JPH07297715A - A/d conversion noise suppression circuit - Google Patents

Abstract

PURPOSE:To detect noise having not been eliminated and to suppress it by allowing a control section to hold and output a digital signal when a noise detection section detects the noise so as to suppress the digital signal from an A/D converter. CONSTITUTION:Most of the noises in an analog signal with noise superimposed thereon are eliminated by an analog filter 1 and the resulting signal is given to an A/D converter 2, in which the signal is converted into a digital signal. The digital signal is given to an input buffer 4 of a control element 3 and a noise detection section 5, and the element 3 reaches a noise detection state from the initial state. When the detection section 5 detects noise, a digital signal is given from the detection section 5 to the control section 6. The control section 6 holds the digital signal and provides a holding digital signal to an output buffer 7. Simultaneously a control signal is provided for the input buffer 4 to allow the buffer 4 not to output the digital signal to the output buffer 7. The element 3 reaches a noise suppression state and keeps the state till no noise is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an A / D conversion noise suppression circuit mainly used in television receivers, video equipment and the like.

[0002]

2. Description of the Related Art In recent years, in video equipment such as television receivers and video equipment, digitization has progressed, and many of them have a digital signal processing portion therein. At that time, an A / D converter that converts an analog signal into a digital signal is indispensable, and the accuracy of the A / D converter affects subsequent digital signal processing. However, no matter how good the accuracy of the A / D converter is, if noise is mixed in the analog signal before conversion, A / D conversion will not be performed accurately, and it will be affected by noise in the subsequent digital signal processing process. I will end up. Therefore, conventionally, noise removal is performed by inserting a filter circuit into the input of the A / D converter.

FIG. 6 shows an example of a conventional noise removal circuit for A / D conversion, which is a noise removal circuit for A / D conversion of a DC voltage. As is clear from the figure, this is a simple CR low-pass filter, R = 10KΩ, C =
When the cutoff frequency fc is calculated with 0.1 μF, fc = 1 / 2πRC≈160 Hz, and the frequency characteristics are as shown in FIG. As described above, in the conventional technique, noise is removed by passing an analog signal before A / D conversion through a filter circuit and removing unnecessary frequency components.

[0004]

By the way, the conventional A / D
In the noise removal circuit at the time of conversion, in order to completely remove unnecessary harmonic components other than the direct current component in the example of FIG. 6,
It is difficult to remove all the noise, and the noise that could not be removed is superimposed on the analog signal input to the A / D converter and is A / D converted. Therefore, noise is generated in the subsequent digital signal processing process. There was a problem that was affected by.

The present invention has been made in order to solve the above problems, and it is possible to detect and suppress noise that cannot be removed by the conventional technique.
A D conversion noise suppression circuit is provided.

[0006]

SUMMARY OF THE INVENTION An A / D conversion noise suppression circuit according to the present invention is an A / D conversion means for converting an analog signal into a digital signal, and a digital signal converted by the A / D conversion means to an A / D conversion means. A noise detection section for detecting noise superimposed on the analog signal before being converted by the / D conversion means, and when this noise detection section detects noise, it holds the digital signal from the noise detection section and outputs it. In addition, a control unit is provided to prevent the digital signal from the A / D conversion means from being output.

Further, the noise detecting section calculates the difference between the current value of the digital signal data and the value one sampling period before in real time, and when the value is within a predetermined number of consecutive | 1 | steps. It is determined that noise has been detected, the control unit is set to the noise suppression state, the difference between the current value of the digital signal data and the value one sample period before is calculated in real time, and the value is equal to or more than | 2 | steps. Then, it is determined that the noise is not noise, and the noise suppression state of the control unit is solved.

Further, the noise detecting section calculates the difference between the current value of the digital signal data and the value one sampling period before in real time, and when the value is within a predetermined number of | 1 | steps continuously. It is determined that noise has been detected, the control unit is set to the noise suppression state, the difference between the current value of the digital signal data and the value one sampling period before is calculated in real time, and the value is calculated twice continuously for +1 step. If it becomes, or if it becomes -1 step twice in succession (all may include 0 between them), it is determined that it is not noise and the noise suppression state of the control unit is solved. is there.

[0009]

The control means according to the present invention enters the noise suppression state when the noise detecting section detects noise. In the noise suppression state, the digital signal data sent from the noise detection section at that time is held by the control section and output to the output side, and at the same time the digital signal data from the A / D conversion means is prevented from appearing on the output side. Suppress noise. When the noise is no longer detected, the noise suppression state is canceled.

[0010]

【Example】

Example 1. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an A / D conversion noise suppression circuit according to the present invention. In the figure, 1 is an analog filter, 2 is an A / D converter, and 3 is a control element. The control element 3 includes an input buffer 4, a noise detection unit 5,
It is composed of a control unit 6 and an output buffer 7.

Next, the operation will be described. When an analog signal on which noise is superimposed is input to the analog filter 1, most of the noise is removed here. The analog signal from which most of the noise is removed is input to the A / D converter 2 and converted into a digital signal. This digital signal is input to the input buffer 4 and the noise detection section 5 of the control element 3, and the control element 3 enters the noise detection state from the initial state. When noise is not detected by the noise detector 5, the digital signal is sent from the input buffer 4 to the output buffer 7, and the digital signal is output from the output buffer 7 to the circuit in the next stage.

When noise is detected by the noise detector 5, a digital signal is input from the noise detector 5 to the controller 6. When the digital signal is input from the noise detection unit 5, the control unit 6 holds the digital signal and outputs the held digital signal to the output buffer 7, and the control unit 6 outputs the control signal to the input buffer 4. The output is performed so that the digital signal is not output from the input buffer 4 to the output buffer 7. In this way, the control element 3 enters the noise suppression state and remains in this state until no noise is detected.

The operation of this embodiment will be described in more detail.
In this example, it is assumed that the analog signal is a DC voltage, the resolution of the A / D converter 2 is 8 bits, and the step is 256 steps, and the analog filter 1 removes noise of | 2 | steps or more. FIG. 2 shows how the digital signal output of the A / D converter 2 is affected by noise. When affected by noise, the DC voltage of the analog signal does not change. ,
The output of the A / D converter 2 changes depending on the binary value of x step and x + 1 step corresponding to noise.

Therefore, the most important point of the present invention is how to detect such noise. FIG. 3 is FIG.
6 is a state transition diagram of a counter that changes from 0 to 0 in such a case. In this embodiment, it is assumed that noise is detected when the noise pattern as described above is continuous for 4 samples, and the current value x _t of the digital signal output of the A / D converter 2 and the value x _t-1 of one sample period before are used. When the difference is 0, | 1 | ... The counter value is incremented by one. When | 2 | or more ... The counter value returns to 0 and is reset. When the counter value reaches, noise is detected, and the digital signal at the time when the counter value becomes is output from the noise detection unit 5 to the control unit 6, and the control unit 6 holds the digital signal to detect the noise. The hold value X is output from the control unit 6 to the output buffer 7 until it disappears.

Example 2. However, in the noise detection method of the first embodiment, for example, the output of the A / D converter is 1, 2,
The noise detection unit 5 also detects this as noise even when going up by 3, 4, 5, ... Step by step. In this embodiment, in order to prevent such malfunction, + and-sign bits are provided in the noise detecting section 5.

FIG. 4 is a state transition diagram of the + and-sign bits, and the + and-sign bits are as follows. And the difference between the current value x _t of the output of the A / D converter 2 and the value x _t-1 of one sample period before, and the difference is 0 ...・ Maintain the previous state. | 2 | More than A ... A The previous state is A, +1 ... B-1 .... C The previous state is B. , +1 ・ ・ ・ ・ A −1 ・ ・ ・ ・ ・ ・ C C in the previous state, +1 ・ ・ ・ ・ ・ ・ ・ ・ B -1 ・ ・ ・ ・ A The state changes.

When the state changes from B to A and from C to A, if the counter value of FIG. 3 is reset to 0 and reset, the output of the A / D converter 2 is increased or decreased step by step. Even in such a case, the noise detector 5
Does not detect this as noise and can prevent malfunction.

The noise suppression algorithm of this embodiment described above is shown in a flowchart of FIG. C in the figure
Indicates a counter value, and the sign bits of + and − change 0 → 1, 1 → 0 by INC (increment) operation. Briefly explaining this flowchart,
When the digital signal after A / D conversion is input to the control element 3, the control element 3 enters the noise detection state from the initial state, and the current value x of the digital signal data after A / D conversion x
_When the difference between _{t and} the value x _t-1 one sample period before is calculated in real time, and the value is within | 1 | steps four times in a row (that is, when the counter value C reaches 4) Assuming that noise is detected, the output is held at X and the noise suppression state is entered. In the noise detection state and a noise suppression state, the value of x _t -x _t-1 is | 2 | or become more than, + 1 or -1 (or across the both zero) when subsequently twice the initial state To return to. As described above, | 2 which is superimposed on the analog signal before A / D conversion
Noises less than | steps are suppressed.

[0019]

As described above, according to the present invention, the A / D
In the conversion noise removal, in addition to removing the noise of the analog signal before A / D conversion as in the conventional case, it is possible to remove the noise of the digital signal after A / D conversion, so that the influence of noise is small This has the effect of performing highly accurate A / D conversion.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a diagram for explaining the influence of noise in A / D conversion.

FIG. 3 is a state transition diagram of a counter showing a noise suppression algorithm of the control element according to the first exemplary embodiment.

FIG. 4 is a state transition diagram of code bits showing a noise suppression algorithm of a control element according to the second embodiment of the present invention.

FIG. 5 is a flowchart showing a noise suppression algorithm of the control element according to the second embodiment.

FIG. 6 is a diagram showing a conventional noise removal circuit for A / D conversion.

7 is a diagram showing frequency characteristics of the circuit of FIG.

[Explanation of symbols]

 1 analog filter 2 A / D converter 3 control element 4 input buffer 5 noise detection unit 6 control unit 7 output buffer

Claims (3)

[Claims] 1. An A / D conversion means for converting an analog signal into a digital signal, and the digital signal converted by the A / D conversion means is superimposed on the analog signal before being converted by the A / D conversion means. A noise detecting section for detecting noise, and when the noise detecting section detects noise, holds the digital signal from the noise detecting section and outputs it, and does not output the digital signal from the A / D converting means. An A / D conversion noise suppression circuit, which is provided with a control unit for performing the above. 2. The noise detecting section calculates the difference between the current value of the digital signal data and the value one sampling period before in real time, and when the value is within a | 1 | step consecutively a predetermined number of times. It is determined that noise has been detected, the control unit is set to the noise suppression state, the difference between the current value of the digital signal data and the value one sample period before is calculated in real time, and the value is equal to or more than | 2 | steps. The A / D conversion noise suppression circuit according to claim 1, wherein the noise suppression state of the control unit is solved when it is determined that it is not noise. 3. The noise detector calculates in real time the difference between the current value of digital signal data and the value one sampling period before, and when the value is within a predetermined number of | 1 | steps consecutively. It is determined that noise has been detected, the control unit is set to the noise suppression state, the difference between the current value of the digital signal data and the value one sampling period before is calculated in real time, and the value is calculated twice continuously for +1 step. If
Alternatively, when the number of steps becomes −1 consecutively twice (all may include 0 between them), it is determined that the noise is not noise, and the noise suppression state of the control unit is solved. Item 2. The A / D conversion noise suppression circuit according to Item 1.