JPS60120611A - Digital filter - Google Patents

Abstract

PURPOSE:To obtain a digital filter having a proper time constant easily at low cost by making variable the time constant of a primary delay element according to the amplitude of an input signal. CONSTITUTION:An input signal SI is sampled and held by a sample and hold circuit 1 then converted by an A/D converter 2 into a digital signal, which is supplied to an amplitude detector 3 and the primary delay element 5. The amplitude detector 3 detects the amplitude of the input signal SI during the past time TA, i.e. difference A between a maximum and a minimum. Further, the difference A is compared with the amplitude AO of a signal SI having no superposed noise in a period TA to evaluate the level of a noise in the input signal. The output of this detector 3 is converted to a time constant by a function generator 4 according to a predetermined function. The primary delay element 5 performs prescribed arithmetic corresponding to the primary delay element on the basis of the time constant and input signal SI.

Description

[Detailed Description of the Invention] [Technical field to which the invention pertains] The present invention provides a method for extracting no.f.s from an input signal on which no.f.
The present invention relates to a filter that removes only the ,'' component, and in particular to a digital filter using a digital arithmetic unit.

[Sub:! 16 techniques and 1 point between them] Sub) 1, as such a filter means - next lag J5
7Z, filters are often used. this is,
This is because the calculation is relatively simple, but if the time constant is too small, noise cannot be removed sufficiently, and conversely, if the time constant is too large, the original 117
It has the disadvantage that even information is removed, making it impossible to extract accurate information.

[Purpose of the invention]

The present invention has been made in order to eliminate such drawbacks, and provides a digital 71 router that can accurately remove noise by determining the time constant of the first-order delay element according to the input signal. The purpose is to

[Key points of the invention]

In this invention, the amplitude lI? of the input signal between j and constant 11q? ), the magnitude of the noise component included in the input signal is evaluated, and the time constant of the first-order lag element corresponding to the magnitude of the noise component is determined based on a predetermined relationship. Accordingly, noise is removed with high accuracy by performing calculations corresponding to the transfer function of the first-order lag element. .

[Embodiments of the invention]

Figure 1 is a configuration diagram showing an embodiment of this invention, and Figure 2 is ↓
, waveform diagram for explaining the operation of the convergence width detector, rrS3
Figure (t41, characteristic ↑1 that shows the Q'! of the function generator
It is a diagram.

In Figure 1, 1 is a sample and hold circuit, 2 is an analog/digital (A/D) converter, 3 is an amplitude detector, 4 is a function generator, 5 is a first-order delay element, 6υ, digital/analog (1) /A) O input signal S1r, l:, after being sampled and held at J1, is converted into a digital signal by the A/] retarder 2, and is converted to a digital signal by the widening P output 3 and first-order lag element 5K'
j engineering lj rel. Shake (T4 111 vessel 3 (bow 1, I (
- Detect the input signal 1)I'7) amplitude over time, ie the difference between its maximum and minimum values. For example, if the input signal-waveform S is shown as shown in FIG. 2, and if the current time is 1, then it can be determined that the amplitude of the past T input time is t↓Δ1. In addition, in Figure 2, 5
This shows a signal on which NkJ and No.fs are not superimposed, but the amplitude of the signal SN within period 'P is
Therefore, by comparing the amplitudes N with each other, it is possible to evaluate the magnitude of noise contained in the input signal sI. Therefore, by sequentially limping the input signal SI as time passes, the latest information regarding noise can always be obtained. Note that the time TA is the period of the expected noise.
(or frequency). The JAR width thus determined is provided to a function generator 4, where it is converted into a time constant according to a predetermined functional relationship. An example of this function is the upper limit of the time constant TfL as shown in No. 31 (A).
1 and the lower limit Tfcl t YJ: is set at 45, and the constant 'rf of 110 may be increased in proportion to the amplitude A of the input signal within this range.
9A There is no way to make the 1[3 constant Tf change significantly after I. Note that instead of the function generator 4,
You can also use memory. -The second delay element 5 is calculated based on the time constant Tf given from the function generator 4 and the input signal S, as expressed by the well-known equation (1) below.
A predetermined operation corresponding to the -th lag element is performed in line 4C.

At this time, the input signal sI is assumed to be limped every τ11!7, and the input C3l of element 5 subtracted by 16 at the K-th limbling). The subscript K is added to p output (SF+). shall be indicated.

...... (1) In other words, the -th lag element 5 is composed of a digital arithmetic circuit, and based on the input signal sI and the time constant Tf, the above (
It can be said that it has a function as a so-called digital 7/ilter circuit 11+15 that performs the (ju rif calculation) of equation 1).The A/D converter 2, D/A converter 6, etc. , are provided because the element 5 is a digital circuit, but if the element 5 is formed by an analog circuit, these are unnecessary.
is provided to ensure time for performing A/D conversion. In this way, by passing through element 5, only the original signal containing no noise components can be extracted from its output.

〔Effect of the invention〕

According to the present invention, since the time constant of the first-order delay element is made variable according to the amplitude of the input signal, it is possible to easily and inexpensively provide a digital filter having an appropriate time constant.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the operation of an amplitude detector, and FIG. 3 is a characteristic diagram showing an example of the characteristics of a function generator. Symbol explanation ■・・・Sample hold circuit, 2・・・・・・
A/D converter, 3... Amplitude detector, 4...
...Function generator, 5...-Next lag element, 6...
...i) / A converter, S... Input signal, So... Output signal Agent Patent attorney Akio Namiki Attorney Patent attorney + Hiroshi Matsuzaki Figure 1 Figure 2 Figure 3 (/'I) (8)

Claims (1)

[Claims] Detection means for lean-bling an input signal and detecting a difference between a maximum value and a minimum value of ripple values within a predetermined time;
means for determining a time constant having a predetermined functional relationship from the detected difference; and determining a transfer function of the first-order lag element based on the determined 1 (I? constant 21) and the lean pull value of the input signal. t(
digital filter.