JPS591039B2 - Multi-channel record phase lock droop - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a phase-locked loop for demodulating multi-channel records. In the phase-locked loop that demodulates the signal, the loop gain of the phase-locked loop (hereinafter abbreviated as PLL) at the high frequency (5kHz or more) of the modulation signal of the angle-modulated wave signal is attenuated. It is an object of the present invention to provide a phase head knockdown loop that reduces the transient response characteristics of a PLL in frequency and reduces abnormal noise that occurs when lock is lost.

FIG. 1 shows a block diagram of an example PLL(7)l.

Generally, when playing a multi-channel record, the PL
The angle modulated wave signal is demodulated using L. That is, in FIG. 1, the reproduced angle-modulated wave signal inputted from the input terminal 1 is supplied to the phase comparator 2, where the voltage-controlled oscillator (hereinafter referred to as VCO) whose center frequency is the carrier frequency of the angle-modulated wave signal is supplied to the phase comparator 2. ) is compared in phase with the signal from 5,
After being made into an error voltage according to these phase differences, it is supplied to the loop filter 3, where its high frequency components are attenuated. The signal taken out from the loop filter 3 is amplified by the DC amplifier 4 and then supplied to the VCO 5 as a control voltage to control its output oscillation frequency, while being taken out from the output terminal 6 as a demodulated signal of the angle modulated wave signal. It will be done. In this way, the PLL can be regarded as a type of filter, and has the characteristic of passing signals in a certain frequency range.

This is the capture range or lock range characteristic, and its passband (lock range) is determined according to the level of the input angle-modulated wave, and it is also possible to vary the range artificially. Therefore, the frequency characteristics of the demodulated signal are determined by the size of the lock range of the PLL. By the way, when playing a multi-channel record, there are many causes, including an abnormal top knob of the carrier of the angle-modulated wave signal to be reproduced, or overmodulation due to interference waves close to the carrier caused by harmonics of the direct wave signal. Shocking abnormal noise may occur in the reproduced sound of the multi-channel record due to cartridge tracing errors during reproduction. Therefore, in order to reduce and eliminate the above-mentioned noise, conventionally, the lock range of the PLL is set to be approximately equal to the shift frequency of the modulation signal, but narrower than that when an abnormal phenomenon occurs, thereby preventing abnormal rota and simultaneously increasing the demodulation signal. The apparent noise level is reduced by attenuating the frequency range (5k1Iz or higher). As is well known, the capture range or lock range of this PLL is determined by the loop gain of the PLL, and this loop gain is determined by the gain of the DC amplifier 4, the amount of passage through the loop filter 3, and the phase comparator 2, V
The main factor is the conversion gain of CO5. This PLL
As a method of varying the lock range by increasing or decreasing the loop gain of the loop filter, a method is usually used in which a desired lock range is obtained by mainly changing the characteristics of a loop filter and controlling its output signal. FIG. 2 shows a specific circuit of an example of a conventional loop filter.

In the figure, 7 is an input terminal connected to the output side of the phase comparator 2, and is connected to an output terminal 8 connected to the input side of the DC amplifier 4 via a resistor R1. A connection point between the resistor R1 and the output terminal 8 is grounded via a series circuit consisting of a capacitor C1 and a variable resistor R2. As a result, a loop filter is formed from a low-pass filter, and usually a variable resistor R
2, a desired frequency characteristic as shown in FIG. 3 can be obtained. That is, as shown in FIG. 3, the frequency characteristics of the lag lead filter conventionally used as the loop filter 3 as shown in FIG. 2 are as follows:
It is attenuated at 6dB/0ct only between the frequency F2 determined by the capacitance value of the capacitor C1 and the resistance value of the variable resistor R2,
At frequencies below 8 and above F2, the characteristics are flat.

The lock range characteristic of the PLL at this time is as shown by the solid line in FIG. Here, F in FIG. indicates the input angle modulated signal key 1/rear frequency. Furthermore, when the resistance value of the variable resistor R2 is made small, the frequency characteristic of the loop filter 3 becomes as shown by the broken line in FIG. The characteristics are varied as shown by the broken line in FIG.

Similarly, when the resistance value of the variable resistor R2 is further reduced, the frequency characteristics of the Loube filter 3 and the lock range characteristics of the PLL become as shown by the dashed-dotted lines in FIGS. 3 and 4, respectively. Normally, the frequency J2 shown in Fig. 3 is selected to be about 10Hz, and the output of the loop filter 3 increases or decreases uniformly at all frequencies, and as a result, the lock range depends on the frequency characteristics. It can be said that it does not have.

In other words, even if an angle-modulated wave signal whose carrier is modulated with a modulation signal of high frequency (51 dIz or more) enters the PLL, the carrier wave (carrier) is modulated with a modulation signal of mid-low frequency (approximately 21 dIz or less). Even if the angle-modulated wave signals modulated by the angle-modulated wave signals enter the PLL, these angle-modulated wave signals are always uniformly controlled.

Therefore, when playing a multi-channel record, if an angle-modulated wave signal whose carrier is modulated with a modulation signal with a large amount of energy distributed particularly in high frequencies (5kI]z or higher) enters the PLL, abnormal noise will occur. To prevent interference from the direct wave signal band to the angle-modulated wave signal band, the variable resistor R1 is varied so that its maximum deviation frequency is narrower than the lock range which is approximately equal to the deviation frequency of the modulated signal. DL also applies to abnormal angle modulated waves that are formed separately from the original angle modulated wave signals caused by the intrusion of waves.
Since the transient response of L is lowered, abnormal locking to the above-mentioned abnormally angle-modulated wave is prevented, and even if locking occurs, the demodulated signal high-frequency attenuation characteristic due to the PLL loop gain reduction reduces the apparent appearance. It has the advantage that the noise level is reduced and abnormal sounds are no longer perceptible to the auditory sense.

However, the modulation signal is particularly low-mid frequency (2k
If the shift frequency of this modulated signal exceeds the lock range, an apparent overmodulation phenomenon occurs due to the narrow lock range, and the angle-modulated wave Although P is normal,
Abnormal noise occurs in the demodulated signal of the LL due to the bead sound between the output of the VCO 5 and the input signal from the input terminal 1 as shown in FIG. 7A.

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. In other words, since the conventional PLL described above uniformly narrows the lock range, abnormal noise can be audibly ignored in the case of high-frequency modulation signals, but in the case of mid-low frequency modulation signals, the angle-modulated wave signal is normal. Despite this, the lock is lost and C
There was a drawback in that a bead sound was generated between the output signal and the input signal of the O5 and was aurally perceptible.

On the other hand, if the lock range is widened, the PLL will steadily maintain the lock state.

That is, the transient response is quick and no slip occurs, so if there is even a slight abnormality in the angle-modulated wave signal, abnormal noise is generated and becomes audible. Therefore, in this case, the PLL does not lose the lock due to the narrow lock range in the middle and low frequencies, but conversely, the modulation signal of the input angle modulated wave signal has a power distribution in the high frequency range. If there is a large amount of
Furthermore, since the frequency characteristic of the demodulated signal is not a high-frequency attenuation characteristic, there is a drawback that abnormal noise becomes audibly perceptible. The present invention eliminates the above-mentioned drawbacks, and the fifth
Each embodiment will be described below with reference to the figures.

FIG. 5 shows a specific circuit of a first embodiment of a loop filter applied to the PLL of the present invention. The present invention attenuates the loop gain of the PLL at high frequencies compared to the conventional one and lowers the transient response characteristics of the PLL. It is characterized by reducing abnormal noise at frequencies (approximately 2kIIz or less). In FIG. 5, the same parts as in FIG. 2 are given the same reference numerals.

A capacitor C3 whose one end is grounded is connected in parallel to a resistor R3, and a series circuit consisting of this resistor R3 and a capacitor C2 is connected in parallel to the resistor R2. As shown by the solid line 1 in FIG. 6, the frequency characteristics of the loop filter configured as described above are approximately flat at frequencies below f1 and at mid-low frequencies from F2 to 8, and between frequencies 8 and F2. At frequencies in a predetermined range of 8 or more, it has a characteristic of attenuating with a predetermined slope.

Here, frequencies Fl and f2 in the figure are respectively equal to frequencies Fl and f2 shown in FIG. 3, frequency f1 is determined by the resistance value of resistor R1 and capacitance value of capacitor C1, and frequency F2 is determined by the resistance value of resistor R2 and It is determined by the capacitance value of capacitor C1. Frequency 8 is about 5kI]z, mainly due to resistance R2
It is determined by the resistance value of C2 and the capacitance value of capacitor C2. As shown in FIG. 6, at eight high frequencies of 5k1Iz or higher, there is an attenuation amount of PdB compared to the conventional loop filter characteristics (indicated by the broken line).

Therefore, compared to a conventional PLL, the amount of input signal to the next stage of the loop filter 3 is smaller, which reduces the loop gain, and as a result, the lock range becomes narrower for the modulated signal to be demodulated around frequency J4. Become. As a result, the PLL of the present invention attenuates the high-frequency demodulated signal, and in addition, is audibly masked by superimposing it with the direct wave signal to reduce the apparent noise level. interference with the reduction can be prevented. This high-frequency demodulated signal sequentially changes as shown in FIG. 7D by solid line 1→dotted chain line→broken line. On the other hand, when the modulated signal to be demodulated is distributed in the middle and low frequencies, the PLL of the present invention
Since it has the same lock range as the conventional one, abnormal noise due to the above-mentioned overmodulation phenomenon occurs in the middle and low frequency demodulated signal.

However, since the PLL of the present invention has the loop gain attenuated at the high frequency, the transient response at the high frequency is reduced (slowed down). Therefore, the mid-low frequency demodulated signal having abnormal noise due to the bead between the VCO 5 and the angle modulated wave signal from the input terminal 1 as shown by a in FIG. 7A is different from the demodulated signal shown by b in FIG. Figure C to c
The signal then progresses to a demodulated signal as shown in . As a result, the intermediate frequency demodulated signal c exhibits the same phenomenon as the simple attenuation in the high frequency demodulated signal shown in FIG. Furthermore, in the PLL of the present invention, since the loop gain at high frequencies is small and the demodulation frequency characteristics also decrease at high frequencies, the angle modulated wave frequency component and its twice higher harmonics are Contains only a small amount of wave components.

Therefore, the configuration of the low-pass filter that extracts only the demodulated signal from the output of the PLL can be simplified. Figure 8 shows the PLL of the present invention.
FIG. 9 shows a specific circuit of a second embodiment of the loop filter applied to the PLL of the present invention, and FIG. 9 shows a specific circuit of the third embodiment of the loop filter applied to the PLL of the present invention.

In FIGS. 8 and 9, the same parts as in FIG. 6 are given the same reference numerals, and their explanations will be omitted. FIG. 8 is characterized in that a capacitor C4 is connected in parallel to the capacitor C1 and resistor R2 of the conventional lag lead filter shown in FIG.

As a result, this loop filter has frequency characteristics as shown in FIG. 6, and the frequency 8 is determined by the capacitance value of the capacitor C4 and the resistance value of the resistor R2. FIG. 9 is characterized in that a series circuit consisting of a capacitor C5 and a resistor R4 is connected in parallel to the series circuit consisting of the capacitor C1 and resistor R2.

The frequency characteristics of this loop filter are as follows:
As in the embodiment, the frequency F3 is as shown in FIG. 6, and the frequency F3 is mainly determined by the resistance value of the resistor R2 and the capacitance value of the capacitor C5. In each of the above embodiments, for convenience of explanation,
Although the loop filter 3 has been described as having a frequency characteristic as shown in FIG. 6, the structure is not limited to this, and P
In order to reduce the transient response characteristics at high frequencies of the LL, characteristics of other PLL component circuits other than the loop filter 3, such as the gain of the DC amplifier 4, the conversion gain of the phase comparator 2, and the CO5, may be varied. Of course.

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. In the demodulating phase locked loop, the loop gain at the high frequency of the modulation signal of the angle modulated wave signal is
Since the loop gain is selected to be smaller than the predetermined value that should have a lock range characteristic in the maximum deviation frequency range that is approximately equal to the maximum deviation frequency of the modulation signal, the transient response of the phase-locked loop at the above-mentioned high frequency is It is possible to reduce the abnormal noise caused by the bead sound between the voltage controlled oscillator and the input angle modulated signal that occurs in the mid-low frequency demodulated signal when the phased locked loop loses lock due to the deterioration of the characteristics, and the lock range at the above-mentioned high frequency is narrow. Therefore, it is possible to remove abnormal noise caused by jumping from the direct wave signal band into the angle modulated wave signal band that occurs in the high-frequency demodulated signal, and the frequency characteristics of the output demodulated signal of the phase-locked loop are similar to the high-frequency attenuation characteristics. Therefore, the amount of angle-modulated wave frequency components and twice the harmonic components included in the demodulated signal is small, and it is possible to easily configure a low-pass filter that extracts only the demodulated signal by the phase-locked loop. It has certain characteristics.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an example of a phase-locked loop, FIG. 2 is a diagram showing a specific circuit of an example of a loop filter applied to a conventional phase-locked loop, and FIG. FIG. 4 is a diagram showing the lock range characteristics of an example of a conventional phase lock loop.
FIG. 5 is a diagram showing a specific circuit of the first embodiment of the loop filter applied to the phase-locked loop of the present invention, and FIG.
This figure shows the frequency characteristics of FIG. 5, FIGS. 7A to 7D are demodulated signal waveform diagrams for explaining the operation of the phase-locked loop of the present invention, and FIGS. 8 and 9 are diagrams of the phase-locked loop of the present invention, respectively. It is a figure which shows the concrete circuit of the 2nd and 2nd Example of the loop filter applied to. 1... Angle modulated wave signal input terminal, 2...
...Phase comparator, 3...Loop filter, 5.
...Voltage controlled oscillator VCOl6...Output terminal.

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 height of the modulation signal of the angle-modulated wave signal is By selecting the loop gain in the range frequency to be smaller than the loop gain of the predetermined value that should have lock range characteristics in the maximum deviation frequency range approximately equal to the maximum deviation frequency of the modulation signal, A phase-locked loop for demodulating multi-channel records, characterized by reducing transient response characteristics at high frequencies.