JPS5916480B2 - Phase lock droop for multi-channel record demodulation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a phase-locked loop for demodulating multi-channel records. The signal is phase locked loop (
When demodulating using a PLL (hereinafter abbreviated as PLL) 5, especially when the modulation signal of the angle modulated wave signal is
The PLL loop gain at frequencies around kHz2) or high frequencies (frequencies around 8kHz and above) will not affect the closed loop outside the closed loop.
It is an object of the present invention to provide a PLL that suppresses generation of detuning noise by increasing or decreasing the detuning noise.

Figure 1 shows a conventional PLL for demodulating multi-channel records.
A block system diagram of one example is shown.

Input terminal 5 An angle-modulated wave signal reproduced from a multi-channel record enters from input terminal 5 and is supplied to a phase comparator 2, where the carrier wave center frequency fc of the angle-modulated wave signal is input.
It is phase-compared with a signal from a voltage-controlled oscillator (hereinafter abbreviated as VCO) 5 with a center frequency of Ru. The carrier wave component of the signal taken out from the amplifier 3 is attenuated by the loop filter 4, and the modulated signal component is taken out.The signal is output from the output terminal 6 as a demodulated signal of the angle modulated wave signal 5, while being controlled by the VCO 5. It is applied as a voltage to control its output oscillation frequency. The PLL consisting of the blocks 2 to 5 described above can be regarded as a type of filter, and has a characteristic of passing 0 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 input angle modulated wave signal level, and the frequency characteristic of the demodulated signal is determined by the size of the lock range of ηL. is determined. Further, the lock range can be varied artificially, and generally by increasing or decreasing the loop gain of the PLL, the lock range work is varied as shown by l or l in FIG. 2.

However, in the conventional PLL described above, it is difficult to vary the loop gain according to the content of the modulation signal of the angle-modulated wave signal. For example, when demodulating an angle-modulated wave signal obtained by modulating a carrier wave with a modulation signal with a large amount of energy distributed in high frequencies (around 8 kHz and above), the direct wave signal band ( For example, 20Hz~1
Harmonic distortion from about 5kHz) mixes into the angle-modulated wave signal band, interferes with the original angle-modulated wave signal, increases the frequency deviation, and also causes abnormal (pseudo) angle-modulated wave signals. There is a possibility that this may occur. For this reason, in conventional PLL,
In order to make the maximum shift frequency range of the lock range substantially equal to or narrower than the shift frequency of the input angle-modulated wave signal, demodulation is performed with a small loop gain. As a result, even if the above-mentioned abnormal angle modulated wave signal occurs, abnormal locking thereof is prevented, and a demodulated signal of high frequency as shown by the solid line in FIG. 5A is normally obtained from the output terminal 6, and the detuning noise is The rate of occurrence of this decreases. In addition, since the demodulated signal is close to the carrier wave center frequency, even if the lock is lost, the demodulated signal becomes a mere attenuated signal 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. In addition, it has the advantage that the apparent noise level is reduced and abnormal sounds are no longer perceptible to the auditory sense. On the other hand, the above modulation signal has a middle-low frequency (2kHz
If a lot of energy is distributed in nearby frequencies),
Since the frequency deviation of the angle-modulated wave signal itself is large, depending on the program source, even though the angle-modulated wave signal is normal, if the PLL's predetermined lock range is exceeded and an apparent overmodulation phenomenon occurs. To prevent this from happening, it is necessary to increase the loop gain to prevent lock loss. When the loop gain is increased, 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 above-mentioned apparent overmodulation phenomenon occurs without increasing the loop gain, the PLL demodulation signal may include the CO5 output and input terminals as shown by the broken line in Figure 3B. Abnormal noise is generated due to the bead with the input signal from 1, and can be perceived aurally as an extremely harsh sound. In this way, when the energy of the modulated signal is distributed mostly in high frequencies, demodulation is performed by reducing the loop gain and narrowing the lock range of the PLL.
On the other hand, if the distribution is mostly in the middle and low frequencies, mutually contradictory conditions are required, such as it is desirable to increase the loop gain and widen the lock range of the PLL for demodulation. It is difficult to change the loop gain depending on the content of the loop filter, and even if the loop filter in the latter stage has frequency characteristics and operates as described above, almost no effect will be obtained; on the other hand, since the loop filter is in a closed loop, the demodulated output will not be affected by it. appears, the output characteristics change, and the conventional PL
It was difficult for L to satisfy this requirement.

The present invention eliminates the above-mentioned drawbacks, and one embodiment thereof will be described below with reference to FIG. 4.

FIG. 4 shows a block diagram of one embodiment of a phase-locked loop for demodulating multichannel records according to the present invention. In the figure, the same parts as in FIG. 1 are designated by the same reference numerals, and their explanations will be omitted. The output signal of the loop filter 4 is applied to the loop gain control circuit 9 and also to the bandpass filter 7, where only the middle and low frequency components around 2 kHz are passed through. The output signal of this bandpass filter 7 is rectified by a rectifier circuit 8 and applied to the loop gain control circuit 9 as a control voltage corresponding to the signal component. Thereby, the loop gain control circuit 9 varies the output signal amount to the CO5 of the loop filter 4 and the output terminal 6, and as a result, the loop gain is controlled. P shown in Figure 4
The lock range of LL is designed to suppress noise generation due to abnormal lock when 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. , has been selected relatively narrowly.

When a modulated signal has a medium-low frequency and an angle-modulated wave signal with a frequency deviation larger than the predetermined lock range enters the PLL of the present invention, the steps 7 to 9 described above are executed.
As a result, the output signal level of the loop filter 4 to CO5 becomes large, and the loop gain is controlled to be large.
For L, the lock range is widened and loss of lock is prevented. Therefore, the occurrence of extremely unpleasant detuning noise as shown by the broken line in FIG. 3B is suppressed, and the input angle-modulated wave signal is normally demodulated. Here, since the band filter 7 and the rectifier circuit 8 are provided outside the closed loop, they have almost no influence on the closed loop. In addition, in FIG. 4, instead of the band filter 7, a high-pass filter that passes only high-frequency components (frequencies around 8 kHz and above) is used, and as the output signal amount of the high-pass filter increases, the loop The gain control circuit 9 may be configured to control the output signal level of the loop filter 4 to the CO 5 to be low.

Further, the maximum deviation frequency range of the PLL opening range shown in FIG. 4 at this time is selected to be approximately equal to or slightly wider than the deviation frequency of the input angle-modulated wave signal. As a result, when a modulated signal has a high frequency and an angle-modulated wave signal with a frequency deviation larger than the above-mentioned predetermined lock range is input, the input signal amount of the VCO 5 is reduced and the loop gain is reduced. As a result, the lock range of the PLL is narrowed.

Therefore, it is possible to prevent abnormal locking of the abnormal angle modulated wave signal, which may occur due to harmonic distortion from the direct wave signal band being mixed into the angle modulated wave signal band, and to suppress the occurrence of detuning noise. . In addition, since the lock range of the PLL in this case is selected to be relatively wide, the angle-modulated wave signal, which has many middle and low frequency components in the modulation signal, is less likely to suppress the apparent overmodulation phenomenon than the conventional PLL. This does not occur and the demodulation is performed normally. As mentioned above, the phase-locked loop for demodulating multi-channel records according to the present invention reproduces the angle-modulated wave signal reproduced from a multi-channel record in which the direct wave signal and the angle-modulated wave signal are multiplexed and recorded. The demodulating phase-locked loop receives as an input signal the output signal of the loop filter that suppresses the carrier component of the angle-modulated wave signal and passes the demodulated signal component. a rectifier circuit that rectifies the output signal of the filter circuit; and a rectifier circuit that receives the output signal of the loop filter as an input signal and varies the loop filter output signal level in accordance with the output signal of the rectifier circuit. One side is taken out as a demodulated output signal,
The other is provided with a loop gain control circuit that applies a control voltage to the voltage controlled oscillator, and variably controls the loop gain according to the modulation signal of the mid-low frequency component (or high frequency component) of the angle modulated wave signal. Since the angle-modulated wave signal is demodulated while the above-mentioned angle-modulated wave signal is demodulated, it is particularly difficult to use when the angle-modulated wave signal is input, which is a modulated signal that has many middle and low frequency components and has a large frequency deviation that exceeds the predetermined target range. By increasing the loop gain, the head range can be widened to prevent out-of-lock, and by preventing out-of-lock of this angle-modulated wave signal, the detuning noise caused by out-of-lock, which is particularly unpleasant, can be reduced. It is possible to suppress the occurrence of detuning noise when demodulating a mid-low frequency modulated signal, and it is also possible to suppress the occurrence of detuning noise when demodulating a modulated signal in the middle and low ranges, and to input an angle-modulated wave signal of a modulated signal that has many high frequency components and has a large frequency deviation exceeding a predetermined reduction range. If a problem occurs, the loop gain is lowered and harmonic distortion from the direct wave signal band mixes into the angle modulated wave signal band, thereby preventing abnormal locking of the abnormal angle modulated wave signal. It has the advantage of being able to suppress the generation of abnormal noise that occurs during locking, and because the filter circuit and rectifier circuit are provided outside the closed loop, the angle modulated wave signal can be demodulated without adversely affecting the closed loop.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an example of a conventional phase-locked loop, Fig. 2 is a diagram showing the lock range characteristics of an example of a phase-locked loop, and Figs. 3A and B respectively explain the operation of Fig. 1. FIG. 4 is a block system diagram of one embodiment of the phase-locked loop according to the present invention. 2... Phase comparator, 4... Loop filter, 5... Voltage controlled oscillator (CO), 7...
...Band filter (or high-pass filter), 8...
... Rectifier circuit, 9... Loop gain control circuit.

Claims (1)

[Claims] 1. In a phase-locked loop that demodulates 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, the carrier wave component of the angle-modulated wave signal is A filter circuit that receives as an input signal the output signal of a loop filter that suppresses and passes the demodulated signal component, and passes only the middle and low frequency components (or high frequency components), and a rectifier that rectifies the output signal of the filter circuit. a circuit, receiving the output signal of the loop filter as an input signal, varying the level of the loop filter output signal in accordance with the output signal of the rectifier circuit, and outputting one of the signals to the outside as a demodulated output signal;
The other is provided with a loop gain control circuit that applies a control voltage to the voltage controlled oscillator, and variably controls the loop gain according to the modulation signal of the mid-low frequency component (or high frequency component) of the angle modulated wave signal. A phase-locked loop for demodulating a multi-channel record, characterized in that it demodulates the angle-modulated wave signal.