JP2000049569A - Noise reducing circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the noise reducing circuit which has superior transient response and can sufficiently remove noise of low frequency by providing a means which sets a cutoff frequency low for sufficient noise reduction and improves transient response characteristics even when the cutoff frequency is set low. SOLUTION: A differentiating circuit 1, a level detecting circuit 2, an adding circuit 3, an error amplifying circuit 4, a switch 5, and an HPF 6 are provided. When an input signal is inputted to the differentiating circuit 1 and a level detecting circuit 2 detects variation in DC level, the switch 5 is so controlled that the inversion input of the error amplifying circuit 4 reaches ground level where the quantity of variation in DC level is large. The AC component extracted by the HPF 6 from the output signal is transmitted to the error amplifying circuit 4 through the switch 5 and the error amplifying circuit 4 compares this AC component with AC reference ground level to extract only a noise component in inverted phase and adding the extracting noise component to the input signal by using the adding circuit 3 to reduce noise.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a noise reduction circuit. More specifically, the present invention relates to a noise reduction circuit capable of removing AC noise superimposed on a signal having DC level information. The noise reduction circuit according to the present invention is suitably incorporated in a power supply circuit.

[0002]

2. Description of the Related Art Conventionally, a low-pass filter (hereinafter abbreviated as LPF) or the like is used to reduce AC noise superimposed on a signal having DC level information.
FIG. 11 is a circuit diagram illustrating an example of a primary LPF including a conventional capacitor (C) and a resistor (R).

The transfer function of an LPF is given by the following equation.

Ω ₀ / (s + ω ₀ ), where ω ₀ = 1 / RC FIG. 12 is a waveform diagram showing an example of input and output waveforms of the above-mentioned conventional primary LPF. A waveform (the output waveform in FIG. 12) in which the AC noise is removed from the input signal on which the AC noise is superimposed (the input waveform in FIG. 12) is output.

[0005] However, the above conventional example has the following problems. The output waveform is a waveform that is dull compared to the original signal. To avoid this waveform dulling to some extent, it is necessary to set the cutoff frequency to a high frequency, in which case the low-frequency noise component Cannot be completely removed.

Due to the relationship between the frequency band of the original signal and the LPF characteristic for reducing noise, if the cutoff frequency of the LPF is set low in order to sufficiently reduce noise, the transient response characteristic deteriorates and the original signal waveform Becomes dull.

[0007] Due to the relationship between the frequency band of the original signal and the LPF characteristic for reducing the noise, if the cut-off frequency of the LPF is set high while emphasizing the transient response characteristic to the original signal, the noise up to the low band can be sufficiently reduced. It cannot be reduced. It is impossible to reduce noise generated in the signal output part.

[0008]

SUMMARY OF THE INVENTION The present invention has excellent transient response and can sufficiently remove low-frequency noise.
It is an object to provide a noise reduction circuit.

[0009]

A first noise reduction circuit according to the present invention comprises a differentiating circuit for detecting an amount of change in the DC level of an input signal, and a part having a large absolute value of the DC level of the output of the differentiating circuit. A level detection circuit for detecting, an addition circuit for adding a reverse phase signal of the noise signal to the input signal, an error amplifier circuit for detecting the noise signal, a switch for switching an input signal to the error amplifier circuit, and an output signal High-pass filter for extracting the AC component from the data (hereinafter abbreviated as HPF)
And characterized in that:

The first noise reduction circuit has an error amplifier circuit for extracting an AC component from an output signal, comparing the extracted AC component with an AC reference, and detecting the noise component. The DC level of the input signal changes rapidly. Since the period can be detected and the feedback loop can be cut, the transient response characteristics can be improved and noise can be reduced.

A second noise reduction circuit according to the present invention is characterized in that a rising edge of the same control signal as a control signal for switching an input signal,
A monomultivibrator (hereinafter abbreviated as MM) for outputting a pulse for a predetermined period from both falling edges, an adding circuit for adding a reverse phase signal of a noise signal to the input signal, and an error amplifier for detecting the noise signal Circuit, a switch for switching an input signal to the error amplifier circuit,
And an HPF for extracting the C component.

The second noise reduction circuit can cut off the feedback loop by detecting a period in which the DC level of the input signal changes rapidly by the input signal switching control signal, so that the transient response characteristic is improved. , Noise can be reduced.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration and operation of a noise reduction circuit according to the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 is a circuit diagram showing an example of a noise reduction circuit according to the present invention, showing a case where a differentiation circuit and a level detection circuit are provided. In FIG.
Reference numeral 1 denotes a differentiating circuit for detecting an amount of change in the DC level of the input signal, 2 a level detecting circuit for detecting a portion having a large absolute value of the level, 3 an adding circuit for adding a reverse phase signal of a noise component to the input signal, 4 Are error amplifier circuits for detecting noise components, 5
Is a switch for switching an input signal of the error amplifier circuit, and 6 is an HPF for extracting an AC component from an output signal.

In the noise reduction circuit having the above configuration, the differentiation circuit 1
When a change in DC level is detected by the level detection circuit 2, the inverting input of the error amplifier circuit 4 is grounded (hereinafter abbreviated as GND) in a portion where the amount of change in DC level is large. The switch 5 is controlled to be at the level. The AC component extracted from the output signal by the HPF 6 is transmitted to the error amplifier circuit 4 via the switch 5, and the error amplifier circuit 4 compares the AC component with a ground level serving as an AC reference. The noise is reduced by extracting only the noise component in the opposite phase and adding the extracted noise component to the input signal using the addition circuit 3.

FIG. 2 is a waveform diagram for explaining the operation of the noise reduction circuit having the above configuration. FIG. 2A shows an input signal, in which AC noise is superimposed on time-varying DC level information. FIG. 2B is a differential waveform of the input signal a, which is a waveform in which a portion where the change of the input signal is sharp is detected. FIG. 2C shows a pulse detected and output by the level detection circuit 2 when the absolute value of the differential circuit output signal b is large. FIG. 2E shows that the AC component of the output signal f is
, And a comparison is made between the GND level, which is an AC reference, and the error amplification circuit 4 to extract only a noise component. FIG. 2c shows that the input signal is rapidly changing.
During the period when the pulse is output, the feedback loop is cut by switching the input of the switch 5 to GND by the pulse in order to remove an unnecessary waveform that is not a noise component. FIG. 2f shows the output signal, and it can be seen that the noise component remains in the period when the input signal is rapidly changing, but the noise is sufficiently reduced in most other important periods.

(Second Embodiment) FIG. 3 is a circuit diagram showing another example of the noise reduction circuit according to the present invention, in which input signals are switched in place of the differentiating circuit and the level detecting circuit of FIG. 1 is different from the circuit of FIG. 1 in that an MM that outputs a pulse for a certain period from both the rising edge and the falling edge of the same control signal is provided. In FIG. 3, reference numeral 7 denotes an MM 3 which outputs pulses for a certain period from both rising and falling edges of the same control signal g as the control signal switching the input signal;
Is an addition circuit that adds an anti-phase signal of a noise component to the input signal,
4 is an error amplification circuit for detecting a noise component, 5 is a switch for switching an input signal of the error amplification circuit, and 6 is A from the output signal.
An HPF for extracting the C component.

In the noise reduction circuit having the above configuration, when the control signal g is input to the MM 7 and a pulse is output during a period in which the DC level may suddenly change, the inverting input of the error amplifier circuit 4 is set to GND. Switch 5 so that it becomes level
Is controlled. Further, the AC component extracted from the output signal f by the HPF 6 is transmitted to the error amplifier circuit 4 via the switch 5, and the error amplifier circuit 4
The noise is reduced by comparing the noise level with the ground level as a target reference, extracting only the noise component in the opposite phase, and adding the extracted noise component to the input signal using the addition circuit 3.

FIG. 4 is a waveform diagram for explaining the operation of the noise reduction circuit having the above configuration. FIG. 4A shows an input signal, which is a state in which AC noise is superimposed on time-varying DC level information. FIG. 4g shows a control signal g which is the same as the control signal switching the input signal. FIG. 4c shows MM7
Is a pulse output for a certain period from both the rising edge and the falling edge of the control signal g, so that the DC level may be rapidly changed. FIG. 4E is a waveform in which the AC component of the output signal f is extracted by the HPF 6 and compared with the GND level, which is the AC reference, by the error amplifier circuit 4 to extract only the noise component. Further, in a period in which the DC level of the input signal may suddenly change, the feedback loop is cut by switching the input of the switch 5 to GND by the pulse c in order to remove unnecessary waveforms that are not noise components. ing. FIG. 4F shows the output signal, and it can be seen that the noise component remains in the period when the input signal is rapidly changing, but the noise is sufficiently reduced in most other important periods.

Therefore, the circuit in FIG. 3 can be simplified as compared with FIG. 1 by using the control signal g.

(Third Embodiment) FIG. 5 is a circuit diagram showing an example in which a noise reduction circuit according to the present invention is applied to a power supply circuit. In FIG. 5, reference numeral 3 denotes an addition circuit for adding a negative-phase signal of a noise component from an input signal, 4 an error amplifier circuit for detecting a noise component, and 6 an H for extracting an AC component from an output signal.
PF and 8 are buffer circuits for boosting the output.

In the power supply circuit having the above configuration, the AC component is extracted from the output f, which is the power supply output, by the HPF 6 and compared with the GND level as the AC reference by the error amplifier circuit 4 to extract only the noise component in the opposite phase. And the addition circuit 3
Noise is reduced by adding to the input a which is the reference voltage. Here, the buffer circuit 8 is a drive circuit for obtaining a sufficient power supply capability.

FIG. 6 is a waveform diagram for explaining the operation of the power supply circuit having the above configuration. FIG. 6a is the input a, which is the reference voltage, with the AC noise weighted. FIG. 6E is a waveform in which the AC component of the output f, which is the power output, is extracted by the HPF 6 and compared with the GND level, which is the AC reference, by the error amplifier circuit 4 to extract only the noise component. FIG. 6F shows the output f which is the power supply output, and it can be seen that the noise is sufficiently reduced by adding the noise component of the opposite phase to the reference voltage.

In the power supply circuit, the output f which is the power supply output
Is compared with the GND level, which is an AC reference, and the feedback is applied, so that not only the noise at the input a, which is the reference voltage, is reduced, but also the noise of the entire circuit and the output impedance at the AC are amplified. The amplification factor of the circuit 4 can be reduced to the reciprocal times.

(Fourth Embodiment) FIG. 7 is a circuit diagram showing another example in which the noise reduction circuit according to the present invention is applied to a power supply circuit. The circuit shown in FIG. Is added. In FIG. 7, reference numeral 9 denotes an edge detection circuit for detecting both rising and falling edges of a control signal for switching an input; 7, an MM for outputting a pulse for a predetermined period from an edge of a pulse output from the edge detection circuit 9; An addition circuit for adding a reverse phase signal of a noise component to an input signal; 4 an error amplifier circuit for detecting a noise component; 5 a switch for switching an input signal of the error amplifier circuit; 6 an HPF for extracting an AC component from an output signal; 8 is a buffer circuit for boosting the output, 10 is a first reference power supply serving as a power supply reference, 11 is a second reference power supply serving as a power supply reference, and 13 is a reference power supply 10
And a switch for switching the reference power supply 11.

In the power supply circuit having the above configuration, when the control signal h for switching the reference power supply is input to the edge detection circuit 9, a pulse having information on the switching timing is input to the MM 7, and the input which is the reference voltage is input. The switch 5 is controlled so that a pulse is output during the period when the DC level of a suddenly changes, and the inverting input of the error amplification circuit becomes the GND level. Further, A extracted from the output signal f by the HPF 6
The C component is transmitted to the error amplifier circuit 4 via the switch 5, and the error amplifier circuit 4 compares the AC component with a GND level serving as an AC reference, and extracts only the noise component in the opposite phase. Then, the noise is reduced by adding the extracted noise component to the input signal using the addition circuit 3.
Here, the buffer circuit 8 is a drive circuit for obtaining a sufficient power supply capability. The input a as the reference voltage is 10 as the first reference power supply and 11 as the second reference power supply.
By the switch 13 controlled by the control signal h.

FIG. 8 is a waveform diagram for explaining the operation of the power supply circuit having the above configuration. FIG. 8H shows a control signal h for controlling a switch 13 for switching between a reference power supply 10 and a reference power supply 11 in order to obtain an input a which is a reference voltage. FIG. 8A shows an input a as a reference voltage output from the switch 13 and A
This shows a state where the C noise is superimposed. FIG. 8i shows an edge detected from the control signal h, which is output in the form of its absolute value. FIG. 8A shows a pulse output during a period in which the DC level rapidly changes by outputting a pulse for a certain period from the edge of the signal output from the edge detection circuit 9 by the MM 7. FIG. 8e shows the AC of output f which is the power supply output.
The components were extracted by HPF6, and the AC standard GND
This is a waveform obtained by comparing the level with the error amplifier circuit 4 and extracting only the noise component. In addition, during a period in which the DC level of the input signal may suddenly change, an unnecessary waveform that is not a noise component is removed to improve a response waveform.
The feedback loop is cut by switching the input of the switch 5 to the GND level by the pulse c. FIG. 8f shows an output f which is a power supply output. The noise component remains in a period when the input signal is rapidly changing, but it is sufficiently reduced in most other important periods. I understand.

(Fifth Embodiment) FIG. 9 is a circuit diagram showing another example in which the noise reduction circuit according to the present invention is applied to a power supply circuit. Instead of the HPF in the circuit of FIG.
The difference from the circuit of FIG. 7 is that a High Speed HPF is used.
In FIG. 9, reference numeral 9 denotes a rising edge of a control signal for switching an input;
An edge detection circuit for detecting both falling edges, 7 is an MM for outputting a pulse for a predetermined period from an edge of a pulse output from the edge detection circuit 9, and 3 is an addition circuit for adding a reverse phase signal of a noise component to an input signal. Reference numeral 4 denotes an error amplifier circuit for detecting a noise component, and reference numeral 12 denotes a Hi for extracting an AC component from an output signal whose speed is increased by being controlled by the MM 7.
gh Speed HPF, 8 is a buffer circuit for boosting the output, 10 is a first reference power supply serving as a power supply reference, 11 is a second reference power supply serving as a power supply reference, and 13 switches between the reference power supply 10 and the reference power supply 11. Switch.

In the power supply circuit having the above configuration, when the control signal h for switching the reference power supply is input to the edge detection circuit 9, a pulse i having switching timing information is output to the MM7.
Is input to Then, a pulse c is output from the MM 7 during a period in which the DC level of the input a as the reference voltage changes abruptly, and the transient response of the High Speed HPF 12 that extracts the AC component from the output f as the power supply output is improved. Is provided.

The conventional primary HPF using a CR has a transient response characteristic determined by a time constant of the CR, and has a problem that it takes time to reach a required DC level. On the other hand, in the High Speed HPF 12, the transient response characteristic can be significantly improved by short-circuiting the resistor R by SW only for a short time immediately after the DC level changes. Therefore, the output signal f is changed to A by the High Speed HPF12.
The noise is reduced by extracting the C component, comparing it with the GND level serving as the AC reference by the error amplifier circuit 4, extracting only the noise component in the opposite phase, and adding the noise component to the input signal by the adding circuit 3. Can be. Here, the buffer circuit 8 is a drive circuit for obtaining a sufficient power supply capability. The input a as the reference voltage is obtained by switching between the first reference power supply 10 and the second reference power supply 11 by the switch 13 controlled by the control signal h.

FIG. 10 is a waveform diagram for explaining the operation of the power supply circuit having the above configuration. FIG. 10h shows a reference voltage input a.
Is a control signal h for controlling the switch 13 for switching between the reference power supply 10 and the reference power supply 11 in order to obtain. FIG. 10a shows an input a as a reference voltage output from the switch 13.
Represents a state in which AC noise is superimposed. FIG.
Is an edge detected from the control signal h, and is output in the form of its absolute value. FIG. 10C shows a pulse output by the MM 7 during a period in which the DC level rapidly changes by generating a pulse for a certain period from the edge of the signal output from the edge detection circuit 9. FIG. 10A is a waveform in which the AC component of the output f that is the power supply output is extracted by the High Speed HPF 12, the GND level that is the AC reference is compared with the error amplification circuit 4, and only the noise component is extracted.
FIG. 10f shows the output f, which is the power supply output. The noise component remains in the period when the input signal is rapidly changing, but the noise is sufficiently reduced in most other important periods. I understand. In particular, according to the circuit configuration of FIG. 9, the period during which the noise remains can be set to be considerably shorter than that of the circuit configuration of FIG.

[0032]

As described above, according to the present invention,
Even if AC noise is superimposed on the input signal, in order to sufficiently reduce the noise, set a low cutoff frequency, and take measures to improve the transient response characteristics even if the cutoff frequency is set low. By providing, excellent transient response and low-frequency noise can be sufficiently removed.
A noise reduction circuit is obtained.

Further, the noise reduction circuit according to the present invention can simultaneously reduce noise generated in the signal output unit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an example of a noise reduction circuit according to the present invention.

FIG. 2 is a waveform diagram illustrating an operation of the noise reduction circuit having the configuration shown in FIG.

FIG. 3 is a circuit diagram showing another example of the noise reduction circuit according to the present invention.

FIG. 4 is a waveform diagram illustrating an operation of the noise reduction circuit having the configuration shown in FIG.

FIG. 5 is a circuit diagram showing an example in which the noise reduction circuit according to the present invention is applied to a power supply circuit.

FIG. 6 is a waveform chart for explaining the operation of the power supply circuit having the configuration shown in FIG. 5;

FIG. 7 is a circuit diagram showing another example in which the noise reduction circuit according to the present invention is applied to a power supply circuit.

FIG. 8 is a waveform chart for explaining the operation of the power supply circuit having the configuration shown in FIG. 7;

FIG. 9 is a circuit diagram showing another example in which the noise reduction circuit according to the present invention is applied to a power supply circuit.

FIG. 10 is a waveform chart for explaining the operation of the power supply circuit having the configuration shown in FIG. 9;

FIG. 11 is a circuit diagram illustrating an example of a conventional primary LPF including a capacitor (C) and a resistor (R).

12 is a waveform chart showing an example of input and output waveforms of the primary LPF shown in FIG.

[Explanation of symbols]

 Reference Signs List 1 differentiation circuit, 2 level detection circuit, 3 addition circuit, 4 error amplification circuit, 5 switch, 6 HPF, 7 MM, 8 buffer circuit, 9 edge detection circuit, 10 reference power supply, 11 reference power supply, 12 High Speed HPF, 13 switch.

Claims (2)

[Claims] 1. A differentiating circuit for detecting an amount of change in a DC level of an input signal, a level detecting circuit for detecting a portion having a large absolute value of a DC level of an output of the differentiating circuit, and a reverse phase of a noise signal to the input signal. An error amplification circuit that detects the noise signal; a switch that switches an input signal to the error amplification circuit; and a high-pass filter that extracts an AC component from an output signal. Noise reduction circuit. 2. A mono-multi vibrator for outputting a pulse for a predetermined period from both rising and falling edges of a control signal which is the same as a control signal for switching an input signal, and adding a reverse phase signal of a noise signal to the input signal. A noise amplification circuit, an error amplification circuit for detecting the noise signal, a switch for switching an input signal to the error amplification circuit, and a high-pass filter for extracting an AC component from an output signal. Reduction circuit.