JPH04122380U - Noise removal circuit for measuring instruments - Google Patents

Abstract

(57) [Summary] [Configuration] A variable gain amplifier 10 that amplifies an input signal with an amplification gain set by a gain control signal, and a waveform whose level is higher than a preset bias voltage level among the output signal waveforms of the amplifier. A signal level slicing circuit 20 outputs only a portion of the signal, and when the level of the received wave that is input between the transmission of the transmitted wave and the expected reception of the reflected wave exceeds a preset reference value, a high noise level judgment signal is generated. and a gain control signal generating circuit 40 that receives the determination signal and sends a gain control signal for reducing the amplification gain to the variable gain amplifier 10. [Effect] The noise present before the target reflected echo signal is removed or reduced, the S/N ratio is improved, and erroneous measurements are less likely to occur even when the mask gate is fully open.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

This invention is based on the time interval between the transmission of a pulsed transmission wave and the reception of a reflected wave from a detection target. This invention relates to a noise removal circuit in a measuring instrument that measures.

0002

[Conventional technology]

Measuring instruments such as berthing speed meters, ultrasonic radars, and ultrasonic level meters use pulsed transmitted waves. The time interval between the transmission of the signal and the reception of the reflected wave from the detection target is measured, and from this time information, It is configured to obtain the desired information. With this type of measuring instrument, the original received wave Noise due to obstacles, medium density changes, multiple reflections, etc. is often received before and after the Happens often.

0003 As an example, the signal waveform received by an ultrasonic range finder is shown in Figure 11a. vinegar. In the same figure, the waveform indicates the transmission leakage signal, and the waveform indicates the noise signal. Indicates the reflected echo signal from the object to be measured using the ultrasonic rangefinder, etc. indicates the number of minutes, and indicates the number of multiple reflection echoes.

0004 As shown in the figure, there is a noise signal before the desired reflected echo signal. Then, a measuring device such as an ultrasonic ranging device detects the reflected echo from the noise signal. -Misidentify it as a signal and mismeasure it.

[0005] In order to prevent such erroneous measurements, measuring instruments such as ultrasonic range finders use After capturing the desired reflected echo signal, the Therefore, applying a mask gate using a transmission mask signal as shown in FIG. 11b above. There is.

[0006] This mask gate is placed immediately before the expected reception of the desired reflected echo signal. It opens and acts to enable reception of subsequent signal components. Figure 11c shows that in this case The resulting signal waveform is shown.

[0007] Additionally, this mask signal is applied only during the expected arrival time of the desired reflected echo signal. Mask gates may be controlled to open and then close again. . This example is shown in dashed lines in Figure 11b. In this case, the belief shown in Figure c. There will be no issue.

[0008] The above mask signal is a movement of the target reflected echo signal (movement of arrival time) It is called a tracking gate because it is controlled to move in synchronization with the , is controlled to open just before the arrival of the target reflected echo signal.

[0009] Ultrasonic distance measuring devices, etc., detect the noise that exists before the target reflected echo signal. The masking using the mask signal as shown in Figure 11b above is not recommended. By applying the gate, a signal waveform as shown in figure c can be obtained, which is extremely safe. It is expected that measurements can be carried out accurately.

0010 The circuit shown in Figure 12 is a conventional noise removal circuit for measuring instruments that has such a function. It is. This noise removal circuit includes an amplifier 1 that amplifies the input signal and a mask signal. A mask signal generation circuit 2 that generates a signal, and an analyzer that opens and closes using the mask signal as a control signal. and a log switch 3. This analog switch 3 is shown in Fig. 11 above. It is open during the mask signal generation period when the mask signal shown in b is at a high level, Prevents output of input signal.

[0011]

[Problem that the idea aims to solve]

As mentioned above, conventional noise removal circuits are somewhat effective in removing noise. This is promising, but depending on the measurement conditions, the following problems may occur.

0012 In other words, due to sudden displacement of the measurement target, etc., the waveform in FIG. As shown in figure d, the reflected echo signal shown as As shown in figure e, the output signal waveform is 0, that is, the target This means that the reflected echo signal cannot be captured. Not only multiple echo signals Alternatively, the next noise signal may be captured and erroneously measured.

[0013] In order to avoid such inconvenience, an ultrasonic ranging device using a conventional mask signal is used. At each fixed period or every fixed number of measurements, as shown in Fig. 11f, Fully open the screen gate and always check whether you are capturing the desired reflected echo signal. This creates a need to check. However, when fully opening this mask gate, Of course, control is performed so as not to pass any transmission leakage signals.

[0014] However, when the mask gate is fully opened, there is a A contradiction arises in that there is a possibility that noise components may be captured.

[0015] In addition, even when mask gate is set, noise that enters just before the reflected echo signal There is also the problem that erroneous measurements may occur.

[0016] The present invention was developed to solve these problems, and the target reflection effect is Improves S/N by removing or reducing the noise that exists before the signal To provide a noise removal circuit for a measuring instrument that is unlikely to cause erroneous measurements even when the gate is fully open. With the goal.

[0017]

[Means to solve the problem]

This invention is based on the time interval between the transmission of a pulsed transmission wave and the reception of a reflected wave from a detection target. A noise removal circuit for a measuring instrument that measures As, Variable gain amplifier that amplifies the input signal with an amplification gain set by a gain control signal and, A bias voltage of a preset level is applied from the output signal voltage of the variable gain amplifier. The part of the signal waveform whose level is higher than the bias voltage level. a signal level slice circuit that outputs only the The level of the input received wave after the transmission of the transmitted wave until the predicted reception of the reflected wave is , compare it with a preset reference value, and when it exceeds it, send a high noise level judgment signal. a noise level judgment circuit to output; In response to the above high noise level judgment signal, a gain control signal is sent to reduce the amplification gain. and a gain control signal generation circuit that generates a gain control signal and sends it to the variable gain amplifier. Features.

[0018] The above signal level slicing circuit, for example, A subtraction circuit that reduces the corresponding bias voltage and outputs signals below the above slice level. and a circuit that prevents this.

[0019] The noise level determination circuit may include, for example, a determination gate means for setting a determination period. , and a comparison circuit that compares the input signal with a reference value.

[0020] Further, the gain control signal generation circuit described above may perform standard gain settings, for example. In addition, a gain setting/gain adjustment is performed to change the standard gain in response to the high noise level judgment signal. and means for converting the set gain into an analog gain control signal. It consists of

[0021]

[Effect]

In the above problem solving means, the signal level slicing circuit is a variable gain amplifier. Subtract the bias voltage at a preset level from the output signal voltage to obtain the signal waveform. Among them, only the waveform portion whose level is higher than the bias voltage level is output. to this As a result, noise waveforms whose peak values are below the bias voltage level are removed.

[0022] The above noise level judgment circuit measures the noise level between the transmission of the transmitted wave and the expected reception of the reflected wave. The level of the received wave input during this period is compared with a preset reference value. As a result of the comparison, When the level of the received wave exceeds the reference value, a high noise level judgment signal is output.

[0023] The gain control signal generation circuit receives the high noise level determination signal and generates an amplification gain. A gain control signal is formed to reduce the gain, and this gain control signal is applied to the variable Send to gain amplifier.

[0024] The above variable gain amplifier receives this gain control signal and reduces the amplification gain of the input signal. and amplify it. As a result, the above signal level slicing circuit and the above noise level A signal waveform whose level has been lowered is input to the determination circuit.

[0025] This eliminates noise waveforms whose peak values exceed the reference value, and increases the signal level. In the chair circuit, all noise signals are removed. Also, the noise level judgment circuit , Similarly, there are no waveforms exceeding the determination reference value. If the noise exceeds the standard value If , the amplification gain will be further reduced due to the same effect as above. can be more responsive.

[0026] Therefore, according to the present invention, the amplification gain of the input signal is determined by the peak value of the noise after amplification. The signal level can be set to be below the slice level of the slice circuit, so the noise is removed and only reflected echo signals greater than the slice level are extracted. As a result, the noise that exists before the target reflected echo signal is removed or reduced. This improves the S/N ratio and makes it difficult to cause erroneous measurements even when the mask gate is fully open. can.

[0027]

【Example】

Embodiments of the present invention will be described with reference to the drawings.

[0028] FIG. 1 shows the configuration of a first embodiment of the noise removal circuit for a measuring instrument according to the present invention.

[0029] The first embodiment of the present invention shown in the figure is applied to an ultrasonic distance measuring device, and is a variable gain gain amplifier 10, signal level slicing circuit 20, noise level determination circuit 30, and gain amplifier 10; The control signal generating circuit 40 is configured to include a control signal generating circuit 40. Note that in this example, the signal level An amplifier 50 is placed after the Rice circuit 20, but this can be omitted. .

[0030] The variable gain amplifier 10 is composed of, for example, an operational amplifier, and generates a gain control signal, which will be described later. Amplify the input signal with the amplification gain dictated by the gain control signal from the raw circuit 40 . In the case of this embodiment, this input signal is a wave received by an ultrasonic receiver (not shown). It is a first wave. However, a pulse signal obtained by detecting this may also be used. .

As shown in FIG. 2, the signal level slicing circuit 20 connects resistors R ₁ and R ₂ forming an input circuit and a resistor R ₃ forming a feedback circuit to an inverting input terminal, and operates an adder. , and a diode D on the output side of the operational amplifier 21 to cut off output of an output voltage below the zero line. The output of the variable gain amplifier 10 is input to the operational amplifier ₂₁ as an input signal via a resistor R1. Further, a bias voltage +E _b from a bias power supply E _B for raising the zero line of the output voltage to a slice level is input via a resistor R ₂ .

As shown in FIG. 3, the noise level determination circuit 30 includes a comparator 31 that compares the input voltage with the reference voltage E _r of the reference power source E _R , a noise level determination gate signal generation circuit 32 , and a noise level determination gate. 33, and a flip-flop circuit 34 that holds the determination result. A transmission mask signal and a tracking gate signal are input to the noise level determination gate signal generation circuit 32. Further, the noise level judgment gate 33 is composed of an AND gate circuit, and performs the logical product of the noise level judgment gate signal and the comparison output of the above-mentioned comparator, and when the input voltage exceeds the reference power supply E _r within the noise level judgment gate. , outputs a high noise level determination signal. The flip-flop circuit 34 is set by this high noise level determination signal and holds the logical product.

[0033] The gain control signal generation circuit 40 performs standard gain settings as shown in FIG. Both have a gain setting that changes the standard gain in response to the above high noise level judgment signal. ・The preset counter 41 constituting the changing means and the analog gain and a decoder 42 constituting means for converting the obtained control signal into a control signal. Preset card The counter 41 has a standard amplification gain set in advance, and can be used for the above-mentioned high noise level judgment. When a signal is sent, it counts down by one pulse.

[0034] Next, regarding the operation of the first embodiment configured as described above, the above-mentioned figures and FIGS. This will be explained with reference to 7.

[0035] In FIG. 1, the input signal amplified by the variable gain amplifier 10 has a signal level The signal is sent to the chair circuit 20 and the noise level determination circuit 30. This input signal typically has , as shown in Figure 5a, the reflected echo signal and the noise signal in front of it, This includes multiple reflected echoes and noise signals.

[0036] Also, in the same figure, the waveform is a transmission pulse, but it is shown for convenience of explanation. This is not included in the actual input signal, and its leakage is also included in the transmission mask game. removed by

[0037] This transmission mask gate is not shown in this embodiment, but for example, as shown in FIG. A gate circuit can be provided after the amplifier. mask gate As shown in Figure 5c, opening/closing is performed by a transmission master that is triggered by a transmission command pulse. By blocking reception during this period, leakage transmission pulses are prevented. This prevents erroneous measurements by preventing signal interference.

[0038] In addition, the ultrasonic distance measuring device to which this embodiment is applied also includes the above-mentioned conventional example. As shown above, the noise signal that enters between the time the transmitted pulse is sent and the reflected echo is received is A mask gate is set for removal purposes. This mask gate usually targets It tracks the movement of the reflected echo signal and changes the opening position of the gate. Because of this, it is especially called a tracking gate.

[0039] Although not shown in this embodiment, this tracking gate is used for the transmission mask described above. It is set by providing a gate circuit in the same way as a gate. This tracking gate Opening/closing is performed by a tracking gate signal. This tracking gate signal The signal is usually set based on the reception position of the previous reflected echo signal.

[0040] Note that a tracking gate can be used as the above transmission mask gate. Wear.

[0041] Therefore, in the ultrasonic distance measuring device to which this embodiment is applied, the above-mentioned tracking The noise signal input just before receiving the reflected echo signal is affected by the minutes are blocked. Therefore, in the following, this tracking gate is in an open state. Explain about the time.

The signal level slice circuit 20 to which the input signal is sent is a circuit that functions to subtract a certain level of voltage from the input signal and output it. That is, noise is removed by applying a bias voltage E _b in the range shown by the following equation to the inverting input terminal of the operational amplifier 21.

[0043]

[Math 1]

[0044] Here, E _r is a reference voltage of a reference power supply E _R of the noise level determination circuit 30, which will be described later. Further, V _f indicates the forward voltage of the diode D of the signal level slice circuit 20.

Now, as shown in FIG. 6a, the input signals to the signal level slicing circuit 20 are a reflected echo signal whose peak value E _e is greater than the reference voltage E _r and a reflected echo signal whose peak value E _n is greater than the reference voltage E r. If a noise signal component smaller than E _r is included, these signals will be as shown in FIG. That is, the peak value E _e of the reflected echo signal is E _e ·R ₃ /R ₁ , and the peak value E _n of the noise signal is E _n ·R ₃ /R ₁ . In this case, E _e exceeds the zero line shown in FIG. 6b, and E _n becomes less than or equal to the zero line.

By the way, in the actual circuit, the diode D is connected to the output side of the operational amplifier 21, so as shown in _FIG . The output of the signal voltage is blocked, and only the original reflected echo signal is output.

[0047] Here, if the noise signal includes a peak value E _n larger than the reference voltage E _r (not shown), in that case, the peak value of the noise signal The portion of the value that exceeds the zero line will be output. In preparation for such a case, the noise level is monitored by the noise level determination circuit 30.

In the noise level determination circuit 30, in order to set this noise level monitoring period, the noise level determination gate signal generation circuit 32 detects the fall of the above-mentioned transmission mask signal and the tracking as shown in FIGS. 5c to 5e. A noise level determination gate signal is created from the falling edge of the gate signal. This noise level determination gate signal opens the noise level determination gate 33 during the period t _n . Note that the noise level determination gate signal generation circuit 32 does not necessarily need to receive the transmission mask signal and the tracking gate signal as long as the same noise level determination gate signal can be generated.

The comparator 31 compares the input voltage with a reference voltage E _r and outputs a high level signal if there is an input voltage exceeding the reference voltage E _r . That is, when there is an input signal shown in FIG. 5a, binarized signals ',',' as shown in FIG. 5f are output to the point A in FIG.

These binary signals are ANDed by the noise level judgment gate 33, and among them, those outputted during the period _tn are outputted as a high noise level judgment signal from the gate 33. "1" is output as . FIG. 5g shows the signal waveform at point B in FIG.

[0051] This judgment signal is input to the terminal of the flip-flop circuit 34, and the judgment signal is input to the terminal of the flip-flop circuit 34. The pull circuit 34 is placed in the set state. As a result, this judgment signal is It is held in circuit 34 and output as a high noise level judgment signal from its Q terminal. Powered. Figure 5h shows the high noise level judgment signal output to point C shown in Figure 3. vinegar. Note that the flip-flop circuit 34 is reset by the transmission command pulse signal. It will be done.

[0052] The gain control signal generation circuit 40 generates a gain set in a preset counter 41 shown in FIG. While outputting the gain control signal, as shown in Figure 7, whether the noise level judgment output is “1” or not. It monitors whether it is “0” and if it is “1”, it lowers the gain of the variable gain amplifier 10 by a certain amount. , the gain control signal is changed, while when it is “0”, the current gain is maintained as it is. Ru.

That is, as shown in FIG. 6a, the gain control signal generation circuit 40 maintains the gain control signal as it is when the peak value of the noise signal is smaller than the reference voltage E _r . On the other hand, as shown in FIG. 5a, when the peak value of the noise signal is larger than the reference voltage E _r , the preset counter 41 is counted down by one pulse, the set value is changed, and the decoder 42 calculates the corresponding gain. Output as a control signal.

[0054] Variable gain amplifier 10 increases the input signal with the gain dictated by this gain control signal. Width.

Now, if the gain is lowered and a noise signal of the same level as the previous one is input, its output level will be lower than the previous one. As a result, if the peak value becomes smaller than the reference voltage E _r , this noise signal is removed in the signal level slice circuit 20. Further, the noise level determination circuit 30 does not output a high level determination signal, and the amplification gain of the variable gain amplifier 10 is maintained as it is.

On the other hand, when a noise signal whose peak value is larger than the reference voltage E _r is input, the same operation as described above is repeated to further lower the amplification gain of the variable gain amplifier 10 by a certain amount.

[0057] In this way, according to the present embodiment, By slicing the input signal by voltage, the noise present in front of the reflected echo signal is This eliminates noise signals and prevents erroneous measurements.

[0058] Note that due to the above-mentioned slice, the waveform of the original reflected echo signal is also reduced. deer However, this can be compensated for by amplifying with the amplifier 50 in the subsequent stage. deer Also, since noise is removed, the S/N of the amplified signal is significantly improved. .

[0059] The present invention is not limited to the first embodiment described above, and various embodiments are possible for each component. . Below are some examples.

[0060] FIG. 8 shows another example of the signal level slice circuit 20.

The signal level slicing circuit 20 shown in the figure inputs the bias power supply E _B ' to the non-inverting terminal of the operational amplifier 21 to form a subtracter, and also connects the diode D in parallel with the feedback resistor R ₃ . It has been done. According to this signal level slicing circuit 20, as shown in FIG. 6d, the influence of the forward voltage V _f of the diode D is eliminated, and the signal is sliced at the zero line.

[0062] FIG. 9 shows another example of the noise level determination circuit 30.

[0063] The noise level determination circuit 30 shown in the same figure uses a noise level determination gate signal as a noise level determination gate signal. This is an example using a tracking signal.

[0064] FIG. 10 shows still another example of the noise level determination circuit 30.

[0065] The noise level determination circuit 30 shown in the same figure has a noise level determination gate that Consisting of a switch 35 that opens and closes in response to a bell judgment gate signal, the switch 35 is provided on the input side of comparator 31, and the input signal is input during the noise level judgment period. Input to comparator 31 only within the range.

[0066] In addition, in the above embodiment, the case where the noise signal component is completely removed is shown. It may be sufficient to simply reduce the peak level. For example, depending on the measuring instrument, Equipped with a circuit that recognizes signals larger than a certain threshold as reflected echo signals, In this case, even if the noise signal is not completely removed, its peak level can be It is sufficient to reduce it to a level that can be identified using a threshold value.

[0067]

[Effect of the idea]

As explained above, the present invention is based on the noise that exists before the target reflected echo signal. Eliminate or reduce noise to improve S/N and prevent erroneous measurements even when the mask gate is fully open. This has the effect of realizing a noise removal circuit for measuring instruments that is difficult to perform.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of a noise removal circuit for a measuring instrument according to the present invention.

FIG. 2 is a circuit diagram showing a signal level slice circuit constituting the first embodiment.

FIG. 3 is a circuit diagram showing a noise level determination circuit constituting the first embodiment.

FIG. 4 is a block diagram showing a gain control signal generation circuit constituting the first embodiment.

FIG. 5 is a waveform chart for explaining the operation of the first embodiment.

FIG. 6 is a waveform chart for explaining the operation of the first embodiment.

FIG. 7 is a flowchart showing the operation of the gain control signal generation circuit constituting the first embodiment.

FIG. 8 is a circuit diagram showing a signal level slicing circuit constituting another embodiment of the noise removal circuit for a measuring instrument according to the present invention.

FIG. 9 is a circuit diagram showing a noise level determination circuit constituting another embodiment of the noise removal circuit for a measuring instrument according to the present invention.

FIG. 10 is a circuit diagram showing a noise level determination circuit constituting another embodiment of the noise removal circuit for a measuring instrument according to the present invention.

FIG. 11 is a waveform diagram showing the operation of a conventional noise removal circuit for a measuring instrument.

FIG. 12 is a block diagram showing a conventional noise removal circuit for measuring instruments.

[Explanation of symbols]

10...Variable gain amplifier circuit, 20...Signal level slice circuit,
21... operational amplifier, 30... noise level judgment circuit, 31... comparator, 32... noise level judgment gate signal creation circuit,
33...Noise level judgment gate, 34...Flip-flop circuit, 40...Gain control signal generation circuit, 41...Preset counter, 42...Decoder, 50...Amplifier, R1 _{to R3 ...} Resistor, D...Diode, E _B ...Bias Power supply, E _R …Reference power supply.

──────────────────────────────────────────────── ─── Continuation of front page (72) Creator Toshio Komatsu 2-16-46 Minami Kamata, Ota-ku, Tokyo Stocks Within the company Tokimetsuku

Claims (2)

[Scope of utility model registration request] 1. A noise removal circuit for a measuring instrument that measures the time interval between the transmission of a pulsed transmission wave and the reception of a reflected wave from a detection target, the circuit for removing an input signal with an amplification gain set by a gain control signal. A variable gain amplifier to amplify, and a signal level slice that subtracts a bias voltage of a preset level from the output signal voltage of the variable gain amplifier and outputs only the waveform portion of the signal waveform whose level is higher than the voltage level. The level of the received wave that is input to the circuit after the transmission of the transmitted wave until the predicted reception of the reflected wave is compared with a preset reference value, and when it exceeds this, a high noise level judgment signal is output. The present invention is characterized by comprising a noise level determination circuit and a gain control signal generation circuit that receives the high noise level determination signal, forms a gain control signal for reducing the amplification gain, and sends it to the variable gain amplifier. Noise removal circuit for measuring instruments. 2. The noise removal circuit for a measuring instrument according to claim 1, wherein the bias voltage level in the signal level slice circuit and the reference value of the noise level determination circuit are set in correspondence.