JPS638429B2 - - Google Patents

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 to realize the expected simple An object of the present invention is to provide a frequency identification circuit capable of detecting whether a signal of one frequency is input.

Structure of the Invention The frequency identification circuit of the present invention takes advantage of the fact that frequency can be detected by counting the number of zero crosses of an input signal, and a protection counter is provided in the zero cross 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 crosses. 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 configuration of an embodiment of the frequency identification circuit of the present 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 is a determination result storage circuit 3
The previous judgment result stored in the polarity judgment circuit 2 is compared with the current judgment result in the polarity judgment circuit 2, and if there is a change in polarity, it is assumed that a zero cross has occurred between the samplings, and the result is sent to the zero cross count circuit 5. Generates output. 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 all values from the value of the number of zero crossings over a period of multiple blocks, and when the count value reaches a certain value, it is assumed that the input of that frequency has been detected,
If it decreases 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 k. The probability P(f, k) is that when k/2n fs<f<(k+1)/2n fs, P(f, k-1)=k+1-2nf/fs P(f, k)= 2nf/fs−k.

FIG. 2 illustrates the frequency probability of the number of zero crossings with respect to the input frequency shown by equation (1).
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 detection to be performed reliably using the conventional method described above, it is necessary that the ratio between the input frequency and the sampling frequency has an integer relationship, that is, 2nf/fs in equation (1) must be an integer. .

However, in reality, the sampling frequency and input frequency are often strictly asynchronous,
The above conditions are not strictly satisfied. In addition, in order to clearly distinguish and detect two very close frequencies, the frequency to be detected must be at least (k-1)/2n・fs to (k+1)/
Since the distance needs to be up to 2n fs, in order to sufficiently reduce Δf = (k + 1) / 2n fs - (k - 1) / 2n fs = 1/n fs, the sampling number n must be
must be made larger. (The sampling frequency fs should not be made too small in relation to the input frequency f.) Furthermore, detection will not occur unless a correct count value is always obtained, 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,
Define k/2n・fs and (k+1)/2n・fs 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. It is possible to distinguish between two frequencies by determining that the corresponding frequency has not been detected when the value falls below a certain value.Also, even if the number of zero-cross counts in a certain block is incorrect due to noise etc., it can be detected as a major error. No.

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. can perform actions.

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

Effects of the Invention As explained above, according to the frequency identification circuit of the present invention, an input signal is sampled, the polarity at each sampling point of the sampled input signal is detected, and polarity changes are detected between adjacent sampling points. It is determined that a zero-crossing has occurred in the signal due to this, the number of zero-crossings in a sampling block consisting of a certain number of sampling points is counted, and the count value of the zero-crossing number counting means is calculated for each frequency to be detected in the protection counter. When the count value of the protection counter reaches a certain value, a signal of the corresponding frequency is detected, and when the count value decreases to a certain value, a signal of the corresponding frequency is detected. Since it is now possible to detect the disappearance of the frequency, it is possible to reliably detect frequencies using only zero-crossing judgments, and it is possible to perform stable frequency detection as well as to reliably identify adjacent frequencies. Therefore, it is extremely effective.

[Brief explanation of the drawing]

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. 3 is a diagram showing the increase/decrease of a predetermined number in the protection counter. FIG. DESCRIPTION OF SYMBOLS 1... Signal sampling circuit, 2... Polarity judgment circuit, 3... Judgment result storage circuit, 4... Zero cross judgment circuit, 5... Zero cross number counting circuit, 6... Protection counter.

Claims (1)

[Claims] 1 A sampling means for sampling an input signal, detecting the polarity at each sampling point of the sampled input signal, and detecting that a zero crossing has occurred in the signal due to a change in polarity between adjacent sampling points. zero-crossing detection means for determining, 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 adding or subtracting a predetermined value from the count value of the zero-crossing number-counting means for each frequency to be detected. A protection counter is provided, and when the count value of the protection counter reaches a certain value, a signal of the corresponding frequency is detected, and when the count value decreases to a certain value, the signal of the corresponding frequency disappears. A frequency identification circuit characterized by detecting that