JPS5997218A - Digital low-pass filter - Google Patents

Abstract

PURPOSE:To make a multiplier unnecessary and realize an optional transfer function, by combining plural fundamental filters each of which consists of a subtractor and a rate multiplier which changes the output frequency in accordance with the absolute value output of the subtractor. CONSTITUTION:A fundamental filter 11 consists of a subtractor 2 which outputs an absolute value output 3 and a sign output 4 of the difference between inputs to input terminals 2A and 2B, a rate multiplier 5 which changes an output frequency 7 in accordance with the output 3, and an up/down counter 8 where up/ down counting is controlled by the output 4 and counting is performed in accordance with the output frequency 7 to output a counted output 9. Plural fundamental filters 11 are so connected that each output 9 attains the input 2A of the next-stage filter 11 and the output 9 of the last-stage filter 11 attains the input 2B of each filter 11.

Description

[Detailed Description of the Invention] The present invention relates to a digital filter that performs F wave filtering by performing predetermined arithmetic processing such as addition and subtraction on digital signals that have been sampled and quantized into binary values. be.

In recent years, analog input signals' (!-) are quantized into binary values with an A/D converter, and arithmetic processing such as addition, subtraction, and multiplication is performed on these digital values to perform signal processing such as p-waves.
A method is often used (increasingly) to convert this digital signal into a D/A converter to obtain an analog output signal. In order to perform this, all calculations must be completed within the signal sampling time interval, and when performing multiplication, etc., which requires a particularly long time, it is necessary to use a special device for calculation processing or to use a dedicated Measures such as using hardware χ are required.

Therefore, the inventors of the present invention have already proposed a circuit shown in FIG. In the figure, 1 is an input signal expressed as x(nT), 2 is a subtracter, and 3 is its absolute value output.

4 is a code output, 5 is a rate multigrapher with output 6 as input, 6 is its clock input, 7 is its output signal, 8
is an up/down counter, and 9 is its output. Since the counter 8 uses the multiplier 5 as a clock input and the sign output 4 of the subtracter 2 as an up/down count input (hereinafter referred to as 1'-U/D input), its output signal 9 is y(n
It is clear from the figure that T).

Next, the operation will be explained. In the following, for simplicity, if we consider a case where the changes in the input signal 1 and the output signal 9 are sufficiently slow compared to the sampling interval T, we will consider that it is a continuous system with respect to time (tl).
If f, the rate multiplier 5 inputs the absolute value output 3 of the subtractor 2, and therefore outputs the output cuff at . Here, M in the denominator 2M is the bit width of the rate multiplier 5. From the reciprocal of equation (2), '/r(tl = , t(tl, 17..e=,.□
It becomes. Next, the up/down counter 8 calculates the sign output 4 of the subtracter 2 at each time interval Δt(tl).
The ascending/descending count Yl is performed according to the sign of . Therefore, since the output 9 of the up/down counter 8 changes by one, let this be Δy(tl), where ΔM τ”” 2 tck ....-
・If we set (5), we get . Here, if ΔV(t)tlt(tl) is a sufficiently small value, Equation (6) can be replaced and the Laplace transform technique can be used.

becomes. Here, Y(s) and X(s) are each y(
tl is the Laplace transform of x(g.

Here, the transfer function H(s) is expressed by equation (8), and is a well-known transfer function of a first-order low-frequency tear wave device.

Although the circuit system described here does not require a multiplier and can be easily constructed, it can only realize the characteristics of a -th order low-pass F-wave device. Therefore, a high-order filter (for example, a 2nd or 8th order filter) y! - To configure.

They had to be connected in cascade, and even in that case, there was a drawback that only the product form of the transfer function expressed by equation (9) could be realized.

This invention was made to eliminate the above-mentioned drawbacks, and it does not require a circuit in which one input of the subtracter is separated from the output signal (or by configuring them in combination, a high-order transfer function can be realized. The purpose of this invention is to provide a digital filter that achieves this.

An embodiment of the present invention will be described below with reference to the drawings.

First, the digital low-frequency offshore transducer of the present invention shown in FIG.
As shown in FIG. 8, this basic filter 11 is configured by combining a plurality of (in this case, n basic filters 111ft), and one input 2A' of the subtractor 2 is input x(tl,
The configuration shown in FIG. 1 is modified so that the other input 2B is input z(tl).

In FIG. 2, 111=-111, 11(1+1)lln is the basic filter 11 shown in FIG. 8, r), 1(i=
1, . . . +n) represents the first basic filter 11. 12 is each basic filter 111 (i=
1,...,n), the clock fCk1 (1=1.+・
Hana, n)y! l# supply clock circuit, 16 and 14
Is this an input to this circuit? (t) and output? (t). (Hereinafter, Q(t) t? (tl will be referred to as the input and output of the filter)) First, the operation in Fig. 3 will be explained.As can be seen by comparing Fig. 1 and Fig. 3, one of the subtracters 2 Similar to the analysis of equations (1) to (7), since the input 2B of is not connected to the output 9, but to another input z (tNO).

is obtained, and by applying Laplace transform to this, s Y(sl
= (X(sl −Z(sl) −”””
"α. Here vc X(s), Y(sl,
Z(s) is each x(t), y(t), z(tl
Let be the Laplace transform of . Also, τ is τ=2tck ・・・・・・・・・(
2). However, tck = 1/rak.

Next, the operation shown in FIG. 2 will be explained. First, what about the filter input? (t) Laplace transform of each of the l output 9(t) and the output yi (tl) of the first fundamental filter 11.

Father (S)? (s), Yi (sl), i.e.

・・・・・・−・ (to). Here, π and 2 represent symbols for multiplication and addition, respectively.

Next, prove this formula and show that when Yn(s) = Y(s), H(sl = Y(sl/X(s)) becomes an n-th order transfer function. First, the formula ( 11 (or (
14') 'a-Prove. To do this, we will use mathematical induction.

(If 111 = 1, then set 1 = 1 in the formula a → (2) When i = i, the formula (to) holds true. So...α] When the following holds true, 1 Examine the relationship between Yi+1(S), X(s), and Y(s) using equation a. Multiplying the equation αQKs... Since α becomes, substitute equation (2) here. hand······
6 o'clock, and the equation Ql (or α4) matches the equation given in IY (1+1). (Proof path) Therefore, in equation 1 (to) Yn (s) - Y(s) = Yi
(s)...(6) This is the n-th low frequency F with gain l at s = 0.
It represents the transfer function of the wave device. Here τ, (i = 1
．． ..., n) are expressed by the formula (
6) is given by

Now consider an 8th order Butterworth low pass filter as an example. The transfer function of this filter is good (as is known, the cutoff angular frequency is ω. Q), so n = 8 is set in Equation 1 (7). By comparing tckl, that is, fckl(
i=1. B, 8) may be determined.

In the above embodiment, an absolute value of 4 and a sign of 3 are obtained as the output of the subtracter 2, but it is also possible to combine a '2's complement' subtracter and a complementer to obtain the absolute value of the subtracter. , in this case, the borrow (carry) output may be used as the code.

As described above, according to the present invention, a digital primary filter is realized by combining a basic filter composed of a counter subtracter, a rate multiplier, etc., so (1) a multiplier is unnecessary. It is inexpensive; (2) it is easy to integrate the basic filter into an IC, and any transfer function can be realized by combining them; There are effects such as

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a conventional digital P-wave device, FIG. 2 is a block diagram of a digital low-pass F-wave device according to an embodiment of the present invention, and FIG. 8 is a block diagram showing the configuration of a conventional digital P-wave device. FIG. 2 is a block diagram of a basic filter configured in a waveform configuration. 1... Input x (tL 2... Subtractor, 5... Rate multiplier, 8... Up/down counter,
9...Output y(tl, I O...Input z(tl
, 11...Basic filter, 12 Representative Shin Kuzuno - (1 other person) Power 1 Figure 2 Figure 3 Figure 3 1.1°Ko-Chief's Palace 1 ・J[Display of item 'R? If! ff Showa 57-
208213 No. 2, Name of the invention Dizicle low-frequency P-wave device 3, Relationship with the person making the amendment Case Patent applicant address 1 Marunouchi Knee, Chiyo N1-ku, Tokyo ■]2
Number 3 Name (601,) Mitsubishi Electric Co., Ltd. Representative Katayuni Yabu 4, Agent I 1 Mi Address 2-1 Marunouchi, Chiyogawa-ku, Tokyo]
2? No. t3 Mitsubishi Electric Corporation 5, Detailed explanation of the invention column 6 of the specification subject to amendment, Contents of amendment (1) [Multiple (in this case n basic filters) in page 6 line 8 of the specification 1” is replaced with “Multiple (in this case, n pieces)”
Basic filter 1” is corrected. (2) r on page 6, line 13 of the specification, 11(i+1
)11n” is r, 11(i+1)...11n
” he corrected. +31 Meisho I book, page 7, line 1 to line 2 [1 zu 3
The operation shown in the figure will be explained. If you compare Figures 1 and 3, you will see that.'' [1] First, let me explain the operation in Figure 2. If you compare Figures 1 and 2, correct it with J so that it is correct. (4) On page 7, line 13 of the specification, the phrase "next in the second country" is corrected to "next in FIG. 3." (The beginning of the Q31 formula on page 7, line 17 of the 51 specification [rsY
i(s)=..." k r s Yi(s)=
"..." I corrected myself. that's all

Claims (1)

[Claims] A subtracter that calculates the absolute value and its sign of the difference between two inputs X(t) and z(t), a rate multiplier that changes the output frequency according to the absolute value output, and a rate multiplier that increases by the sign output of the subtracter. /Descent count t? 1ilI#, counted according to the output of the rate multiplier and output y
(tl A circuit consisting of an acpudown counter/ritto that outputs Y is used as a basic filter, and each basic filter has the first (i
=1. ..., an integer n) of the above basic filter yi (tl is the input x1 of the (i+1)th basic filter
(tl), the input ?(t) becomes the input xt(tl) of the first basic filter, and the output yn(tl of the nth basic filter is connected to each human power z 1(t
The digital low-frequency ν wave is connected in such a manner that it is inputted to K and outputted as the overall output 9 (tl), and is further provided with a clock circuit for supplying a clock signal to each basic filter. vessel.