JPH0420124A - Digital signal processor - Google Patents

Abstract

PURPOSE:To reduce the effect of quantizing noise when an A/D converter with a comparatively nonlinear error is employed by providing an emphasis means emphasizing a high frequency component of an input signal and outputting the result and a de-emphasis means attenuating the high frequency component and outputting the result. CONSTITUTION:An analog input signal inputted from an input terminal 1 is inputted to an emphasis circuit 2, in which the high frequency component is emphasized and a noise level included in the input signal is increased and converted into a digital signal by an A/D converter 3. Then the result is subject to digital signal processing by a digital signal processing circuit 4 and then converted into an analog signal by a D/A converter 5. The signal outputted from the D/A converter 5 is inputted to a de-emphasis circuit 6, where the high frequency component is attenuated, the noise level is attenuated and outputted from an output terminal 7. Thus, even when an A/D converter with a comparatively nonlinear error is employed, the effect of quantization noise is relieved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention performs analog-to-digital conversion (hereinafter abbreviated as A-D conversion) on an input signal, performs signal processing, and then performs digital-to-analog conversion (D-A conversion). This invention relates to a digital signal processing device that performs conversion.

BACKGROUND ART FIG. 10 shows a block diagram of a conventional digital signal processing device. Reference numeral 1 designates an input terminal to which an analog signal is input. 3 is an A-D converter, which converts an analog signal into a digital signal. 4 is a digital signal processing circuit. 5. is a D-A converter and converts a digital signal into an analog signal. 7 is an output terminal.

In the conventional digital signal processing device configured as described above, an analog input signal inputted from the input terminal 1 is converted into a digital signal by the A-D converter 3, and then converted into a digital signal by the digital signal processing device. The signal is processed, then converted into an analog signal by the A-A converter 5, and output to the output terminal 7.

Problems to be Solved by the Invention However, in the above configuration, when the analog input signal input from the input terminal 1 is converted into a digital signal by the A-D converter 3, quantization noise is added. Put it away. In particular, when the non-linearity error of the A-D converter 3 is large, this quantization noise has unique properties and has the problem of greatly increasing the noise level contained in the analog input signal. Was. For that purpose A-D
For the converter 3, it is necessary to use a converter with a nonlinearity error as small as possible or to increase the number of quantization bits depending on the noise level of the analog input signal.

In view of this, an object of the present invention is to provide a digital signal processing device that does not increase the noise level even when an A-D converter with a relatively large nonlinearity error is used.

Means for Solving the Problems The present invention includes: emphasis means for emphasizing and outputting high-frequency components of an input signal; and analog-to-digital conversion means for converting the output of the emphasis means into a digital signal.
digital signal processing means for processing the digital signal output from the analog-to-digital conversion means; digital-to-analog conversion means for converting the digital signal output from the digital signal processing means into an analog signal; and the digital-to-analog conversion means. The digital signal processing apparatus includes de-emphasis means for attenuating and outputting high-frequency components of an analog signal output from the means.

Effect of the Invention With the above-described configuration, the emphasis means emphasizes the high-frequency components of the input signal, thereby increasing the noise level contained in the input signal. Since the analog-to-digital conversion means performs AD conversion of the input signal with its high-frequency components emphasized and the noise whose level has increased, the influence of quantization noise is reduced.

Embodiment FIG. 1 shows a block diagram of a digital signal processing apparatus in a first embodiment of the present invention. In FIG. 1, 1 is an input terminal to which an analog signal is input.

2 is an emphasis circuit, which emphasizes the high frequency components of the input signal. 3 is an A-D converter, which converts an analog signal into a digital signal. 4 is a digital signal processing circuit.

5 is a DA converter, which converts a digital signal into an analog signal. 6 is a de-emphasis circuit that attenuates high-frequency components of the input signal. 7 is an output terminal.

The operation of the digital signal processing device of this embodiment configured as described above will be described below.

An analog input signal inputted from input terminal 1 is inputted to emphasis circuit @2, and high-frequency components are emphasized. As the frequency characteristic of the emphasis circuit 2, for example, the frequency response shown in FIG. 5 is used. At this time, the high frequency components of the input signal are emphasized, and the noise level included in the input signal is also increased. The input signal with increased noise level is converted into a digital signal by the AD converter 3. The signal is then digitally processed by a digital signal processing device, and then converted into an analog signal by a DA converter 5.

The signal output from the DA converter 5 is input to a de-emphasis circuit 6 to attenuate high frequency components.

As the frequency characteristic of the de-emphasis circuit 6, for example, the frequency response shown in FIG. 6 is used.

The frequency response shown in FIG. 6 has completely opposite characteristics to the frequency response shown in FIG. Therefore,
The high-frequency components and noise level of the input signal emphasized by the emphasis circuit 2 are attenuated by the de-emphasis circuit 6 and returned to the original signal, and the influence of quantization noise added by the A-D converter 3 is reduced. be done.

The signal output from the de-emphasis circuit 6 is output from the output terminal 7.

Next, the increase in the noise level of the input signal due to the nonlinearity error of the A-D converter 3 will be explained in more detail based on FIGS. 2 to 4. Figure 2 shows A- with less non-linearity error.
It shows the input/output characteristics of noise signals in the D converter. In FIG. 2, the horizontal axis shows the analog input level, and the vertical axis shows the digital output level, that is, the output level from the DA converter. Even if the non-linear positive error of the A-D converter is small, quantization noise based on the number of quantization bits always exists, resulting in step-like input/output characteristics as shown in the figure. Although the input noise signal a has an amplitude of 9 frequencies and is random, its effective maximum amplitude is set to Vai, which is about 3 to 5 times the minimum quantization level. If the sampling point of the input noise signal a is the point marked * in the figure, the output noise signal a will be as shown in Figure 2, and its amplitude will be Vao, which is equal to the amplitude Vai of the input noise signal a. The level will not change that much.

FIG. 3 shows the input/output characteristics of noise signals in an A-D converter with large nonlinearity errors. In FIG. 3, the settings of the horizontal and vertical axes are the same as in FIG. 2.

Furthermore, the setting of the input noise signal a is exactly the same as the input noise signal a in FIG. However, due to the large nonlinearity error, the output noise signal becomes as shown in Figure 3.
Its amplitude becomes Vbo, and the amplitude of the input noise signal V
The level is considerably higher than bi. As described above, it can be seen that even in A-D converters having the same number of quantization bits, the influence of quantization noise varies greatly depending on the difference in nonlinearity error. The number of quantization bits including the influence of such nonlinearity errors is sometimes referred to as the effective number of bits.

Next, FIG. 4 shows the input/output characteristics of a noise signal whose level is increased in the emphasis circuit 2 in an A-D converter with a large nonlinearity error. In FIG. 4, the settings of the horizontal and vertical axes are the same as in FIG. 3. However, the effective maximum amplitude Vci of the input noise signal C is set to about twice the effective maximum amplitude Vbi of the input noise signal C shown in FIG. 3, assuming that the level is increased by the emphasis circuit 2. In this case, the output noise signal C becomes as shown in FIG. 4, and its amplitude becomes Vco, which is a level not significantly different from the amplitude Vci of the input noise signal C. As described above, it can be seen that by increasing the level of the noise signal in the emphasis circuit and then inputting it to the AD converter, the noise signal is less susceptible to the non-linearity error of the AD converter.

Furthermore, as described above, the de-emphasis circuit 6 in the configuration of FIG. It also has the effect of attenuating the influence of quantization noise added by the D converter 3.

As explained above, according to this embodiment, by providing an emphasis circuit and a de-emphasis circuit, even an A-D converter with a large nonlinearity error can be made less susceptible to quantization noise. can.

Next, FIG. 7 is a block diagram of a digital signal processing device showing a second embodiment of the present invention. In Figure 7, 1
3 is an input terminal, 3 is an AD converter, 4 is a digital signal processing circuit, 5 is a DA converter, and 7 is an output terminal, which is the same as the configuration shown in FIG. The difference from the configuration shown in FIG. 1 is that a nonlinear emphasis circuit 8 is provided in place of the emphasis circuit 2, and a nonlinear deemphasis circuit is provided in place of the deemphasis circuit 6.

As the frequency characteristic of the nonlinear emphasis circuit 8, for example, the frequency response shown in FIG. 8 is used. Further, as the frequency characteristic of the nonlinear de-emphasis circuit 9, for example, the frequency response shown in FIG. 9 is used. The frequency response in Fig. 8 is
The characteristics are completely opposite to the frequency response shown in the figure. The frequency responses in FIGS. 8 and 9 both have nonlinear emphasis characteristics in which the smaller the input level, the larger the amount of emphasis.

In the digital signal processing device of the second embodiment configured as described above, the analog input signal inputted from the input terminal 1 is inputted to the nonlinear emphasis circuit 8, and the high frequency components of the input signal are emphasized. The noise level contained in the input signal is also increased. At this time, the smaller the input, the greater the amount of emphasis, so the noise level can be increased more greatly than the amount of emphasis of the high-frequency components of the input signal. As a result, the influence of quantization noise due to non-linearity errors of the subsequent A-D converter 3 can be further reduced.

As explained above, according to this embodiment, by providing a nonlinear emphasis circuit and a nonlinear deemphasis circuit, it is possible to further reduce the influence of quantization noise of an A-D converter with a large nonlinearity error. can.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, even if an A-D converter with a relatively large nonlinearity error is used, the noise level of the input signal does not increase. As a result, an inexpensive A-D converter can be used, and the total cost can be reduced, which has great practical effects.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a digital signal processing device according to a first embodiment of the present invention, FIGS. 2 to 4 are operational waveform diagrams of the same embodiment, and FIG. 5 is a frequency response of an emphasis circuit of the same embodiment. 6 is a frequency response characteristic diagram of the de-emphasis circuit of the same embodiment, FIG. 7 is a block diagram of the digital signal processing device in the second embodiment of the present invention, and FIG. 8 is a nonlinear diagram of the same embodiment. FIG. 9 is a frequency response characteristic diagram of the emphasis circuit, FIG. 9 is a frequency response characteristic diagram of the nonlinear de-emphasis circuit of the same embodiment, and FIG. 10 is a block diagram of a conventional digital signal processing device. 2...Emphasis circuit, 3...A-D converter, 4...Digital signal processing circuit, 5...D-
A converter, 6... de-emphasis circuit, 8
...Nonlinear emphasis circuit, 9...Nonlinear de-emphasis circuit. Figure Figure Figure Figure 1 Crane Figure Decline Shark Figure Figure 1 Figure O

Claims (2)

[Claims] (1) Emphasis means for emphasizing and outputting high frequency components of an input signal; analog-to-digital conversion means for converting the output of the emphasis means into a digital signal; and a digital signal output from the analog-to-digital conversion means. digital signal processing means for processing; digital-to-analog conversion means for converting the digital signal output from the digital signal processing means into an analog signal; A digital signal processing device comprising de-emphasis means for attenuating and outputting components. (2) The emphasis means is a non-linear emphasis means having a high-frequency emphasis characteristic in which the amount of emphasis becomes larger as the input signal has a lower level. 2. The digital signal processing device according to claim 1, wherein the digital signal processing device is a nonlinear de-emphasis means having attenuation characteristics.