JPH05152951A - Analog digital conversion method - Google Patents

Abstract

PURPOSE:To eliminate a dither component in an excellent way by applying A/D conversion to a dither signal added to an analog information signal and a dither signal required for subtraction. CONSTITUTION:An analog information signal from a terminal 11 and an output from an analog dither generating circuit 6 are added by an adder circuit 3 and the sum is converted into a digital signal by an A/D converter 4. On the other hand, an output of the circuit 6 is converted into a digital signal by an A/D converter 7 and subtracted from an output of the converter 4 at a subtractor circuit 5. The dither signals of the same characteristic are used through the converters 4,7 to eliminate undesired subtraction residue and the dither component is eliminated in an excellent way.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analog / digital conversion method for converting an analog signal such as an audio signal into a digital signal with superposition (addition) and subtraction of a dither signal. is there.

[0002]

2. Description of the Related Art Quantization noise (difference between quantized output and input sample value) becomes a problem in PCM recording / reproduction of an audio signal. Especially, when the input signal level is low and the number of quantization steps is small, the quantization noise has a strong correlation with the input, and becomes a kind of distortion (higher harmonic) of the input signal rather than noise. Also, even if the input signal level is high,
For a very slowly changing signal, annoying noise is generated each time the quantization step changes. In order to solve the above problems, it is already known to add white noise called dither to an input signal for digital signal processing, or to add dither and then subtract dither (for example, Edited by Heitaro Nakajima, November 20, 1979
4th "Introduction to Digital Audio Technology" published by Nihon Ohmsha
Page 6, or Yoshio Yamazaki, "Prospects for Digital Audio," in the "1983 Electronic Industries Conference Documents" published by the Japan Electronic Machinery Manufacturers Association). When A / D conversion is performed by adding dither to the information signal, even if an A / D converter having a variable quantization step and poor linearity is used, the linearity is improved because the variation is averaged. That is, in an audio signal, it is usual that substantially the same waveform is repeatedly generated a plurality of times, and if D / A conversion is performed by adding dither to the waveform repeatedly generated a plurality of times, a plurality of identical waveforms are generated. Points at the same level of the waveform will be at different levels due to dither, and each will have A / D at different quantization steps.
It will be D-converted. Therefore, an averaging effect of A / D conversion error and non-linearity occurs, and A / D conversion with less distortion is achieved. Since the dither is removed after A / D conversion, theoretically, the dither is not included in the information signal.

FIG. 3 shows a conventional dither addition and subtraction method. In the system shown in FIG. 3, the output of the digital dither generation circuit 1 is converted into an analog signal by the D / A converter 2, and this is superposed on the analog information signal by the adder circuit 3,
The dither addition information signal obtained by this is converted into a digital signal by the A / D converter 4, and this is sent to the subtraction circuit 5, and at the same time, the dither is sent from the digital dither generation circuit 1 to the subtraction circuit 5, and the dither circuit 5 performs The digitized dither signal is subtracted from the addition information signal.

[0004]

However, in the method of FIG. 3, the dither generation circuit 1 to the D / A converter 2 and the addition circuit 3 are used.
Since the dither path reaching the subtraction circuit 6 via the A / D converter 4 and the dither path directly connected to the subtraction circuit 6 from the dither generation circuit 1 have different characteristics, It is difficult to input the same dither at the same time, a subtraction error occurs, and the purpose of dither addition and subtraction cannot be sufficiently achieved.

Therefore, an object of the present invention is to provide an analog / digital conversion method which can sufficiently obtain the effect of dither addition and subtraction.

[0006]

SUMMARY OF THE INVENTION To achieve the above object, the present invention provides a step of receiving an analog information signal, a step of generating an analog dither signal from an analog dither signal generating means, and a step of generating the analog information signal from the analog information signal. Adding the dither signals to form an analog dither addition information signal; converting the analog dither addition information signal to a digital dither addition information signal using a digital-to-analog converter;
Converting the analog dither signal generated by the analog dither signal generating means into a digital dither signal using an analog-digital converter; and subtracting the digital dither signal from the digital dither addition information signal. And a step of obtaining a digital information signal, which is related to an analog-digital conversion method.

[0007]

According to the present invention, since the dither signal added to the analog information signal and the dither signal necessary for subtraction are both A / D converted, it is possible to reduce the difference between the two and the digital information. The dither component included in the dither addition information signal of 1 is achieved well, and A / D conversion with less noise or distortion is possible.

[0008]

[First Embodiment] Next, referring to FIG. 1 and FIG. 2, an analog circuit for PCM recording according to a first embodiment of the present invention will be described.
A digital conversion device and method will be described. In FIG. 1, reference numeral 11 denotes an analog input terminal, which is a portion for inputting an audio signal. Reference numeral 12 is a first gate circuit, which converts the analog information signal supplied from the input terminal 11 to
It selectively passes the signal in response to the control signal of FIG. 2B given from the control circuit 13. In this embodiment, the first gate circuit 12 responds to the high level pulse generated at the first time TB, which is the one sampling time TA shown in FIG. Passes an analog information signal (audio signal).

Reference numeral 14 is an analog dither signal generating circuit, which is a circuit for generating white noise, that is, dither. 15
Is a sampling circuit, which responds to the analog dither signal obtained from the dither signal generating circuit 14 by the pulse of one sampling time TA shown in FIG. Is sent.

The adder circuit 16 analog-adds (superimposes) the output of the first gate circuit 12 and the output of the sampling circuit 15. An information signal is output from the first gate circuit 12 corresponding to the first time TB of FIG. 2B, and the sampling circuit 15 corresponds to the one sampling time TA of FIG. 2A. Since the dither signal is output, the adder circuit 16 outputs the dither addition information signal obtained by adding the dither signal to the information signal within the first time T B, and the second dither addition information signal in FIG. Only the dither signal is output at time TC. As a result, time division transmission of the dither addition information signal and the dither signal is achieved.

Reference numeral 17 denotes an A / D converter, which is an adder circuit 16
From the dither addition information signal and the dither signal are time-divisionally A / D-converted, the digital dither addition information signal is output corresponding to the first time TB, and the digital dither signal is Output corresponding to time Tc of 2.

Reference numeral 18 denotes a second gate circuit, which responds to the pulse of the first time TB shown in FIG. 2B from the control circuit 13 from the output of the A / D converter 17 and outputs the dither addition information signal. Is to be extracted. Since the A / D converter 17 outputs the dither addition information signal corresponding to the first time TB, by turning on the gate circuit 18 at this first time TB, only the dither addition information signal passes.

Reference numeral 19 denotes a memory, which is the second gate circuit 1
The dither addition information signal obtained from 8 is written in synchronization with the first time TB in FIG. 2B, and the second dither information signal in FIG.
The data is read in synchronization with the time TC. 20 is the third
2 which is a gate circuit of FIG.
The dither signal included in the output of the A / D converter 17 is extracted in response to the pulse of the second time TC in (C). 21 is a digital subtraction circuit, which is a memory 1
The digital subtraction processing of the digitized dither addition information signal read from 9 at the second time TC and the digitized dither signal obtained from the third gate circuit 20 at the second time TC is performed, and the digital subtraction processing is performed at the output terminal 22. It provides the digital output for PCM recording.

P is connected to the input terminal 11 of the D / A converter of FIG.
When an audio signal for CM recording is input as an analog information signal, a dither addition information signal and a dither signal are obtained in a time division state at the output stage of the adder circuit 16, and these are the same A / D converter 17. Is converted into a digital signal by. The output of the A / D converter 17 is separated into a dither addition information signal and a dither signal, and dither is subtracted from the dither addition information signal. Since one and the other inputs of the subtraction circuit 21 are obtained based on the same A / D converter 17, the A / D conversion error contained in one input and the A / D conversion contained in the other input.
There is practically no difference from the D conversion error. Therefore, the generation of noise or distortion due to the difference in A / D conversion error is significantly reduced.

[0015]

[Second Embodiment] FIG. 4 shows an A / D converter according to a second embodiment of the present invention. In FIG. 4, the analog information signal input terminal 11 is connected to one input terminal of the adder circuit 3. The analog dither generation circuit 1 is connected to the other input terminal of the adder circuit 3. The adder circuit 3 is the first A / D
It is connected to one input terminal of the subtraction circuit 5 via the converter 4. A second A / D converter 7 is connected between the other input terminal of the subtraction circuit 5 and the analog dither generation circuit 6.

In the apparatus of FIG. 4, the analog dither signal output from the analog dither generation circuit 6 is added to the input analog information signal by the adder circuit 3 to form an analog dither addition information signal. This analog dither addition information signal is converted by the first A / D converter 4 into a digital dither addition information signal. The second A / D converter 7 converts the analog dither signal into a digital dither signal. In the subtraction circuit 5, the digital dither signal is subtracted from the digital dither addition information signal to obtain an information signal, which is output.

In this system, the analog dither signal output from the analog dither signal generating circuit 6 passes through the adding circuit 3 and the first A / D converter 4 and reaches the subtracting circuit 5 and also the second A / D converter. The subtraction circuit 5 is reached through the D converter 7.
Therefore, the A / D conversion process is executed in any of the two paths from the dither generation circuit 6 to the subtraction circuit 5, and the phase characteristics of both inputs of the subtraction circuit 5 are the same, so that sufficient dither subtraction is possible and dither subtraction is possible. The effect of the use of can be obtained satisfactorily.

[0018]

[Modification] The present invention is not limited to the above-described embodiment, but can be modified. For example, the dither may be arranged first in the signal arrangement within one sampling time.

[Brief description of drawings]

FIG. 1 is a block diagram showing an analog-digital conversion apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a waveform of each part of FIG.

FIG. 3 is a block diagram showing a conventional analog-digital conversion device.

FIG. 4 is a block diagram showing an analog-digital conversion device of a second embodiment.

[Explanation of symbols]

 3 Addition circuit 4, 7 A / D converter 5 Subtraction circuit 6 Analog dither generation circuit

Claims (1)

[Claims] 1. A step of receiving an analog information signal, a step of generating an analog dither signal from an analog dither signal generating means, and a step of adding the analog dither signal to the analog information signal to form an analog dither addition information signal. A step of converting the analog dither addition information signal into a digital dither addition information signal using a digital-analog converter; and an analog-digital conversion of the analog dither signal generated from the analog dither signal generating means. Digital dither signal using a converter, and a step of subtracting the digital dither signal from the digital dither addition information signal to obtain a digital information signal. How to convert.