of comparator 4c
becomes low level.

As a result, the diode _D3 becomes reverse biased, the output signal AL is no longer input to the 6th pin of the IC circuit 7, and the multipath noise detection section is input to the antenna switching control section ACC (see Fig. 4) in the switching circuit 7b. Antenna switching control is executed depending on the multipath noise count value N input from 7a. In other words, the antenna switching control unit ACC does not generate much multipath noise, and the calculated value N
is less than the set value S, the current antenna is continued to be selected. However, if multipath noise is occurring at a considerable density and the calculated value N exceeds the set value S, the state of the flip-flop FF is reversed and a different antenna than the currently selected one is switched to the antenna switching section. AST is selected and the antenna output is input to the front end 2.

In parallel with the above, the low level comparator output AL is connected to the separation/high cut drive circuit 9.
is also applied, thereby stopping the separation control operation and high cut operation.

Also, during medium electric field, transistor TR2 of switching transistor circuit 4' is off,
Since the comparator 4c output AL is at a low level (below the set level E _S ), the comparator CMP output of the noise detection sensitivity control section 6 becomes high level, and as a result, the transistor TR of the noise detection sensitivity control section 6
1 is turned on and the noise detection sensitivity increases.

On the other hand, when the antenna switching frequency increases during medium electric field and the level of the switching frequency signal ACF exceeds a predetermined level, the separation/high-cut drive circuit 9 performs separation control and high-cut control. At this time, when the level of the switching frequency signal ACF becomes higher than the set voltage E _S set by the resistors R2 and R3 in the noise detection sensitivity control section 6, the comparator
The output of CMP becomes low level, and the transistor
TR1 turns off and noise detection sensitivity decreases.

At the time of large electric field (SL ₂ < EL) When the received electric field strength becomes large (40 dBμV or more), the transistor of switching transistor circuit 4'
Since TR2 is turned on, a high level signal is input to the base terminal of the transistor TR1 of the noise detection sensitivity control section 6. Therefore, the transistor TR2 is turned on regardless of the output level of the comparator CMP, increasing the noise detection sensitivity.

<Effects of the invention> According to the invention, the antenna can be fixed in a weak electric field regardless of multipath noise, and
Since the noise detection sensitivity is reduced and the noise detection sensitivity is reduced even in medium electric fields when the frequency of antenna switching is high, the proportion of signals that are cut out based on noise reduction is reduced, and the fidelity is improved. It improves your listening comprehension and makes it easier to listen.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of the diversity receiver according to the present invention, Fig. 2 is a block diagram of the noise removal circuit, Fig. 3 is a waveform diagram of each part in Fig. 2, and Fig. 4 is a multipath noise detection section and switching. FIG. 5 is a block diagram of a conventional diversity receiver. 1a, 1b...Antenna, 2...Front end, 3...Level detection circuit, 4...Comparison section, 4c
...Comparator, 4'...Switching transistor circuit, 5...Noise removal circuit, 6...Noise detection sensitivity control section, 7a...Multipath noise detection section, 7b...Switching circuit, 8...Separation/
High-cut circuit, 9... Separation/high-cut drive circuit, 10... Stereo demodulation circuit.

Claims (1)

[Claims for Utility Model Registration] At least two receiving antennas, a level detection circuit that detects a received electric field level, a comparator that compares the received electric field level with a predetermined threshold level, and multipath noise. a multipath noise detection unit that outputs a signal having a value according to the magnitude of the multipath noise; A switching circuit that selects a book and selects a predetermined main antenna when the received electric field level is below a predetermined level and outputs a switching frequency signal according to the antenna switching frequency; and a pulse included in the detection output. a noise removal circuit that removes static noise and inputs it to a stereo demodulation circuit; and when the received electric field level is below the threshold level, and when the switching frequency signal is above the predetermined level even above the threshold level. 1. A diversity receiving device comprising: a noise sensitivity control section that lowers the noise detection sensitivity in the noise removal circuit and increases the noise detection sensitivity in other cases.