JPH03117216A - A/d converter - Google Patents

Abstract

PURPOSE:To improve the characteristic after conversion even when no analog signal input exists by generating a signal with a prescribed amplitude and a frequency at the outside of the band of A/D conversion by an A/D converter means and inputting the signal to the A/D converter means. CONSTITUTION:When an analog signal is inputted to an A/D converter 1 and the signal has a large positive DC offset, an MSB data outputted from an MSB extraction circuit 2 takes a negatively consecutive prescribed value. Then MSB data pass through an integration circuit 3 and is inputted to the converter 1 to cancel the DC offset. When no analog signal is inputted to the converter 1 and the DC offset reaches a small value, then the MSB data from the circuit 2 is a signal having a frequency of 48kHz by a signal generated from a signal generating circuit 4. Since the signal is sufficiently attenuated by the circuit 3 and eliminated by a digital filter 8, then the signal is not included in an output signal. Thus, even when no analog signal is inputted, the characteristic after conversion is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an A/D conversion device used in a digital audio device such as a DAT.

(Prior art) An analog signal that is converted into a digital signal by an A/D converter is processed by an input buffer or the like placed before it.
Even if a C offset is not included, a DC offset is included in the converted digital signal due to errors in each parameter related to the conversion.

For this reason, conventionally, for example, MSB servo is used to remove such a C offset.

The MSB servo is a 2-S servo, as shown in Figure 3(a).
The MSB of conbriment data represents the positive or negative of the signal, and since analog signals such as music signals inherently do not contain D/C components, as shown in FIG. 3(b),
MS from the digital signal converted by the A/D converter
Extract and integrate B data. And this integral value is ”
This integrated value is fed back to the analog signal converted by the A/D converter so that it takes an intermediate value without being biased toward either "1 (positive)" or "0 (negative)".

However, if no analog signal is input to the A/D converter, noise remaining on the input side as shown in Figure 4(a) or noise generated by the A/D converter itself may cause the As shown in FIG. 4(b), the MSB data has contents corresponding to these noises. That is, the circuit for extracting MSB data becomes a noise amplifier with a wide spectrum. Then, such MSB data is sent to the A/D
A problem arises in that the signal goes around to the input side of the converter and deteriorates the S/N ratio of the A/D converter.

(Problems to be Solved by the Invention) As described above, in an A/D converter equipped with a means for removing DC offset using the conventional MSB servo, when an analog signal is not input to the A/D converter, the input side Due to the noise remaining in the A/D converter and the noise generated by the A/D converter itself, the MSB data becomes a content corresponding to these noises, wraps around to the input terminal of the A/D converter, and the S of the A/D converter This causes a problem of deteriorating the /N ratio.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an A/D converter with good characteristics after conversion even when no analog signal is input.

[Structure of the Invention] (Means for Solving the Problems) The present invention includes an A/D conversion means for converting an input analog signal into a digital signal, and an MSB from the digital signal converted by the A/D conversion means. MSB extracting means for extracting data, integrating the MSB data extracted by the MSB extracting means, and transmitting the integration result to the A/D
an integrating means which is fed back to the input side of the converting means, and a signal having a frequency outside the band of A/D conversion by the A/D converting means and having a predetermined amplitude is generated, and this signal is input to the input side of the A/D converting means. and a signal generating means input to the side.

(Function) In this invention, a signal having a frequency outside the A/D conversion band and a predetermined amplitude is generated by the A/D conversion means, and this signal is input to the input side of the A/D conversion means. Therefore, even when no analog signal is input, the characteristics after conversion are good.

(Example) Next, one embodiment of the present invention will be described.

FIG. 1 is a diagram showing the configuration of an A/D converter according to this embodiment.

In the same figure, 1 converts the input analog signal to 98Kl.
An A/D converter 2 converts the digital signal into a digital signal at a conversion rate of 1z, and 2 is an MSB extraction circuit that extracts MSB data from the digital signal converted by the A/D converter 1.

Further, 3 is an integration circuit that integrates the MSB data extracted by the MSB extraction circuit 2, and 4 is an A/D converter 1.
This is a signal generating circuit that generates a square p''p wave signal at a frequency outside the /D conversion band, for example, 48 KHz and a predetermined amplitude, for example, 1 mV. This signal generation circuit 4 is connected to a signal generation source 5 in order to generate the above-mentioned signal.
An attenuator 6 of about 60 to -80 dB is provided.

7 is an adder that superimposes the integration result by the integrating circuit 3 and the signal from the signal generating circuit 4 on the input side of the A/D converter 1; This is a digital filter that removes signals of 20 Kllz or more.

Next, the operation of the A/D converter configured as described above will be explained based on FIG. 2.

As shown in FIG. 2(a), if an analog signal is input to the A/D converter 1 and the signal has a large positive DC offset, the MSB extraction circuit 2 outputs an
As shown in FIG. 2(b), the SB data takes a continuous constant value on the negative side.

Then, this MSB data passes through the integrating circuit 3 and is sent to the A/D
It is input to the input side of the converter 1 and serves to cancel the above DC offset. Incidentally, the same applies when the analog signal has a large negative DC offset (Fig. 2(a) -) (Fig. 2(b) -).

Next, as shown in FIG. 2(a), for example, when the analog signal is no longer input to the A/D converter 1 and the DC offset becomes minute (for example, about 500 μV or less), the MS
The MSB data outputted from the B extraction circuit 2 becomes a signal with a frequency of 48 Kllz, as shown in FIG.

Since the signal at this frequency can be sufficiently attenuated by the integrating circuit 3 and removed by the digital filter 8, it is not included in the output signal.

Therefore, according to the A/D converter of this embodiment, the characteristics after conversion are good even when no analog signal is input.

[Effects of the Invention] As explained above, according to the present invention, a signal having a frequency outside the A/D conversion band and a predetermined amplitude is generated by the A/D conversion means, and this signal is converted into an A/D conversion signal. Since it is input to the input side of the means, the characteristics after conversion are good even when no analog signal is input.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an A/D conversion device according to an embodiment of the present invention, FIG. 2 is a diagram for explaining the operation of this device, and FIGS. 3 and 4 are diagrams for explaining a conventional example. This is a diagram for 1... A/D converter, 2... MSB extraction circuit, 3...
・Integrator circuit, 4... Signal generation port, 5... Signal generation source, 6... Attenuator, 7... Adder, 8... Digital filter.

Claims (1)

[Claims] A for converting an input analog signal into a digital signal
MSB extracting means extracting MSB data from the digital signal converted by the A/D converting means; integrating the MSB data extracted by the MSB extracting means; an integrating means that feeds back to the input side of the D converting means; and generating a signal having a frequency outside the band of A/D conversion by the A/D converting means and having a predetermined amplitude, and transmitting this signal to the A/D converting means.
An A/D conversion device comprising: signal generation means input to the input side of the D conversion means.