JPS60198410A - Detecting circuit for rotation signal - Google Patents

Abstract

PURPOSE:To detect a rotation signal with a high S/N by using a variable frequency type band-pass filter, controlling its center frequency to an output side frequency, and narrowing down the passing band width sufficiently. CONSTITUTION:The rotation signal is amplified 1 and then inputted to the band- pass filter 2. The center frequency of the filter 2 is determined by the frequency of a control signal C. Then, the rotation signal having a noise removed is shaped by a waveform shaping circuit 3, and inputted to a phase-locked loop 4 while appearing at an output terminal. The loop 4 synchronizes the output frequency of a VCO43 with a frequency Nf which is N times as high as the rotation signal to obtain the control signal C to the filter 2, so that the center frequency of the filter 2 is also controlled to the frequency (f) of the rotation signal. Thus, the center frequency of the filter 2 follows up the frequency of the input rotation frequency continuously and automatically, so the passing band width of the filter 2 is set sufficiently narrow and the rotation signal with the high S/N is detected.

Description

[Detailed description of the invention] [Field of application of the invention] The present invention relates to a rotation signal detection circuit.

[Background of the invention]

Noise countermeasures in conventional rotation signal detection circuits are often implemented using waveform shaping circuits (for example, Japanese Patent Application Laid-Open No. 57-59171
, % open 57-49863, etc.), but if the signal is weak υ or the noise environment is bad, a filter circuit such as a band pass filter matched to the frequency of the rotation signal is added after preamplification.

The narrower the passband width of this filter, the greater the noise removal effect.However, if the frequency fluctuation of the rotation signal itself is large, the passband of the filter circuit must include the range of this fluctuation. Therefore, the passband cannot be made narrower, which has the disadvantage that the noise removal effect cannot be improved.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a rotation signal detection circuit capable of detecting a rotation signal with a high S/N even when the noise environment is weak or the noise environment is poor and the frequency fluctuation of the rotation signal is large.

[Summary of the invention]

A feature of the present invention is that the bandpass filter is a frequency variable part, and the center frequency is controlled to match the output side frequency by feeding back the output after waveform shaping, and in this way, its passband width is This is because we have made it possible to make it sufficiently narrow.

[Embodiments of the invention]

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

FIG. 1 is a block diagram showing an embodiment of the present invention. A rotation signal detected by a rotation sensor or the like is amplified by a preamplifier 1 and then input to a bandpass filter 2. In FIG. In this embodiment, the filter 2 is a switched capacitor type filter, and its center frequency is determined by the frequency of the input control signal C.

The rotational signal from which noise has been removed by the filter 2 is shaped by the waveform shaping circuit 3 and goes to the output terminal as well as to the phase locked loop 4.
is input to. In this loop 4, the output frequency of the voltage controlled oscillator 43, whose output frequency is approximately N times that of the rotation signal f, is multiplied by 1/N by the frequency dividing circuit 5, and the frequency of the shaping circuit output is determined by the phase comparator 41. The oscillator 4
The output frequency of No. 3 is synchronized with a frequency Nf which is N times the rotation signal. By using the output of the oscillator 43 as the control signal C to the bandpass filter 2, its center frequency is also controlled to match the frequency f of the rotation signal. However, N is an integer constant determined by the configuration of the switched capacitor filter 2. Therefore, once the center frequency of the filter 2 matches the frequency of the input rotation signal, an output can be obtained even if there is a frequency fluctuation of the rotation signal within the passband width of the filter 2.
As a result, the center frequency of the filter 2 follows that of the rotation signal, and even if there is a variation in the rotation signal frequency, it follows in the same manner. Since the center frequency of the filter 2 automatically follows that of the input continuously in this way, the passband width of the filter 2 can be selected to be sufficiently narrow, and therefore a rotational signal with a high S/N ratio can be detected.

FIG. 2 shows another embodiment of the present invention, in which the bandpass filter 2 in FIG. Replaced with 6. This filter 6 can be realized by using, for example, a varactor or the like whose capacitance changes depending on the voltage applied to the capacitor constituting the filter. Correspondingly, a conversion circuit (a type of FM
The center frequency of the filter 6 is controlled by converting it with a wave detector) and adjusting it to an appropriate external power positive value with an amplifier 8.

In this way, the same effects as in the previous embodiment can be achieved.

〔Effect of the invention〕

As described above, according to the present invention, a rotation signal can be detected with a high 8/N.

[Brief explanation of the drawing]

1 and 2 are circuit block diagrams showing embodiments of the present invention, respectively. DESCRIPTION OF SYMBOLS 1... Preamplifier circuit, 2.6... Center frequency variable band pass filter, 3... Waveform shaping circuit, 4... Phase synchronization circuit, 5... Frequency dividing circuit, 7... Frequency/voltage conversion circuit, 8... amplifier. Agent Patent Attorney Akio Takahashi 1 verbal abuse 21EJ? 57

Claims (1)

[Claims] 1. A variable frequency filter that receives a rotation signal as an input and whose center frequency is variable by a control signal, a waveform shaping circuit that shapes the output waveform of the filter, and a signal shaped by the circuit that corresponds to the frequency of the rotation signal. A rotation signal detection circuit comprising: a control circuit that generates a control signal of a value and feeds it back to the variable frequency filter so that the center frequency of the filter follows the frequency of the rotation signal.