JPH02285717A - Dither device - Google Patents

Abstract

PURPOSE:To disperse the conversion error of a D/A converter by using a digital filter to attenuate a low frequency component being generated in an irregular digital signal, adding the result together with the input signal, and applying D/A conversion to the summing output. CONSTITUTION:A pseudo random pulse outputted from an M series generator 13 is subject to low frequency component attenuation by a digital filter 14, and the result is added to a digital signal inputted from an input terminal 11 at an adder 15. An output of the adder 15 is inputted to a D/A converter 16, where the signal is converted into an analog signal and outputted to an output terminal 12. The output signal is of the digital filter 14 is used as a dither signal. Thus, the conversion error of the D/A converter is effectively dispersed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a digital/analog (D/A) converter that converts a digital signal into an analog signal, particularly a D/A converter whose signal band is a low frequency range. The present invention relates to a device for generating a dither signal used in the present invention.

There are many types of conventional D/A converters, but each method always has its own conversion error. This error is often caused by noise (harmonic distortion, zero-cross distortion) that has a correlation with the input. etc.) and noise with a specific frequency (natural oscillation frequency), and noise caused by this conversion error is particularly noticeable in high-precision D/A converters.

As a countermeasure to this problem, a method can be considered to make the existence of the noise less noticeable by dispersing the frequency of the generated noise and making it so-called white noise that is uniformly distributed within the signal band. A known method is to add a dither signal to the digital signal to be converted in advance, perform D/A conversion, and then subtract the separately D/A converted dither signal from the resulting analog signal to obtain an output signal. ing. An example of a D/A conversion circuit using a dither device conventionally used in this method is shown in FIG. 4, and will be described below. Regarding this technology, for example, rJAS Conference '8B Proceedings <E-
2> “Application of dither to DA conversion””.

In Figure 4, 41 is an input terminal, 42 is an output terminal, and 43 is an M
44 is an adder, 45 and 46 are D/A converters, and 47 is an operational amplifier. The digital signal input from the input terminal 41 is added to the output signal of the M-sequence generator 43 in an adder 44 . Here, the M series is Maximum.
Length Pulse Sequence ° (Maxlma
m Length pulsesequences
) is a method of generating pseudo-random pulses with the maximum period using the smallest circuit. Here, the output signal of the M-sequence generator 43 is used as a dither signal. The output of the adder 44 and the output of the M-sequence generator 43 are input to a D/A converter 45 and a D/A converter 48, respectively, where they are converted into analog signals, subtracted by an operational amplifier 47, and sent to an output terminal 42. Output.

Next, how the distortion of the input signal is dispersed in the circuit shown in FIG. 4 will be explained using FIG. FIG. 5(a) shows the M-sequence generator 4.
Figure 5 (b) shows the output signal spectrum when the input signal is directly D/A converted without adding the output signals of step 3.
Output signal spectrum of sequence generator 43, FIG. 5(C)
is the output signal spectrum of the D/A converter circuit using the conventional dither device shown in FIG.

As shown in FIG. 5(a), when there is no dither signal, third-order distortion occurs due to conversion errors of the D/A converter. On the other hand, if the output signal of the M-sequence generator 43, that is, the dither signal shown in FIG. The frequency components of the third-order distortion shown in FIG. 5(a) are dispersed and become so-called white noise, which is distributed uniformly over the entire signal band. Since the dither signal is added to this white noise in the analog output of the D/A converter 45 in FIG.
The output signal of the sequence generator 43 is separately converted into an analog signal by a D/A converter 46, and the dither signal component is removed from the analog output of the D/A converter 45 by an operational amplifier 47.

As described above, the output signal spectrum of the circuit of FIG. 4 becomes as shown in FIG. 5(C). It is known that this white noise is more noticeable than third-order distortion or signals having a correlation with the input, such as third-order distortion, and that the reproducibility of the original input signal is improved.

Problems to be Solved by the Invention However, in the conventional configuration shown in FIG. 4, in addition to the D/A converter 45 for original signal conversion, there is a separate D/A converter 46 for converting the dither signal into an analog signal. It becomes necessary. Furthermore, since the D/A converters 45 and 46 have relative conversion errors, the analog signal output of the D/A converter 46 is different from the dither signal component included in the analog signal output of the D/A converter 45. It doesn't match completely. Therefore, the dither signal cannot be completely removed. Furthermore, there were many problems, such as the need for the operational accuracy of the operational amplifier 47 to be sufficiently high.

The present invention solves the above-mentioned conventional problems, and has the effect of dispersing the conversion error of the D/A converter with a simple configuration that does not require a D/A converter that converts a dither signal to an analog signal or an operational amplifier. An object of the present invention is to provide a device that generates a large dither signal.

Means for Solving the Problems To achieve this object, the present invention comprises a digital adder to which a digital input signal is applied, a D/A converter for D/A converting the output of the digital adder, and an integrated circuit. A signal generator that generates a regular digital signal; and a base digital filter that attenuates low frequency components of the digital signal output from the signal generator and supplies the attenuated signal to the digital adder. It consists of a dither device.

Operation With the above-described configuration, the present invention attenuates the low frequency components of the generated irregular digital signal having a -like frequency distribution by a digital filter and adds the resulting low frequency components together with the input signal. By converting the addition output into an analog signal using a D/A converter, a dither signal that is highly effective in dispersing conversion errors of the D/A converter can be effectively generated with a simple configuration.

EXAMPLES Hereinafter, examples of the present invention will be described with reference to the drawings.

FIG. 1 shows a D
This is an example of a /A conversion circuit. In FIG. 1, 11 is an input terminal, 12 is an output terminal, 13 is an M-sequence generator, 14 is a digital filter, 15 is an adder, and 16 is a D/A converter. Here, the M-sequence generator 13, adder 15, and D/A converter 18 are the same as the M-sequence generator 43, adder 44, and D/A converter 45 shown in FIG. 4, respectively.

The pseudo-random pulse output from the M-sequence generator 13 has its low frequency components attenuated by the digital filter 14, and is added to the digital signal input from the input terminal 11 by the adder 15, and the output of the adder 15 is converted into a D/A signal. converter 1
6 and is converted into an analog signal and sent to output terminal 12.
Output to.

Here, the output signal of the digital filter 14 is used as a dither signal.

An embodiment of the digital filter 14 of FIG. 1 is shown in FIG. In Figure 2, 21 is an input terminal, 22 is an output terminal, 23
is a delay device, and 24 is a subtracter.

The digital signal inputted from the input terminal 21 is inputted to the addition terminal of the subtracter 24 and also inputted to the subtraction terminal of the subtracter 24 via the delay device 23, and the output signal of the subtracter 24 is outputted to the output terminal 22. Ru.

When the transfer characteristic of the digital filter shown in FIG. 2 is expressed by a Z function, it becomes H(z): (1-z-1). As is clear from the transfer characteristics, the digital filter shown in FIG. 2 constitutes a so-called differentiator, which has a characteristic of gently attenuating toward lower frequencies. Therefore, large attenuation is obtained at low frequencies, and amplification is achieved at high frequencies.

Next, the manner in which distortion of an input signal is dispersed in the circuit shown in FIG. 1 will be explained using FIG. 3. In FIG. 3(a), the input signal is directly input to D without adding the output signal of the digital filter 14.
/A conversion output signal spectrum, Figure 3 (b
) is the output signal spectrum of the digital filter 14,
FIG. 3(C) is an output signal spectrum of an example of a D/A conversion circuit according to an embodiment of the dither device of the present invention shown in FIG.

As shown in FIG. 3(a), when there is no dither signal, a second-order type and a third-order type occur due to the conversion error of the D/A converter. On the other hand, if the output signal of the digital filter 14 shown in FIG. 3(b), that is, the dither signal, is added in advance, the amplitude of the input signal is randomly varied and the conversion error of the D/A converter is dispersed and The quadratic and cubic components shown in FIG. 3(a) become white noise that is uniformly distributed over the entire signal band. Since the dither signal is added to this white noise, the output signal spectrum of the circuit of FIG. 1 becomes as shown in FIG. 3(C). Figure 3 (C) and Figure 5 (
Comparing C), the noise in the low frequency range is as shown in Figure 3 (
C) is smaller. This is because the low frequency components of the dither signal to be added to the input signal are attenuated in advance.
Even if the dither signal is not removed using an operational amplifier as shown in the figure, the noise at low frequencies is white noise due to the dispersion of quadratic and cubic components caused by the conversion error of the D/A converter. This is because the majority of

As explained above, by using a dither signal whose low frequency components have been attenuated by the digital filter 14, a simple configuration is possible that does not require a D/A converter or an operational amplifier to convert the dither signal into an analog signal. , noise within the signal band can be reduced and the dispersion effect of conversion errors of the D/A converter can be increased.

The high frequency components of the dither signal generated here, especially the frequency components close to one half of the sampling frequency, are large compared to conventional dither devices. However, in the case of audio signals, for example, the low frequency components are more important than half of the sampling frequency, and the auditory characteristics of low sensitivity to high frequencies rarely cause problems. It won't happen.

Further, when the sampling frequency itself is set high, the present invention is even more effective because the high frequency components of the dither signal can be easily removed by using the aliasing prevention analog filter required at the time of D/A conversion.

Note that although the M-sequence generator 13 is used in this embodiment,
Any digital signal generator that can generate a digital signal with uniformly irregular frequency distribution may be used. Further, in this embodiment, the circuit shown in FIG. 2 is used as an example of the digital filter 14, but the present invention is not limited to this. In short, any digital filter may be used as long as it has a characteristic of attenuating low frequencies.

Effects of the Invention As described above, the present invention includes a signal generator that generates an irregular digital signal, and a digital filter that attenuates low frequency components of the digital signal output from the signal generator. Although it is a simple configuration that does not require a D/A converter or operational amplifier to convert the dither signal to an analog signal, the D
This makes it possible to realize an excellent dither device that is highly effective in dispersing conversion errors of the /A converter.

[Brief explanation of drawings]

FIG. 1 shows a D/
A block diagram showing an example of the A conversion circuit; FIG. 2 is a block diagram showing an example of the digital filter 14 in FIG. 1;
FIG. 3 is a frequency spectrum diagram showing how the distortion of the input signal is dispersed in the circuit of FIG. 1, FIG. 4 is a block diagram showing an example of a D/A conversion circuit using a conventional dither device, and FIG.
The figure is a frequency spectrum diagram showing how the distortion of the input signal is dispersed in the circuit of FIG. 4. 1...Input terminal, 12...Output terminal, 1
3...M sequence generator, 14...Digital filter, 15...Adder, 16...D/A converter. Name of agent: Patent attorney Shigetaka Awano Haka 1 person 11-11 Rikiko/Z--Ichidegari@ko 3rd figure 16--- Dip, 2 薯U艮1 WS31 琙 Yami Rumaki frequency 41゛°-hekiho 42-...out 27 @ child 43'-1-1 thread de T! ! G-mu μ

Claims (1)

[Claims] a digital adder provided with a digital input signal;
a D/A converter that D/A converts the output of the digital adder; a signal generator that generates an irregular digital signal; and attenuates low frequency components of the digital signal output from the signal generator; A dither device comprising: a digital filter that provides an attenuated signal to the digital adder.