KR910003438B1 - Frequency modulation demodulation circuit - Google Patents

Abstract

No content.

Description

FM demodulation circuit

1 is a block diagram of a first embodiment of the present invention.

2 is a waveform diagram of a first embodiment of the present invention.

3 is a block diagram of a fundamental wave peak detection circuit of a first embodiment of the present invention.

4 is a waveform diagram of a fundamental wave peak detection circuit of a first embodiment of the present invention.

5A and 5B are circuit diagrams of differential circuits in a fundamental wave peak detection circuit.

6 is a waveform diagram of the differential circuit of FIG. 5 (b).

7 is a block diagram of another fundamental wave peak detection circuit of the present invention.

8 is a block diagram of a second embodiment of the present invention.

9 is a waveform diagram of a second embodiment and a circuit of FIG.

10 is a block diagram of a third embodiment of the present invention.

11 is a waveform diagram of a third embodiment of the present invention.

12 is a circuit diagram of a level adjustment circuit.

13A to 13E are block diagrams of a control circuit, and FIG. 13F is a waveform diagram of a 100% white signal.

14 and 15 are block diagrams of another embodiment of the present invention.

16 is a block diagram of a conventional example.

17 is a waveform diagram of a conventional example.

* Explanation of symbols for main parts of the drawings

1: Terminal 2: fundamental wave peak detection circuit

3: pulse generator circuit 4: adder

5,40 Demodulator 6: BPF

7: differential circuit 8: limiter circuit

9 delay circuit 10 comparator

11: 90 ° transition circuit 12, 39: equalizer circuit

30: level adjusting circuit 31: control circuit

32: FET 33, 34, 35: terminal

36, 38: detection circuit 37, 41: LPF

The present invention relates to an FM demodulation circuit for demodulating a frequency modulated (FM) signal. [0003] The conventional technique is a magnetic recording and reproducing apparatus for FM single-wavelength reproducing wave low-carrier FM recording, such as a commercially available video tape recorder (VTR). When the FM signal has a large frequency modulation index, the zero crossing point is often faithful in the FM demodulator. It cannot be reproduced, and signal inversion or inversion is likely to occur. This phenomenon occurs when the level of the lower wave component (J _-1 ) becomes larger than the level of the FM fundamental wave component (J ₀ ), and when J ₋₁ <J ₀ when the reproduction noise is superimposed. Even inversion occurs because of the influence of noise.

In order to avoid this inversion, Japanese Patent Application Laid-Open No. 57-189311 (1982) proposes a frequency demodulator that superimposes a pulse on an input FM signal before demodulating the FM signal. The superimposed pulses are generated at a time when a predetermined time is delayed from the zero crossing point of the chief wave component of the FM signal, and the predetermined time is set by superimposing the pulses on the peak point of the FM signal at the carrier frequency. This operation is described in detail with reference to the block diagram of FIG. 16 and the waveform diagram of FIG.

The fundamental wave component i of the input FM signal h is extracted by the band pass filter 20 and becomes a signal j whose predetermined time is delayed by the delay circuit 21. The signal j passes through the limiter 22 to become the signal k, and the pulse generating circuit 23 obtains the pulse signal l. The pulse signal 1 indicates the zero crossing point of the delayed fundamental wave signal j, which is basically different from the present invention. When the pulse signal l is superimposed on the reproduction FM signal h by the adder 24, the signal m is obtained. Therefore, even when the modulation index is high, there is a zero crossing point, so that no discharge phenomenon occurs.

However, since it has time information fundamentally different from the pulse signal l, which is the time information of the zero crossing point of the fundamental wave signal j, which is delayed by a predetermined time, and the time information of the peak point of the reproduced FM signal waveform, different time information is obtained. The added signal has distortion of the information of the FM signal, which causes the following problems.

If the FM divider at VIR is set to 5 to 7 MHz, the black clip is 100%, and the back clip is 200%, the black clip frequency is 3 MHz, the back clip frequency is 9 MHz, and the fundamental wave existence range is 3 to 9 MHz. do. That is, the inversion period of the fundamental wave varies between approximately 333/2 nsec and 111/2 nsec.

When the fundamental wave signal i is delayed by 100 nsec and becomes the (j) signal, the FM signal m with overlapping pulses indicates that the phase relationship between the overlapping pulses and the FM signal changes with frequency. That is, when the frequency of the fundamental wave signal i is low, the pulse is superimposed at a position adjacent to the peak point of the fundamental wave signal, but when the frequency of the fundamental wave signal is high, the pulse is moved from the peak point of the fundamental wave signal. Overlaid on location Therefore, the zero crossing point cannot be restored to the (x ₁ ) point, so-called black brake is generated, and the white break occurs at the (x ₂ ) point where the zero crossing point is exceeded.

When the delay time is shortened to 50 nsec, the signals j, k, l, and m become signals j ₂ , k ₂ , l ₂ , and m ₂ , respectively. In particular, the signal m ₂ indicates that a white brake is generated at the point (x ₃ ). If the delay time is further shortened, the pulse signal is superimposed more closely to the zero crossing point region, and the waveform of the zero crossing point of the reproduction FM signal is changed, which adversely affects the frequency characteristics after demodulation. Therefore, it is not desirable to simply reduce the delay time.

As described above, the conventional FM demodulator disclosed in Japanese Patent Laid-Open No. 57-189311 (1982) does not achieve the prevention of the inversion phenomenon over the entire frequency range of the FM signal. Deteriorates the quality of the signal waveform.

It is an object of the present invention to provide an FM demodulation circuit that performs precise frequency demodulation without inversion.

Another object of the present invention is to provide an FM demodulation circuit for performing precise frequency demodulation with a high signal-to-noise ratio (S / N ratio).

In order to achieve this object, according to the present invention, a pulse having a small width is superimposed on each peak of the input FM signal irrespective of frequency before the FM signal is supplied to a conventional frequency demodulator. The pulses of polarity overlap approximately at each positive peak of the FM signal, and the pulses of negative polarity overlap approximately at each negative peak of the FM signal. The pulses are superimposed so that all zero crossings of the FM signal are reproduced correctly in the frequency demodulator. The pulse width is preferably at most 1/2 cycle of the FM signal at its maximum frequency.

The FM demodulation circuit of the present invention generates a peak detection circuit for detecting a peak of an input FM signal and a pulse having the same polarity as that of each corresponding peak at the time when the peak is present according to the detection result by the peak detection circuit. Demodulating a pulse generating circuit, an adder for adding pulses generated by the input FM signal and the pulse generating circuit so as to obtain an overlapping FM signal at the peak of the input FM signal, and a pulse overlapping FM signal output from the adder; It consists of a frequency demodulator.

The peak detection circuit is preferably replaced by a fundamental wave peak detection circuit that detects the peak of the fundamental wave of the input FM signal. Since the peak of the fundamental wave is almost the same as the peak of the FM signal, an FM signal whose pulses are approximately superimposed at the peak of the FM signal is obtained as the output of the adder. In this case, the fundamental wave peak detection circuit has a bandpass filter for extracting the fundamental wave components from the input FM signal, and this bandpass filter has an effect of reducing noise.

The input FM signal is passed through an equalizer that compensates for signal delays generated in the peak detection circuit and the pulse generation circuit, before being supplied to the adder. This equalizer has a lowpass filter characteristic to remove low S / N highpass component of FM signal.

In order to impart a further improved function, the frequency demodulation circuit may include a level adjusting circuit for adjusting the level of the pulse generated by the pulse generating circuit and a control circuit for controlling the level adjusting circuit in accordance with a desired signal.

These and other objects and features and advantages of the present invention will become apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.

FIG. 1 is a block diagram of a first embodiment of the present invention, and FIG. 2 is a waveform diagram of portions corresponding to (a) to (e) of FIG. The FM signal input from the terminal 1 is supplied to the fundamental wave peak detection circuit 2. The fundamental wave peak detection circuit 2 outputs a rectangular signal c whose transition edge indicates the peak point of the fundamental wave component b of the FM signal a. The pulse generating circuit 3 generates the positive pulse d at the rising edge of the signal c and the negative pulse d at the falling edge of the signal c from the signal c. The pulse generating circuit 3 may be a differential circuit. The FM signal a and the pulse d are added by the adder 4 to obtain a signal e. Since the pulse generation point of the pulse d coincides completely with the peak point of the signal b, the pulse d always overlaps the peak point of the FM signal a to become the signal e.

The signal (e) restores the zero crossing point at the cross section between (Z ₁ ) and (Z ₂ ) where the conventional inversion phenomenon has occurred, and the inversion phenomenon indicates that the signal (e) is a conventional pulse counter type demodulator (5). Since it does not occur when demodulated by, precise frequency demodulation is realized.

3 is a first embodiment of the fundamental wave peak detection circuit 2 for detecting the peak point of the fundamental wave, and FIG. 4 is a waveform diagram of the circuit of FIG.

The input FM signal (a) passes through a band pass filter (BPF) 6 to extract the FM fundamental wave b. Here, the pass band of the BPF is roughly set to cover the deflection of the FM signal.

Then, in order to detect the peak point of the signal b, the signal b is differentiated by the differential circuit 7 to obtain a signal b2. Here, the zero crossing point of the signal b2 represents the peak point of the signal b. In the limiter circuit 8, the signal c1 can be obtained by limiting the signal b2, and the signal c can be obtained by inverting the signal c1. The polarity in the limiter circuit 8 is adjusted to be equal to the phase of the FM signal.

5A is an example of the differential circuit 7. It consists of the differential circuit, the resistor R, and the capacitor | condenser C in FIG. 5 (a). In this structure, the order of the BPF 6 and the differential circuit 7 may be reversed.

Another example of the differential circuit 7 is shown in FIG. 5 (b), which is a delay circuit 9 and a comparator which obtains the signal b3 by delaying the signal b by a small time t ₁ . It consists of 10. The operation of the circuit in FIG. 5B is explained using the waveform diagram shown in FIG. The FM fundamental wave b and the signal b3 delayed from the signal b to (t ₁ ) are compared in the comparator 10 to obtain (c). In this case, the transition edge of the signal c is shifted from the peak point of the signal b by the minute time t1, but the amount shifted is (t ₁ ) time small (for example, The time t ₁ is 20 nsec). If such a configuration is used for the differential circuit 7, there is an advantage that the limiter circuit 8 in FIG. 3 may be omitted.

A second embodiment of the fundamental wave peak detection circuit 2 shown in FIG. 7 will be described with reference to the waveform diagram of FIG. The FM fundamental wave b is extracted from the FM signal a by the BPF 6. In the 90 ° transition circuit 11, the phase of the signal b is shifted by 90 ° in the band in which the fundamental wave b is present. As a result, signal b4 is obtained. The zero crossing point of signal b4 coincides with the peak point of signal b. That is, the signal b4 is limited by the limiter circuit 8, so that the signal c can be obtained. Here, the 90 ° transition circuit 11 can also be configured with a capacitor and a resistor.

Also, as in the second embodiment of the present invention shown in FIG. 8, it is also possible to configure a 90 ° transition circuit with a delay element. The 90 ° transition circuit 11 shown in FIG. 8 is a kind of comb-shaped filter, and with respect to the signal a1 delayed by the time t ₂ , the signal a by the input FM signal a and the time 2t ₂ . The phase difference from the signal a2 generated by synthesizing the delayed signal from?) Is always 90 °.

The signal a1 is sent to the adder 4, and the signal a2 is sent to the BPF 6 to obtain a fundamental wave b4. The zero crossing point of the fundamental wave b4 coincides with the peak point of the signal a1. By limiting the signal b4 by the limiter circuit 8, it is possible to obtain the signal c. In the configuration shown in Fig. 8, since the input FM signal is also delayed by (t2), this configuration is slightly different from the block diagram of Fig. 1, but this difference due to the configuration of the 90 ° transition circuit is fundamentally different. not different.

FIG. 10 is a block diagram of a third embodiment of the present invention, and FIG. 11 is a waveform diagram of portions corresponding to (a) to (e) of the block diagram of FIG. The FM signal a input from the terminal 1 is supplied to the fundamental wave peak detection circuit 2. The fundamental wave peak detection circuit (2) outputs a rectangular signal (c) in which the transition edge indicates the peak point of the fundamental wave component (b) of the FM signal. From the pulse generating circuit 3 signal c, a pulse d is generated which is bipolar at the rising edge of the signal c and negative at the falling edge of the signal c. The pulse generating circuit 3 may be a differential circuit. The pulse d is adjusted to the level d1 by the level adjusting circuit 30 and sent to the adder 4. The level adjustment circuit 30 is controlled by the control circuit 31. The signal input through the terminal 100 and the control circuit 31 will be described later.

The FM signal a and the pulse d1 are added by the adder 4 to obtain a signal e. Since the pulse generation point of the pulse d1 coincides completely with the peak point of the signal b, the pulse d1 is always superimposed on the peak point of the FM signal a to become the signal e.

The signal (e) restores the zero crossing point at the cross section between (Z ₁ ) and (Z ₂ ) where the conventional inversion occurs, and thus inverts when the signal (e) is demodulated in the conventional pulse counter type demodulator (5). Since no phenomenon occurs, precise frequency demodulation can be realized.

12 shows an example of the level adjusting circuit 30, which is composed of the resistors R1, R2 and the FET 32. As shown in FIG. The output signal of the pulse generating circuit 3 is input through the terminal 34, and a small level is output from the terminal 35 when the signal from the control circuit 31 input through the terminal 33 is High. When the signal from the control circuit 31 is low, a large level is output from the terminal 35.

Examples of the control circuit 31 are shown in Figs. 13A to 13E.

The control circuit shown in Fig. 13A uses the recording time mode signal set in the recording / reproducing apparatus as an input signal, and outputs a low signal during a long time recording mode, thereby controlling the level adjusting circuit to increase the addition level. do.

The control circuit shown in FIG. 13 (b) uses, as an input signal, a high frequency recording mode signal indicating a normal FM carrier frequency set in the recording / reproducing apparatus or a high frequency FM carrier frequency which has transitioned to a high frequency band. By outputting a signal, the level adjusting circuit is controlled to increase the addition level.

The control circuit shown in FIG. 13 (c) is composed of a detection circuit 36 for detecting the amplitude level of the FM signal, and outputs a low signal when the amplitude level of the FM signal is small, so as to increase the addition level. Control the adjustment circuit.

The control circuit shown in FIG. 13 (d) is composed of a low pass filter 37 passing through the lower band of the FM signal and a detection circuit 38 for detecting the lower band level. By outputting a signal, the level adjusting circuit is controlled to increase the addition level.

The control circuit shown in FIG. 13E passes through the equalizer circuit 39 which emphasizes only the fundamental wave components of the FM signal, the demodulator 40 which demodulates the output of the equalizer circuit 39, and the low pass component of the demodulator output. The low pass filter 41 is configured to control the output S1 so as to increase the addition level when the output signal level of the low pass filter approaches the level indicating that the FM signal is in the high range. The equalizer is inserted to prevent inversion occurring in the demodulator. When the carrier frequency of the white level of the video signal is demodulated higher than the carrier frequency of the black level of the video signal, the closer the video signal is to the white level of the demodulated signal in the demodulator, the lower the output S1 of the control circuit 31 is. do. A signal waveform without deemphasis is preferable. FIG. 13 (f) is a waveform diagram when the video signal is 100% white.

In the above embodiment, it is effective to improve the BPF 6 and the S / N (or O / N of the recording and reproducing apparatus) which are the components of the fundamental wave peak detection circuit 2.

The improvement effect of S / N is improved by narrowing the pass band of the BPF 6. However, if the band is too narrow to pass the FM fundamental wave, the peak detection of the fundamental wave is incomplete. Therefore, it is preferable to perform adaptive control so that the bandwidth of the BPF becomes optimal according to the carrier frequency of the FM signal and the state of S / N. The information to be used for adaptive control may be an output level of the FM signal, a recording mode of the recording / reproducing apparatus (for example, standard recording, long time recording or standard recording, high band recording in a VTR), or the like.

Furthermore, since the small delay is generated due to the action of the filter or the circuit in the fundamental wave peak detection circuit 2 and the pulse generating circuit 3, in order to compensate for such a small delay, as shown in FIGS. It is preferable to insert the equalizer circuit 12 into the direct current FM signal path from the terminal 1 to the adder 4.

The equalizer circuit 12 preferably has a group delay frequency characteristic and a flat frequency characteristic. However, in terms of S / N improvement, the equalizer circuit 12 may have a low pass filter characteristic that attenuates high frequency components in which S / N of the FM signal is poor.

Conventionally, the improvement of S / N by attenuation of the high frequency component of the FM signal in the previous stage of the demodulator 5 is known. However, when the attenuation amount is increased, an inversion phenomenon often occurs. However, by using the present invention, it is possible to increase the attenuation amount of the high range of the equalizer 12 large enough so that S / N can be effectively improved and at the same time prevent the occurrence of reversal. That is, the present invention also has an effect of improving S / N as a secondary effect.

Furthermore, in the first embodiment of the detection circuit 2, the bandwidth of the BPF 6 is widened to pass the FM sideband wave, or the peak point of the FM signal having the sideband wave by the differential circuit 7 is obtained. The BPF 6 may be omitted to directly detect. However, in this case, since there is no band limitation, there is no improvement effect of S / N, and the reliability of the output signal C of the limiter circuit 8 is also lower than in the above embodiment. In order to enhance the S / N improvement effect, the band of the BPF 6 is made as narrow as possible while containing a high range of deflection from the center of the FM signal carrier.

According to another aspect, the pulse d superimposed on the FM signal is a high harmonic signal including an absorption harmonic component of the fundamental wave of the FM signal higher than a certain number. Therefore, a circuit composed of the basic peak detection circuit 2 and the pulse generation circuit 3 can be referred to as a high harmonic signal generation circuit.

The FM demodulation circuit of the present invention described above with reference to some specific embodiments records audio and / or video signals in the form of FM signals on a recording medium, and reproduces the recorded signals. It is used in various systems for frequency demodulation, including playback devices.

While certain embodiments have been described, it has been disclosed to the extent that it is sufficient to understand the invention, and various changes and modifications are possible within the scope of the invention as defined in the appended claims.

Claims (31)

A peak detection circuit 2 for detecting peaks of the input frequency modulation (FM) signal, and a pulse for generating pulses having the same polarity as that of the corresponding peaks at the time when the peak is present according to the detection result by the peak detection circuit. A generator (3), an adder (4) for adding the pulses generated by the input FM signal and the pulse generator circuit to obtain an FM signal in which the pulses approximately overlap the peaks of the input FM signal, respectively, and outputted from the adder; FM demodulation circuit, characterized in that consisting of a frequency demodulator (5) for demodulating the FM signal. 2. An equalizer (12) as claimed in claim 1 comprising an equalizer (12) for delaying the input FM signal before being supplied to the adder (4) to compensate for signal delays generated in the peak detection circuit (2) and the pulse generation circuit (3). FM demodulation circuit, characterized in that. 3. The FM demodulation circuit according to claim 2, wherein the equalizer (12) has a low pass filter characteristic to remove high frequency components of an input FM signal having a low signal to noise ratio. 2. The peak detection circuit (2) according to claim 1, wherein the peak detection circuit (2) generates a rectangular waveform signal having a level shift timing corresponding to the peak of the input FM signal from the input FM signal, and the pulse generation circuit (3) generates a level of the rectangular waveform signal. FM demodulation circuit, characterized in that to generate a pulse at each transition time. 5. The FM demodulation circuit according to claim 4, wherein said pulse generating circuit (3) comprises a differential circuit for differentiating a rectangular waveform signal. 5. The peak detection circuit (2) according to claim 4, wherein the peak detection circuit (2) comprises a differential circuit (7) for differentiating the input FM signal so as to obtain a signal having a zero crossing point corresponding to the peak of the input FM signal, and a signal output from the differential circuit. An FM demodulation circuit comprising a limiter (8) which obtains a rectangular waveform signal by limiting the level of 5. The peak detection circuit (2) according to claim 4, wherein the peak detection circuit (2) compares the delay circuit (9) for delaying the input FM signal by a minute time to obtain a micro delayed FM signal, and the level of the micro delayed FM signal and the input FM signal. An FM demodulation circuit comprising a comparator (10) which obtains a signal approximately equal to a rectangular waveform signal. 5. The phase shift circuit according to claim 4, wherein the peak detection circuit (2) is configured to shift the phase of the input FM signal by 90 degrees so as to obtain a 90 degree phase shifted FM signal having a zero crossing point corresponding to the peak of the input FM signal. And a limiter (8) which obtains a rectangular waveform signal by limiting the level of the FM signal which has been phase shifted by 90 degrees. 2. The level adjusting circuit according to claim 1, wherein the level adjusting circuit is inserted between the adder (4) and the pulse generating circuit (3) to adjust the level of the pulse generated by the pulse generating circuit so as to be at a predetermined level in accordance with the predetermined control signal. FM demodulation circuit comprising a 30). The FM demodulation circuit according to claim 1, wherein said peak detection circuit (1) comprises a fundamental wave peak detection circuit (2) for detecting a peak of a fundamental wave of an input FM signal. 11. An equalizer (12) as claimed in claim 10 comprising an equalizer (12) for delaying an input FM signal before being fed to the adder (4) to compensate for signal delays generated in the peak detection circuit (2) and the pulse generator circuit (3). FM demodulation circuit, characterized in that. 12. The FM demodulation circuit according to claim 11, wherein the equalizer (12) has a low pass filter characteristic to remove high frequency components of an input FM signal having a low signal to noise ratio. 12. The rectangular wave signal detection circuit according to claim 10, wherein the fundamental wave peak detection circuit (2) generates a rectangular waveform signal having a level shift time corresponding to the peak of the fundamental wave from an input FM signal, and the pulse generating circuit (3) generates a rectangular waveform signal. FM demodulation circuit, characterized in that to generate each pulse at the time of the level transition. 14. The FM demodulation circuit as claimed in claim 13, wherein said pulse generating circuit (3) comprises a differential circuit for differentiating a rectangular waveform signal. 14. The fundamental wave peak detection circuit (2) according to claim 13, wherein the fundamental wave peak detection circuit (2) comprises a band pass filter (6) for extracting the fundamental wave from the input FM signal, and a signal such that the zero crossing point corresponds to the peak of the fundamental wave. And a limiter (8) for obtaining a rectangular waveform signal by limiting the level of a signal output from the differential circuit. 14. The fundamental wave peak detection circuit (2) according to claim 13, wherein the fundamental wave peak detection circuit (2) comprises a band pass filter (6) for extracting the fundamental wave from an input FM signal, and a delay for delaying the fundamental wave by a minute time to obtain a minute delayed fundamental wave. And a circuit (9) and a comparator (10) which obtains a signal such as a rectangular waveform signal by comparing the levels of the fundamentally delayed fundamental wave and the fundamental wave. The fundamental wave peak detection circuit (2) according to claim 13, wherein the fundamental wave peak detection circuit (2) includes a band pass filter (6) for extracting the fundamental wave from an input FM signal, and a 90 ° phase shift fundamental wave having a zero crossing point corresponding to the peak of the fundamental wave. FM phase, characterized in that it consists of a phase shift circuit (11) for shifting the phase of the fundamental wave by 90 ° to obtain a signal, and a limiter (8) for obtaining a rectangular waveform signal by limiting the level of the fundamental wave that has been phase shifted by 90 °. As your inquiry. According to the fundamental wave peak detection circuit 2 for detecting the peak of the fundamental wave of the input FM signal and the detection result by the peak detection circuit, a pulse having a polarity and a polarity corresponding to each peak is generated at the time when the peak is present. The pulse generating circuit 3, the level adjusting circuit 30 for adjusting the level of the pulse generated by the pulse generating circuit, the control circuit 31 for controlling the level adjusting circuit in accordance with a predetermined signal, and the level An adder 4 which adds the pulse adjusted by the level to the input FM signal so as to obtain an FM signal whose level adjusted by the output circuit is approximately superimposed on the peak of the input FM signal, and an FM output from the adder; FM demodulation circuit comprising a frequency demodulator (5) for demodulating the signal. 19. The equalizer of claim 18, further comprising: an equalizer for delaying an input FM signal before being fed to an adder to ensure signal delay generated in said peak detection circuit 2, pulse generating circuit 3 and level adjusting circuit 30. FM demodulation circuit comprising a 12). 20. The FM demodulation circuit according to claim 19, wherein the equalizer (12) has a low pass filter characteristic to remove high frequency components of an input FM signal having a low signal to noise ratio. 19. The rectangular wave signal detecting circuit (2) according to claim 18, wherein the fundamental wave peak detection circuit (2) generates a rectangular waveform signal having a level shift timing corresponding to the peak of the fundamental wave from an input frequency modulated signal, and the pulse generating circuit (3) And an FM demodulation circuit for generating pulses at each level transition time. 22. The FM demodulation circuit according to claim 21, wherein said pulse generating circuit (3) is made of a differential circuit for differentiating a rectangular waveform signal. 22. The fundamental wave peak detection circuit (2) according to claim 21, wherein the fundamental wave peak detection circuit (2) comprises a band pass filter (6) for extracting the fundamental wave from an input FM signal, and a signal having a zero crossing point corresponding to the peak of the fundamental wave. And a limiter (8) for obtaining a rectangular waveform signal by limiting the level of a signal output from the differential circuit. 22. The delay signal for delaying a fundamental wave according to claim 21, wherein the fundamental wave peak detection circuit (2) comprises a band pass filter (6) for extracting a fundamental wave from an input FM signal and a delay time by a minute time to obtain a minute delayed fundamental wave. And a comparator (10) which obtains a signal approximately equal to a rectangular waveform signal by comparing the circuit (9) with the level of the fundamental wave and the delayed fundamental wave. 22. The fundamental wave peak detection circuit (2) according to claim 21, wherein the fundamental wave peak detection circuit (2) comprises a band pass filter (6) for extracting the fundamental wave from an input FM signal, and a 9 ° phase transition fundamental having a zero crossing point corresponding to the peak of the fundamental wave. FM double, characterized by consisting of a phase transition circuit 11 for shifting the phase of the fundamental wave 90 degrees to obtain a wave, and a limiter 8 for obtaining a rectangular waveform signal by limiting the level of the 90 ° phase transition fundamental wave. As your inquiry. 19. The control circuit (31) according to claim 18, wherein said control circuit (31) comprises a detection circuit (36) for receiving an input FM signal as a predetermined signal for detecting an amplitude level of an input FM signal, and said level adjustment circuit (30) FM demodulation circuit, characterized in that when the detected amplitude level decreases, it responds to the detected amplitude level to increase the level of the pulse output from the pulse generating circuit (3). The control circuit (31) according to claim 18, wherein said control circuit (31), which receives an input FM signal as a predetermined signal, detects the low pass filter (37) for extracting the lower band signal from the input FM signal and the amplitude level of the lower band signal. And the level adjusting circuit 30 responds to the detected amplitude level to increase the level of the pulse output from the pulse generating circuit 3 when the detected amplitude level increases. FM demodulation circuit, characterized in that. 19. The control circuit (31) according to claim 18, wherein said control circuit (31) for receiving an input FM signal as a predetermined signal includes: an equalizer (39) for emphasizing only the fundamental wave of the input FM signal, and a demodulator for demodulating the output signal from the equalizer. 40, and a low pass filter 41 which passes low frequency components of the output signal from the demodulator, wherein the level adjusting circuit 30 sets the level of the output signal in the low pass filter to the high frequency of the fundamental wave. And an FM demodulation circuit, responsive to an output signal from a low pass filter to increase the level of the pulse output from the pulse generating circuit (3) when changing in the direction indicating that the signal is in the direction of. 19. A signal recording and reproducing apparatus according to claim 18, wherein said control circuit (31) receives a signal representing a recording time mode of said apparatus as a predetermined signal, and generates a pulse when the recording time mode is a long recording mode. FM demodulation circuit, characterized in that for controlling the level adjustment circuit (3) to increase the level of the pulse output from the circuit (3). 19. A high frequency signal according to claim 18, used in a signal recording and reproducing apparatus, wherein the control circuit 31 is a predetermined signal and indicates a high frequency indicating whether a carrier frequency of the FM signal is a normal frequency set above the device or higher than the normal frequency. And a level demodulating circuit (30) for controlling the level adjusting circuit (30) to increase the level of the pulse output from the pulse generating circuit (3) when the recording mode signal is received and the carrier frequency is a high frequency. A high harmonic signal generating circuit (2) (3) which generates an odd harmonic signal of the input FM signal as a whole higher than a predetermined number is generated from the input FM signal, and the high harmonic signal is added to the input FM signal. Therefore, a bin 4 and a demodulator 5 for demodulating an FM signal superimposed with a pulse output from an adder, each of which obtains an FM signal whose polarity is the same as the polarity of each corresponding peak. FM demodulation circuit, characterized in that consisting of.

Images