JPS6329298Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a tracking filter, particularly a tracking filter that is simple in structure and inexpensive.

2. Description of the Related Art Filters that filter an input signal at a desired cutoff frequency or center frequency are well known and are used in various AC devices. As one type of these filters, a filter that can arbitrarily change its pass frequency or change the pass frequency to follow the frequency of a pass band signal supplied separately from the filter input has been put into practical use. , known as a tracking filter or active filter. These tracking filters are widely used in ordinary high frequency equipment, and have an extremely wide range of applications such as vibration analysis and stress analysis. For example, this type of tracking filter can be used for engine vibration analysis, etc.
In this case, the engine vibration detection signal is supplied to the filter input of the tracking filter, while
Its trigger input is supplied with an engine explosion pulse signal or the like. The engine vibration detection signal includes a wide frequency band component, but since the passing frequency of the tracking filter matches the engine explosion pulse frequency, only the engine explosion primary component included in the vibration detection signal is extracted as the filter output. This makes it possible to accurately determine the cause of vibration, which is extremely useful for noise countermeasures and other purposes.

In addition, as another applied analysis, by supplying the stress detection signal of the vehicle transmission to the filter input of the tracking filter, and on the other hand, supplying the rotation signal of the propeller shaft etc. to the trigger input, the stress of the transmission can be detected. It is understood that tracking filters can be analyzed into various factors and have an extremely wide range of applications.

In a conventional tracking filter, a voltage controlled resistor is used to change a filter constant, and a field effect transistor is usually used as this type of voltage controlled resistor. F-V to this
A tracking filter is formed by combining a converter, an amplifier, etc., but with this conventional device,
Since field effect transistors have non-linear characteristics, a complicated equalizer is required to linearize the characteristics, resulting in an extremely large structure and high cost. Furthermore, because conventional devices using voltage-controlled resistors have large temperature-dependent characteristics, they require long warm-up operations under actual usage conditions, making them difficult to use for various types of analysis. It had drawbacks.

The present invention has been devised in view of the above-mentioned conventional problems, and its purpose is to provide a tracking filter that is easy to handle and has a simple structure.

In order to achieve the above object, this device passes a filter input containing a wide frequency band component at the frequency of a passband signal corresponding to the trigger signal, and the pass frequency at this time changes according to the trigger signal frequency. a capacitor filter; and a phased locked loop that inputs a passband signal whose frequency fluctuates and outputs an integer multiple of a trigger signal to the switched capacitor filter in accordance with changes in the frequency of the signal. Zdrotsukdrup is
a phase comparator that compares the phase of the passband signal and a signal divided by an integer of the trigger signal; a voltage controlled oscillator that outputs a trigger signal having a pulse frequency according to the comparison signal of the phase comparator; The filter is characterized in that it includes a counter that divides the frequency of the trigger signal into an integer and supplies the frequency to the phase comparator, and causes the pass frequency of the filter to follow the frequency change of the passband signal.

Preferred embodiments of the present invention will be described below based on the drawings.

The figure shows a preferred embodiment of the present invention, in which a switched capacitor filter 10 passes a filter input 100 containing a wide frequency band component at a predetermined pass frequency to obtain a filter output 200, and the pass frequency is determined by a trigger. It can be arbitrarily changed depending on the frequency of the signal 300.

This type of switched capacitor filter 10 is known as R5604 manufactured by EG & G Reticon Co., Ltd., and the filter constant can be changed by repeating charging and discharging of the capacitor at high speed using the trigger signal 300. The filter constant at this time corresponds to the frequency of the trigger signal 300. Normally, the frequency of the trigger signal 300 needs to be an integer multiple of the desired passband signal, for example, an engine explosion pulse signal for an engine vibration detection signal as a filter input; 300 is set to a frequency that is 100 times or more that of the passband signal.

A filter input 100 of the switched capacitor filter 10 is supplied with an engine vibration detection signal in the vibration analysis through a pre-filter 20, and the pre-filter 20 is supplied with a filter input 100 through which the switched capacitor filter 10 passes. Since it has a transmission characteristic for harmonic components of band signals, it is used to remove such harmonic components in advance.

The trigger signal 300 to the switched capacitor filter 10 needs to follow a frequency that is an integer multiple of the passband signal 400, but in the present invention, the trigger signal is set correctly for the passband signal 400 whose frequency varies. A phase-locked loop 30 is provided on the trigger input side of the switched capacitor filter 10 for tracking. That is, this phase-locked loop 30 follows the frequency change of the input passband signal 400, multiplies it by an integer, and outputs it as a trigger signal 300. In the illustrated embodiment, the phase comparator 32, the voltage It includes a controlled oscillator 34 and a 1/n counter 36.

One input of the phase comparator 32 receives the passband signal 4.
00, for example, in the case of engine vibration analysis, an engine explosion pulse signal is supplied, and the output of a 1/n counter 36, which will be described later, is supplied to the other input, the phases of the two are compared, and the phase difference is adjusted accordingly. A voltage signal is output.

The output voltage of the phase comparator 32 is supplied to a voltage controlled oscillator 34, and a pulse signal having a pulse frequency corresponding to the input voltage value is output as a trigger signal 300.

The frequency of the trigger signal 300 is divided by an integer by a 1/n counter 36, and in the embodiment, since the frequency of the trigger signal 300 is multiplied by 108 times the frequency of the passband signal 400, the frequency is divided by 1/n. The n counter 36 is formed as a 1/108 counter.

The embodiment of the present invention has the above configuration, and its operation will be explained below.

When the passband signal 400 is supplied to the phase comparator 32 of the phased locked loop 30, the voltage controlled oscillator 34 multiplies the frequency of the passband signal 400 by a predetermined integer based on a comparison with the output of the counter 36 at this time. That is, in the embodiment, a trigger signal 300 multiplied by 108 is output. That is, since the counter 36 always sets the trigger signal 300 to 1/108, the phase comparator 32 increases the output voltage to the voltage controlled oscillator 34 until the frequency of the trigger signal 300 becomes 108 times the frequency of the passband signal 400. This phase comparison is repeated until the input and output frequencies of the phase-locked loop 30 have a correct integral multiple relationship, and as a result, the phase-locked loop 3
0 has extremely good followability and can output a trigger signal 300 that is an integral multiple of the passband signal 400. Therefore, in the present invention, when the frequency of the passband signal 400 fluctuates, the trigger signal 300 that correctly follows it can be supplied to the trigger input of the switched capacitor filter 10, and the center of the filter 10 It becomes possible to change the frequency or cutoff frequency to follow the frequency of the passband signal 400.

Therefore, the switched capacitor filter 10
is the passband signal 4 from the filter input 100.
00 frequency is filtered and output, filter output 2
It can be supplied externally as 00.

As explained above, according to the present invention, a phase-locked loop is provided on the trigger input side of the switched capacitor filter, and by making the frequency of the trigger input follow the frequency of the passband signal without delay, an extremely simple operation can be achieved. With this configuration, it is now possible to obtain a tracking filter at a low cost, and it has become possible to obtain such a tracking filter at a price several tenths of that of a conventional filter including an equalizer or the like.

Further, according to the present invention, since it is a phase comparator, it is possible to reliably control the pass frequency even if there is a change in the amplitude of the pass band signal. Furthermore, unlike conventional methods, field-effect transistors are not used as voltage-controlled resistors, and digital processing is possible with phase-locked loops, which eliminates the need for warm-up operations due to temperature dependence, as in conventional methods. It has the advantage of being extremely easy to handle.

[Brief explanation of the drawing]

The figure is a block diagram showing a preferred embodiment of the tracking filter according to the present invention. 10...Switched capacitor filter, 30
... Phase locked loop, 32 ... Phase comparator, 34 ... Voltage controlled oscillator, 36 ... 1/n counter.

Claims (1)

[Claims for Utility Model Registration] A switched capacitor filter that passes a filter input containing a wide frequency band component at the frequency of a pass band signal corresponding to a trigger signal, and the pass frequency at this time changes according to the trigger signal frequency. , a phased locked loop that inputs a passband signal whose frequency fluctuates and outputs an integer multiple trigger signal to the switched capacitor filter in accordance with the signal frequency change, the phased locked loop , a phase comparator that compares the phase of the passband signal and a signal divided by an integer of the trigger signal, and a voltage controlled oscillator that outputs a trigger signal having a pulse frequency according to the comparison signal of the phase comparator. A tracking filter comprising: a counter that divides the frequency of the trigger signal into an integer and supplies the frequency to the phase comparator, and causes a pass frequency of the filter to follow a frequency change of the pass band signal.