JPH098660A - A/d converter - Google Patents

Abstract

PURPOSE: To suppress high-frequency noise generated at an analog system from appearing in quantized data after A/D conversion and to improve the S/N of an A/D converted output. CONSTITUTION: This device consists of a first signal system for quantizing an input signal through an A/D converter 2 and a second signal system for quantizing a signal amplified by an amplifier 3 through an A/D converter 4 and multiplying a coefficient with a coefficient multiplier 5 while using the A/D converters 2 and 4 for which full scale is larger than the output level of the amplifier (gain 0dB) 1 at the time of analog signal input and smaller than the output level of the amplifier (gain + GdB) 3. A discriminating circuit 6 discriminates whether the A/D converter 4 is full scale over or not and when it is not over, the ratio calculated by a level ratio arithmetic circuit 7 is defined as a coefficient K(i) of the coefficient multiplier 5. Then, a multiplexer 8 outputs the data of the second signal system. When the A/D converter is over the full scale, the data of the first signal system are outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an A / D converter,
The present invention relates to a device that is applied to a digital signal processing unit or the like in an AV (Audio-Visual) system and prevents high frequency noise generated in an analog system from deteriorating the S / N ratio of a digital output.

[0002]

2. Description of the Related Art Conventionally, an A / D converter has been used for converting an analog signal into a digital signal.
In the analog system before the / D conversion, high frequency noise is mixed due to various factors. In that case, generally, the high frequency noise in the analog system has a frequency higher than the frequency bandwidth of the amplifier provided before the A / D converter and is not amplified by the amplifier. However, in recent digital signal processing, a high resolution A / D converter tends to be used, and high frequency noise is included in the digital signal after A / D conversion because 1 LSB of the A / D converter is small. I will end up.

The decrease in the S / N ratio at the output side of the A / D converter due to high frequency noise causes an error in digital signal processing, and when the processed signal reproduces video or audio. It causes deterioration of image quality and sound quality. In particular, when the amplitude level of the input signal is small, the S / N ratio is significantly deteriorated, and the influence of high frequency noise cannot be ignored in the digital processing and reproduction stages.

Therefore, it is desired to remove high-frequency noise at the A / D conversion stage, but conventionally, a measure for removing the quantization noise of the A / D converter with a digital filter or the like has been taken. However, no measures have been taken for high-frequency noise generated in analog systems, and it is extremely difficult to design a digital filter that removes high-frequency noise.

[0005]

Therefore, the present invention suppresses the appearance of high-frequency noise generated in an analog system in the quantized data after A / D conversion, and the S / N of the A / D conversion output. It was created for the purpose of improving the ratio and preventing the occurrence of errors in digital signal processing and the deterioration of reproduced image quality and sound quality.

[0006]

A first aspect of the present invention is, in an A / D converter, a first amplifying means for amplifying an input analog signal with a gain A1, and a gain A1 of the first amplifying means for the input analog signal. A second amplification means for amplifying with a larger gain A2, and a full scale larger than the output level of the first amplification means and smaller than the output level of the second amplification means when the maximum level of the input analog signal is input. A
/ D converting means for quantizing the output of the first amplifying means, having the same full scale and resolution as the first converting means, and quantizing the output of the second amplifying means. A second converting means for converting the second converting means into a full scale over state and a determining means for determining whether or not the second converting means is in a full scale over state; Ratio calculating means for calculating a level ratio of the data to the quantized data by the second converting means; multiplying means for multiplying the quantized data by the second converting means by the level ratio obtained by the ratio calculating means; If the determination result of the determining means is not the full scale over state, the multiplication result obtained by the multiplying means is used. If the determination result of the determining means is the full scale over state, the first result is obtained. According to A / D conversion device, characterized by comprising an output switching means for outputting the quantized data of the switch means.

A second invention is an A / D converter,
A first amplifying means for amplifying an input analog signal with a gain A1; and a gain A of the first amplifying means for amplifying the input analog signal.
Second amplification means for amplifying with a gain A2 larger than 1; and the first amplification means when the maximum level of the input analog signal is inputted.
A / D conversion means having a full scale larger than the output level of the amplification means and smaller than the output level of the second amplification means, the first conversion means quantizing the output of the first amplification means; A second conversion means having the same full scale and resolution as the first conversion means, which quantizes the output of the second amplification means, and 1 in the quantized data of the second conversion means.
Second multiplication means for multiplying a coefficient corresponding to the gain of / A2, determination means for determining whether or not the second conversion means is in a full scale over state, and the determination result of the determination means is not in a full scale over state. A ratio calculation means for calculating a level ratio of the multiplication result of the second multiplication means to the quantized data by the first conversion means; and a level ratio obtained by the ratio calculation means for the quantized data of the first conversion means. When the determination result of the first multiplying means and the determining means of the determining means is not in the full scale over state, the multiplication result obtained by the second multiplying means is used when the determination result of the determining means is in the full scale over state. Relates to an A / D conversion device comprising an output switching means for outputting the multiplication result obtained by the first multiplication means.

[0008]

[Action]

Regarding the first invention; the input analog signal is amplified by the first amplifying means and the second amplifying means, but the output level of the second amplifying means is (A2 / A1) times the output level of the first amplifying means. However, since the high frequency noise included in the input analog signal is not amplified by each amplification means, the noise level is almost the same at the input / output stage of each amplification means.

Then, the respective input analog signals amplified by the first amplifying means and the second amplifying means are quantized by the first converting means and the second converting means, respectively, but since the respective converting means have the same resolution, The second conversion means is (A2 /
A1) will be roughly quantized. Therefore, when the level of the high frequency noise is smaller than the coarse quantization step in the second conversion means, it is dropped from the quantization target of the second conversion means.

By the way, if only the removal of high-frequency noise is a problem, the coefficient (A1
It is possible to obtain the quantized data of the input analog signal from which the high frequency noise has been removed only by multiplying the output signal by multiplying / A2) and outputting it. A / D means with a large full scale must be applied to. On the other hand, when the amplitude level of the input analog signal is high, even if the high frequency noise is quantized by the first conversion means, the S / S of the quantized data is
The N ratio becomes large, the influence on the subsequent digital signal processing is small, and the quality deterioration of the image and the sound due to the reproduced signal is also slight.

Therefore, according to the present invention, as the first and second converting means, the output level is larger than the output level of the first amplifying means and smaller than the output level of the second amplifying means when the maximum level input analog signal is input. The full-scale A / D conversion means is applied, and the determination means determines whether or not the second conversion means is in the full-scale over state. Then, when the determination result of full scale over is obtained, the output switching means outputs the quantized data of the first converting means, and in the opposite case, the ratio calculating means quantizes by the first converting means. The level ratio of the data to the quantized data by the second conversion means is calculated, the multiplication means multiplies the quantized data by the second conversion means by the level ratio obtained by the ratio calculation means, and the output switching means calculates the multiplication result. Output. That is, when the input analog signal is large, the quantized data of the first conversion means is output, and when the input analog signal is small, the quantized data in which high frequency noise is removed and the level is returned is output.
Note that the ratio calculating means calculates the successive level ratio and uses it as the multiplication coefficient of the multiplying means. However, since the signals amplified by the amplifying means having different gains are quantized in the present invention, if the multiplication coefficient is fixed, the output data will be continuous. This is because there is a possibility that the property may be impaired, and it is necessary to prevent the defect.

Regarding the second invention: In this invention, the quantized data obtained from the two systems is selectively output according to the high frequency noise removal method when the level of the input analog signal is small and the level of the input analog signal. The method is the same as that of the first invention, but the second multiplication means multiplies the quantized data output by the second conversion means by a fixed multiplication coefficient (a coefficient corresponding to a gain of 1 / A2). And the ratio calculation means calculates the level ratio of the multiplication result of the second multiplication means to the quantized data of the first conversion means, and the first multiplication means converts the level ratio into the quantized data of the first conversion means. The difference is that they are multiplied. Therefore,
Only the method to ensure the continuity of the output data is different,
The basic function is similar to that of the first invention.

[0013]

Embodiments of the A / D converter of the present invention will be described in detail below with reference to the drawings. << Embodiment 1 >> The circuit configuration of this embodiment is shown in FIG.
In the figure, 1 is an amplifier with a gain of 0 dB, and 2 is an M-bit A.
/ D converter, 3 is gain + GdB amplifier, 4 is M bit A
/ D converter, 5 is a coefficient multiplier, amplifier 1 and A / D converter 2 constitute a first signal system, and amplifier 3, A / D converter 4 and coefficient multiplier 5 constitute a second signal system. are doing. However, each A / D
The full scale of converters 2 and 4 is larger than the maximum level of the input analog signal, and the signal of that maximum level is gained +
It is smaller than the level amplified by GdB. Further, 6 is a discriminating circuit for discriminating whether or not the A / D converter 4 is in a full scale over state, and 7 is a level for computing the level ratio of the quantized data output by each A / D converter 2, 4. A ratio calculation circuit, 8 is a multiplexer for selectively outputting the digital data of the first signal system or the second signal system, and 9 is a switching control circuit for controlling the multiplexer 8, which constitute an output control system.

Hereinafter, the A / D according to the circuit configuration of this embodiment will be described.
The conversion / output operation will be described with reference to the flowchart of FIG. 3 and the graph of FIG. First, if there is an input analog signal, that signal is branched and input to each amplifier 1 and 3 and amplified separately. The amplified signals So (t) and Sg (t) are each A / D converted. It is quantized by the units 2 and 4 (F1, F2).

In that case, So (t) is always quantized within the full-scale range of the A / D converter 2, but Sg (t) is + GdB.
Since it is × So (t), it may be quantized within the full scale range of the A / D converter 4 or may not be quantized beyond the full scale. That is, the quantized data of Sg (t) is M of 2 which corresponds to the full scale of the A / D converter 4.
If it becomes larger than the power of binary data (Ath), quantization becomes impossible.

In this embodiment, the discriminating circuit 6 monitors the change of the MSB of the A / D converter 4 by means such as Sg (t) is A /
It is determined whether or not full scale over of the D converter 4 is performed. If not full scale over, the level ratio calculation circuit that receives the determination result determines that the quantized data Do (i) of the A / D converter 2 is reached. To the quantized data Dg (i) of the A / D converter 4: K (i) = | Do (i) / Dg (i) |
Calculate K (i) · Dg (i) with 5 (F3 → F4, F5). Then, the determination circuit 6 also notifies the switching control means 9 of the above determination result, and the switching control circuit 9 that has received the determination result receives the determination result.
By controlling the connection state between the coefficient multiplier 5 and the output side to output the multiplication result K (i) · Dg (i) of the coefficient multiplier 5 to a digital signal processing circuit or the like (not shown) (F6). .

On the other hand, when the discriminating circuit 6 discriminates the full scale over of the A / D converter 4, the switching control circuit 9
Controls the multiplexer 8 so that the A / D converter 2 is connected to the output side, and outputs the quantized data Do (i) of the A / D converter 2 (F7). Then, in the same manner thereafter, each A / D converter 2, 4 quantizes So (t), Sg (t) at the sampling interval Δt, and repeats the above steps F2 to F7 to obtain A / D. converter
K (i) .Dg (i) or Do (i) is output while discriminating whether or not 4 becomes full scale over (F8 → F1 to F8).

In the above operation, when the input analog signal contains high frequency noise having a frequency higher than the frequency bandwidth of each amplifier 1, 3, the noise component is the noise component of each amplifier 1, 3.
Although not amplified by 3, if the noise level is 1 LSB or more of each A / D converter 2, 3, it will appear as quantized data by each A / D converter 2, 3. But each A
Since the full scale and resolution (M bits) of the / D converters 2 and 4 are the same, the quantized data Dg (i) of the A / D converter 4 that quantizes the analog signal of the amplifier 3 of + GdB is 0 dB. The input analog signal of the amplifier 1 is quantized more coarsely than the quantized data Do (i) of the A / D converter 2 by + G dB. Therefore, the quantized data Do on the A / D converter 2 side
Gain + GdB even for high-frequency noise components appearing in (i)
Can be set so as not to be included in the quantized data Dg (i) on the A / D converter 4 side.

According to the above-mentioned principle, if A /
If the full scale of the D converter 4 is set to cover the maximum level of the signal Sg (t), the quantized data from which the high frequency noise is always removed can be obtained only by the second signal system. However, an A / D converter having a large full scale has a special specification and is naturally expensive. On the other hand, when the level of the input analog signal is high, the high-frequency noise itself is not amplified, and the S / N ratio becomes large.
Even if the quantized data of the signal system is output, it does not significantly affect the subsequent digital signal processing. For that reason, in this embodiment, as the A / D converters 2 and 4,
A full scale that is larger than the maximum level of the input analog signal and smaller than the level obtained by amplifying the signal of that maximum level by gain + GdB is applied. While using a normal full scale A / D converter, the input analog The quantized data with a large S / N ratio is obtained by selectively outputting the quantized data by the first signal system and the second signal system according to the signal level.

As shown in FIG. 4, time zones 0 to t1, t2 to t3,
At t4 to t5, the quantized data K (i) · Dg (i) of the second signal system from which the high frequency noise component is removed because the input analog signal is at a low level is Since the input analog signal is at a high level, the quantized data Do (i) of the first signal system is output. Just A / D
The converter 2 converts the input analog signal that has not been amplified to A /
The D converter 4 quantizes the signal obtained by amplifying the input analog signal with a gain of + G dB. If the multiplication coefficient of the coefficient multiplier 5 is fixed, the quantized data of the first signal system and the second signal system are switched. It becomes impossible to ensure accurate continuity when outputting the output. Therefore, in this embodiment, the coefficient multiplier 5 sequentially uses the ratio K (i) obtained by the level ratio calculation circuit 7 to obtain A /
The level of the quantized data Dg (i) of the D converter 4 is returned to ensure the continuity of the output data.

<< Embodiment 2 >> The circuit configuration of this embodiment is shown in FIG.
Is shown in In the figure, the circuit elements denoted by the same reference numerals as in FIG. 1 are the same as in the case of the first embodiment, and the circuit configuration of this embodiment is equivalent to -G dB for the quantized data by the A / D converter 4. Fixed coefficient: A coefficient multiplier 10 for multiplying J is provided, and the level ratio calculation circuit 11 is a coefficient multiplier 10
Quantized data Do by the A / D converter 2 of the multiplication result by
Ratio to (i): X (i) = | J · Dg (i) / Do (i) | is found, and the quantized data Do (i) by the A / D converter 2 is used as a level ratio calculation circuit. It is characterized in that a coefficient multiplier 12 for multiplying the ratio X (i) obtained by 11 is provided.

The A / D conversion / output operation by this circuit configuration is shown in the flow chart of FIG. 5 and the graph of FIG.
In this embodiment, the coefficient multiplier 10 always multiplies the quantized data by the A / D converter 4 from which the high frequency noise component is removed by a fixed coefficient: J to restore the original input analog signal level. (F11 to F13). When the determination circuit 6 determines that the A / D converter 4 is not full scale over, the switching control circuit 9 controls the multiplexer 8 to the connection state between the coefficient multiplier 10 and the output side to perform the coefficient multiplication. The multiplication result J · Dg (i) by the device 10 is output to a digital signal processing circuit or the like (not shown) (F14 → F18).

On the other hand, when the discrimination circuit 6 discriminates that the A / D converter 4 is in full scale over, the level ratio calculation circuit 11 calculates the multiplication result J · Dg (i) calculated by the coefficient multiplier 10. ) To the quantized data Do (i) of the A / D converter 2: X (i), and the coefficient multiplier 12 calculates the ratio: X (i)
Multiply the quantized data Do (i) of the D / D converter 2 (F14 → F1
5, F16). Then, the switching control circuit 9 which receives the notification of full scale over from the determination circuit 6 controls the multiplexer 8 to the connection state between the coefficient multiplier 12 and the output side, and the coefficient multiplier 12
X (i) · Do (i) obtained by is output (F17). After that, by repeating the above steps F12 to F18 at the sampling interval Δt, J · Dg (i) or X (i) · Do is determined while determining whether the A / D converter 4 becomes full scale over. Output (i) (F19 → F11 to F19). As shown in FIG. 6, time zones 0 to t1,
At t2 to t3 and t4 to t5, since the input analog signal is at a low level, the coefficient multiplier 10 from which the high frequency noise component has been removed
The multiplication result J · Dg (i) of the coefficient multiplier 12 is high because the input analog signal is at a high level in the time zones t1 to t2 and t3 to t4.
The multiplication result of X (i) · Do (i) is output.

Therefore, the multiplication result J.Dg (i) by the coefficient multiplier 10 and the multiplication result X (i) .Do (i) by the coefficient multiplier 12 are selectively output corresponding to the level of the input analog signal. ,
As in the case of the first embodiment, the high frequency noise component is removed from the output quantized data Dg (i) when the signal level is low, and the output quantized data X (i) · when the signal level is high. Since Do (i) has a large S / N ratio even if it contains a high frequency noise component, output quantized data with a large S / N ratio can always be obtained. Note that this embodiment is different from the first embodiment in that the coefficient multiplier 10 is a multiplier with a fixed coefficient J, and the continuity of output data is ensured on the coefficient multiplier 12 side. The basic principle is similar to that of the first embodiment.

[0025]

The A / D converter according to the present invention has the following effects due to the above configuration. The high frequency noise generated in the analog system is suppressed from appearing in the quantized data after A / D conversion, the S / N ratio of the A / D conversion output is improved, and an error is generated or reproduced in the digital signal processing. Prevents deterioration of image quality and sound quality.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram according to a first embodiment of an A / D conversion device of the present invention.

FIG. 2 is a circuit configuration diagram according to a second embodiment.

FIG. 3 is a flowchart showing an operation procedure of the A / D conversion device according to the first embodiment.

FIG. 4 is a graph showing the output of each A / D converter and the quantized data that is selectively output in the A / D converter of the first embodiment.

FIG. 5 is a flowchart showing an operation procedure of the A / D conversion device according to the second embodiment.

FIG. 6 is a graph showing the output of each A / D converter and the quantized data that is selectively output in the A / D converter of the second embodiment.

[Explanation of symbols]

1, 3 ... Amplifier (1; first amplifying means, 3; second amplifying means), 2, 4 ...
A / D converter (2; first conversion means, 4; second conversion means), 5, 10,
12 ... Coefficient multiplier (5; multiplying means, 10; second multiplying means, 12; first
Multiplying means), 6 ... Discriminating circuit (discriminating means), 7, 11 ... Level ratio arithmetic circuit (ratio arithmetic means), 8 ... Multiplexer (output switching means), 9 ... Switching control circuit (output switching means).

Claims (3)

[Claims] 1. An A / D converter, wherein a first amplifying means for amplifying an input analog signal with a gain A1 and a second amplifying means for amplifying the input analog signal with a gain A2 larger than the gain A1 of the first amplifying means. Means and full-scale A / D conversion means that is higher than the output level of the first amplifying means and is lower than the output level of the second amplifying means when the maximum level of the input analog signal is input. First transforming means for quantizing the output of the first amplifying means; second transforming means for quantizing the output of the second amplifying means, having the same full scale and resolution as the first transforming means; A discriminating means for discriminating whether or not the second converting means is in the full scale over state, and the second of the quantized data by the first converting means when the discriminating result of the discriminating means is not in the full scale over state. The ratio calculation means for calculating the level ratio of the quantized data by the conversion means, the multiplication means for multiplying the quantized data by the second conversion means by the level ratio obtained by the ratio calculation means, and the determination result of the determination means are Output switching means for outputting the multiplication result obtained by the multiplying means when not in the full scale over state, and outputting the quantized data of the first converting means when the determination result of the determining means is in the full scale over state. An A / D conversion device characterized by being provided. 2. In the A / D conversion device, first amplification means for amplifying an input analog signal with a gain A1 and second amplification means for amplifying the input analog signal with a gain A2 larger than the gain A1 of the first amplification means. Means and an A / D conversion means having a full scale that is larger than the output level of the first amplifying means and is smaller than the output level of the second amplifying means when the maximum level of the input analog signal is input. First conversion means for quantizing the output of the first amplifying means, and second converting means for quantizing the output of the second amplifying means having the same full scale and resolution as the first converting means. A second multiplication means for multiplying the quantized data of the second conversion means by a coefficient corresponding to a gain of 1 / A2;
A discriminating means for discriminating whether or not the converting means is in the full scale over state; and, when the discriminating result of the discriminating means is not in the full scale over state, for the quantized data by the first converting means of the multiplication result by the second multiplying means. A ratio calculation means for calculating a level ratio, a first multiplication means for multiplying the quantized data of the first conversion means by the level ratio obtained by the ratio calculation means, and a determination result of the determination means are not in a full scale over state. In this case, there is provided output switching means for outputting the multiplication result obtained by the second multiplication means, and outputs the multiplication result obtained by the first multiplication means when the determination result of the determination means is in a full scale over state. An A / D conversion device characterized by the above. 3. The A / D conversion device according to claim 1, wherein the gain A1 of the first amplification means is zero.