JPS5934040B2 - Multi-channel record demodulation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multi-channel record demodulation circuit, which phase modulates an angle-modulated wave signal reproduced from a multi-channel record in which a direct wave signal and an angle-modulated wave signal are multiplexed and recorded. Locked loop (hereinafter abbreviated as PLL)
When demodulating the angle-modulated wave signal, it is possible to prevent the angle-modulated wave signal from losing lock on the normal angle-modulated wave signal, which has a large frequency deviation exceeding the lock range of the PLL, especially in the mid-low range, without causing detuning noise. It is an object of the present invention to provide a demodulation circuit that can demodulate signals satisfactorily.

Figure 1 shows a conventional multi-channel record demodulation circuit.
An example block diagram is shown.

Reference numeral 1 denotes an input terminal for an angle-modulated wave signal reproduced from a multi-channel record, and the angle-modulated wave signal inputted from this is supplied to a phase comparator 2, where the angle-modulated wave signal is centered at the carrier frequency fc of the angle-modulated wave signal. The signal is phase-compared with a signal from a voltage-controlled oscillator (hereinafter abbreviated as VCO) 5, which has a frequency, and is made into an error voltage according to the phase difference between them, and is then supplied to an amplifier 3 and amplified.

The signal extracted from the amplifier 3 is passed through a loop filter 4
After high-frequency components are attenuated at , it is supplied to the VCO 5 as a control voltage to control its output oscillation frequency, and is taken out from an output terminal 6 as a demodulated signal of the angle-modulated wave signal. In this way, each of the blocks 2 to 5 constitutes a PLL, and this PLL can be regarded as a type of filter, and has a characteristic of passing signals in a certain frequency range.

This is the capture range or lock range characteristic, and its pass band (lock range) is determined according to the level of the input angle modulated wave, and therefore the frequency characteristic of the demodulated signal is determined by the size of the lock range of the PLL. Furthermore, the lock range can be varied artificially, and generally by increasing or decreasing the loop gain of the PLL, the lock range is varied as shown by l or in FIG. 2. However, in the conventional demodulation circuit described above, it is difficult to vary the loop gain according to the content of the modulation signal. When demodulating the angle-modulated wave signal obtained in this way, harmonic distortion from the direct wave signal band mixes into the angle-modulated wave signal band and interferes with the original angle-modulated wave signal. In order to increase the frequency deviation and potentially generate an abnormal (pseudo) angle-modulated wave signal, the loop gain is adjusted to make the maximum deviation frequency range of the lock range narrower than the deviation frequency of the angle-modulated wave signal. need to be small.

As a result, even if the above-mentioned abnormal angle modulated wave signal occurs, abnormal locking thereof is prevented, and a demodulated signal of a high frequency as shown by the solid line in FIG. will never occur. Furthermore, even if the lock is lost, the demodulated signal becomes as shown by the broken line in Figure 3A due to the high-frequency attenuation characteristics of the demodulated signal due to the decrease in the loop gain of the PLL, and the apparent noise level decreases, which improves the audibility. , the feature is that abnormal sounds are no longer recognized. On the other hand, the above modulation signal has a middle-low frequency (1kI
1z to 3kHz), the frequency deviation of the angle modulated wave signal itself is large, so depending on the program source, the lock range of the PLL may change even though the angle modulated wave signal is normal. In order to prevent an apparent overmodulation phenomenon from occurring beyond this value, it is necessary to increase the loop gain to prevent lock loss.

By increasing the loop gain to prevent lock loss, a demodulated signal of medium and low frequencies as shown by the solid line in FIG. 3B is output from the output terminal 6. However, if the apparent overmodulation phenomenon described above occurs without increasing the loop gain, the output of CO5 and the input terminal 1 as shown by the broken line in FIG. Abnormal noise occurs due to the bead with the input signal. This abnormal noise is different from the case of the above-mentioned high-frequency modulation signal, and can be perceived audibly as an extremely harsh sound. On the other hand, if the lock range of the PLL is widened, the PLL steadily maintains the locked state.

That is, since the transient response is quick and no reslip occurs, if there is even a slight abnormality in the angle-modulated wave signal, abnormal noise is generated and audible. Therefore, the PLL in this case does not suffer from lock loss due to the narrow lock range of the modulation signal in the middle and low frequencies. However, conversely, if the modulation signal of the input angle-modulated wave signal has a lot of energy distribution in the high range, it will respond even to a slight abnormality, and harmonic distortion from the direct wave signal band will cause the angle-modulated wave signal to be modulated. It also locks onto the abnormally angle-modulated wave signal that occurs when it mixes into the wave signal band, and furthermore, since the frequency characteristics of the demodulated signal are not high-frequency attenuation characteristics, the abnormal noise is audibly recognized. As described above, conventional demodulation circuits using PLL control the loop gain according to the modulation signal frequency, making it difficult to increase or decrease the lock range of the PLL, and the drawback is that abnormal (detuning) noise may be audibly perceptible. It was hot.

The present invention eliminates the above-mentioned drawbacks, and is shown in FIGS. 4 and 5.
One embodiment will be described with reference to FIGS. A and B.

FIG. 4 shows a block diagram of one embodiment of the multi-channel record demodulation circuit according to the present invention.

In the figure, a reproduced angle modulated wave signal from a multi-channel record inputted from an input terminal 7 is supplied to a frequency converter 8, where it is frequency-converted by multiplication with an output signal from a VCO 5, which will be described later. It is applied to a bandpass filter 10 through an amplifier 9. The frequency-converted angle-modulated wave signal whose lower sideband is removed and only the upper sideband is passed through the bandpass filter 10 is applied to the next stage phase comparator 11, where it is in phase with the output signal of the VCOl 8, which will be described later. be compared. That is, the angle-modulated wave signal from the input terminal 7 is applied to the phase comparator 11 with its frequency shift ratio compressed. For example, if the input angle modulated wave signal band is 30kHz±10kHz1C015 and the output center frequency is 150kHz, the band filter 1
0 output angle modulated wave signal band is 180kHz±10k
Hz, and the ratio of frequency deviation with respect to the carrier wave center frequency is compressed from ±33% to ±5.5%. The output signal of the phase comparator 11 is passed through the amplifier 12 to the output terminal 19.
On the other hand, the output signal of the amplifier 12 is applied to CO15 as an oscillation frequency control voltage through an amplifier 13 and an external loop filter 14, respectively. As a result, the blocks 8 to 15 each constitute a first feedback loop, and the amplifier 13 and the external loop filter 14
and VCO15 constitute a first gain setting circuit that varies the loop gain of this first feedback loop. In this embodiment, the external loop filter 14 has a frequency characteristic that allows the entire demodulated signal band to pass through, and the loop gain of the first feedback loop is determined by the first gain setting circuit based on the frequency deviation of the input angle-modulated wave signal. The first feedback loop is selected to have a relatively small amount so as to be slightly narrow, thereby slowing down the transient response of the first feedback loop. Therefore, this feedback loop is less susceptible to interference due to harmonic distortion from the direct wave signal band mixed into the input angle modulated wave signal, and even if lock is lost, the apparent noise level is reduced due to the high frequency attenuation characteristics of the demodulated signal. Can be reduced.
Further, the output signal (demodulated signal) of the amplifier 12 is applied as a control voltage to the VCO 18 through an amplifier 16 and an internal loop filter 17, respectively, to control its output oscillation frequency.

As a result, the phase comparator 11, amplifiers 12, 16, internal loop filter 17, and VCO18 each constitute a second feedback loop (PLL), and the loop gain of this second feedback loop is the same as that of the amplifier 16, internal loop filter 17, and VCO18. 17 and a second gain setting circuit consisting of VCO18. Here, the frequency characteristic of the loop filter 17 is selected so as to pass a signal portion of the demodulated signal that particularly contains a large amount of middle and low frequency components. Therefore, the loop gain of this PLL is determined by the internal loop filter 1 especially when demodulating an angle modulated wave signal modulated with a modulation signal in which a large amount of energy components are distributed in the middle and low frequencies.
7, the lock range will be expanded. As a result, the angle-modulated wave signal inputted from the input terminal 7 is transmitted to the first feedback circuit whose lock range is selected to be relatively small for interference waves generated due to the mixing of the high-frequency distortion into the angle-modulated wave signal band. The loop allows normal demodulation without abnormal locking.

The normal demodulated signal waveform when the modulated signal has a high frequency is as shown by the solid line in Figure 5A, and the normal demodulated signal waveform when the modulated signal has a middle to low frequency is shown by the solid line in Figure 5B. It will be as shown. On the other hand, when an angle-modulated wave signal with a frequency deviation exceeding the lock range of the first feedback loop enters the input terminal 7, the lock is lost, but the modulated signal has a large amount of energy distributed in the high frequency range. When the demodulated signal is close to the carrier center frequency,
For example, as shown by the broken line in FIG. 5A, a simply attenuated demodulated signal with a high frequency is obtained.

Furthermore, when the modulated signal has a large amount of energy distributed in the middle and low frequencies, the loop gain of the second feedback loop increases and its lock range expands, making it difficult for the lock to go out of order. As shown by the broken line in B, the rate of noise generation can be suppressed. In addition, frequency conversion is performed by multiplying the input angle-modulated wave signal by the output modulated by the feedback signal from the first feedback loop, and the relative phase difference is compressed by the negative feedback loop gain. By reducing the frequency deviation range, the lock range of the second feedback loop can be relatively expanded and lock loss can be prevented.

Note that even if the loop filters 14 and 17 are replaced, the desired purpose can be achieved.

As described above, the multi-channel record demodulation circuit according to the present invention is a circuit for demodulating the angle-modulated wave signal reproduced from a multi-channel record in which a direct wave signal and an angle-modulated wave signal are multiplexed and recorded. , first and second voltage-controlled oscillators each oscillate at a predetermined center frequency, and frequency-converts the angle-modulated wave signal using the output signal of the first voltage-controlled oscillator to reduce the frequency deviation with respect to the carrier wave center frequency. a frequency deviation ratio compression circuit that outputs an angle-modulated wave signal whose ratio is smaller than that of the input angle-modulated wave signal, and an output signal of this compression circuit and an output signal of the second voltage-controlled oscillator. a phase comparator that compares the phases and outputs the resulting signal as a demodulated signal; ), which receives the output signal of the phase comparator as an input signal, passes only its middle and low frequency components, and applies the signal to the second (or first) voltage controlled oscillator. The second filter reduces the absolute amount of frequency deviation of the input angle-modulated wave signal when the energy components of the modulated signal are largely distributed in the middle and low frequencies. In order to demodulate the input angle modulated wave signal, a first (or second) compression circuit comprising the above compression circuit having an independent lock range depending on the frequency component of the modulation signal of the input angle modulated wave signal, a phase comparator, a first voltage controlled oscillator and a first (or second) filter is used. 1
and a second feedback loop consisting of the phase comparator, the second voltage controlled oscillator, and the second (or first) filter are separately controlled to generate the angle modulated wave signal. can be demodulated, and the first (or second)
) feedback loop prevents the generation of abnormal noise due to the mixing of harmonic distortion from the direct wave signal band into the angle modulated wave band, and also reduces the apparent detuning because the frequency characteristics of the demodulated signal become high-frequency attenuation characteristics. The second (or first) feedback method can reduce the noise level and at the same time reduce the leakage of the carrier center frequency component and twice its harmonic components in the demodulated signal, and also has a large lock range, especially in the middle and low frequencies. The loop prevents and removes the apparent overmodulation phenomenon during demodulation of the angle-modulated wave signal when the modulated signal has a large amount of energy distributed in the middle and low frequencies. It has many features such as being able to reduce the separation noise in the center, and in addition, the above frequency deviation ratio compression circuit can relatively expand the lock range, preventing the angle modulated wave signal with a large frequency deviation from going out of lock. It is something that you have.

[Brief explanation of drawings]

Figure 1 is a block system diagram of an example of a conventional circuit, Figure 2 is a diagram showing an example of the lock range characteristics of Figure 1, and Figures 3A and B.
are demodulated signal waveform diagrams for explaining the operation of FIG. 1, FIG. 4 is a block system diagram of one embodiment of the circuit of the present invention, and FIGS. 5A and B are demodulated signal waveform diagrams for explaining the operation of FIG. 4, respectively. be. 1, 7... Angle modulated wave signal input terminal, 2, 1
1... Phase comparator, 5, 15, 18...
・Voltage controlled oscillator, 10...Band filter, 1
4...External loop filter, 17...
Internal loop filter.

Claims (1)

[Claims] 1. In a circuit that demodulates the above-mentioned angle-modulated wave signal reproduced from a multi-channel record in which a direct wave signal and an angle-modulated wave signal are multiplexed and recorded, the first and second waves each oscillate at a predetermined center frequency. and a voltage controlled oscillator, and the frequency of the angle modulated wave signal is converted by the output signal of the first voltage controlled oscillator so that the ratio of frequency deviation with respect to the carrier wave center frequency is smaller than that of the input angle modulated wave signal. a frequency shift ratio compression circuit that outputs an angle-modulated wave signal; a phase comparison is made between the output signal of the compression circuit and the output signal of the second voltage-controlled oscillator, and the resulting signal is output as a demodulated signal. a first filter that receives the output signal of the phase comparator as an input signal, passes substantially the entire frequency band of the demodulated signal, and applies the signal to the first (or second) voltage controlled oscillator; A second filter receives the output signal of the phase comparator as an input signal, passes only the middle and low frequency components thereof, and applies the filter to the second (or first) voltage controlled oscillator. A multi-channel record demodulation circuit is characterized in that it demodulates an input angle-modulated wave signal by reducing the absolute amount of frequency shift of the input angle-modulated wave signal when the angle-modulated wave signal is largely distributed in the middle and low frequencies.