JP3132279B2 - FM demodulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM demodulator for reproducing and demodulating an FM signal recorded on an optical disk or the like.

[0002]

2. Description of the Related Art In recent years, an address signal of an optical disk is FM-modulated and recorded on the optical disk.
To obtain demodulated data by demodulating such an FM signal,
Conventionally, as shown in JP-A-61-177007, a pulse corresponding to the period of an FM carrier is generated,
The FM demodulated output was obtained by passing through a low-pass filter.

However, in such a conventional configuration, since the low-pass filter for smoothing the FM demodulated output becomes an analog filter, the chip area in the case of an IC is increased, and an external element is required. There is a problem of becoming.

Therefore, a configuration for obtaining the FM output as a digital signal is considered. FIG. 12 is a configuration diagram of such a conventional FM demodulator.

[0005] The FM carrier is a reproduction signal from an optical disk or the like, is a signal output from an optical head or the like for reproducing the optical disk, and is input to the FM demodulator shown in FIG.

Reference numeral 1 denotes a binarizing means for converting a binary signal of high and low at the center of the amplitude of the FM carrier. Numeral 2 is a counting means for counting the frequency of the FM carrier by a clock.

The counting means 2 outputs a counter value every one cycle of the FM carrier, that is, a cycle value of the FM carrier, and is reset each time to start counting the next cycle.

Reference numeral 3 denotes a holding means for sequentially holding the output of the counting means 2. In this manner, the periodic value sequence sequentially output from the counting means 2 is output as an amplitude by the holding means 3, so that the FM demodulated signal can be detected. Further, since the FM demodulated signal is a count value, a smoothed FM demodulated signal can be obtained by passing through a digital filter constituted by a logic circuit or the like.

FIG. 13 is a signal diagram showing the operation of such a conventional example. The period of the FM carrier is counted by the counting means 2, and the count value is held by the holding means 3.

FIG. 12 shows that the periods of the FM carrier are A, B, and C.
The count value counted by the counting means 2 is shown below the FM carrier as the holding output of the holding means 3. The count values counted by the counting means are values such as A, B, and C, respectively.

Accordingly, the held output is output while successively holding the values of A, B, C, etc., so that the output is smoothed by the low-pass filter 4 to obtain a smoothed FM demodulated signal. Can be.

[0012]

However, in such a conventional configuration, when an instantaneous noise such as a defect occurs in the FM carrier, an unnecessary signal appears in the FM demodulated signal.

An object of the present invention is to provide an FM demodulator capable of easily removing an unnecessary signal generated by a defect or the like.

[0014]

In order to achieve this object, an FM demodulator according to the present invention sequentially counts the period of an FM carrier, outputs the period as a period value, and is reset to count the next period. Counting means, a delay means for delaying an input value for each cycle of the FM carrier, an output of the counting means, and an output of the delay means or an output obtained by arithmetically processing the output of the delay means. If the output value of the delay means is greater than a first predetermined value than the count value of, or the current count value is greater than a second predetermined value than the output value of the delay means In this case, the current count value is corrected and output, and in the cases other than the two cases, the current count value is output without being corrected, and the output is used as an input of the delay means. A count value correcting means, and sequentially holds the count value output of said count value correcting means, and a holding means for amplitude output is obtained by a configuration of obtaining an FM demodulated signal.

[0015]

The count value correcting means corrects and outputs the current count value when the current count value is abnormally larger or abnormally smaller than the previous count value.
The effect of an abnormal signal such as a defect on the M carrier can be removed.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an FM demodulator according to a first embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows an FM according to a first embodiment of the present invention.
It is a block diagram of a demodulation device. The FM carrier is a reproduction signal from an optical disk or the like, is a signal output from an optical head or the like for reproducing the optical disk, and is input to the FM demodulator of FIG.

1 is a binarizing means, 2 is a counting means, which counts the time length of the period of the FM carrier by a clock, and sequentially outputs the value as a period value every period of the FM carrier.

Numeral 30 is a delay means for changing the input value to F
It is delayed by the period of the M carrier.

Numeral 5 is a count value correcting means, which receives the output of the counting means 2 and the output of the delay means 30 as inputs, and counts the current count value detected by the counting means 2 one cycle earlier. If the output value (that is, the output value of the delay unit 30) is larger than a predetermined value, or conversely, if the output value of the delay unit 30 is larger than the current count value, the input is Corrected count value is output. The output is input to the delay means 30 and input to the count value correcting means 5 again.

Numeral 3 is a holding means for sequentially holding the output of the count value correcting means 5 and converting it into an amplitude to obtain an FM demodulated signal.

Reference numeral 4 denotes a low-pass filter, which receives an FM demodulated signal and reduces quantization noise generated by the counting means 2 and high-frequency noise included in the FM carrier, thereby obtaining an FM demodulated signal. Is smoothed.

Next, the operation of the FM demodulator will be described with reference to the drawings. FIG. 2 is a signal diagram showing the operation of the first embodiment of the present invention.

The period of the FM carrier is counted by the counting means 2, and the count value is held by the holding means 3 via the count value correcting means 5.

FIG. 2 shows the period from the fall to the fall of the FM carrier by A, B, and C.
And the output of the holding means 3 is described below the FM carrier. The count value is A,
The values are shown as B, C, Y, Z, and the like.

For example, if the optical disk has a defect or the like, a signal of a large amplitude is suddenly superimposed on the FM carrier read from the optical disk during the normal amplitude.

Therefore, the period of the FM carrier is abnormally large or abnormally small as compared with the normal period. Usually, an abnormally large cycle and an abnormally small cycle tend to occur successively.

Since the counting means 2 detects the period of the FM carrier, it sequentially outputs count values A, B, and C according to the periods of A, B, and C, respectively.

The count value correcting means 5 includes a counting means 2
If the current count value detected by the delay means 30 is larger than the value output by the count value correction means 5 one cycle before (that is, the output value of the delay means 30) by a predetermined value or more, When the output value is larger than the current count value by a predetermined value or more, the input count value is corrected and output.

In other cases, the input count value is output as it is. Therefore, if the time is A, for example, the count value correcting means 5
Is output. The count value A is directly input to the delay means 30, and the output value A of the delay means 30 is input again to the count value correction means 5.

However, when there is a defect as described above and the currently detected count value B is abnormally larger than the previous count value A, for example, when the count value becomes equal to or more than A + X, as in the cycle B, the current The count value correcting means 5 outputs a value Y smaller than the detected count value B.

The output value Y of the count value correcting means 5 is directly input to the delay means 30, and the output value Y of the delay means 30 is input again to the count value correcting means 5.

When the currently detected count value C is abnormally smaller than the output value Y of the delay means 30 and becomes, for example, a value equal to or less than YX, as in a cycle C, the currently detected count value The count value correcting means 5 outputs a value Z larger than C.

As described above, the count value Z is input to the delay means 30 as it is, and is again input to the count value correction means 5 as the previous count value.

As a result, the held outputs are output as A, Y, and Z, and the demodulated signal is generated more smoothly than the output as A, B, and C.

As described above, when the currently detected count value is abnormally larger or smaller than the previous count value, the count value is corrected by the count value correcting means 5 so that the difference does not increase. Since the signal is output, a signal disturbed by the defect is output without affecting the demodulated signal, and an unnecessary signal due to the defect can be removed.

Next, a second embodiment will be described. FIG. 3 is a configuration diagram of an FM demodulator according to a second embodiment of the present invention.

The FM carrier is a reproduction signal from an optical disk or the like, is a signal output from an optical head or the like for reproducing the optical disk, and is input to the FM demodulator shown in FIG.

1 is a binarizing means, 2 is a counting means, which counts the period of the FM carrier by a clock.

Numeral 30 is a delay means, and the inputted value is represented by F
It is delayed by the period of the M carrier.

Reference numeral 5 denotes a count value correcting means comprising a range designating means 10 and a correcting means 11, the output of which is input to the delay means 30.

The range specifying means 10 determines the allowable range of the current count value output from the counting means 2 based on the value output from the delay means 30.

The correcting means 11 receives the output of the counting means 2 and the output of the range specifying means 10 as inputs and, if the current count value exceeds the allowable range determined by the range specifying means 10, corrects the count value and outputs it. Is what you do.

For example, assuming that the previous count value is A and the current count value is B, the output of the delay means 30 is A, so that the range specifying means 10 sets the first predetermined value to X, the second
Is designated as -X, and the range AX to A + X is designated.

The correcting means 11 determines that B is from AX to A
When the value falls within the range of + X, B is output as it is,
When smaller than -X, AX is output, and when B is larger than A + X, A + X is output.

As described above, the count value correcting means 5 composed of the range designating means 10 and the correcting means 11 changes the count value when the count value is abnormally large or abnormally smaller than the previous count value. The output can be modified.

Numeral 3 is a holding means for sequentially holding the output of the count value correcting means 5 and converting it into an amplitude to produce an FM demodulated signal.

Reference numeral 4 denotes a low-pass filter, which receives an FM demodulated signal and reduces quantization noise generated by the counting means 2 and high-frequency noise included in the FM carrier to obtain an FM demodulated signal. Is smoothed.

Here, the range designating means 10 and the correcting means 1
Details of 1 will be described with reference to FIG.

FIG. 4 is a block diagram showing details of the count value correcting means 5. In FIG. 4, the range designating means 10 comprises a first adding means 31 for adding a predetermined value X to the output value A of the delay means 30 and a second adding means 32 for adding -X. And A + X are output.

The correcting means 11 compares the output A + X of the range specifying means 10 with the current count value B, and finds B> A +
A first comparing means 33 for outputting an output when X, a second output for comparing the output AX of the range specifying means 10 with the current count value B, and outputting an output when B <AX Comparison means 3
4 and a selecting means 35 for selecting a correction value.

The selecting means 35 sets A + X and AX as correction candidate values when the output from the first comparing means 33 is output.
+ X is selected and output as a correction value, and the second comparison means 3
When the output is obtained from 4, the data A-X is selected and output as a correction value, and otherwise, B is selected and output.

As described above, by configuring the range specifying means 10 and the correcting means 11, the count value correcting means 5
Desired operation can be realized.

The operation of the FM demodulator thus configured will be described with reference to the drawings. FIG. 5 shows a second embodiment of the present invention.
FIG. 5 is a signal diagram showing the operation of the embodiment of FIG.

The period of the FM carrier is counted by the counting means 2, and the count value passes through the count value correcting means 5 and is held by the holding means 3.

In FIG. 5, the periods of the FM carrier are indicated by A, B, and C, and the count value counted by the counting means 2 and the output held by the holding means 3 are superimposed and described below the FM carrier.

The count values are shown as A, B, C, A + X, and the like. For example, if an optical disc has a defect or the like, a signal having a large amplitude is suddenly superimposed on the FM carrier read from the optical disc during a normal amplitude.

For this reason, the period of the FM carrier is abnormally large or abnormally small as compared with the normal period. Usually, an abnormally large cycle and an abnormally small cycle tend to occur successively.

Since the counting means 2 detects the period of the FM carrier, it sequentially outputs count values A, B, and C according to the periods of A, B, and C, respectively.

The range specifying means 10 calculates the count value as
When A is input, an allowable range in which the next count value B is to be entered is designated, such as AX to A + X. In the example of FIG. 4, B is larger than A + X.

The correcting means 11 corrects the value of B when it exceeds the range specified by the range specifying means 10. In this case, since B is larger than A + X, the original count value B
Is corrected and A + X is output.

Next, when A + X is input as the current count value, range designating means 10 changes A + XX to A + XX.
The allowable range in which the next count value C is to be entered is specified, such as X + X. In the example of FIG. 5, the next input count value C is smaller than A + XX. The correction means 11 corrects the value of C when the value exceeds the allowable range specified by the range specification means 10, so that the original count value C is corrected to A + X
-X is output.

By doing so, the held output becomes
A, A + X, A + XX−X are output, so A, B, C
The demodulated signal is generated more smoothly than is output.

As described above, the range specifying means 10 specifies the allowable range of the next count value, and the correcting means 11 corrects the count value when the count value exceeds the allowable range. The count value currently detected is abnormally larger than the previous count value (one cycle before) or
When it is abnormally small, make sure that the difference does not increase
Since the count value can be corrected and output, and a signal disturbed by the defect is output without affecting the demodulated signal, an unnecessary signal due to the defect can be removed.

Next, a third embodiment will be described. FIG. 6 is a configuration diagram of an FM demodulator according to a third embodiment of the present invention.

1 is a binarizing means, 2 is a counting means, 3 is a holding means, 4 is a low-pass filter, and 30 is a delay means, which has the same function as in the second embodiment.

5 is a difference detecting means 12 and a level discriminating means 1
3 is a count value correcting means composed of 3 and a correcting means 11.

The difference detecting means 12 has a current count value B output from the counting means 2 and an output value A
And outputs the difference B-A.

The level determining means 13 determines whether the output of the difference detecting means 12 falls within a range from -X to + X, where X is a first predetermined value and -X is a second predetermined value. .

The correction means 11 determines that the difference BA is from -X to +
When it is in the range of X, B is output, and BA is -X
If smaller, AX is output instead of B, and B-A
When A is larger than + X, A + X is output instead of B.

As described above, the differential value of the count value is detected by the difference detecting means 12, the differential value of the count value is determined by the level determining means 13, and the count value is corrected by the correcting means 11. Similarly to the second embodiment, when the current count value is abnormally larger or abnormally smaller than the previous count value, the count value can be corrected and output in the range of ± X.

The operation of the FM demodulation device thus configured will be described with reference to FIG. In FIG. 7, as in FIGS. 2 and 5, the periods of the FM carrier are indicated by A, B, and C, and the count value counted by the counting unit 2 and the holding output of the holding unit 3 are superimposed below the FM carrier. Has been described. The count value is illustrated by a value such as A, B, C, Y, or Z.

The output of the difference detecting means 12 is shown as a difference output below the holding output.

The level discriminating means 13 determines whether the difference output of the difference detecting means 12 exceeds a range of a predetermined level ± X.
For example, in this example, the correction unit 11 corrects and outputs the original count value B as A + X when the cycle is B, and outputs the original count value C as A + when the cycle is C.
XX is corrected and output.

By doing so, the held output becomes
A, A + X, A + XX−X are output, so A, B, C
The demodulated signal is generated more smoothly than is output.

As described above, the difference between the next count value and the previous count value is detected by the difference detection means 12, the level is determined by the level determination means 13, and then corrected by the correction means 11, whereby the count value correction means No. 5, when the currently detected count value is abnormally larger or abnormally smaller than the previous count value, the count value can be corrected and output so that the difference does not increase.

By doing so, the signal disturbed by the defect is output without affecting the demodulated signal, so that unnecessary signals due to the defect can be removed as in the second embodiment.

Next, a fourth embodiment will be described. Usually F
The low-pass filter for smoothing the M demodulated signal sets the cutoff frequency to about 1 to 2 times the FM demodulated signal.
It is said to be good.

The frequency of the FM carrier is generally at least four times the cutoff of the low-pass filter.

In this case, from the 20 kHz FM carrier,
A method of applying a low-pass filter with a cut-off frequency of 5 kHz to an FM demodulated signal of Hz at the stage of outputting a periodic value will be described.

FIG. 8 shows an FM according to the fourth embodiment of the present invention.
It is a block diagram of a demodulation device. In the figure, reference numeral 1 denotes a binarizing means, which operates in the same manner as in the first embodiment.

Numeral 2 is a counting means for counting the period from the fall to the fall of the FM carrier. 19
Is reset means for ignoring the falling once and resetting the counting means 2.

The counting means 2 reset by the resetting means 19 counts two periods of the FM carrier, so that the output period value is the sum of the two periods.

Reference numeral 3 denotes a holding unit which holds the output of the counting unit 2 and converts it into an amplitude to generate an FM demodulated signal.
Is a low-pass filter, which inputs an FM demodulated signal,
This is for reducing the quantization noise generated by the counting means 2 and smoothing the FM demodulated signal.

As described above, by resetting the reset means 19 every two cycles so that the count means 2 counts two cycles of the FM carrier, the count means 2 becomes F
The sum of the two periods of the M carrier, that is, a constant multiple of the average value of the periods, can be detected.

As described above, by maintaining the average value of the counter value (a constant multiple thereof), the transfer characteristic becomes 1 + Z ^-1.
It is known that the low pass characteristic is obtained.

The cutoff frequency is f / 4, where f is the average frequency of the FM carrier. In this example, since f = 20 kHz, the cutoff frequency is f
As a result, a retained output that has passed through a low-pass filter of / 4 and 5 kHz is obtained.

As described above, the counting unit 2 and the resetting unit 19 count the signal every period that is 1 to 4 times the frequency of the frequency of the FM demodulated signal obtained by the FM demodulation. A bandpass filter characteristic can be provided. Therefore, the holding means 3
The filter used for the low-pass filter 4 attached to the latter stage of the output may be of low order, and the number of elements constituting the device can be reduced.

Next, a fifth embodiment will be described. FIG. 9 shows a configuration diagram of an FM demodulator according to the fifth embodiment of the present invention.
The difference from the first embodiment is that a range varying means 20 for determining the allowable range output from the counting means 2 based on the absolute value of the output of the delay means 30 is provided.

The range varying means 20 sets the delay range so that when the output value of the delay means 30 is close to the center of the demodulated signal, the range is wide, and when the output value is far from the center of the demodulated signal, the delay range is narrow. The allowable range is varied according to the absolute value of the output value of the means 30.

The operation of the FM demodulator thus configured will be described with reference to FIG.

FIG. 10 is similar to FIGS.
The periods of the carrier are indicated by A, B, and C, and the count value counted by the counting means 2 and the output of the holding means 3 are described so as to be superimposed below the FM carrier. The count values are A, B,
It is illustrated by values such as C, Y, and Z.

The range values generated by the range changing means 20 are indicated by double-headed arrows such as A1 and A2.

For example, assuming that the current count value is B and the output of the delay means 30 is A, the range variable means 2
0 sets the permissible range of the current count value B according to the output value A of the delay means 30. Assuming that A is slightly larger than the center of the average demodulated signal level, the range from A-A2 to A + A1 is set according to the deviation amount from the center, with positive values A1 and A2 satisfying A1 <A2.

The count value correcting means 5 detects whether or not the current count value B falls within the range from A-A2 to A + A1. If the current count value B exceeds the range, A-A2 or
Correct the value closer to any one of A + A1.

In this case, when the current count value is B, it is larger than A + A1.
Thus, the count value is corrected and output as Y = A + A1.

Next, when the output of the delay means 30 becomes Y, since Y is larger than the center of the demodulated signal, the range varying means 20 sets the positive value B1 such that B1 <A1 <A2 <B2.
A range from Y-B2 to Y + B1 is set with 1, B2.

The count value correcting means 5 detects whether or not the current count value C falls within the range from Y-B2 to Y + B1, and if it exceeds the value, Y-B2 or Y + B.
Correct the value to a value closer to 1 and output it. Since the current count value C is smaller than Y-B2, the count value is Z = Y
−B2 is corrected and output, and Z becomes the output value of the delay means 30 again.

Since Z is smaller than the average center value of the demodulated signal, this time, Z-C2 has a positive value of C1> C2.
The range variable means 20 sets the range from to Z + C1, and the count value correcting means 5 detects whether or not the current count value falls within the range from Z-C2 to Z + C1, and if it exceeds that value, it is closer to either. To correct.

By doing so, the held output becomes
Since the signals are output as A, Y, and Z, the demodulated signal is generated more smoothly than the signals are output as A, B, and C. In addition, near the center of the demodulated signal, as much as possible, the phase information of the input FM carrier wave It is faithfully reproduced.

As described above, the range varying means 20 varies the permissible range of the count value correcting means 5 according to the absolute value of the count value, so that the signal disturbed by the defect is output without affecting the demodulated signal. Needless to say, an FM demodulator can be obtained in which only the phase information near the center of the demodulated signal is small.

Next, a sixth embodiment will be described. FIG. 11 is a block diagram showing an FM demodulator according to the sixth embodiment of the present invention.

The sixth embodiment is different from the first embodiment or the fifth embodiment in that the output of the delay means 30 outputs the correction value corrected by the count value correction means 5 and the output of the delay means 3.
It is provided with a correction value calculating means 21 for generating from the output value of the second delay means 36 connected in series with 0.

In the fifth embodiment, at the time of the cycle C, the count value correcting means 5 detects whether or not the count value C falls within the range from Y-B2 to Y + B1, where Y is the output value of the delay means 30. Later, if it exceeds, the correction was made closer to Y-B2 or Y + B1.

In this embodiment, the average value of the output value Y output from the delay means 30 and the output value A of the second delay means 36,
(A + Y) / 2 is calculated by the correction value calculation means 21, and this value is input to the count value correction means 5 to make this value a correction candidate value.

In this way, the count value can be corrected to a value calculated using the previous count value, an integration effect is obtained, and unnecessary signals generated due to defects and the like are broken. The FM demodulated signal can be obtained with little disturbance even when defects occur continuously.

In each embodiment, the counting by the counting means 2 is performed from the fall of the period of the FM carrier to the fall. However, even from the rise to the rise, the rise and fall are alternately counted. The same effect can be obtained.

Further, since a configuration in which both the rise and fall of the FM carrier are detected alternately can be considered, the same effect can be obtained regardless of the number of counting means and reset means.

The holding means 3 functions as the holding means if the low-pass filter is constituted by a digital filter or the like.

In the sixth embodiment, the calculation performed by the count value correcting means is performed so as to be the average value of the immediately preceding period value and the immediately preceding period value. The previous value may be used, and it is not always necessary to use an average value, and any operation using the period value up to that time may be used, or an operation with the current count value may be used.

[0111]

As described above, when the present count value, which is the period value of the FM carrier detected by the count means, is abnormally larger or abnormally smaller than the previous count value by the count value correcting means, as described above. Since the count value is corrected and output so that the difference does not increase, a signal disturbed by the defect is output without affecting the demodulated signal, and an unnecessary signal due to the defect can be removed.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an FM demodulator according to a first embodiment of the present invention.

FIG. 2 is a signal waveform chart for explaining the operation of the first embodiment.

FIG. 3 is a block diagram illustrating a configuration of an FM demodulator according to a second embodiment of the present invention.

FIG. 4 shows a count value correcting means 5 in the second embodiment.
Block diagram showing the configuration of

FIG. 5 is a signal waveform chart for explaining the operation of the second embodiment.

FIG. 6 is a block diagram illustrating a configuration of an FM demodulator according to a third embodiment of the present invention.

FIG. 7 is a signal waveform chart for explaining the operation of the third embodiment.

FIG. 8 is a block diagram showing a configuration of an FM demodulator according to a fourth embodiment of the present invention.

FIG. 9 is a block diagram illustrating a configuration of an FM demodulator according to a fifth embodiment of the present invention.

FIG. 10 is a signal waveform chart for explaining the operation of the fifth embodiment.

FIG. 11 is a block diagram illustrating a configuration of an FM demodulator according to a sixth embodiment of the present invention.

FIG. 12 is a block diagram showing a configuration of a conventional FM demodulator;

FIG. 13 is a signal waveform diagram for explaining the operation of the conventional example.

[Explanation of symbols]

 2 counting means 3 holding means 5 count value correcting means 30 delay means

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-34604 (JP, A) JP-A-61-192103 (JP, A) JP-A-57-54407 (JP, A) 82154 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03D 3/00

Claims (7)

(57) [Claims] 1. Counting means for sequentially counting the frequency of an FM carrier, outputting the frequency as a cycle value, resetting and counting the next frequency, and delaying means for delaying an input value for each frequency of the FM carrier. An output of the counting means and an output of the delay means or an output obtained by performing an arithmetic processing on the output of the delay means are input, and an output value of the delay means is equal to or more than a first predetermined value than a current count value. Or the current count value is larger than the output value of the delay means by the second value.
If the current count value is larger than the predetermined value, the current count value is corrected and output. An FM demodulation apparatus comprising: a count value correcting unit that performs the above operation; and a holding unit that sequentially holds the count value output from the count value correcting unit to output the amplitude value. 2. A count value correcting means, based on an output value of a delay means, a range designating means for determining a permissible range of a next input count value; 2. The FM according to claim 1, further comprising correction means for correcting and outputting the count value when the value exceeds the specified allowable range, and outputting the count value without correction when the value does not exceed the allowable range.
Demodulator. 3. The FM demodulator according to claim 2, wherein the range designating means comprises an adding means or a subtracting means for adding or subtracting a predetermined value to or from the output of the delay means. 4. A correction means for comparing a value representing an allowable range designated by the range designation means with an output value of the counting means, and a plurality of correction candidate values according to a result of the comparison means. 3. The method according to claim 2, further comprising selecting means for selecting a correction value from among them.
M demodulator. 5. A count value correction means, a difference detection means for detecting a difference between a current count value output from the count means and an output value from the delay means, and a difference output from the difference detection means being a first predetermined value. Is greater than or smaller than a second predetermined value, a level discriminating means for discriminating whether the value is an abnormal value, and correcting the count value when the level discriminating means detects an abnormal value. 2. The FM demodulator according to claim 1, further comprising correction means for outputting the count value and outputting the count value without correction when the count value is not detected. 6. A counting means for sequentially counting the period of the FM carrier and outputting the period as a period value, resetting and counting the next period, and a delay unit for delaying an input value for each period of the FM carrier. Range changing means for generating an allowable range of the count value output from the counting means from the absolute value of the output value of the delay means; If the value is out of the range, the current count value is corrected and output, and if the value is within the allowable range value, the current count value is output without correction,
An FM demodulator comprising: a count value correcting unit that uses the output as an input to the delay unit; and a holding unit that sequentially holds the count value output by the count value correcting unit and outputs the count value as an amplitude output. 7. Counting means for sequentially counting the cycle of the FM carrier and outputting the cycle as a cycle value, resetting and counting the next cycle, and delay means for delaying an input value for each cycle of the FM carrier. Calculating an output value of the delay means, and determining a correction candidate value for correcting the count value output by the counting means according to the calculation result; an output of the counting means; When the output of the delay means and the output of the correction value calculation means are input, and the output value of the delay means is larger than the current count value of the count means by a first predetermined value or more, If the current count value is greater than a second predetermined value than the output value of the means, the current count value is corrected to the correction candidate value and output. In addition to outputting the current count value without correction,
An FM demodulator comprising: a count value correcting unit that uses the output as an input to the delay unit; and a holding unit that sequentially holds the count value output by the count value correcting unit and outputs the count value as an amplitude output.