JPH0722951A - Noise shaper - Google Patents

Abstract

PURPOSE:To always set the output signal to be zero when a non-signal is inputted by setting the sign of a constant so as to be negative, positive, or zero when a storage data before one sample delay is positive, negative, or zero. CONSTITUTION:A difference signal between the output signal of a quantizer C delayed by a delay D and an input signal is inputted to an integrator S1, and integrated. Also, a difference signal between the output signal of the integrator S1 and the two-fold signal of the output of the quantizer C delayed by the delay D and amplified by an amplifier A is inputted to an integrator S2, integrated, and inputted to the quantizer C. The quantizer C outputs '+1' when the input is more than +1/2, outputs '0' when the input is between -1/2 and +1/2, and outputs '-1' when the input is less than -1/2. When the non- signal is inputted, and the initial values of the integrators S1 and S2 are zero, the output code is zero, and when the initial value of the integrator S1 is a constant value except zero, the absolute value is gradually decreased by the addition of the fixed constant for controlling the sign by the sign of the storage data, and finally turned to zero. Therefore, the output of the noise shaper can be always set to be zero.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise shaper that outputs no output signal when no input signal is present and does not generate noise in a low frequency region.

[0002]

2. Description of the Related Art A conventional noise shaper that outputs three values has a structure as shown in FIG. 6, for example. That is, the first and second integrators S1 and S2, the quantizer C that receives the output of the second integrator as an input and outputs a ternary signal, and the output of the quantizer to the first and second integrators. And a feedback circuit having a delay device D that feeds back to the two integrators S1 and S2. The output of the first integrator S1 is subtracted from the output of the delay device D doubled by the amplifier A and input to the second integrator. Also, the integrator is composed of a digital circuit,
This is realized by the circuit shown in FIG.

Next, the operation of the conventional noise shaper will be described with reference to FIG. The difference signal between the output signal of the quantizer C delayed by the delay device D and the input signal is input to the first-stage integrator S1 and integrated. In addition, the first-stage integrator S
The difference signal between the output signal of 1 and the doubled output signal of the quantizer C delayed by the delay device D is input to the second-stage integrator S2 and integrated. The output of the second-stage integrator S2 is input to the quantizer C. At this time, the output is +1 when it is larger than +1/2, and 0 when it is between -1/2 and +1/2.
When it is smaller than -1/2, -1 is output. With such a configuration, assuming that the quantization noise generated in the quantizer C is Q, the noise shaper input signal X and the output signal Y have the relationship shown in the following equation.

Y (z) = X (z) + (1-z ⁻¹ ) ² · Q (Z) (1) Therefore, the output spectrum of the noise shaper is the second derivative of the quantization noise at the input of the noise shaper. It will have a spectrum in which the generated signal is superimposed. That is, since the quantization noise is shaped and superimposed in the high frequency region, the total noise in the signal band is significantly reduced.

Now, consider the case where no signal is input to this noise shaper. As shown in FIG.
It is clear that the output signal becomes zero when the data of the delay devices D1 and D2 forming 1, S2 are zero in the initial state. On the other hand, the delay devices D1 and D that form the integrators S1 and S2
It is assumed that the data of 2 is not zero in the initial state and the initial value of the integrator S1 of the first stage is 0.5, for example. At this time, the output of the noise shaper repeats +1 and -1, and does not become zero. If the initial value of the integrator S1 of the first stage is smaller than 0.5, for example, 0.1, +
It repeats -1, -1, and 8 consecutive zeros, +1, -1, and 8 consecutive zeros steadily. From these, it can be seen that the output of the noise shaper does not become zero when the initial value of the integrator S1 of the first stage is not zero. In addition, the smaller the initial value of the integrator S1 of the first stage, the more the number of 0s following +1 and -1 increases, so that a low frequency component appears in the spectrum included in the output.

[0006]

In the above-mentioned conventional noise shaper shown in FIG. 6, the smaller the initial value of the integrator S1 of the first stage is, the more the noise is included in the output signal when no signal is input. There was a problem that low frequency components appeared due to the spectrum.

[0007]

According to the present invention, a noise shaper comprising one or more stages of integrating circuits, a ternary quantizer having 0 and ± 1 as outputs, and a feedback circuit is used as the input of the noise shaper. A connection for inputting a signal and one or more output signals of the feedback circuit to the integrator circuit; a connection for inputting the output signal of the integrator circuit to the quantizer; and output terminals of the quantizer and noise shaper. With connections of
The integration operation of at least one or more integrator circuits is an incomplete integration operation realized by adding the accumulated data before one sample delay, the present data and a constant whose absolute value is a constant value or zero, A noise shaper having means for controlling the sign of a constant according to the sign of accumulated data before delay is obtained.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. S1 is a first-stage integrator, S2 is a second-stage integrator, and C is ± 0.
A quantizer that outputs a ternary level with 5 as a threshold,
D is a delay device, and A is an amplifier with an amplification factor of 2. The difference signal between the output signal of the quantizer C delayed by the delay device D and the input signal is input to the first-stage integrator S1 and integrated. Further, the difference signal between the output signal of the integrator S1 at the first stage and twice the output signal of the quantizer C delayed by the delay device D and then amplified by the amplifier A is the integration signal of the second stage. Input to the vessel S2,
Integrated. The output of the second-stage integrator S2 is input to the quantizer C. In the quantizer C, the input is +1
When it is larger than / 2, the output is +1 and from -1/2 to + 1 /
0 between 2 and -1 when less than -1/2
Is output. Further, the integrators S1 and S2 are, for example, as shown in FIG.
Can be configured as shown in. As shown in FIG.
The first-stage integrator S1 adds the accumulated data before one sample delay, the current data, and the fixed constant (± 2 ^-18 ).
At this time, the sign of the fixed constant is negative when the accumulated data before one sample delay is positive, positive when the accumulated data before one sample delay is negative, and is zero when the accumulated data before one sample delay is zero. Is controlled by the sign control circuit CONT1 so that the fixed constant becomes zero. The second-stage integrator S2 is a perfect integrator realized by adding the accumulated data before one sample delay and the current data.

With such a configuration, assuming that the quantization noise generated by the quantizer C is Q, the relationship between the noise shaper input signal X and the output signal Y is approximately expressed by the following equation.

Y (z) = z ⁻¹ · X (z) / P (z) + (1−z ⁻¹ ) ² · Q (z) (2) Therefore, the output spectrum of the noise shaper is the input of the noise shaper. It has a spectrum in which a signal obtained by almost second-order differentiation of the quantization noise is superimposed on. That is, since the quantization noise is shaped and superimposed in the high frequency region, the total noise in the signal band is significantly reduced without deteriorating the characteristics of the conventional noise shaping.

Consider the case where no signal is input to the noise shaper in the operation described above. Now, it is clear that the output code becomes zero when the initial values of the integrators S1 and S2 of the first and second stages are zero. Next, when the initial value of the integrator S1 of the first stage is a constant value other than zero, the absolute value gradually decreases by addition of a constant constant whose sign is controlled by the sign of the accumulated data, and eventually becomes zero. . Therefore, the output of the noise shaper is always zero.

Next, a second embodiment of the present invention will be described. In the first embodiment, the first stage integrator S1 is shown in FIG.
It was realized by the circuit shown in. FIG. 3 shows a circuit diagram of the integrator used in the second embodiment. As shown in FIG. 3, the first-stage integrator S1 adds the accumulated data before the delay of one sample, the current data, and the fixed constant (± 2 ⁻¹⁶ ). At this time, the sign of the fixed constant is negative when the accumulated data before one sample delay is positive, and is positive when the accumulated data before one sample delay is negative.
When the accumulated data before the sample delay is zero, the fixed constant is controlled to zero by the sign control circuit CONT2. The second-stage integrator S2 is a perfect integrator realized by adding the accumulated data before one sample delay and the current data.

With such a configuration, assuming that the quantization noise generated in the quantizer C is Q, the relationship between the noise shaper input signal X and the output signal Y is shown by the following equation.

Y (z) = z ⁻¹ · X (z) / P (z) + (1−z ⁻¹ ) ² · Q (z) (3) Therefore, the output spectrum of the noise shaper is the input of the noise shaper. It has a spectrum in which a signal obtained by almost second-order differentiation of the quantization noise is superimposed on. That is, since the quantization noise is shaped and superimposed in the high frequency region, the total noise in the signal band is significantly reduced without degrading the characteristics of the conventional noise shaper.

Consider the case where no signal is input to the noise shaper in the above-described operation. Now, the first stage,
It is obvious that the output code becomes zero when the initial values of the second-stage integrators S1 and S2 are zero. Next, when the initial value of the integrator S1 of the first stage is a constant value other than zero, the absolute value gradually decreases by addition of a constant constant whose sign is controlled by the sign of the accumulated data, and eventually becomes zero. . Therefore, the output of the noise shaper is always zero.

Next, a third embodiment will be described. FIG. 4 is a circuit diagram showing the third embodiment. In FIG.
S1 is a first stage integrator, S2 is a second stage integrator, C
Is a quantizer that outputs ternary levels with ± 0.5 as a threshold value, and D is a delay device. The difference signal between the output signal of the quantizer C delayed by the delay device D and the input signal is input to the first-stage integrator S1 and integrated. Further, a difference signal between the output signal of the integrator S1 of the first stage and the output signal of the quantizer C delayed by the delay device D is input to the integrator S2 of the second stage and integrated. The output of the second-stage integrator S2 is input to the quantizer C. At this time, the output is +1 when it is larger than +1/2, 0 is output when it is between -1/2 and +1/2, and -1 is output when it is smaller than -1/2. Further, the integrators S1 and S2 can be configured as shown in FIG. 5, for example. As shown in FIG. 5, the first-stage integrator S1 adds the accumulated data before the delay of one sample, the current data, and the fixed constant (± 2 ^-18 ). At this time, the sign of the fixed constant is negative when the accumulated data before one sample delay is positive, positive when the accumulated data before one sample delay is negative, and is zero when the accumulated data before one sample delay is zero. Is controlled by the sign control circuit 3 so that the fixed constant becomes zero. The second-stage integrator is a perfect integrator which is realized by adding the accumulated data before one sample delay and the current data.

With such a configuration, assuming that the quantization noise generated in the quantizer C is Q, the relationship between the noise shaper input signal X and the output signal Y is shown by the following equation.

Y (z) = z ⁻¹ · X (z) / P (z) + (1−z ⁻¹ ) ² · Q (z) (4) Therefore, the output spectrum of the noise shaper is the input of the noise shaper. It has a spectrum in which a signal obtained by almost second-order differentiation of the quantization noise is superimposed on. That is, since the quantization noise is shaped and superimposed in the high frequency region, the total noise in the signal band is significantly reduced without deteriorating the characteristics of the conventional noise shaping.

Consider the case where no signal is input to the noise shaper in the above-described operation. Now, the first stage,
It is obvious that the output code becomes zero when the initial values of the second-stage integrators S1 and S2 are zero. Next, when the initial value of the integrator S1 of the first stage is a constant value other than zero, the absolute value gradually decreases by addition of a constant constant whose sign is controlled by the sign of the accumulated data, and eventually becomes zero. . Therefore, the output of the noise shaper is always zero.

In the addition of constant constants whose sign is controlled by the accumulated data before one sample delay for realizing incomplete integration in the first to third embodiments shown above,
It is obvious that the output is zero when there is no signal input, even if a positive or negative constant constant is added instead of adding zero when the accumulated data before sample delay is zero. is there.

[0022]

As described above, in the noise shaper of the present invention, the output signal can be made zero when no signal is input without impairing the S / N characteristic.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a first embodiment of the present invention.

FIG. 2 is a circuit diagram of an integrator that constitutes the first embodiment of the present invention.

FIG. 3 is a circuit diagram of an integrator which constitutes a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a third embodiment of the present invention.

FIG. 5 is a circuit diagram of an integrator which constitutes a third embodiment of the present invention.

FIG. 6 is a circuit diagram of a conventional noise shaper.

FIG. 7 is a circuit diagram of an integrator that constitutes a conventional noise shaper.

[Explanation of symbols]

 S1 First integrator S2 Second integrator D, D1, D2 Delay device C Quantizer A Amplifier

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[Procedure amendment]

[Submission date] March 26, 1992

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 5

[Correction method] Change

[Correction content]

[Figure 5]

Claims (3)

[Claims] 1. A noise shaper comprising one or more stages of an integrating circuit, a ternary quantizer which outputs 0 and ± 1 and a feedback circuit, wherein an input signal of the noise shaper and one or more of the feedback circuits are provided. And a connection for inputting an output signal to the integrating circuit, a connection for inputting an output signal of the integrating circuit to the quantizer, and a connection between the quantizer and an output terminal of a noise shaper. Is an incomplete integration operation realized by adding the accumulated data before one sample delay, the current data, and a constant whose absolute value is a constant value or zero, and the one sample delay When the previous accumulated data is positive, the sign of the constant is negative, when the accumulated data before the one sample delay is negative, the sign of the constant is positive, and when the accumulated data before the one sample delay is zero. Is the above Noise shaper, characterized in that it has a sign control circuit with zero number. 2. A noise shaper comprising one or more stages of an integrating circuit, a ternary quantizer which outputs 0 and ± 1 and a feedback circuit, wherein an input signal of the noise shaper and one or more of the feedback circuits are provided. And a connection for inputting an output signal to the integrating circuit, a connection for inputting an output signal of the integrating circuit to the quantizer, and a connection between the quantizer and an output terminal of a noise shaper. Is an incomplete integration operation realized by adding the accumulated data before one sample delay, the current data and a constant whose absolute value is a constant value, and the accumulation before the one sample delay A noise shaper comprising a sign control circuit for making the sign of the constant negative when the data is positive or zero and for making the sign of the constant positive when the accumulated data before the one-sample delay is negative. 3. A noise shaper comprising one or more stages of integrating circuits, a ternary quantizer having 0 and ± 1 as outputs, and a feedback circuit, wherein an input signal of the noise shaper and one or more of the feedback circuits are provided. And a connection for inputting an output signal to the integrating circuit, a connection for inputting an output signal of the integrating circuit to the quantizer, and a connection between the quantizer and an output terminal of a noise shaper. Is an incomplete integration operation realized by adding the accumulated data before one sample delay, the current data and a constant whose absolute value is a constant value, and the accumulation before the one sample delay A noise shaper comprising a sign control circuit for making the sign of the constant negative when the data is positive and for making the sign of the constant positive when the accumulated data before the one-sample delay is negative or zero.