JPH02211720A - A/d converting device - Google Patents

Abstract

PURPOSE:To accurately transmit the output of a digital filter regardless of the use of an A/D converter having an offset by preliminarily eliminating the offset component included in the output signal of the A/D converter by an offset eliminating device. CONSTITUTION:This device consists of an input terminal 11, an output terminal 12, an A/D converter 13 which converts an analog signal to a digital signal and has a plus offset, an offset eliminating device 14 which eliminates the offset component, and a low-pass type digital filter 15 which eliminates a high frequency component. The analog signal inputted to the input terminal 11 is converted to a digital signal by the A/D converter 13, and this digital signal is inputted to the offset eliminating device 14 and has the offset eliminated. Thus, the output of the digital filter is accurately transmitted through the A/D converter 13 having the offset is used.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to an A/
This relates to a D conversion device.

Conventional technology There are many types of A/D converters, but one of the most commonly used methods recently is the oversampling type A/D converter.
There is a /D conversion device. FIG. 5 is a block diagram showing an example of a conventionally used oversampling type A/D converter. In FIG. 5, 51 is an input terminal;
2 is an output terminal, 53 is an A/D converter with a positive offset that converts an analog signal into a digital signal, 54
55 is a low-pass type digital filter that removes high frequency components, and 55 is an offset removal device that removes offset components.

The analog signal input to the input terminal 51 is converted into a digital signal by the A/D converter 53. At this time, a feature of the oversampling method is that A/D conversion is performed at a frequency that is twice or more the Nyquist frequency (twice the highest frequency of the signal) to improve conversion performance.

Next, the digital signal output from the A/D converter 53 is input to the digital filter 5'4.

As mentioned above, the digital signal output from the A/D converter 53 is more than twice as high as the normal sampling frequency, so it is necessary to lower this frequency, and in order to eliminate the influence of aliasing noise that occurs at this time. A low-pass digital filter is used. Note that when reducing the sampling frequency by decimation after passing through a digital filter, filter calculations and decimation are usually performed at the same time because eliminating unnecessary data calculations can increase the operating time of the digital filter circuit.

The digital signal output from the digital filter 54 is input to an offset removal device 55.

Since an offset normally exists in the analog signal input to the input terminal 51 and the A/D converter 53, this offset is digitally removed here. The offset removal device 55 may be implemented using, for example, a high-pass digital filter with an extremely low cutoff frequency.

The output signal of the offset removal device 55 is output from the output terminal 52, and the entire device constitutes an A/D conversion device.

FIG. 6 shows signal waveforms at various parts of the A/D converter shown in FIG. In FIG. 6, (A) is the output waveform of the A/D converter 53, (B) is the output waveform of the digital filter 54, (
C) is the output waveform of the offset removal device 55.

First, (A) shows that the amplitude is limited near the maximum value on the positive side because the A/D converter 53 has a positive offset. Since high frequency components are removed from this signal by the digital filter 54, ringing occurs in the amplitude-limited portion. This situation is (B
), but since the ringing on the plus side is subject to amplitude limitations, only the ringing on the minus side appears.

Further, this signal is processed by an offset removing device 55 (C
), it is output as a signal without offset.

Problem to be Solved by the Invention However, in the conventional configuration, when the output signal of the A/D converter 53 exceeds the maximum value of digital data due to the influence of offset even if the output signal is less than the maximum amplitude, the output signal of the digital filter 54 is There is a problem that the output cannot be transmitted accurately.

The present invention solves the above-mentioned conventional problems, and aims to provide an A/D converter that can accurately transmit the output of a digital filter even when using an A/D converter with an offset. .

Means for Solving the Problems To achieve this object, the present invention provides an A/D converter that converts an analog signal into a digital signal, and an offset component included in the digital signal output from the A/D converter. The A/D conversion device is comprised of an offset removal device that removes the offset, and a digital filter that gives predetermined characteristics to the digital signal output from the offset removal device.

Operation With the above-described configuration, the present invention can accurately transmit the output of the digital filter by removing the offset component included in the output signal of the A/D converter using the offset removal device in advance.

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

FIG. 1 shows an embodiment of an A/D conversion device according to the present invention. In FIG. 1, 1 is an input terminal, 12 is an output terminal, 13 is an A/D converter with a positive offset that converts an analog signal into a digital signal, 14 is an offset removal device that removes an offset component, and 15 is an A/D converter with a positive offset. is a low-pass digital filter that removes high frequency components.

FIG. 2 shows signal waveforms at each part of the A/D converter shown in FIG. 1. In FIG. 2, (A) is the output waveform of the A/D converter 13,
(B) shows the output waveform of the offset removal device 14, and (C) shows the output waveform of the digital filter 15.

The analog signal input to the input terminal 11 is converted into a digital signal by the A/D converter 13. This digital signal is sent to the A/D converter 13 as shown in FIG. 2(A).
has a positive offset, so the amplitude is limited near the maximum value on the positive side. Next, this digital signal is input to the offset removing device 14 and the offset is removed, so that the output signal waveform of the offset removing device 14 becomes as shown in FIG. 2(B).

Further, when the high frequency component of the output signal of the offset removing device 14 is removed by the digital filter 5, ringing occurs in the portion where the amplitude has been limited. This state is shown in FIG. 2(C), but since the offset has already been removed by the offset removal device 14, the ringing is not subject to any amplitude limitation, and the output of the digital filter 15 is accurately output as is. be able to.

FIG. 3 shows another embodiment of the A/D converter according to the present invention, and is an embodiment in which a so-called noise shaving type A/D converter is used. In Fig. 3, 31 is an input terminal, 32 is an output terminal, 33 is a noise-shaving type A/D converter with a positive offset that converts an analog signal into a digital signal, and 34 is a low-pass filter that removes high frequency components. 35 is an offset removal device for removing offset components, and 36 is a low-pass type second digital filter for removing high frequency components.

FIG. 4 shows signal waveforms at each part of the A/D converter shown in FIG. 3. In FIG. 4, (A) is the output waveform of the A/D converter 33,
(B) is the output waveform of the first digital filter 34, (
C) is the output waveform of the offset removal device 35, and (D) is the output waveform of the second digital filter 36.

The analog signal input to the input terminal 31 is converted into a digital signal by the A/D converter 33. Here, a noise-shaving type A/D converter performs A/D conversion at a frequency several times that of a normal oversampling type A/D converter, but the number of quantization bits is reduced, and high-frequency noise components and Contains a lot of. This situation is shown in Figure 4 (
Shown in A). Since this is a unique signal containing many high frequency noise components, it is difficult to directly remove the offset from the digital signal output from the A/D converter 33. Therefore, in order to remove high frequency noise components, A/
The output digital signal of the D converter 33 is input to a first digital filter 34.

The output signal waveform of the first digital filter 34 is shown in FIG. 4(B). This waveform corresponds to Figure 2 (A), but whereas the waveform in Figure 2 (A) has a limited amplitude near the maximum value on the positive side, Figure 4 (B)
It has been shown that one of the characteristics of the noise shaving type waveform is that a slight excess amplitude can be output. Of course, the output of this waveform requires the addition of one bit above the most significant bit.

Now, the output signal of the first digital filter 34 is input to the offset removal device 35, where the offset is removed and the signal is outputted as a waveform shown in FIG. 4(C).

Since the signal at this time is within the original maximum amplitude, there is no need to add one bit above the most significant bit. Further, this signal is passed through a second digital filter 36 to the filter shown in FIG.
) is output as a waveform. Here, the second digital filter 36 is a low-pass type, and the high frequency noise component has already been considerably removed by the first digital filter 34, so that the waveform shown in FIG. 4(C) is output almost as is.

As explained above, by removing the offset component included in the output signal of the A/D converter in advance, the A/D converter can accurately transmit the output of the digital filter.
A conversion device can be configured. In particular, when a noise-shaving type A/D converter is used, distortion due to amplitude limitation can be avoided, so even if there is a slight offset in the A/D converter, the output is hardly affected.

In addition, A shown in FIGS. 1 and 3 which is an embodiment of the present invention
The signal input to the offset remover 14.35 of the A/D converter has a higher sampling frequency than the signal input to the offset remover 55 of the conventional A/D converter shown in FIG. Since the offset removal device operates in response to an input signal, the higher the sampling frequency, the more quickly the offset can be removed.

Effects of the Invention As described above, the present invention provides an A/D converter that converts an analog signal into a digital signal, and an offset removal device that removes an offset component included in the digital signal output from the A/D converter. , a digital filter that gives predetermined characteristics to the digital signal output from the offset removal device, and an A/D conversion device having an offset.
This makes it possible to realize an excellent A/D conversion device that can accurately transmit the output of a digital filter even if a converter is used.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an A/D converter according to the present invention, FIG. 2 is a waveform diagram showing signal waveforms of each part of the A/D converter shown in FIG. 1, and FIG. 3 is a block diagram showing an embodiment of the A/D converter according to the present invention. FIG. 4 is a block diagram showing another embodiment of the A/D converter according to FIG. 2, and FIG.
The figure is a block diagram showing a conventional A/D converter, and FIG. 6 is a waveform diagram showing signal waveforms of various parts of the A/D converter shown in FIG. 11.31... Input terminal, 12.32... Output terminal, 13, 3.3... A/D converter, 14
．． 35...Offset removal device, 15...Digital filter, Fig. 2 (A)...A/D converter 1
3, FIG. 2(B)... Output waveform of the offset removal device 14, FIG. 2(C)... Output waveform of the digital filter 15, 34... First digital filter, 36. ...Second digital filter, FIG. 4(A)...Output waveform of A/D converter 33,
FIG. 4(B)...First digital filter 34
FIG. 4(C): Output waveform of the offset removal device 35; FIG. 4(D): Output waveform of the second digital filter 36. Name of agent: Patent attorney Shigetaka Awano and 1 other person

Claims (2)

[Claims] (1) A/D that converts analog signals to digital signals
A converter, an offset removal device that removes an offset component included in a digital signal output from the A/D converter, and a digital filter that gives predetermined characteristics to the digital signal output from the offset removal device. An A/D conversion device characterized by: (2) A/D that converts analog signals to digital signals
a converter, a first digital filter that imparts predetermined characteristics to the digital signal output from the A/D converter, and an offset that removes an offset component included in the digital signal output from the first digital filter. An A/D comprising: a removal device; and a second digital filter that imparts predetermined characteristics to the digital signal output from the offset removal device.
conversion device.