JPH0282702A - Frequency demodulating circuit - Google Patents

Abstract

PURPOSE:To prevent the inverting phenomenon over all frequency ranges where a fundamental wave exists by faithfully reproducing a zero cross point when a frequency modulating wave signal with a high frequency modulating wave is demodulated. CONSTITUTION:When a reproducing FM signal (a) inputted from a terminal 1 is inputted to a fundamental wave peak detecting circuit 2, the fundamental wave peak detecting circuit 2 outputs information (b) to show the peak point of the fundamental wave component of a reproducing FM signal, a pulse generating circuit 3 generates a signal (c) at the rise edge of a signal (b) and generates a signal (d) at the fall edge. By inputting the signal (a) to a limitter circuit 4, a signal (e) is obtained, and by operating the signal (e) with the information of signals (c) and (d) at an arithmetic circuit 5, a signal (f) is obtained. Here, since the signal (f) restores a zero cross point at sections Z1 and Z2, the inversion phenomenon does not occur. Thus, the inversion phenomenon can be prevented over all frequency ranges where the FM fundamental wave exists.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to FMfi! in a magnetic recording/reproducing device. This relates to the No. 11 circuit, and is intended to prevent the inversion phenomenon that tends to occur particularly when reproducing an FM modulated wave signal with a high FM modulated wave.

Conventional technology In a magnetic recording and reproducing device that performs low carrier wave FM recording and reproduction and FM single-band wave reproduction, such as a consumer VTR,
When demodulating an FM modulated wave signal with a large FM modulation index,
The zero cross point cannot be faithfully reproduced in the FM demodulator, and an inversion phenomenon is likely to occur.

This means that the level of the lower sideband component J is the FM fundamental wave component J.
This occurs when the signal becomes larger than the 0(7) level, and when reproduction noise is superimposed, an inversion phenomenon occurs even when J<Jo due to the influence of the noise.

Conventionally, various demodulation methods have been proposed to reduce this inversion phenomenon.For example, as shown in Japanese Patent Laid-Open No. 189311/1983, the fundamental wave component of the reproduced FM signal is converted into a square wave by a limiter circuit. Then, after generating a pulse using this square wave and superimposing this pulse on the reproduced FM signal,
The second limiter circuit demodulates the signal. This will be explained using the block diagram in FIG. 12 and the waveform diagrams in FIGS. 13(A) to (J).

A fundamental wave component i is extracted from the reproduced FM signal by a bandpass filter 20 and delayed for a predetermined time to obtain a signal j. A signal j is applied to a limiter to obtain a signal k, and a pulse signal 1 is obtained from the signal. Here, the signal l is a pulse indicating information on the zero cross point of the fundamental wave signal j, which is essentially different from the present invention. Then, a signal m is obtained by superimposing a pulse l on the reproduced FM signal, and a zero crossing point exists even at a point where the degree of modulation is high, and no inversion phenomenon occurs.

However, even though the time information of signal 1, which is the time information of the zero cross point of signal j obtained by delaying the FMi main wave by a predetermined time, and the time information of the peak point of the reproduced FM signal waveform are essentially different time information, , superimposing them would distort the information contained in the FM signal, resulting in the following problems.

Currently, the FM allocation on the VTR is set to 5 to 7 MHz, with dark clips at 100% and white clips at 20%.
If it is 0%, the dark clip frequency is 3M) (z, the white clip frequency is 9 MHz, and the range where the fundamental wave exists is 3 to 9 MHz.

In other words, the inversion period of the fundamental wave is approximately 333/2 n5ee
It will change between ~111/2 nsec.

In Figure 13, the reproduced FM signal and fundamental wave signal are shown as i, the superimposed pulse waveform when the delay time is 100 nsec is shown as 1, and the waveform when superimposed is shown as m.

Looking at m, the phase relationship between the superimposed pulse and the reproduced wave shifts depending on the frequency. In other words, when the fundamental wave signal i has a low frequency, the peak points of the pulse and the fundamental wave signal coincide, but when the fundamental wave signal i has a high frequency, they deviate. Therefore, the zero cross cannot be restored at the χ1 point. First, so-called black blurring occurs, and an extra zero cross occurs at the χ2 point.So-called white blurring occurs.Next, we shorten the delay time, set it to 50nsec, and change the pulse waveform to 12. 0m where the waveform is shown in m2
2, it can be seen that white blurring occurs at the χ8 point. Furthermore, if the delay time is set short, the pulse waveform 12 will be superimposed near the zero-crossing point of the signal, which will change the waveform at the zero-crossing point of the reproduced FM signal, which will adversely affect the frequency characteristics after demodulation. is sufficiently considered,
It is not preferable to simply set the delay time short.

Furthermore, superimposing the above pulse waveform on the reproduced FM signal means that the maximum amplitude of the reproduced FM signal increases, and in a system such as an IC where the amplitude value is limited, the increase in the maximum amplitude of the FM signal is large. It was a problem.

Problems to be Solved by the Invention As described above, in the conventional example, the time information possessed by the zero cross point of the fundamental wave of the reproduced FM modulated wave is superimposed on the peak point of the FM reproduced signal, which is another time information, as the essential point. It's impossible,
The effect of preventing the inversion phenomenon is not established over the entire frequency range where the FM fundamental wave exists, and depending on the FM reproduction signal, it has not been possible to prevent inversion phenomena such as blurred blacks and blurred whites. Furthermore, an increase in the maximum amplitude of the FM signal has been a major problem in systems such as ICs where the amplitude value is limited.

Means for Solving the Problems In order to solve the above problems, the demodulation circuit of the present invention includes a peak detection circuit that detects the peak point of an FM modulated wave, and a demodulation circuit that responds to the rising or falling edge of the output signal of the peak detection circuit. a pulse generation circuit that generates pulses with minute widths, a limiter circuit that limits the FM modulated wave, an arithmetic circuit that inputs the output of the limiter circuit and the output of the pulse generation circuit, and calculates the output of the arithmetic circuit; It consists of a pulse counting circuit that counts pulses.

Effect of the present invention With the above-described configuration, the inversion phenomenon can be prevented over the entire frequency range in which the FM fundamental wave exists, and furthermore, since the maximum amplitude value of the reproduced FM signal is not increased, the amplitude of the IC, etc. This is extremely effective in systems with limited values.

EXAMPLE Hereinafter, one embodiment of the present invention will be described with reference to the drawings. A block diagram of the first embodiment of the present invention is shown in FIG. 1, and waveform diagrams corresponding to each part a y f are shown in FIG. A) ~ (F)
The reproduced FM signal a input from the terminal summer shown in FIG. 1 is input to the fundamental wave peak detection circuit 2. The fundamental wave peak detection circuit 2 outputs information indicating the peak point of the fundamental wave component of the reproduced FM signal. The pulse generating circuit 3 generates a pulse in the signal d at the rising edge of the signal C1 and at the falling edge of the signal C1, as shown in the signal C%d. Here, the pulse generation points of signals c and d coincide with the peak point of signal a.

By inputting the signal a to the limiter circuit 4, the signal e is obtained. In this signal e, the lower side band wave is too emphasized in sections Zl and Z2, so that a normal zero crossing is not performed and an inversion phenomenon occurs.

A signal f is obtained by calculating this signal e with the information of signals c and d in an arithmetic circuit 5. Here, the signal [is the section Zl, Z
Since the zero crossing point is restored in step 2, no inversion phenomenon occurs.By FM demodulating the signal f in pulse count circuit 6, a demodulated signal without inversion phenomenon can be obtained.

Here, the pulse count circuit 6 outputs pulses for a certain period of time from both edges of the input signal, and since it is well known, the explanation will be omitted.

Next, the first embodiment of the fundamental wave peak detection circuit 2 for detecting the peak point of the fundamental wave is shown in FIG. 3, and the waveforms of each part are shown in FIG.
As shown in A) to (D), the input FM playback signal a is passed through a bandpass filter BPF7 to extract the FM fundamental wave g, where the passband of BPF7 is set to approximately the deviation of the FM signal. In order to detect the peak value of the signal g, the signal g is differentiated by a differentiating circuit 8 to obtain the signal g. Here, the zero cross point of the signal g indicates the peak point of the signal g. Therefore, by limiting the signal by the limiter circuit 9, the signal can be obtained.

Here, the signal is the same as the signal in FIGS. 1 and 2. Here, the order of the BPF 7 and the differentiating circuit 8 may be changed.

Next, a first circuit example of the differentiating circuit 8 is shown in FIG. 5(A). FIG. 5(A) shows a differential circuit consisting of a resistor R and a capacitor C.

Next, a second circuit example of the differential circuit is shown in FIG. 5(B). This is composed of a delay circuit 10 that delays by a minute time and a comparator 11. The operation in Figure 5 (B) is shown in Figure 6.
This will be explained using the waveform diagram shown in the figure.

Here, the signals g, b, shown in FIG. 5B and FIG.
i corresponds to each. The FM fundamental wave color minute time can also be obtained by comparing the delayed signal i. Here, b is shifted from the peak point of the signal g by a minute interval t1 at most, but it is possible to make Ll negligibly small (for example, 20 nsec). Furthermore, since the output signal of the comparator 1O is already a square wave, there is an advantage that the limiter circuit 9 of FIG. 3 can be omitted when this configuration is used for the differentiating circuit 8 of FIG. 3.

Next, a second embodiment of the fundamental wave peak detection circuit 2 will be described. The BPF 7 extracts the FM fundamental color from the reproduced FM signal a, whose block diagram is shown in FIG. 7 and waveform diagrams are shown in FIGS. 8(A) to 8(D). The 90° shift circuit 12 shifts the phase of the signal g by 90° in the band where the FM fundamental color exists. This results in signal j. The zero cross point of signal j coincides with the peak point of signal g. That is, by limiting the signal J using the limiter circuit 9, the signal J can be obtained. Here, the 90° shift circuit 12 can be configured with a capacitor and a resistor, or can also be configured with a delay element.

An example of shifting the phase by 90° using a delay element is shown in FIG. 7(B).

The 901 shift circuit 12 shown in FIG. 7 is a type of comb filter, and the phase difference between the input signal and the signal j2 delayed by the time 2t2 is always 90° with respect to the signal 1 delayed by the time t2. Therefore, when the signal j1 is sent to the limiter circuit 4 and the signal j2 is sent to the BPF 7 to extract the fundamental wave j3, the zero cross point of this fundamental wave j3 coincides with the peak point of the signal j1. Become.

Therefore, by limiting the signal j3 with the limiter circuit 9, the signal j3 can be obtained. Here, it is assumed that the polarity of the signal is adjusted by the limiter circuit 9. In the configuration shown in FIG. 7(B), since the reproduction FMjl is also delayed by L2, the block diagram is slightly different from the block diagram shown in FIG. 1. This is due to the configuration of the 90° shift circuit and is not an essential problem of the present invention.

Next, a circuit example of the pulse generation circuit 3 and the arithmetic circuit 5 is shown in FIG. 9, and waveforms of each part are shown in FIGS. 10(A) to 10(H).

The pulse generating circuit 3 is composed of an inverter, an AND gate, and a NOR gate, and the arithmetic circuit 5 is composed of two NOR gates. Here, the signals a~[ are shown in FIG.
The signals correspond to signals a to f in the figure. Since the operation of each gate is obvious, the explanation will be omitted. Further, FIG. 9 shows one embodiment, and the circuits of the pulse generation circuit 3 and the arithmetic circuit 5 can be realized with other combinations of gates.

The fact that the pulse generation circuit 3 and the arithmetic circuit 5 can be realized entirely by digital processing is extremely advantageous for IC implementation. Further, as seen in the conventional example, since no other signal is added to the FM modulated wave before the limiter, deterioration of the C/N of the FM modulated wave and distortion of the demodulated waveform do not occur.

Here, in the first embodiment described above, the C/N of the BPF 7, which is a component of the fundamental wave peak detection circuit 2, is improved as the band becomes narrower because the amount of noise within the band is reduced.
The effect of improving the reversal phenomenon is significant. However, if it is too narrow, on the other hand, the FMM main wave will not be able to pass through, resulting in incomplete peak detection of the fundamental wave. Therefore, it may be configured to adaptively control the BPF band to an optimum value in accordance with the carrier frequency and C/N state of the reproduced FM signal. Information for control includes the output level of the reproduced FM signal and the recording mode of the recording/reproducing device (for example, for a VTR, is it standard recording or long-time recording?

Alternatively, standard records, high band records), etc. can be considered.

Next, it is conceivable that a slight delay may occur in the fundamental wave peak detection circuit 2 and the pulse generation circuit 2 according to the second embodiment of the present invention due to circuit calculations and filters. Therefore, in order to compensate for this minute delay, as shown in Figure 11,
Equalizer circuit 1 It is desirable to insert an equalizer circuit 13, which is a type of delay circuit, before the limiter circuit 4.
3, it is desirable that the group delay characteristic is constant and the frequency characteristic is at the lower end. However, it is also possible to use the characteristics of a low-pass filter that attenuates high-frequency components with poor C/N of the reproduced FM signal with the intention of further improving the S/N of the demodulated signal.
Conventionally, as a means of improving the S/N of the demodulated signal, it is known to attenuate the high frequency components of the reproduced FM signal at the stage before the demodulator 5. However, if the amount of attenuation is increased, an inversion phenomenon will occur, so the attenuation amount is too large. could not be made larger. However, by using the present invention, it is possible to increase the high-frequency attenuator of the equalizer circuit 13 and to increase the amount of S/N improvement after demodulation without causing the inversion phenomenon. In other words, the present invention also has the effect of improving S/N.

In addition, in the detection circuit 2, the band of the BPF 7 is made wide enough to include the FM sideband, and furthermore, the BPF 7 is omitted.
Differentiating circuit 8 calculates the peak point of the FM signal including sidebands.
Direct detection is also possible. In other words, the fundamental wave peak detection circuit 2 is considered to be an FM modulated wave peak detection circuit. In this case, the waveform deterioration of the demodulated signal is further improved, but since there is no band limitation in the BPF 7, there is no C/N improvement effect, and the reliability of the output signal of the limiter circuit 9 is also lower than in the above embodiment. It will become.

Further, in the embodiment, the demodulation circuit of a VTR has been described, but the demodulation circuit is not limited to this, and the demodulation circuit can be used for a disc.

It goes without saying that the present invention is effective for all FM demodulation circuits for FM broadcasting and the like.

Effects of the Invention As described above, the present invention includes a fundamental wave peak detection circuit that detects the peak point of the fundamental wave of FMf:11 waves, and a minute peak detection circuit that detects the peak point of the fundamental wave of the FMf:11 wave, and a minute a circuit that generates pulses of a certain width, a limiter circuit that limits the FM modulated wave, an arithmetic circuit that receives the output of the limiter circuit and the output of the pulse generator circuit as input, and counts the output of the arithmetic circuit as a pulse. By being composed of a pulse count circuit, it is possible to prevent the FM inversion phenomenon without changing the zero crossing point of the normal FM signal, and furthermore, without increasing the maximum amplitude of the FM reproduction signal. The present invention provides an FM demodulation circuit which is very advantageous in IC implementation because the main circuit can be realized by digital processing, and this effect is extremely large for VTRs and the like that perform FM single-band wave reproduction.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a first embodiment of the present invention, FIG. 2 is a waveform diagram of the first embodiment of the present invention, and FIG. 3 is a first embodiment of the fundamental wave peak detection circuit of the present invention. FIG. 4 is a waveform diagram of the first embodiment of the fundamental wave peak detection circuit of the present invention, FIG. 5 is a circuit diagram of the differentiation circuit in the fundamental wave peak detection circuit of the present invention, and FIG. A waveform diagram of the differentiating circuit in the fundamental wave peak detection circuit of the invention, FIG. 7 is a schematic diagram of the second embodiment of the fundamental wave peak detection circuit of the invention, and FIG. 8 is a waveform diagram of each part of FIG. 7. , Figure 9 is a circuit diagram of the pulse generation circuit and arithmetic circuit, Figure 1O is a waveform diagram of each part in Figure 9, and Figure 1
1 is a block diagram of a second embodiment of the present invention, FIG. 12 is a block diagram of a conventional example, and FIG. 13 is a waveform diagram of a conventional example. 2...Fundamental wave peak detection circuit, 3...
Pulse generation circuit, 4...Limiter circuit, 5...
... Arithmetic circuit, 6 ... Pulse count circuit, 7 ... Band pass filter, 8 ...
Differential circuit, 9... Limiter circuit, 10...
...Delay circuit, ll...Comparator, 12.
...90° shift circuit, 13... Equalizer circuit. Name of agent: Patent attorney Shigetaka Awano Haka 1 person 1 fig. 1 υ fig. Figure (b ~ Figure? Figure CD) Figure 10ffl LH) Chi Figure 11

Claims (9)

[Claims] (1) A peak detection circuit that detects the peak point of the FM modulated wave, a pulse generation circuit that generates a minute width pulse according to the rising or falling edge of the output signal of the peak detection circuit, and a pulse generating circuit that detects the peak point of the FM modulated wave. FM demodulation characterized by comprising a limiter circuit that limits, an arithmetic circuit that inputs and calculates the output of the limiter circuit and the output of the pulse generator circuit, and a pulse count circuit that counts the output of the arithmetic circuit as pulses. circuit. (2) The peak detection circuit is comprised of a differentiating circuit that differentiates the FM modulated wave, and a limiter circuit that limits the output signal of the differentiating circuit to detect a zero cross point. FM demodulation circuit described in ). (3) A fundamental wave peak detection circuit that detects the peak point of the fundamental wave of the FM modulated wave, and a pulse generation circuit that generates a pulse with a minute width according to the rising or falling edge of the output signal of the fundamental wave peak detection circuit. , a limiter circuit that limits the FM modulated wave, an arithmetic circuit that inputs the output of the limiter circuit and the output of the pulse generator circuit, and a pulse count circuit that counts the output of the arithmetic circuit as a pulse. An FM demodulation circuit characterized by: (4) The fundamental wave peak detection circuit includes a bandpass filter that passes the fundamental wave of the FM modulated wave, a 90° shift circuit that shifts the phase of the output signal of the bandpass filter by 90°, and a 90° shift circuit that shifts the phase of the output signal of the bandpass filter by 90°. 4. The FM demodulation circuit according to claim 3, wherein the FM demodulation circuit comprises a limiter circuit that limits the output signal and detects a zero cross point. (5) The fundamental wave peak detection circuit includes a bandpass filter that passes the fundamental wave of the FM modulated wave, a differentiation circuit that differentiates the output of the bandpass filter, and a limiter for the output signal of the differentiation circuit to detect the zero cross point. Claim (3) comprising a limiter circuit for detecting
FM demodulation circuit described in ). (6) The FM modulated wave is input to the limiter circuit after passing through a peak detection circuit or a fundamental wave peak detection circuit and an equalizer circuit having a delay time corresponding to the calculation time in the pulse generation circuit. The FM demodulation circuit according to claim 1 or 3. (7) Claim (7) characterized in that the equalizer circuit has a characteristic of attenuating high frequency components of the frequency of the FM modulated wave.
6) FM demodulation circuit as described. (8) The FM demodulation circuit according to claim 1 or 3, wherein the arithmetic circuit is composed of two NOR gates. (9) The differentiating circuit is composed of a delay circuit that delays an input signal by a minute time and a comparator, and the input signal and the output signal of the delay circuit are inputted to two inputs of the comparator to obtain a differentiated signal. The FM demodulation circuit according to any one of items (2) and (5).