JPH10123053A - Apparatus for removal of spike noise - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus by which a spike noise mixed with the output of an NOx sensor in a chemiluminescence analytical method can be removed surely with a simple and low-cost configuration. SOLUTION: Only a noise component in a definite frequency region out of a spark noise is separated by a noise separation circuit 4, it is amplified by an amplifier circuit 5 on the basis of the separated noise, and the spark noise is restored in a pseudo manner. Then, a substation circuit subtracts the restored spike noise from the output of a signal follower circuit 3 which substantially output a signal containing an original spike noise, and the spike noise is removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to a device for removing a spike noise mixed in a sensor used in the detected NO _x or the like based on chemiluminescence analysis.

[0002]

2. Description of the Related Art FIG.
CLD to detect the O _x is a diagram showing a schematic structure of a (chemiluminescence analyzer) 70. The silicon photodiode 71 is
Of the light generated by the reaction between NO _x and O ₃ , only the light of a specific frequency that has passed through the filter 72 is received, and the NO _x concentration is detected based on the output. Here, since the current output from the silicon photodiode 71 is at a very low level (for example, about 3 pA), it is easily affected by noise. For example, Johnson noise caused by the silicon photodiode itself or its external element (mainly high resistance) has a relatively low noise level and therefore has little effect, but spike noise having a noise level several times that of the noise is originally detected. This makes it difficult to distinguish from high-speed signals. Such spike noise is caused by, for example, a cosmic ray, thermal noise of a silicon crystal, or a current flowing through a cooling element provided in the silicon photodiode 71 to keep dark current constant.

[0003] In order to remove the spike noise as described above, there is known an apparatus for detecting a signal and noise using two sensors. According to this device, one of the two sensors is supplementarily used as a noise detection sensor.
If a spike signal is input to both sensors at the same time, it is determined to be a signal to be detected, and if only one of the spike signals is detected, it is determined to be noise and this noise is removed.

[0004]

The conventional spike noise eliminator as described above has a problem that two expensive sensors are required. In addition, there is a problem in that noise is increased because a high-resistance element is used to increase the gain in a subsequent amplifier that processes the outputs of the two sensors. Further, there is a problem that a timing generator or the like for comparing two systems of outputs is required, and post-processing becomes complicated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a spike noise eliminator capable of reliably eliminating spike noise with a simple and inexpensive configuration by solving the above problems.

[0006]

Means for Solving the Problems] spike noise removal device of the present invention to solve the above problems is an apparatus for removing spike noise contained in the sensor output of the NO _x sensor in the chemical emission spectrometry A signal follower circuit that receives an input signal based on a sensor output and generates an output signal that is substantially the same as the input signal, a noise separation circuit that passes only noise components in a constant frequency region from the input signal, and a noise separation circuit. It comprises an amplifier circuit for amplifying spike noise attenuated by passing through with an amplification factor that is the reciprocal of the attenuation factor, and a subtraction circuit for subtracting the output of the amplifier circuit from the output of the signal follower circuit. In the spike noise elimination device configured as described above,
The noise separating circuit separates only a noise component in a certain frequency region from the spike noise, and amplifies the spike noise by an amplifier circuit based on the separated noise to restore the spike noise in a pseudo manner. The subtraction circuit cancels and removes the spike noise by subtracting the restored spike noise from the output of the signal follower circuit that outputs the signal including the original spike noise substantially as it is.

In the above spike noise removing device,
The input signal may be configured to be a signal from which high-speed noise of a certain frequency or higher has been removed in advance. If the high-speed noise is amplified in the restoration process, it may become larger than the original high-speed noise, and such a situation can be prevented by removing it in advance.

[0008] The spike noise eliminator includes an N
It may be provided at the last stage of the circuit processing the sensor output of the O _x sensor. By doing so, the noise on all circuits up to the final stage is removed by the spike noise removing device.

[0009]

Figure 1 DETAILED DESCRIPTION OF THE INVENTION is a block diagram illustrating, according to one embodiment, a device for removing spike noise contained in the sensor output of the NO _x sensor in the chemiluminescence assay of the present invention. In the figure, the output of the sensor 1, that is, the silicon photodiode of the CLD is input to an LPF (low-pass filter) 7 directly or after a predetermined process such as amplification, and a high-speed noise component having a certain frequency or higher is removed there. . Subsequently, the LPF 7 from which the high-speed noise component has been removed
Is input to the spike noise elimination device 2.
The spike noise elimination device 2 includes a signal follower circuit 3, a noise separation circuit 4, an amplification circuit 5, and a subtraction circuit 6. The output signal of the LPF 7 is a signal follower circuit 3
And an output signal equal to the input signal is input to the subtraction circuit 6. On the other hand, the output signal of the LPF 7 is also input to the noise separating circuit 4, where it separates and outputs spike noise of a certain frequency or more by passing only AC components of a certain frequency or more. The output is amplified by the amplification circuit 5, and the amplified output is input to the subtraction circuit 6. The subtracter 6 subtracts the output of the amplifier 5 from the output of the signal follower 3 and outputs the result to the subsequent stage.

FIG. 2 is a circuit diagram showing an example of a specific circuit configuration of the spike noise removing device 2 shown in FIG. Parts corresponding to those in FIG. 1 are denoted by the same reference numerals. 3 (A), (B), (C) and (D) show signals A, B, C and C at respective parts on the circuit of FIG. 2 when spike noise is input to the spike noise eliminator 2. It is a waveform diagram of D. However, this signal waveform shows a state in which the DC component has been removed to simplify the description. Signal A shows the original form of the spike noise.

In FIG. 2, a signal follower circuit 3 is a voltage follower provided with a negative feedback loop in an operational amplifier 31, and correctly transmits an input voltage to a subtracter 61 in a subtraction circuit 6. Therefore, the signal A is input to the subtractor 61 with the same waveform. The noise separating circuit 4 includes a capacitor 41 and a resistor 4
2 and 43, which separates a signal having a frequency equal to or higher than a predetermined frequency and outputs the signal to the amplifier circuit 5. The cutoff frequency of the noise separating circuit 4 is selected so that the attenuation ratio, that is, the level of the spike noise that passes with respect to the signal level of the original signal A is 1/2 to 1/3. The passed separation noise B has a waveform that is attenuated as compared with the signal A as shown in FIG. The cutoff frequency decreases as the capacitance of the capacitor 41 increases, so that it is possible to separate even low-frequency signals. However, when the capacitance is increased, the response of the signal transmission of the circuit deteriorates. Become intolerable. Therefore, it is preferable to select the capacitance of the capacitor 41 so that the attenuation ratio becomes 1/2 to 1/3 as described above.

The amplifier circuit 5 includes an operational amplifier 51 and resistors 52 and 53, and amplifies the separation noise B. The gain at this time is set to be the reciprocal of the above-mentioned attenuation ratio. The restored noise C after amplification has a waveform substantially similar to that of the original signal A, though there is a slight phase delay due to passing through the CR filter. As described above, the LPF 7 is provided in front of the spike noise eliminator 2 to remove the high-speed noise component. If the high-speed noise component passing through the noise separation circuit 4 is amplified by the amplification circuit 5, This is because the amplified high-speed noise component may have a peak value higher than the original high-speed noise. The subtracter 61 obtains an output signal D by subtracting the restoration noise C from the same signal as the original signal A. Since most of the spike noise components are removed by the subtraction processing, the output signal D has a flat waveform from which the noise components have been almost removed.

In the above embodiment, since the spike noise eliminator 2 can be inserted at an arbitrary position in the circuit system, noise can be eliminated from the entire amplification system by placing it in the last stage of the amplification system. Further, since the signal can be sufficiently amplified and then taken into the spike noise elimination device 2, offset drift does not become a problem. In the above embodiment, the CR filter is used for the noise separating circuit 4, but a band pass filter may be used.

[0014]

As described above, the spike noise eliminator of the present invention separates only noise components in a certain frequency region from the spike noise by the noise separating circuit, and amplifies the noise component by the amplifier circuit based on the separated noise. Since the spike noise is pseudo-reconstructed and the spike noise is removed by subtracting the restored spike noise from the output of the signal follower circuit that outputs the signal including the original spike noise substantially as it is by the subtraction circuit, With a low-cost configuration, spike noise can be reliably removed. Further, since all spike noise components are not separated in the noise separating circuit, the quick response of the circuit is not impaired.

In the above spike noise removing device,
When high-speed noise of a certain frequency or higher is removed from the input signal in advance, it is possible to prevent the high-speed noise from being amplified in the restoration process and becoming larger than the original high-speed noise. Therefore, noise can be more reliably removed.

Further, the spike noise elimination device is provided with NOx
If it is provided in the last stage of the circuit system that processes the sensor output of the sensor, noise on all circuits up to the last stage can be removed by the spike noise eliminator, thus reducing noise in the entire circuit system. Also contributes.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a circuit system including a spike noise removing device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a specific example of the spike noise removing device shown in FIG.

FIG. 3 is a diagram showing waveforms of signals A, B, C, and D in respective units on FIG.

FIG. 4 is a diagram showing a schematic structure of a CLD (chemiluminescence analyzer) for detecting NOx contained in exhaust gas of an automobile.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sensor (CLD silicon photodiode) 2 Spike noise elimination device 3 Signal follower circuit 4 Noise separation circuit 5 Amplification circuit 6 Subtraction circuit

Continuing on the front page (72) Inventor Masaru Hattori 3-5-8 Minamisenba, Chuo-ku, Osaka-shi Inside Koyo Seiko Co., Ltd. (72) Inventor Akira Tanizawa 3-58-8 Minamisenba, Chuo-ku, Osaka-shi Koyo Seiko Co., Ltd. (72) Inventor Kenichi Takahashi 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Co., Ltd. (72) Inventor Futa Kondo 7-1, Shimo-Toba Jinokoshi-cho, Fushimi-ku, Kyoto

Claims (3)

[Claims] 1. A device for removing spike noise contained in the sensor output of the NO _x sensor in chemiluminescence analysis, receives an input signal based on the sensor output, the input signal substantially identical to the output A signal follower circuit that generates a signal; a noise separation circuit that passes only noise components in a certain frequency region from the input signal; and a spike noise attenuated by passing through the noise separation circuit, an amplification factor that is a reciprocal of an attenuation factor. A spike noise eliminator, comprising: an amplifier circuit that amplifies the signal with the following; and a subtraction circuit that subtracts the output of the amplifier circuit from the output of the signal follower circuit. 2. The spike noise eliminator according to claim 1, wherein the input signal is a signal from which high-speed noise of a predetermined frequency or higher has been removed in advance. 3. The spike noise eliminator according to claim 1, wherein the spike noise eliminator is provided at a last stage of a circuit system for processing a sensor output of the NO _x sensor.