JP2000114971A - Digital signal generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably output a one bit SDM signal by executing a pre-emphasis processing emphasizing a high frequency band on an inputted analog signal, outputting the analog signal, shaving noise with sigma/delta modulation, outputting the one bit SDM signal, de-emphasizing it and outputting a multi-bit PCM signal. SOLUTION: A one bit SDM system A/D converter 3 converts an analog signal into a one bit SDM signal and primarily shaves a quantization noise component. The one bit SDM system A/D converter 3 outputs the one bit SDM signal to a digital de-emphasis circuit 4. A de-emphasis characteristic is added to the digital de-emphasis circuit 4 since it attenuates the signal component of the high frequency band of the inputted one bit SDM signal. The de-emphasis characteristic is almost opposite to the pre-emphasis characteristic of the analog pre-emphasis circuit 2 and they compensate each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
Bit sigma delta modulation (hereinafter Sigma Delta Modulati)
The acronym for on is called SDM. The present invention relates to a digital signal generator for converting a signal.

[0002]

2. Description of the Related Art Conventional compact discs (hereinafter referred to as Comp
The acronym of act Disk is called CD. ), Multi-bit pulse code modulation having a sampling frequency of 44.1 kHz and a quantization bit number of 16 bits (hereinafter, pulse code modulation is referred to as Pulse Code Mod)
It is written as PCM using the initials of ulation. ) The signal is encoded and recorded.

In recent years, in order to improve sound quality, 1-bit S bits that are quantized at high speed by 1 bit and sigma-delta modulated are used.
The digital signal processing of the DM system converts the input analog signal to a sampling frequency of 2.8224 MHz.
A 1-bit SDM technique for converting a 1-bit SDM signal having a quantization bit number of 1 bit has attracted attention.

An outline of the 1-bit SDM technique will be described. FIG. 10 is a block diagram of a recording / reproducing system using 1-bit SDM technology, and FIG. 11 is a frequency spectrum diagram of an output signal output from each block of the recording / reproducing system using 1-bit SDM technology.

First, a case where a 1-bit SDM signal is generated from an analog signal and stored in an information medium will be described. As shown in FIG. 10, an analog signal having a frequency spectrum as shown in FIG. 11A is input to an input terminal 10 from an external device (not shown).

The signal component of this analog signal is 100 k
It is a frequency band of about Hz, and includes a high frequency analog signal exceeding an audible frequency. This analog signal is a 1-bit SDM analog-digital (hereinafter, an
alog / Digital is abbreviated to A / D).

[0007] The 1-bit SDM A / D converter 20 comprises:
The input analog signal is sampled at a sampling frequency of 2.
The signal is converted into a 1-bit SDM signal having 8224 MHz and a quantization bit number of 1 bit.

FIG. 11B shows a frequency spectrum of a 1-bit SDM signal. The 1-bit SDM signal includes a signal component and a quantization noise component generated by the SDM, respectively. By SDM, for example, noise shaping is performed in which quantization noise moves to a frequency band from 100 kHz, which is the upper limit of an analog signal, to 1.4112 MHz, which is half the sampling frequency. 1-bit SD
The M-system A / D converter 20 outputs the converted 1-bit SDM signal to the 1-bit SDM signal recording / reproducing device 30.

Recording / reproducing apparatus 30 for 1-bit SDM signal
Records a 1-bit SDM signal on an information medium. Here, the 1-bit SDM signal recording / reproducing device 30 is, for example, a tape device, an optical disk device, a magnetic disk device, or a computer including the optical disk device or the magnetic disk device. In this way, the analog signal
A bit SDM signal is generated and recorded and stored on an information medium.

Next, a case where a 1-bit SDM signal reproduced from an information medium is converted into an analog signal will be described. The 1-bit SDM signal recording / reproducing device 30 reproduces the 1-bit SDM signal in response to an operation from the operator.

Recording / reproducing apparatus 30 for 1-bit SDM signal
Outputs the reproduced 1-bit SDM signal to the analog low-pass filter 40. Analog low-pass filter 40
Is a filter having a cutoff frequency up to an upper limit of 100 kHz of an analog signal, for example, by filtering an input 1-bit SDM signal.
An analog signal having a frequency band up to kHz is reproduced.

The analog low-pass filter 40 extracts a signal component from the 1-bit SDM signal by performing low-pass filtering on the 1-bit SDM signal. This signal component is an analog signal up to 100 kHz. The quantization noise component in a frequency band higher than 100 kHz is removed by the analog low-pass filter 40.

FIG. 11C shows a frequency spectrum of an analog signal output from the analog low-pass filter 40. As described above, the filtering by the analog low-pass filter 40 removes a large part of the quantization noise component included in the 1-bit SDM signal, and extracts the signal component included in the 1-bit SDM signal.

The analog low-pass filter 40 outputs an analog signal to an output terminal 50. The analog signal is
The signal is output to an amplifying device or a speaker device (not shown) and reproduced as music or voice.

[0015]

When performing noise shaping by SDM, the 1-bit SDM A / D converter 2 is designed to have a predetermined noise shaping characteristic.
0, the 1-bit SDM A / D converter 20
May not generate a 1-bit SDM signal by predetermined noise shaping.

One reason why a 1-bit SDM signal is not generated by predetermined noise shaping is, for example, 1
The bit SDM A / D converter 20 does not operate stably.

The reason why the 1-bit SDM A / D converter 20 does not operate stably is that a signal inputted to a 1-bit A / D converter or an operational amplifier included in the 1-bit SDM A / D converter 20 is not used. It can be assumed that there is an uncertain factor such as a limit of response speed that cannot follow the frequency and phase delay or phase advance depending on the frequency of the input signal. However, it is not precisely understood.

These 1-bit SDM A / D converters 2
It is desirable to realize a noise shaping characteristic of moving quantization noise to a predetermined high frequency band while satisfying predetermined conditions such as stabilizing the operation of 0.
In order to satisfy a predetermined condition such as stabilizing the operation, a predetermined noise shaping characteristic of the quantization noise is sacrificed.

Specifically, in order to satisfy a predetermined condition such as stabilizing the operation, the noise shaping characteristic of the 1-bit SDM signal output from the 1-bit SDM A / D converter 20 is 1-bit SDM A The quantization noise of the / D converter 20 cannot be moved to a frequency band exceeding 100 kHz, and has a noise shaping characteristic such that the signal level of the quantization noise increases from around 50 kHz.

That is, there is a disadvantage that the quantization noise remains despite the desire to remove the quantization noise from the analog signal having a frequency band up to 100 kHz. There is a need for an A / D converter that can generate a 1-bit SDM signal from which quantization noise has been removed.

An object of the present invention is to provide a digital signal generator for stably generating a 1-bit SDM signal having a predetermined noise shaping characteristic.

[0022]

According to a first aspect of the present invention, there is provided a digital signal generator which performs a pre-emphasis process for emphasizing a high frequency band on an input analog signal to convert the analog signal. An analog pre-emphasis circuit for outputting, and a 1-bit signal for outputting a 1-bit SDM signal by noise-shaping the pre-emphasized analog signal by sigma-delta modulation
A DM A / D converter, a digital de-emphasis circuit for performing a de-emphasis process on the 1-bit SDM signal and outputting a multi-bit PCM signal, and a digital sigma-delta modulation of the de-emphasized multi-bit PCM signal A digital SDM circuit that outputs a 1-bit SDM signal by noise shaping.

According to a second aspect of the present invention, there is provided a digital signal generating apparatus, comprising: an analog pre-emphasis circuit for performing a pre-emphasis process for emphasizing a high frequency band on an input analog signal and outputting the analog signal; A multi-bit PCM A / D converter that outputs a multi-bit PCM signal by noise-shaping the analog signal obtained by sigma-delta modulation and outputs a multi-bit PCM signal by performing de-emphasis processing on the multi-bit PCM signal A digital de-emphasis circuit and a digital SDM circuit for noise-shaping the de-emphasized multi-bit PCM signal by digital sigma-delta modulation to output a 1-bit SDM signal.

According to a third aspect of the present invention, in the digital signal generator according to the first or second aspect, the frequency characteristic of the transfer function of the analog pre-emphasis circuit is the digital de-emphasis. It is characterized by being substantially equal to the frequency characteristic of the inverse function of the transfer function of the circuit.

[0025]

FIG. 1 is a block diagram of a digital signal generator according to a first embodiment of the present invention. FIG. 2 is a block diagram of a 1-bit SDM A / D converter of the digital signal generator according to the first embodiment.
FIG. 3 is a block diagram of a digital SDM circuit of the digital signal generator of the first embodiment.

FIG. 4 is a frequency spectrum diagram of signal components output from each block of the digital signal generator of the first embodiment, and FIG. 5 is a frequency characteristic diagram of transfer functions of the analog emphasis circuit and the digital de-emphasis circuit. ,
FIG. 6 is a frequency spectrum diagram of a quantization noise component output from each block of the digital signal generator of the first embodiment.

Hereinafter, the first embodiment of the present invention will be described with reference to FIGS.
A digital signal generator according to an embodiment will be described. The signal processing of the digital signal generator according to the first embodiment of the present invention will be described with reference to FIGS. For explanation, a signal component and a quantization noise component are illustrated separately.

The digital signal generator of the first embodiment is
As shown in FIG. 1, an input terminal 1, an analog pre-emphasis circuit 2, a 1-bit SDM A / D converter 3, a digital de-emphasis circuit 4, a digital SDM circuit 5
And an output terminal 6.

The 1-bit SDM A / D converter 3
Includes a subtractor 3a, a 1-bit D / A converter 3b, an H (f) analog filter 3c, and a 1-bit A / D converter 3d, as shown in FIG. In this embodiment, the 1-bit SDM A / D converter 3 is described as performing primary noise shaping.

As shown in FIG. 3, the digital SDM circuit 5 has a subtractor 5a, a one-sample delay
(Z) Digital filter 5c, subtractor 5d, N (z)
A digital filter 5e and a 1-bit quantizer 5f are provided. In this embodiment, the digital SDM circuit 5 is described as performing secondary noise shaping.

Next, the signal processing of the digital signal generator of the first embodiment will be described. An analog signal having a frequency spectrum as shown in FIG. 4A is input to an input terminal 1 of FIG. 1 from an external device (not shown). Here, the external device is, for example, an amplifier device that amplifies an analog signal output from a microphone, a magnetic tape device that reproduces an analog signal, or the like.

This analog signal is output to the analog pre-emphasis circuit 2 via the input terminal 1. The analog pre-emphasis circuit 2 adds a pre-emphasis characteristic to emphasize a high frequency band of the analog signal.

In this embodiment, the pre-emphasis characteristic is, for example, substantially the same as the frequency characteristic of the quantization noise component as shown in FIG. However, as another example, the frequency characteristic up to 100 kHz may be substantially the same as the frequency characteristic of the quantization noise component, and the frequency characteristic exceeding 100 kHz may be an arbitrary characteristic.

The reason for setting such frequency characteristics is that a quantization noise component in a frequency band exceeding 100 kHz at the time of reproduction is removed by an analog low-pass filter of the reproducing apparatus, so that the frequency characteristics exceeding 100 kHz are not affected. That's why.

The analog pre-emphasis circuit 2 has the configuration shown in FIG.
An analog signal to which the pre-emphasis characteristic is added as shown in (b) is output to the 1-bit SDM A / D converter 3. The analog signal to which the pre-emphasis characteristic has been added is input to the subtractor 3a in FIG.

In the subtracter 3a, the analog signal to which the pre-emphasis characteristic has been added is subtracted by the output signal of the 1-bit D / A converter 3b which is input simultaneously, and the difference signal is supplied to the H (f) analog filter 3c. Is entered.

The H (f) analog filter 3c has a high gain in a low frequency band, a low gain in a high frequency band, and has an integrator characteristic. The output of the H (f) analog filter 3c is input to the 1-bit A / D converter 3d.

The 1-bit A / D converter 3d generates a 1-bit SDM signal having a sampling frequency f0 and a quantization number of 1 bit from the difference signal output from the H (f) analog filter 3c, and converts the 1-bit SDM signal. Output.

A 1-bit SDM signal output from the 1-bit A / D converter 3d is input to the 1-bit D / A converter 3b, converted into an analog signal, and then input to the subtractor 3a. Is configured. The analog signal is converted by the 1-bit SDM A / D converter 3 into:
It is converted to a 1-bit SDM signal.

Also, quantization noise is generated with the quantization of the 1-bit A / D converter 3d. The quantization noise power spectrum is generated independently of the input to the 1-bit A / D converter 3d.

If a quantization noise component is output from an A / D converter that does not perform sigma-delta modulation, the power spectrum of the quantization noise is calculated from the DC component to the sampling frequency f0 as shown in FIG. The distribution becomes flat up to.

However, since the quantization noise output from the 1-bit SDM A / D converter 3 is subjected to primary noise shaping, the power spectrum of the quantization noise of the 1-bit SDM A / D converter 3 is shown in FIG. As shown in FIG.
The distribution is such that the quantization noise in a low frequency band from a certain frequency to a certain frequency is reduced, and the quantization noise in a high frequency from a certain frequency to a half of the sampling frequency is increased.

As described above, the 1-bit SDM A / D converter 3 converts an analog signal into a 1-bit SDM signal and performs primary noise shaping on the quantization noise component. The 1-bit SDM A / D converter 3 has a 1-bit S
The DM signal is output to the digital de-emphasis circuit 4.

FIG. 4C shows the 1-bit SDM system A
FIG. 6B shows the frequency spectrum of the signal component of the 1-bit SDM signal output from the 1-bit SDM system A / D converter 3.
The frequency spectrum of the quantization noise component of the DM signal is shown. Actually, it is a 1-bit SDM signal in which the signal component and the quantization noise component are added.

The digital de-emphasis circuit 4 adds a de-emphasis characteristic as shown in FIG. 5 (b) in order to attenuate the high frequency band signal component of the input 1-bit SDM signal. The de-emphasis characteristic is a frequency characteristic substantially opposite to the pre-emphasis characteristic of the analog pre-emphasis circuit 2, and is a characteristic that cancels out each other.

Since the de-emphasis characteristic is the inverse characteristic of the pre-emphasis characteristic, the signal component of the multi-bit PCM signal output from the digital de-emphasis circuit 4 is, for example, the input analog signal as it is in the multi-bit PCM system. It becomes the same as the signal component of the multi-bit PCM signal obtained by A / D conversion by the A / D converter.
The digital de-emphasis circuit 4 is a multi-bit PC
The M signal is output to the digital SDM circuit 5.

FIG. 4 (d) shows the frequency spectrum of the signal component of the multi-bit PCM signal output from the digital de-emphasis circuit 4, and FIG. 6 (c) shows the frequency spectrum of the multi-bit PCM signal output from the digital de-emphasis circuit 4. The frequency spectrum of the quantization noise component of the bit PCM signal is shown.

The quantization noise component output from the digital de-emphasis circuit 4 is reduced by a de-emphasis characteristic that attenuates a signal component in a high frequency band. In fact, it is a multi-bit PCM signal in which the signal component and the quantization noise component are added.

At this time, the digital de-emphasis circuit 4
Converts a 1-bit SDM signal into a multi-bit PCM signal and outputs it. The reason for this is that the digital de-emphasis circuit 4 multiplies the 1-bit SDM signal, which is either 1 or 0, by a predetermined coefficient over past samples and adds the 1-bit SDM signal. Because there is no.

To generate a 1-bit SDM signal again,
The digital de-emphasis circuit 4 converts the multi-bit PCM signal with the de-emphasis
Output to DM circuit 5. The multi-bit PCM signal to which the de-emphasis characteristic has been added is input to the subtractor 5a in FIG.

In the subtracter 5a, the multi-bit PCM signal to which the de-emphasis characteristic is added is subtracted by the output signal of the one-sample delay unit 5b which is input simultaneously, and this difference signal is input to the M (z) digital filter 5c. Is done.

The M (z) digital filter 5c has a high gain in a low frequency band, a low gain in a high frequency band, and an integrator. The output of the M (z) digital filter 5c is input to a subtractor 5d.

In the subtractor 5d, the output signal of the M (z) digital filter 5c is subtracted by the output signal of the one-sample delay unit 5b which is input simultaneously, and the difference signal is input to the N (z) digital filter 5e. You.

The N (z) digital filter 5e has a high gain in a low frequency band, a low gain in a high frequency band, and an integrator.
The output of the N (z) digital filter 5e is input to a 1-bit quantizer 5f.

The 1-bit quantizer 5f generates a 1-bit SDM signal having a sampling frequency f0 and a quantization number of 1 bit from the difference signal output from the N (z) digital filter 5e, and outputs a 1-bit SDM signal. .

The 1-bit SDM signal output from the 1-bit quantizer 5f is input to a 1-sample delay unit 5b.
A feedback loop is formed in which the signal is delayed by one sample and then input to the subtractor 5a. Digital SDM
The circuit 5 converts the multi-bit PCM signal into a 1-bit SDM signal, performs secondary noise shaping of the quantization noise component, and outputs the result to the output terminal 6.

FIG. 4D shows the frequency spectrum of the signal component of the 1-bit SDM signal output from the digital SDM circuit 5, and FIG.
4 shows the frequency spectrum of the quantization noise component of the 1-bit SDM signal output from the circuit 5. Actually, it is a 1-bit SDM signal in which the signal component and the quantization noise component are added.

1-bit SDM output from output terminal 6
The signal is output to a 1-bit SDM signal recording / reproducing device (not shown) and recorded on an information medium. Where 1 bit S
The recording / reproducing device for a DM signal is, for example, a tape device, an optical disk device, a magnetic disk device, or a computer incorporating the optical disk device or the magnetic disk device.

In the first embodiment, the 1-bit SDM A / D converter 3 performs primary noise shaping, and the digital SDM circuit 5 performs secondary noise shaping. However, 1-bit SDM system A /
Noise shaping order of D converter 3 and digital S
The order of the noise shaping of the DM circuit 5 can be set to an arbitrary order.

The digital SDM circuit 5 may perform high-order noise shaping that cannot be realized by the 1-bit SDM A / D converter 3 having an uncertain element peculiar to the analog circuit. Since noise shaping is performed by digital signal processing and there is no uncertain element peculiar to analog circuits, noise shaping as designed can be realized regardless of the order.

An analog pre-emphasis circuit 2, a 1-bit SDM A / D converter 3, and a digital de-emphasis circuit 4 use a multi-bit PCM signal that is sampled at high speed and free from quantization noise to produce a digital SDM circuit. 5 performs sigma-delta modulation, so that a 1-bit SDM signal with high sound quality can be obtained.

The digital signal generator according to the first embodiment of the present invention removes uncertainties peculiar to analog circuits and processes digital signals, so that it is possible to stably generate high-order 1-bit SDM signals. it can.

Next, a second embodiment of the present invention will be described. FIG. 7 is a block diagram of a digital signal generator according to a second embodiment of the present invention, FIG. 8 is a block diagram of a multi-bit PCM A / D converter of the digital signal generator of the second embodiment, and FIG. FIG. 10 is a circuit diagram of a multi-bit PCM A / D converter of the digital signal generator according to the second embodiment. Hereinafter, a digital signal generator according to a second embodiment of the present invention will be described with reference to FIGS.

The digital signal generator of the second embodiment is
As shown in FIG. 7, an input terminal 1, an analog pre-emphasis circuit 2, a multi-bit PCM A / D converter 7,
A digital de-emphasis circuit 4, a digital SDM circuit 5, and an output terminal 6 are provided. Here, the same blocks as those of the digital signal generator of the first embodiment are denoted by the same reference numerals, and will be briefly described.

As shown in FIG. 8, the multi-bit PCM A / D converter 7 includes a subtracter 7a, a multi-bit D / A converter 7b, an H (f) analog filter 7c, and a multi-bit A / D converter. A D converter 7d is provided. In this embodiment, the multi-bit PCM A / D converter 7 is described as performing primary noise shaping. Also,
In the present embodiment, the digital SDM circuit 5 is described as performing secondary noise shaping.

Next, the signal processing of the digital signal generator according to the second embodiment will be described. An analog signal is input to the input terminal 1 of FIG. This analog signal is output to the analog pre-emphasis circuit 2 via the input terminal 1.

The analog pre-emphasis circuit 2 has a first
The pre-emphasis characteristic as described in the embodiment is added to the analog signal. The analog signal to which the pre-emphasis characteristic is added is input to the multi-bit PCM A / D converter 7.

The analog signal to which the pre-emphasis characteristic has been added is input to a subtractor 7a as shown in FIG. In the subtracter 7a, the analog signal to which the pre-emphasis characteristic has been added is subtracted by the output signal of the multi-bit D / A converter 7b which is input simultaneously, and the difference signal is input to the H (f) analog filter 7c. .

The H (f) analog filter 7c has a characteristic of a high gain in a low frequency band, a low gain in a high frequency band, and a characteristic of an integrator. The output of the H (f) analog filter 7c is input to the multi-bit A / D converter 7d.

The multi-bit A / D converter 7d outputs H
(F) A multi-bit PCM signal having a sampling frequency f0 and a quantization number of 24 bits is generated and output from the sum signal output from the analog filter 7c.

The multi-bit PCM signal output from the multi-bit A / D converter 7d is input to the multi-bit D / A converter 7b, converted into an analog signal, and then output to the subtractor 7a. Construct a loop. The multi-bit PCM A / D converter 7
The multi-bit PCM signal is output to the de-emphasis circuit 4.

The digital de-emphasis circuit 4 adds a de-emphasis characteristic to the input multi-bit PCM signal and outputs a multi-bit PCM signal with the de-emphasis characteristic added.

In order to generate a 1-bit SDM signal, the digital de-emphasis circuit 4 converts a multi-bit PCM signal with a de-emphasis characteristic into a digital SDM signal.
Output to the circuit 5. The multi-bit PCM signal to which the de-emphasis characteristic is added is converted by the digital SDM circuit 5 into a 1-bit SDM signal.

The digital SDM circuit 5 has a 1-bit SD
The M signal is output to the output terminal 6. The 1-bit SDM signal output from the output terminal 6 is a 1-bit SDM signal (not shown).
The signal is output to the signal recording / reproducing device and recorded on the information medium.

Multi-bit PCM A / D converter 7
Is a circuit as shown in FIG. The input analog signal is filtered by the H (f) analog filter 7c, and the analog signal output from the H (f) analog filter 7c is input to the multi-bit A / D converter 7d.

When the number of quantization bits is N, the multi-bit A / D converter 7d divides the reference voltage by using 2 N resistors, and inputs each comparison voltage to the comparator. The comparator compares the comparison voltage with the input voltage by using (2 @ N -1) comparators, finds the comparison voltage closest to the input voltage, and outputs the comparison voltage to the latch circuit.

The data output from the latch circuit is input to a multi-bit PCM signal encoder to generate and output a multi-bit PCM signal of N bits per sample. Multi-bit PCM with noise shaping
Signal.

According to the second embodiment, the multi-bit PCM
Since the operation of the A / D converter 7 is stable, a desired noise shaping characteristic can be obtained from the 1-bit SDM A / D converter. The digital SDM circuit 5 at the subsequent stage can stably output the 1-bit SDM signal from which the quantization noise component has been removed by noise shaping.

As described above, according to the digital signal generators of the first and second embodiments of the present invention, high-order noise shaping for removing quantization noise components included in a low frequency band in which signal components exist is performed. be able to.

[0080]

According to the digital signal generator of the present invention, it is possible to provide a digital signal generator which stably generates a 1-bit SDM signal having a predetermined noise shaping characteristic.

[Brief description of the drawings]

FIG. 1 is a block diagram of a digital signal generator according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a 1-bit SDM A / D converter of the digital signal generator according to the first embodiment.

FIG. 3 is a block diagram of a digital SDM circuit of the digital signal generator according to the first embodiment.

FIG. 4 is a frequency spectrum diagram of signal components output from each block of the digital signal generator of the first embodiment.

FIG. 5 is a frequency characteristic diagram of a transfer function of the analog emphasis circuit and the digital de-emphasis circuit.

FIG. 6 is a frequency spectrum diagram of a quantization noise component output from each block of the digital signal generator of the first embodiment.

FIG. 7 is a block diagram of a digital signal generator according to a second embodiment of the present invention.

FIG. 8 is a block diagram of a multi-bit PCM A / D converter of the digital signal generator according to the second embodiment.

FIG. 9 is a circuit diagram of a multi-bit PCM A / D converter of the digital signal generator according to the second embodiment.

FIG. 10 is a block diagram of a recording / reproducing system using the DSD technology.

FIG. 11 is a frequency spectrum diagram of a signal output from each block of the recording / reproducing system using the DSD technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Input terminal 2 ... Analog pre-emphasis circuit 3 ... 1-bit SDM A / D converter 3a ... Subtractor 3b ... 1-bit D / A converter 3c ... H (f) Analog filter 3d ... 1-bit A / D conversion Device 4 ... Digital de-emphasis circuit 5 ... Digital SDM circuit 5a ... Subtractor 5b ... 1 sample delay device 5c ... M (z) digital filter 5d ... Subtractor 5e ... N (z) digital filter 5f ... 1 bit quantizer 6 ... Output terminal 7... Multi-bit PCM A / D converter 7 7a... Subtractor 7b... Multi-bit D / A converter 7c... H (f) analog filter 7d.

Claims (3)

[Claims] 1. An analog pre-emphasis circuit for performing pre-emphasis processing for emphasizing a high frequency band on an input analog signal and outputting the analog signal, and noise shaping the pre-emphasized analog signal by sigma-delta modulation. 1 bit SDM (Sigm
a 1-bit SDM A / D (analog / Digital) converter for outputting a Delta Modulation signal and a digital data for performing a de-emphasis process on the 1-bit SDM signal and outputting a multi-bit PCM (Pulse Code Modulation) signal. A digital signal generator, comprising: an emphasis circuit; and a digital SDM circuit that outputs a 1-bit SDM signal by noise shaping the multi-bit PCM signal subjected to the de-emphasis processing by digital sigma delta modulation. 2. An analog pre-emphasis circuit for performing pre-emphasis processing for emphasizing a high frequency band on an input analog signal to output an analog signal, and noise shaping the pre-emphasized analog signal by sigma-delta modulation. A multi-bit PCM A / D converter that outputs a multi-bit PCM signal;
A digital de-emphasis circuit that performs de-emphasis processing on the multi-bit PCM signal to output a multi-bit PCM signal; and a noise shaping of the de-emphasized multi-bit PCM signal by digital sigma delta modulation to form a 1-bit SDM signal. A digital signal generator comprising: a digital SDM circuit for outputting. 3. The digital signal generator according to claim 1, wherein a frequency characteristic of a transfer function of the analog pre-emphasis circuit is substantially equal to a frequency characteristic of an inverse function of a transfer function of the digital de-emphasis circuit. Digital signal generator characterized by being equal.