JP2001166039A - Signal detection dircuit and ultrasonic type detector having the circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a signal detection circuit capable of preventing the occurrence of erroneous detection even if a noise level fluctuates, detecting a receiving signal at as small level as possible, and being used even in a place where noise level and its fluctuation are large. SOLUTION: This signal detection circuit is provided with a variable gain amplifying means 1 amplifying an input signal, a noise attenuation means 3 attenuating noise component from an output of the variable gain amplifying means 2, a receiving signal detection means 4 detecting the presence or absence of a receiving signal by comparing an output level of the noise attenuation means 3 with a threshold for detecting the receiving signal, and a noise detection means 2 which detects a noise level of the input signal and controls gain of the variable gain amplifying means 1 so that a noise level in an output signal of the variable gain amplifying means 1 becomes constant in accordance with the noise level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a signal detection circuit, and more particularly to a signal detection circuit suitable for use in an ultrasonic detection device such as an ultrasonic vehicle detection device.

[0002]

2. Description of the Related Art Conventionally, a signal detection circuit in an ultrasonic detection device amplifies a signal received by an ultrasonic transducer, and then attenuates unnecessary frequency components to reduce only a target frequency component signal. The detection signal is output when the wave height of the separated signal reaches an arbitrary threshold value or more, and the presence or absence of a received signal is determined based on the detection signal.

[0003]

In this conventional signal detection circuit, erroneous detection may occur when the reception noise level changes to a higher level due to a change in the surrounding noise environment during circuit operation. Also, if the signal detection level is set in advance so as not to cause erroneous detection in consideration of changes in the surrounding noise environment, a detection margin corresponding to the change in the surrounding noise environment is required. It cannot be detected.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and does not cause erroneous detection even when the reception noise level changes to a higher level due to a change in the surrounding noise environment during circuit operation. It is an object of the present invention to provide a signal detection circuit that can detect a reception signal at a level as low as possible and can be used in a place where the noise level is large and a place where the noise level varies greatly.

[0005]

A first signal detection circuit according to the present invention comprises: a variable gain amplifying means for amplifying an input signal; a noise attenuating means for attenuating a noise component from an output of the variable gain amplifying means; Receiving signal detecting means for detecting the presence or absence of a received signal by comparing the output level of the noise attenuating means with a received signal detecting threshold value; detecting a noise level in the input signal; And a noise detecting means for controlling the gain of the variable gain amplifying means so that the noise level in the output signal of the variable gain amplifying means becomes constant. With this configuration,
Even if the noise level in the received signal fluctuates, the noise level input to the received signal detection means becomes constant, so that it is not necessary to consider the fluctuation of noise when setting the threshold for detecting the received signal. The received signal detection level can be set lower accordingly.

Further, a first ultrasonic detecting apparatus according to the present invention includes the first signal detecting circuit according to the present invention. With this configuration, even if the noise level in the received signal fluctuates, the noise level input to the received signal detection means is constant. As a result, the received signal detection level can be set lower accordingly, so that the dynamic range of the detection target signal, which is the level difference between the maximum value of the received signal level and the received signal detection threshold value, can be widened.

[0007] The second signal detection circuit of the present invention comprises:
In the first signal detection circuit, the noise detection means has a noise detection threshold that can be arbitrarily set. With this configuration, it is possible to set an optimal noise detection threshold value for the surrounding noise environment in which the signal detection circuit operates.

According to a second aspect of the present invention, there is provided an ultrasonic detecting apparatus including the second signal detecting circuit according to the present invention. With this configuration, it is possible to set an optimum noise detection threshold value for the ambient noise environment in which the signal detection circuit operates. The dynamic range of the target signal can be widened.

Further, a third signal detection circuit according to the present invention comprises:
In the second signal detection circuit, the reception signal detection threshold can be arbitrarily set. With this configuration, the signal detection threshold value can be set in accordance with the optimum noise detection threshold value for the surrounding noise environment. Therefore, in the ambient noise environment in which the signal detection circuit operates, the signal detection threshold value can be minimized. And can be set to the best.

[0010] A third ultrasonic detecting apparatus according to the present invention includes the third signal detecting circuit according to the present invention. With this configuration, it is possible to set the signal detection threshold value corresponding to the optimum noise detection threshold value for the ambient noise environment, and to set the reception signal detection threshold value in the ambient noise environment in which the signal detection circuit operates. Since it can be set to the minimum and the best, the dynamic range of the detection target signal, which is the level difference between the maximum value of the reception signal level and the reception detection threshold value, can be widened.

Further, the fourth signal detection circuit of the present invention comprises: a noise attenuating means for attenuating a noise component in the input signal;
Reception signal detection means for detecting the presence or absence of a reception signal by comparing the output level of the noise attenuation means with a reception signal detection threshold value, and detecting a noise level in the input signal; Noise detection means for variably controlling the reception signal detection threshold value so that the noise level does not exceed the threshold value in response to the threshold value. With this configuration, even if the noise level in the received signal fluctuates, the received signal detection threshold value changes in conjunction with the noise level, so that erroneous detection due to noise in the received signal can be prevented.

Further, a fourth ultrasonic detecting apparatus according to the present invention includes the fourth signal detecting circuit according to the present invention. With this configuration, the threshold value for detecting the received signal changes in accordance with the fluctuation of the noise level in the received signal, so that erroneous detection due to the noise in the received signal does not occur, and the maximum value of the received signal level and the detected value of the received signal are detected. The dynamic range of the signal to be detected, which is the level difference from the threshold value for use, can be widened.

A fifth signal detection circuit according to the present invention is characterized in that in the fourth signal detection circuit, the noise detection means has a noise detection threshold which can be set arbitrarily. With this configuration, it is possible to set an optimal noise detection threshold value for the surrounding noise environment in which the signal detection circuit operates.

Further, a fifth ultrasonic detecting apparatus according to the present invention includes the fifth signal detecting circuit according to the present invention. With this configuration, it is possible to set an optimal noise detection threshold value for the surrounding noise environment in which the signal detection circuit operates, and thus the level difference between the maximum value of the received signal level and the detection threshold value. The dynamic range of the detection target signal can be widened.

The sixth signal detection circuit of the present invention comprises:
In the fifth signal detection circuit, the reception signal detection threshold can be arbitrarily set. With this configuration, it is possible to set a signal detection threshold value in accordance with the optimum noise detection threshold value for the surrounding noise environment. Can be set to the minimum and the best.

Further, a sixth ultrasonic detecting apparatus according to the present invention includes the sixth signal detecting circuit according to the present invention. With this configuration, it is possible to set the signal detection threshold value corresponding to the optimum noise detection threshold value for the ambient noise environment, and to set the reception signal detection threshold value in the surrounding noise environment in which the signal detection circuit operates. Can be set to the minimum and the best, so that the dynamic range of the detection signal, which is the level difference between the maximum value of the reception signal level and the threshold value for reception detection, can be widened.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

(First Embodiment) In the first embodiment of the present invention, even if the noise level in the received signal fluctuates,
The noise level input to the reception signal detection means is made constant, so that it is not necessary to consider the noise fluctuation when setting the reception signal detection threshold value, and the reception signal detection level can be set lower accordingly. I made it.

FIG. 1 is a circuit diagram of a signal detection circuit according to a first embodiment of the present invention. This signal detection circuit includes a buffer amplifier 6 to which a reception signal is input from a signal input terminal 5.
Receiving signal amplification gain switching means (variable gain amplification means) 1 to which the output of buffer amplifier 6 is input, and noise attenuation means 3 to which the output of reception signal amplification gain switching means 1 is input.
And a reception signal detection unit 4 to which an output of the noise attenuation unit 3 is input. The signal detection circuit also includes a noise detection unit 2 to which the output of the buffer amplifier 6 is input and the output of which is output to the reception signal amplification gain switching unit 1.

The received signal amplification gain switching means 1 includes a gain setting resistor 7 to which the output of the buffer amplifier 6 is input, an operational amplifier 9 having a feedback resistor 10, and a feedback resistor 10.
, A series circuit of a resistor 11 and a gain switch 14, a series circuit of a resistor 12 and a gain switch 15, and a series circuit of a resistor 13 and a gain switch 16.

The noise detecting means 2 includes a band elimination filter (hereinafter, referred to as BEF) 17 to which the output of the buffer amplifier 6 is input, a buffer amplifier 18 to which the output of the BEF 17 is input, an output of the buffer amplifier 18, and A noise detection threshold voltage set by the noise detection voltage setting resistors 20, 21, 22, and 23 is input, and the output of the comparison result is a comparator 25 for turning on / off the gain changeover switches 16, 15, and 14. 26 and 27.

The noise attenuating means 3 includes a band-pass filter (hereinafter referred to as BPF) 28 to which the output of the operational amplifier 9 is input, and a buffer amplifier to which the output of the BPF 28 is input.
29.

The reception signal detecting means 4 includes a buffer amplifier 29
And the received signal detection threshold voltage set by the received signal detection voltage setting resistors 31 and 32, and the comparator 34 outputs the comparison result to the detection output terminal 35 as a received signal detection output. It is configured.

In the signal detection circuit configured as described above, a reception signal received by an unillustrated ultrasonic transducer is input to the input terminal 5. This received signal is
The signal is input to the reception signal amplification gain switching means 1 and the noise detection means 2. The noise detecting means 2 attenuates the received signal component by the BEF 17 and inputs the signal component to the comparators 25, 26 and 27 via the buffer amplifier 18. Comparators 25, 26, 27
Compares the input voltage with the noise detection threshold voltage set by the noise detection voltage setting resistors 20, 21, 22, and 23, and outputs the noise detection output when the input voltage reaches the noise detection threshold voltage. Receiving signal amplification gain switching means 1
The gain changeover switches 16, 15, and 14 are turned on.

The received signal amplification gain switching means 1 amplifies the input signal by the operational amplifier 9. At this time, according to the level of the noise detection signal output from the noise detection means 2,
The gain changeover switches 14, 15 and 16 are turned on, and the feedback gain of the operational amplifier 9 is changed to change the amplification gain so that the output noise level of the reception signal amplification gain changeover means 1 becomes constant.

The output signal of the received signal amplification gain switching means 1 passes through the BPF 28 and the buffer amplifier 29 and is input to the comparator 34 of the received signal detection means 4. The comparator 34 outputs a reception signal detection voltage when the input voltage exceeds the reception signal detection threshold voltage.

At this time, even if the noise level in the received signal fluctuates, the noise level input to the comparator 34 is constant. Therefore, it is not necessary to consider the noise fluctuation when setting the reception signal detection threshold, and the reception signal detection threshold can be set lower accordingly.
Thereby, the dynamic range of the received signal, which is the level difference between the maximum value of the received signal level and the detection threshold, can be widened.

In the above description, the noise detection voltage setting resistors 20, 21, 22 and 23 are fixed resistors, but any one of them is a variable resistor so that the noise detection threshold Can be set to any value. This makes it possible to set an optimum reception noise detection voltage for the surrounding noise environment in which the signal detection circuit operates.

The reception signal detection voltage setting resistor 31 or
By setting any of 32 as a variable resistor, the threshold voltage for detecting a received signal can be set to an arbitrary value. Thus, the threshold value for detecting the received signal can be set to the minimum and the best in the surrounding noise environment in which the received signal detection circuit operates.

(Second Embodiment) In a second embodiment of the present invention, the threshold value for detecting the received signal is changed in conjunction with the fluctuation of the noise level in the received signal, so that Erroneous detection due to the noise of the system can be prevented.

FIG. 2 is a circuit diagram of a signal detection circuit according to a second embodiment of the present invention. This signal detection circuit includes a buffer amplifier 40 to which a reception signal is input from a signal input terminal 39.
, A noise attenuating means 36 to which the output of the buffer amplifier 40 is input, a reception signal detecting means 37 to which the output of the noise attenuating means 36 is input, and an output of the buffer amplifier 40 to which the output is And a noise detecting means 38 output to the control unit 37.

The noise attenuating means 36 includes a buffer amplifier 41 to which the output of the buffer amplifier 40 is input, and a buffer amplifier 41.
It comprises a BPF 42 to which the output of 41 is input, and a buffer amplifier 43 to which the output of BPF 42 is input.

The reception signal detecting means 37 includes a buffer amplifier 43
Output and received signal detection voltage setting resistors 45, 46, 47, 48,
A comparator 54 receives the received signal detection threshold voltage set at 49 and outputs a comparison result to a detection output terminal 55 as a received signal detection output.
The reception signal detection voltage setting resistors 47, 48, and 49 are connected in parallel with the reception signal detection voltage setting resistor 46 by turning on the detection voltage changeover switches 50, 51, and 52 that are connected in series.

The noise detection means 38 includes a BEF 56 to which the output of the buffer amplifier 40 is input, a buffer amplifier 57 to which the output of the BEF 56 is input, an output of the buffer amplifier 57, and noise detection voltage setting resistors 59, 60, 61. , And 62, and the comparator 64, 65, and 66 turn on / off the detection voltage changeover switches 50, 51, and 52. .

In the signal detection circuit configured as described above, a reception signal received by an unillustrated ultrasonic transducer is input to the input terminal 39. This received signal is
It is input to the noise attenuating means 36 and the noise detecting means 38.
The noise detecting means 38 attenuates the received signal component by the BEF 56 and outputs the result to the comparators 64, 65,
Enter 66. The comparators 64, 65, and 66 compare the input voltage with the noise detection threshold voltage set by the noise detection voltage setting resistors 59, 60, 61, and 62, and the input voltage reaches the noise detection threshold voltage. Then, the noise detection outputs are output, and the detection voltage changeover switches 50, 51, 52 of the reception signal detection means 37 are turned on.

On the other hand, the received signal input to the noise attenuating means 36 passes through the buffer amplifier 41, the BPF 42, and the buffer amplifier 43 and is input to the received signal detecting means 37.
The reception signal detection means 37 compares the input voltage with the reception signal detection threshold voltage by the comparator 54, and outputs the reception signal detection voltage when the input voltage exceeds the reception signal detection threshold voltage. I do.

Here, the reception signal detection threshold voltage is
Switch 50, based on the detection output of comparators 64, 65, 66
Turn on 51 and 52 to change the noise voltage in the received signal so as not to exceed the received signal detection threshold voltage of the comparator 54.
No detection signal is output from 55. That is, even if the noise level in the received signal changes, the received signal detection threshold value changes in conjunction therewith, so that erroneous detection due to the received noise does not occur. Therefore, the dynamic range of the detection signal, which is the level difference between the maximum value of the received signal level and the detection threshold, can be widened.

In the above description, the noise detection voltage setting resistors 59, 60, 61, and 62 are fixed resistors, but any one of them is a variable resistor to provide a noise detection threshold. The voltage can be set to any value. This makes it possible to set an optimum reception noise detection voltage for the surrounding noise environment in which the reception signal detection circuit operates.

Further, by making the reception signal detection voltage setting resistor 45 a variable resistor, the reception signal detection threshold voltage can be set to an arbitrary value. Thus, in an ambient noise environment in which the reception signal detection circuit operates, the reception signal detection threshold can be set to the minimum and the optimum.

[0040]

As described above, according to the present invention, even if the noise level in the received signal fluctuates, the noise level input to the received signal detecting means is constant, and therefore, when the received signal detection level is set. There is no need to consider the fluctuation of noise, and the effect that the received signal detection level can be set low accordingly.

According to the present invention, even if the noise level in the received signal fluctuates, the threshold value for detecting the received signal changes in conjunction with the noise level. Can be prevented.

Therefore, according to the present invention, even if the noise level fluctuates, erroneous detection does not occur and a received signal of the lowest possible level can be detected, so that the place where the noise level is large and the fluctuation of the noise level are large. Even in places
The effect that a signal detection circuit can be used is obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a signal detection circuit according to a first embodiment of the present invention;

FIG. 2 is a circuit diagram showing a signal detection circuit according to a second embodiment of the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 reception signal amplification gain switching means 2, 38 noise detection means 3, 36 noise attenuation means 4 reception signal detection means 8 operating potential bias 9 operational amplifier 10, 11, 12, 13 gain setting resistors 14, 15, 16 gain switching switch 17, 56 BEF 19, 30, 44, 58 Power supply 20, 21, 22, 23, 31, 32, 45, 46, 47, 48, 49 Detection voltage setting resistor 25, 26, 27, 34, 54, 64, 65, 66 Comparator 28, 42 BPF 31, 32 Detection voltage setting resistor 37 Received signal detection voltage selection and detection means 50, 51, 52 Detection voltage selection switch

Claims (12)

[Claims] A variable gain amplifying means for amplifying an input signal; a noise attenuating means for attenuating a noise component from an output of the variable gain amplifying means; By comparison,
Reception signal detection means for detecting the presence or absence of a reception signal; and a noise level in the input signal, wherein the noise level in the output signal of the variable gain amplifying means is constant according to the detected noise level. And a noise detecting means for controlling a gain of the variable gain amplifying means. 2. An ultrasonic detecting apparatus having the signal detecting circuit according to claim 1. 3. The signal detection circuit according to claim 1, wherein said noise detection means has a noise detection threshold that can be set arbitrarily. 4. An ultrasonic detecting apparatus having the signal detecting circuit according to claim 3. 5. The signal detection circuit according to claim 3, wherein the reception signal detection threshold can be set arbitrarily. 6. An ultrasonic detection device having the signal detection circuit according to claim 5. 7. A received signal detecting means for detecting presence or absence of a received signal by comparing a noise attenuating means for attenuating a noise component in an input signal with an output level of said noise attenuating means with a threshold value for detecting a received signal. Means for detecting a noise level in the input signal, and variably controlling the reception signal detection threshold value in accordance with the detected noise level so that the noise level does not exceed the threshold value. And a signal detecting circuit. 8. An ultrasonic detection device having the signal detection circuit according to claim 7. 9. The signal detection circuit according to claim 7, wherein said noise detection means has a noise detection threshold which can be set arbitrarily. 10. An ultrasonic detection device having the signal detection circuit according to claim 9. 11. The signal detection circuit according to claim 9, wherein said reception signal detection threshold can be set arbitrarily. 12. An ultrasonic detection device having the signal detection circuit according to claim 11.