JP3110589B2 - A / D converter and D / A converter - Google Patents

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 for converting an analog signal to a digital signal and a D / A converter for converting a digital signal to an analog signal. The present invention relates to an A / D converter and a D / A converter suitable for handling signals that are typically heard by human ears, for example, for taking in electronic musical instruments and the like.

[0002]

2. Description of the Related Art Conventionally, A / D converters and D / A converters have been used in various fields. Here, these A
As an example of use of the / D converter and the D / A converter, a musical performance is recorded by a microphone to obtain an analog tone signal, which is converted into a digital tone signal by the A / D converter, and stored. In this case, it is considered that the signal is read out as necessary, converted again into an analog tone signal by the D / A converter, amplified as appropriate, and the tone is emitted from the speaker.

At this time, there is a moment when a loud musical tone is generated when playing a musical instrument, and at a certain moment, almost no sound is produced. When such a performance is listened to as a musical tone through the above-described system, it is inaudible when the musical tone is loud, but an annoying noise such as white noise is heard when the musical tone is close to silence. This is for example A / D
When an analog signal is A / D-converted using a converter,
Due to noise components superimposed on the analog signal or noise of the A / D converter itself, even at the time of silence, the least significant bit or several bits are repeatedly turned on / off irregularly, and this is finally heard as noise. That's why. If the resolution of the A / D converter is not as high as, for example, 16 bits, even if only the least significant bit is turned on / off, it will be heard as quite large noise. In the case of D / A conversion, there is a similar problem, and quantization noise is heard as noise.

As described above, for example, in the field of electronic musical instruments and the like, it is desired to reduce the noise accompanying the A / D conversion and the D / A conversion in order to finally enjoy a clear musical tone with little noise.

[0005]

In order to solve the above-mentioned problem, taking A / D conversion as an example, two A / D converters are prepared and the same analog signals are amplified by amplifiers having different amplification factors. , And in the area where the signal level is small, the signal A /
The output of the D converter is attenuated by an amount corresponding to the amplification to obtain an A / D conversion output. On the other hand, in a region where the signal level is large, the output of the A / D converter to which a signal passed through an amplifier having a small amplification factor is input is used as the amplification output. A technology is known in which the A / D conversion output is only attenuated to substantially improve the resolution and thereby reduce noise (for example, Japanese Patent Application Laid-Open No.
2-155953).

However, when this technology is adopted, individual A /
The D converters have variations such as offset and drift, so that when the outputs of the two A / D converters are switched, the output levels of the two A / D converters do not match, and switching noise occurs. This causes a new problem that the switching noise is heard as harsh noise. In order to solve this new problem, it is necessary to adopt an expensive A / D converter having sufficiently small offset and drift and to adjust the characteristics of the two A / D converters sufficiently. The cost is comparable to the case where an A / D converter with high resolution is adopted.

The present invention has been made in view of the above circumstances, and has been made in consideration of a plurality of A / D
In an A / D converter and a D / A converter in which the resolution is substantially improved by using a converter or a D / A converter, the generation of switching noise can be suppressed, thereby realizing low noise and low cost. It is an object to provide an A / D converter and a D / A converter.

[0008]

According to the present invention, there is provided an A / D converter comprising: (1) a plurality of A / D converters; and (2) amplifying input analog signals at different amplification factors. (3) The above analog signal or the analog signal is distributed to each of the plurality of A / D converters.
/ D, based on the digital signal obtained by the / D, each weight of each input signal input to each of the plurality of A / D converters, or each output signal output from each of the plurality of A / D converters (4) A weight assigner for assigning each weight to each of the input signals or each output signal. (5) Each of the input signals to which each of the weights is assigned is converted to an A / D converter. And an adder for mutually adding each digital signal obtained by being input to each of the digital signals or each of the weighted output signals.

In the A / D converter of the present invention,
It is preferable that the weight calculator is configured to calculate the weights such that the weight of the signal amplified at a high amplification factor increases as the absolute value or the envelope value of the analog signal decreases. The D / A converter of the present invention, which achieves the above object, comprises: (6) a plurality of D / A converters; (7) multiplying an input digital signal by mutually different coefficients to each of the plurality of D / A converters; (8) Each weight of each input signal input to each of the plurality of D / A converters based on the digital signal or an analog signal obtained by D / A conversion of the digital signal. Or a weight calculator for calculating each weight of each output signal output from each of the plurality of D / A converters. (9) A weight assigner for assigning each weight to the input signal or each output signal. ) The input signals with the weights are D
And an adder for adding the respective analog signals obtained by being input to the / A converter or the respective output signals having the respective weights to each other.

In the above D / A converter of the present invention,
It is preferable that the weight calculator is configured to obtain the weights such that the weight of a signal multiplied by a coefficient having a larger value increases as the absolute value or envelope value of the digital signal decreases.

[0011]

The A / D converter and the D / A converter of the present invention are:
Each uses a plurality of A / D converters and a plurality of D / A converters, and does not simply switch the output signals of the plurality of A / D converters and the plurality of D / A converters. Since the output signals are weighted based on the absolute value or envelope value of the signal and are added to each other, A
Even if the / D converter and the D / A converter have variations such as offset and drift, switching noise is not conspicuous, so that a low-cost and high-resolution A / D converter and D / A converter can be realized.

[0012]

Embodiments of the present invention will be described below. FIG. 1 is a circuit block diagram of an embodiment of an A / D converter according to the present invention. An analog tone signal is input from an input terminal 11 of the A / D converter 10, and the input analog tone signal is directly input to an A / D converter 12 and is AG-multiplied by an amplifier 13 to A / D. It is input to the converter 14. Each of the A / D converters 12 and 14 has a resolution of 16 bits.

FIG. 2 is a schematic diagram of an analog tone signal input to the A / D converter 10 shown in FIG. The input analog tone signal 1 is input to the A / D converter 12 and AG-multiplied by the amplifier 13 and input to the A / D converter 14 as described above. When the signal level of the analog tone signal 1 reaches the threshold value TH shown in FIG. 2, the analog tone signal 1 is amplified to a level at which the A / D converter 14 has the maximum value.

The digital tone signal output from the A / D converter 14 is converted into an envelope detector 15 and a multiplier 16
Is input to The envelope detector 15 calculates the envelope 2 of the input digital tone signal.
However, since the analog tone signal amplified by the amplifier 13 is input to the A / D converter 14, the envelope determined by the envelope detector 15 is an envelope saturated with the threshold value TH.

The digital tone signal output from the A / D converter 12 is input to a multiplier 17, and the digital tone signal output from the A / D converter 14 is input to a multiplier 16.
Are multiplied by the coefficient C1 = 1 / AG, and then input to the multiplier 18. In the multipliers 17 and 18, based on the envelope obtained by the envelope detector 15, the coefficients C2 and C3 to be multiplied by the input digital musical tone signals are obtained as described later. The digital tone signals input to the multipliers 17 and 18 are multiplied by the coefficients C2 and C3 by the multipliers 17 and 18, respectively.
The signals are added to each other by an adder 19, and the A
It is output as an output digital signal of the / D converter 100.

The coefficients C2 and C3 are determined as follows. When the envelope obtained by the envelope detector 15 is saturated at the threshold value TH shown in FIG.
That is, in the section B shown in FIG. 2, C2 = 1.0, C3 = 0.0 (1), and only the A / D converter 12 is valid. When the envelope is not saturated, that is, in the section A shown in FIG. 2, for example, at point a shown in FIG. 2, C2 = d2 / (d1 + d2) (2) C3 = d1 / (d1 + d2) ( As in 3), the coefficients C2 and C3 are determined by the point a 'on the detection envelope at the point a.

Thus, the smaller the input signal, the more the A / D
The specific gravity on the converter 14 side increases. The A / D converter 14 is
Since only a region having a small signal level is quantized to 16 bits, noise accompanying quantization is reduced. Moreover, since the digital signals output from the A / D converter 12 and the A / D converter 14 are weighted and added, the switching noise is hardly annoying as compared with the conventional method of selectively switching each digital signal. Therefore, offset and drift are somewhat tolerated, and low-cost A / D
A low-cost A / D converter 10 can be configured using the converter.

In the above embodiment, since the envelope of the tone signal is obtained, while the envelope exceeds the threshold value TH (section B shown in FIG. 2), the tone signal is instantaneously changed to the low level. Even then, only the signal on the A / D converter 12 side is used. This is because when the envelope is large, the quantization noise is hardly heard even if the tone signal instantaneously goes low. However, in this case as well, when it is desired to suppress the quantization noise, an absolute value detector is provided in place of the envelope detector 15 for obtaining the absolute value of a form in which all the tone signals are folded back positively, as shown by a broken line in FIG. The same operation as described above may be performed based on the magnitude of the instantaneous value of the absolute value.

The calculation at that time is as follows: C2 = d2 '/ (d1' + d2 ') C3 = d1' / (d1 '+ d2') In the above-described calculation, C2 becomes 0 when the absolute value of the instantaneous value of the envelope or the waveform is 0. However, by providing a second threshold value ST, the absolute value of the instantaneous value of the envelope or the waveform is obtained. Is less than or equal to ST, C2 = 0.0 and C3 = 1.0.

The calculation in the case where the envelope detection value is between the threshold values TH and ST at that time will be described. C2 = d2 ″ / (d1 + d2 ″) C3 = d1 / (d1 + d2 ″) In the case of an instantaneous value, an operation according to this operation may be performed.

FIG. 3 is a circuit block diagram of one embodiment of the D / A converter of the present invention. A digital tone signal is input to the D / A converter 30 from an input terminal 31 of the D / A converter 30, and a multiplier 32, a multiplier 33, and an absolute value detector 3
4 is input. The digital tone signal input to the multiplier 33 is multiplied by a coefficient C2 = G. This coefficient C2
= G is the threshold value TH shown in FIG.
Has a value that saturates. Coefficient C in multiplier 33
The digital tone signal multiplied by 2 = G is multiplied by a multiplier 35
Is input to

When the input digital tone signal has a negative value, the absolute value detector 34 inverts its sign to obtain an absolute value as shown by a broken line in FIG. Based on this, the coefficients C1 and C3 in the multipliers 32 and 35 are obtained as follows. That is, here, two threshold values TH, as shown in FIG.
ST (TH> ST) is set, and each coefficient C1, C2 is
When the absolute value exceeds the threshold value TH, C1 = 1.0, C3 = 0.0 (4) When the absolute value is equal to or less than the threshold value ST, C1 = 0.0, C3 = 1. 0 (5) C1 = d4 / (d3 + d4) when the threshold value is intermediate between the two threshold values ST and TH as shown at point b in FIG. 2 C6 = d3 / (d3 + d4) … (7)

It is also possible to set ST = 0,
In this case, no threshold value ST is provided. The digital tone signals multiplied by the coefficients C1 and C3 in the multipliers 32 and 35 are input to the D / A converters 36 and 37 and converted into analog tone signals. D / A converter 36
The analog tone signal output from the D / A converter 37 is directly input to the adder 39, and the analog tone signal output from the D / A converter 37 is input to the adder 39 after being attenuated to 1 / G by the attenuator 38. In the adder 39, the input 2
The two analog tone signals are added to each other and output from an output terminal 40 as an output signal of the D / A converter 30.

In the D / A converter 30, as in the case of the above-described A / D converter 10 (see FIG. 1),
Since two D / A converters 36 and 37 are used to input digital musical tone signals having different magnifications and perform D / A conversion, quantization noise can be reduced. Further, since the output signals of the two D / A converters 36 and 37 are not used alternatively, but are weighted and added, discontinuity due to switching is dispersed, and unpleasant noise is prevented. .

Although the D / A converter 30 shown in FIG. 3 is provided with an absolute value detector 34, like the A / D converter 10 described above, Alternatively, an envelope detector for obtaining the envelope of the tone signal may be provided, and the same weighted addition may be performed based on the envelope. In the D / A converter 30 shown in FIG. 3, multipliers 32 and 35 for weighting are provided in front of the D / A converters 36 and 37.
This is provided for the digital side because it is easier to perform signal processing. The effects of the D / A converter 36 and the D / A converter 37 increase when the level of the musical tone signal is high and low, respectively, when the coefficient C1 and the coefficient C3 have large values. There is almost no problem even if the configuration is as shown in FIG. However, it is a matter of course that, instead of the multipliers 32 and 35, amplifiers having variable amplification factors for analog signals may be provided on the output sides of the D / A converters 36 and 37. Also, like this,
The multipliers 17 and 1 in the A / D converter 10 shown in FIG.
Instead of 8, an amplifier having a variable amplification factor for an analog signal may be provided before the A / D converters 12 and 14.

[0026]

As described above, the A / D converter and the D / A converter of the present invention perform A / D conversion or D / A conversion of signals having different amplification factors (magnifications). Since the envelope or absolute value of the signal is obtained, a weight is obtained based on the envelope or the absolute value, and the signal after A / D conversion or D / A conversion is weighted and added, the quantization noise is reduced. The noise associated with the switching is also reduced, and when this is used for the processing of musical sounds, unpleasant noise is reduced and clear music can be enjoyed. In addition, since noise caused by the switching is dispersed and unpleasant noise does not occur, variations such as offset and drift of the A / D converter and D / A converter are allowed, and a low-cost A / D converter, D / A A conversion device can be configured.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of an embodiment of an A / D converter according to the present invention.

FIG. 2 is a schematic diagram of an analog tone signal input to the A / D converter shown in FIG.

FIG. 3 is a circuit block diagram of a D / A converter according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Musical sound wave form 2 Envelope 10 A / D converter 11 Input terminal 12, 14 A / D converter 13 Amplifier 15 Envelope detector 16, 17, 18 Multiplier 19 Adder 20 Output terminal 30 D / A converter 31 Input terminal 32, 33, 35 Multiplier 34 Absolute value detector 36, 37 D / A converter 38 Attenuator 39 Adder 40 Output terminal

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code Fig10H 7/00 511D

Claims (4)

(57) [Claims] A plurality of A / D converters; an amplifier for amplifying input analog signals at different amplification factors and distributing the analog signals to each of the plurality of A / D converters; Based on a digital signal obtained by A / D conversion of each of the plurality of A / D converters, or each weight of each input signal input to each of the plurality of A / D converters or output from each of the plurality of A / D converters. A weight calculator for calculating each weight of each output signal, a weight assigner for assigning each weight to each of the input signals or each output signal, and the input signals having the weights being A / A Each digital signal obtained by being input to the D converter,
Alternatively, an A / D converter comprising an adder for adding the respective output signals having the respective weights to each other. 2. The weight calculator according to claim 1, wherein each of the weights is such that the weight of the signal amplified at a high amplification factor increases as the absolute value or envelope value of the analog signal decreases. Claim 1 characterized by the following:
The A / D converter according to the above. 3. A plurality of D / A converters, a multiplier for multiplying an input digital signal by different coefficients and distributing each of the plurality of D / A converters, the digital signal or the digital signal To D / A
Based on the analog signal obtained by the conversion, each weight of each input signal input to each of the plurality of D / A converters, or each weight of each output signal output from each of the plurality of D / A converters A weight calculator for obtaining each weight; a weight assigner for assigning each weight to each of the input signals or each output signal; each of the input signals having each of the weights being input to the D / A converter A D / A converter comprising: an adder that adds together each analog signal obtained by the above-mentioned processing or each of the output signals having the respective weights. 4. The weight calculator calculates the weights such that the weight of a signal multiplied by a coefficient having a larger value increases as the absolute value or envelope value of the digital signal decreases. The D / A converter according to claim 3, wherein: