JPH0247912A - Filter - Google Patents

Abstract

PURPOSE:To simplify the constitution and to make the size of the filter small by combining a switched capacitor filter and a required filter preventing noise from the switched capacitor filter in a tracking filter for analyzing the vibration of an automobile whose frequency changes with number of revolutions of its engine. CONSTITUTION:The cut-off frequency of a switched capacitor filter(SCF) 34 receiving an external clock via a frequency multiplication means 37 is controlled. Simultaneously, a frequency switching control means 38 receiving an output of the means 37 controls the cut-off frequency of an anti-aliasing filter(AF) 35 and a smoothing filter(SF) 36 interrupting aliasing noise and sampling noise respectively from the SCF 34 synchronously with the cut-off frequency of the SCF 34. Thus, lots of components such as operational amplifiers, resistors and capacitors in the tracking filter used to analyze a vibration electric signal representing the vibration of an automobile or the like are not required, the constitution is simplified and the size is made small.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a tracking filter that removes aliasing and sampling noise by combining a switched capacitor filter with an anti-aliasing filter and a smoothing filter, and the present invention aims to provide a small and inexpensive filter. This is a filter that is controlled by an externally applied clock with a changing frequency and that cuts off the oscillating electrical signal that is generated in synchronization with the clock at a cutoff frequency that is multiplied by the clock frequency. A switched capacitor filter that receives a changing electrical signal of vibration and outputs a cutoff frequency of the electrical signal, an anti-aliasing filter that is provided before the switched capacitor filter and prevents aliasing, and a switch. Do
A smoothing filter is provided after the capacitor filter to remove sampling noise, a frequency multiplier circuit multiplies the clock frequency, and an anti-aliasing filter and and a frequency switching control means for switching and controlling the input and output frequencies of the smoothing filter, and the frequency switching control means switches the frequency and synchronizes it with the frequency multiplied by the clock input to the switched capacitor filter. do.

[Industrial Application Field] The present invention relates to a tracking filter that removes aliasing and sampling noise by combining a switched capacitor filter with an anti-aliasing filter and a smoothing filter.

For example, tracking filters are used to analyze the vibrations generated by the rotation of a car engine, but since these filters are made of discrete components, they are large and expensive, so there are ways to improve this. is desired.

[Conventional technology]

Figure 4 is an example of analyzing the vibration of a car body that changes depending on the engine speed.As shown in the figure, 1 is an encoder that generates a clock with a frequency proportional to the engine speed, 2 3 is a signal generator that converts vibrations that vary depending on the engine speed into an electrical signal and outputs the electrical signal, and 3 is a tracking filter.

The trunking filter 3 includes a frequency detection circuit 31.degree. cutoff frequency control circuit 32. When a clock signal is input, it is detected by the frequency detection circuit 31 and the frequency is multiplied. Based on the multiplied frequency, the frequency cutoff circuit 33 is controlled by the cutoff frequency control section circuit 32 based on the multiplied frequency. Outputs the cut-off frequency of the vibration electrical signal input to the

Therefore, the clock signal from the encoder 1 and the vibration electric signal from the signal generator 2 are transmitted to the tracking filter 3.
, the tracking filter 3 extracts and outputs a cutoff frequency corresponding to the frequency of the clock according to the rotational speed.

The output cutoff frequency is sent to an oscilloscope (not shown) and displayed, and vibration analysis is performed.

[Problem to be solved by the invention]

According to the above-mentioned conventional method, since the tracking filter is made discretely using many components such as operational amplifiers, resistors, and capacitors, there are problems in that the tracking filter is large in size and high in cost.

The present invention aims to provide a small and inexpensive filter.

[Means to solve the problem]

FIG. 1 is a block diagram of the principle of the present invention.

In the figure, 34 is a switched capacitor filter (hereinafter referred to as SCF) which receives an oscillating electrical signal that changes in response to changes in the clock and outputs the cutoff frequency of the electrical signal.
, 35 is an anti-aliasing filter (hereinafter referred to as AF) provided before the 5CF34 to prevent aliasing, and 36 is a smoothing filter (hereinafter referred to as SF) provided after the 5CF34 to remove sampling noise.
, 37 is a frequency multiplier for multiplying the frequency of the clock, and 38 is a frequency switching control means for switching and controlling the input and output frequencies of the AF 35 and 5F 36 based on the frequency of the clock multiplied by the frequency multiplier 37.

Therefore, the frequency switching control means 38 is configured to switch the frequency and synchronize it with the frequency multiplied by the clock input to the 5CF 34.

[Effect]

The input clock signal is converted into a multiplied frequency by the frequency multiplier 37, and sent to the 5CF34 as well as to the frequency switching control means 38, which changes the input/output frequency of the AF35 and 5F36 based on the frequency of the multiplied clock. By switching and synchronizing with the vibration electric signal input to the 5CF 34, it is possible to obtain a cut-off frequency of the signal signal from which aliasing and sampling noise are removed.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 2 to 4. The same reference numerals indicate the same objects throughout the figures.
In the figure, parts corresponding to FIG. 1 are surrounded by a dashed line.

In the tracking filter 3a shown in FIG. 2, which is used when analyzing vibrations that change with changes in the rotational speed of an automobile engine, for example, 5CF34a changes in response to changes in the clock frequency f+'m. The frequency fc of the electric signal of vibration is input, and the electric signal of vibration fC
This is an integrated circuit (hereinafter referred to as IC) that outputs a cutoff frequency fscr/A corresponding to a change in (A is a constant).

That is, the cutoff frequency f varies widely depending on the clock frequency FIN.
scr/A can be switched. Also 5CF34
Since a is a kind of sampling system, it generates "elagging" and "sampling noise." For this reason, an AF35a is installed in the front stage of the 5CF34a to prevent elliaging, and a 5F36a is installed in the rear stage to remove sampling noise.
Similar to CF34a, it is wide (cutoff frequency can be switched).

The AF 35a includes a digital/analog converter (hereinafter referred to as DAC), and the cutoff frequency changes in proportion to a digital code value N of the DAC based on a count value sent from a frequency counter 38a, which will be described later. That is, the cut-off frequency fc' of the input vibration electric signal is converted to Nf and output, thereby preventing ellazing. (Here, fl is a constant.) The SF 36a includes a DAC, and the cutoff frequency changes in proportion to the digital code value N of the DAC based on the count value sent from the frequency counter 38a.

That is, the cutoff frequency fc'' of the input vibration electric signal is converted to Nf and output, thereby removing sampling noise.

The frequency multiplier circuit 37a multiplies the clock frequency f4 and outputs rscr.

The frequency counter 38a counts the frequency hcW of the clock multiplied by the frequency multiplier circuit 37a and converts the count value (=digital code value N of the DAC) into AF3.
5a and 5F36a.

Here, the clock and cutoff frequency of 5CF34a, AF
The correspondence relationship between the digital code value N and cut-off frequency of 35a and 5F36a will be explained below.

The relationship between the clock frequency rscr of 5CF34a and its cutoff frequency fc is f C” f sc F / A ---
--(1) AF35a and 5F36a using DAC
The cutoff frequency fc'' is fc'' = N f I ------- (2) fc and f
It is desirable that c'' be proportional, but since fc takes a continuous value, fc'' takes a discrete value, so fc
” (here B is a constant) fc ” = B
fc .==-(3) From equations (1) to (3), the relationship between fscW and N is expressed by the following equation (4).

N”q(B/Aft)fscr --------(4
) Therefore, for the clock frequency fscW of 5CF34a, the values of the DAC of AF35a and 5F36a are expressed by formula (4).
automatically set according to

Since it has such a configuration and function, the operation will be explained next.

(1) First, a clock signal flN is input from the outside to the frequency multiplier circuit 37a, and the frequency f56. is 5CF
34a, and also to a frequency counter 38a that satisfies the above equation (4).

(2) The 5CF34a provides a cutoff frequency fc=fscr/A proportional to the clock frequency flN.

The count value counted by the 0 frequency counter 38a is sent to the AF 35a and 5F 36a, and the count value is sent to the AF 35a and 5F 36a, and
given to.

■Thus, the cutoff frequency fc of the electrical signal of vibration is DAC
A cutoff frequency Nf proportional to the digital code N is obtained.

Fig. 3 shows a different embodiment, and the difference from the embodiment shown in Fig. 2 is that a frequency/voltage converter (hereinafter referred to as FVC) and an analog/digital converter (hereinafter referred to as ADC) are used instead of the frequency counter. This is what we have set up.

That is, in the figure, the FVC 38b is the frequency multiplier circuit 3.
The multiplied frequency f3cr sent from 7a is converted into a voltage and sent to the ADC 38C.

ADC38C AD converts the voltage sent from FVC38b.
Convert to AD conversion value (=DAC digital code N)
is sent to AF35a and 5F36a.

Therefore, similarly to the above embodiment, the cutoff frequencies of the AF 35a and the 5F 36a can be changed according to the cutoff frequency of the 5CF 34a.

In this way, it is possible to obtain a tracking filter that combines AF for preventing ellipsis by using SCF and SF for removing sampling noise.

The SCF is composed of an IC and is small and inexpensive, and the other APs, SFs, etc. are discrete, but the overall size can be reduced and costs can be improved.

〔Effect of the invention〕

As explained above, according to the present invention, prevention of aliasing and sampling noise caused by using an SCF can be achieved by providing an AP and an SF and synchronizing their cut-off frequencies with the cut-off frequency of the SCF. Therefore, it is possible to reduce the size of the tracking filter and reduce costs.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the principle of the present invention, FIG. 2 is a block diagram showing an embodiment according to the present invention, FIG. 3 is a block diagram showing a different embodiment, and FIG. 4 is a block diagram showing a conventional example. In the figure, 34, 34a are S CF, 35, 35a are A
P. 36.36a is SF, 37 is frequency multiplication means,
37a is a frequency multiplier circuit, 38 is a frequency switching control means,
38a is a frequency counter, and 38b is an FVC. 38c indicates ADC. This report was published on September 0, 2017, the first day of the 2nd house in Chirifu.
figure

Claims (1)

[Scope of Claims] A filter that is controlled by an externally applied clock with a changing frequency and that cuts off an oscillating electrical signal generated in synchronization with the clock at a cutoff frequency that is multiplied by the clock frequency, the filter comprising: a switched capacitor filter (34) into which an oscillating electrical signal that changes in response to a change is input and outputs a cutoff frequency of the electrical signal; , an anti-aliasing filter (35) that prevents aliasing, a smoothing filter (36) that is provided after the switched capacitor filter (34) and removes sampling noise, and a smoothing filter (36) that multiplies the frequency of the clock. Frequency multiplication means (37)
and a frequency switching control means for switching and controlling the input and output frequencies of the antialiasing filter (35) and the smoothing filter (36) based on the frequency of the clock multiplied by the frequency multiplier (37). 38)
A filter characterized in that the frequency is switched by the frequency switching control means (38) and synchronized with the multiplied frequency of the clock input to the switched capacitor filter (34).