JPS6039569A - Frequency discrimination circuit - Google Patents

Abstract

PURPOSE:To discriminate exactly a near-by frequency by a low sampling frequency and a short detection time by increasing or decreasing a value of a protective counter by a count value of the number of times of zero-crossing in accordance with a prescribed rule. CONSTITUTION:An input signal is sampled by a constant period in a sampling circuit 1, and a polarity deciding result by a polarity deciding circuit 2 is stored in a storing circuit 3. A zero-crossing deciding circuit 4 compares the previous deciding result with the present deciding circuit, and when there is a variation in the polarity, an output is generated in a counting circuit 5, a prescribed sampling number is made one block and the number of times of zero-crossing is counted. Subsequently, a protective counter 6 increases or decreases a prescribed value in accordance with the number of times of detection of zero-crossing, a signal of a corresponding frequency is detected by a fact that a count value of the protective counter 6 has reached a prescribed value, and also, it is detected that the signal of the corresponding frequency has annihilated, by a fact that the count value has decreased to the prescribed value.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a frequency detection circuit that detects the frequency of an input signal, and in particular to a frequency detection circuit that detects the frequency of an input signal, and in particular, a frequency detection circuit that can reliably identify adjacent frequencies with a relatively small number of samples using only zero-cross frequency determination. This relates to an identification circuit.

Conventional technology and problems Conventionally, frequency detection circuits have been designed to perform sampling at a sufficiently high speed compared to the frequency to be detected and also use signal amplitude information for detection. There is one that detects a sufficiently large number of zero crossings so that However, the former circuit has the disadvantage of requiring high-speed sampling and complex signal processing, while the latter circuit not only requires a long detection time, but also has few protection functions against errors and noise, and The disadvantage is that when two or more frequencies to be detected are close to each other, the number of samples must be increased in order to distinguish them.

Purpose of the Invention The present invention aims to solve the problems of the prior art, and its purpose is to use a relatively simple algorithm, a low sampling frequency, and a short detection time, which are expected in advance. An object of the present invention is to provide a frequency identification circuit capable of detecting whether or not a signal of a single frequency is input.

Structure of the Invention The frequency identification circuit of the present invention makes use of the fact that the frequency can be detected by counting the number of zero crossings of an input signal.A protection counter is provided in the zero crossing detection process, and the value of the protection counter is set to a constant value based on the count value of the number of zero crossings. By increasing and decreasing the frequency according to a law, it is possible to easily and reliably perform high-speed frequency detection.

Embodiment of the Invention FIG. 1 shows the structure of an embodiment of the frequency identification circuit of the invention. In the figure, 1 is a signal sampling circuit;
2 is a polarity determination circuit, 3 is a determination result storage circuit, 4 is a zero-cross determination circuit, 5 is a zero-cross count circuit, and 6 is a protection counter.

In FIG. 1, an input signal is sampled at a constant cycle in a signal sampling circuit 1. Normally, sampling is performed at a rate that is twice or more than the frequency to be detected.

The polarity of the sampled signal is determined in the polarity determination circuit 2, and the determination result is stored in the determination result storage circuit 3.

The zero cross determination circuit 4 compares the previous determination result stored in the determination result storage circuit 3 with the current determination result in the polarity determination circuit 2, and if there is a change in polarity, it indicates that there was a zero cross between the samplings. As a result, an output is generated for the zero crossing number counter I-circuit 5. The zero-crossing count circuit 5 counts the number of zero-crossings between blocks, with a fixed number of samplings as one block. The protection counter 6 increases or decreases a certain value from the value of the number of zero crossings over a period of multiple blocks,
When the count value reaches a certain value, it is assumed that the input of that frequency has been detected, and when the count value has decreased to a certain value, it is assumed that the input has not been detected.

In this case, if the number of zero crossings is simply counted as in the conventional case, the protection counter 6 is not necessary. In other words, if the input frequency (frequency to be detected) is f, the sampling frequency is fs, the number of samplings in one block is n, and the number of detected zero crosses is k, then when the input frequency is f, the number of zero crosses in one sampling period is The probability that P (f, k) is P (f, k) = +1-2nf/fsP (
f, 'k) = 2nf/fs -.

FIG. 2 illustrates the frequency probability of the number of zero crossings with respect to the input frequency shown by Equation 11.

The reason why the number of zero crossings in FIG. 2 is not constant even when the input frequency is the same is because the phase between the sampling point at the beginning of the block and the input signal is arbitrary.

From this fact, in order for the conventional method described above to perform detection reliably, the ratio of the input frequency to the sampling frequency must have an integer relationship, that is, 2nf/fs in equation (1).
must be an integer.

However, in reality, the sampling frequency and the input frequency are often strictly asynchronous, and the above conditions are not strictly satisfied. In addition, in order to clearly distinguish and detect two extremely close frequencies, in Figure 2,
The frequency to be detected is at least (k 1 )/2n−
Since it is necessary to be away from f s by (k+1)/2n-fs, Δf= (k+1)/2n-fs - (k
-1) In order to sufficiently reduce /2n-fs=l/n-fs, the number of samplings n must be increased. (The sampling frequency fs should not be made too small in relation to the input frequency f. Furthermore, if a correct count value is not always obtained, it will not be detected, and if an error occurs in the number of zero crossings due to noise etc., a problem arises in that frequency detection cannot be performed.

On the other hand, if a protection counter is provided as in the present invention, k/2n
-fs and (k+1)/2n・fs are determined as adjacent detection frequencies, for example, as shown in Figure 3, and when the protection counter exceeds a certain value, it is determined that the corresponding frequency has been detected. If the value falls below this value, it is determined that the corresponding frequency has not been detected, so that the two frequencies can be distinguished, and even if the number of zero-cross counts in a certain block is incorrect due to noise or the like, this will not result in a large error in detection.

Since the method of the present invention is provided with a protection counter, it requires a little extra time to judge detection-no-detection and no-detection-detection, but considering the stability of the judgment, it is more reliable than the conventional method. can perform actions.

Furthermore, when it is necessary to distinguish between two close frequencies, the number of samplings must be increased even in the conventional method, so the above-mentioned time difference is not very large in practice.

As described in detail, the frequency identification circuit of the present invention samples an input signal, detects the polarity at each sampling point of the sampled input signal, and detects the polarity at each sampling point of the sampled input signal. means for determining that a zero-crossing has occurred in the signal due to a change in polarity between the two, counting the number of zero-crossings in a sampling block consisting of a certain number of sampling points, and counting the number of zero-crossings for each frequency to be detected in the protection counter. Increase or decrease a predetermined value to the count value of
The signal of the corresponding frequency is detected when the count value of the protection counter reaches a certain value, and the disappearance of the signal of the corresponding frequency is detected when the count value decreases to a certain value. Frequency can be detected reliably only by zero-crossing judgment,
This method is extremely effective because stable frequency detection can be performed and adjacent frequencies can be reliably identified.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of the frequency identification circuit of the present invention, FIG. 2 is a diagram showing the relationship between the input frequency and the frequency probability of the number of zero crossings, and FIG. It is a figure explaining increase and decrease. 1-signal sampling circuit, 2-polarity determination circuit, 3.-
Judgment result storage circuit, 4-Zero cross judgment circuit, 5-Zero cross count circuit, 6-Protection counter Patent applicant Fujitsu Ltd. agent Patent attorney Gobe Tamamushi (1 other person) Figure 1 Figure 2 Probability Figure 3 Figure 432

Claims (1)

[Claims] a sampling means for sampling an input signal; and a zero cross for detecting the polarity at each sampling point of the sampled input signal and determining that a zero crossing has occurred in the signal due to a change in polarity between adjacent sampling points. a detection means, a zero-crossing number counting means for counting the number of zero-crossings in a sampling block consisting of a fixed number of sampling points, and a protection counter that increases or subtracts a predetermined value from the count value of the zero-crossing number counting means for each frequency to be detected. A signal of the corresponding frequency is detected when the count value of the protection counter reaches a certain value, and a signal of the corresponding frequency is detected when the count value decreases to a certain value. Features a frequency identification circuit.