JPS591038B2 - 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, and in particular, the present invention relates to a phase-locked loop for demodulating multi-channel records. In a phase-locked loop (hereinafter abbreviated as PLL) that demodulates a wave signal, abnormal noise is removed by increasing the loop gain of the phase-locked loop in the middle and low frequencies of the modulated signal of the angle-modulated wave signal. The present invention also aims to provide a phase-locked loop in which the influence of interference waves from the direct wave signal band to the angle-modulated wave signal band is reduced by reducing the loop gain at the high frequency of the modulated signal. purpose.

FIG. 1 shows a block system diagram of an example of a PLL.

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 a voltage-controlled oscillator (hereinafter referred to as VCO) whose center frequency is the carrier frequency of the angle-modulated wave signal is supplied. After being phase-compared with the signal from (omitted) 5 and made into an error voltage according to their phase difference, it is supplied to the loop filter 3, where its high frequency components are attenuated. The signal extracted from the loop filter 3 is sent to a DC amplifier 4.
After being amplified, it is supplied to the VCO 5 as a dividing voltage to control its output oscillation frequency, and is taken out from the output terminal 6 as a demodulated signal of the angle-modulated wave signal.

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 the range can also be artificially varied.Therefore, the PLL lock The frequency characteristics of the demodulated signal are determined by the size of the range.By the way, when playing a multi-channel record, there is an abnormality in the carrier of the angle-modulated wave signal to be reproduced, or if the carrier is close to the carrier due to harmonics of the direct wave signal. Abnormal noise may occur in the playback sound of the multi-channel record due to overmodulation caused by interference waves.Therefore, in order to reduce and eliminate the above noise, conventionally, the lock range of the PLL was set to the maximum deviation of the modulating signal. By making it approximately equal to the frequency or narrower than it when an abnormal phenomenon occurs, abnormal locking is prevented and, at the same time, the high frequency (near 8K1Iz) of the demodulated signal is attenuated to reduce the apparent noise level.

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 booster 4 and the loop filter 3.
The main factors are the amount of passage of CO5 and the conversion gain of the phase comparator 2 and CO5. As a method of varying the lock range by increasing or decreasing the loop gain of the PLL, 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, the loop filter is established as a reduction filter, and usually the variable resistance 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 f1 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, Fc in FIG. 4 indicates the carrier frequency of the input angle-modulated wave signal. 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 loop filter 3 and the lock range characteristics of the PLL become as shown by the dashed lines in FIGS. 3 and 4, respectively. Normally, the frequency F2 shown in Fig. 3 is selected to be about 10 Hz, and the output of the loop filter 3 increases or decreases uniformly at all frequencies, and as a result, the lock range has frequency characteristics. It can be said that it is not.

In other words, even if an angle-modulated wave signal whose carrier is modulated with a modulation signal of high frequency (around 80Hz) enters the PLL, the carrier wave (carrier) is modulated with a modulation signal of mid-low frequency (around 2Kkg 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, an angle-modulated wave signal whose carrier is modulated with a modulation signal that has a lot of energy distributed especially in high frequencies (around 8 degrees), such as cymbal sounds, enters the PLL. In this case, in order to prevent abnormal noise, the angle-modulated wave can be changed from the direct wave signal band by varying the variable resistor 8 so that its maximum deviation frequency is narrower than the lock range that is approximately equal to the deviation frequency of the modulating signal. The transient response of the PLL also decreases to abnormal angle modulated waves that are formed separately from the original angle modulated wave signal caused by interference waves entering the signal band. At the same time, abnormal lock is prevented, and even if lock is lost, the high-frequency attenuation characteristics of the demodulated signal due to the decrease in the loop gain of the PLL reduce the apparent noise level and the abnormal sound becomes unrecognizable. It has the following features.

However, if the above modulation signal has a lot of energy distributed especially in the middle and low frequencies (around 20Hz or less), such as a trumpet sound, and the deviation frequency of this modulation signal exceeds the lock range, the An apparent overmodulation phenomenon occurs due to the narrow lock range, and abnormal noise as shown in FIG. 5B occurs in the PLL demodulated signal even though the angle-modulated wave is normal.

This abnormal noise is different from the case of the above-mentioned high frequency modulation signal shown in FIG. 5A, and can be audibly perceived 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, there was a drawback that the lock was lost and a bead sound was generated between the output signal of the VCO 5 and the input signal of the PLL, which was audibly perceptible. On the other hand, if the lock range is widened, the PL
L continues to steadily hold the locked 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 near the middle and low frequencies, but on the contrary, the modulation signal of the input angle modulated wave signal has an energy distribution in the high frequency range. If it has a large number of signals, it will respond to even the slightest abnormality, interference waves will jump from the direct wave signal band to the angle modulated wave band, and the frequency characteristics of the demodulated signal will have high-frequency attenuation characteristics. This has resulted in the disadvantage that abnormal noise becomes audibly perceptible. The present invention eliminates the above-mentioned drawbacks, and one embodiment thereof will be described with reference to FIG. 6 and subsequent figures.

FIG. 6 shows a specific circuit of a first embodiment of a loop filter applied to the PLL of the present invention. The present invention is characterized in that by setting the frequency characteristics of the loop filter to predetermined characteristics, the above-mentioned mutually contradictory characteristics during multi-channel record reproduction can be improved. In FIG. 6, 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. 7, the frequency characteristics of the loop filter configured as described above are approximately flat at frequencies below f1 and from frequencies F2 to F3, and have a predetermined slope from f1 to F2 and at frequencies above f'3. It has a characteristic of attenuating at .

Here, the frequencies Fl and f2 are the frequencies Fl and f2 shown in FIG.
respectively equal to f2. Frequency F3 is a mid-range frequency of about 2KIIz, and the loop gain at this frequency F is 7th.
The gain is increased by 9 dB compared to the gain of the loop filter 3 in FIG. 2, which is indicated by a broken line in the figure. Therefore, the present invention P
LL has a larger loop gain than conventional ones for angle-modulated wave signals whose modulation signals are mostly distributed near the mid-range frequency F3, and the lock range is as shown by the dashed line in Fig. 8, and as shown by the solid line in the same figure. The lock range is wider than that of the conventional PLL shown in FIG. Also, the frequency indicated by F4 in Figure T is 8Vk,
The gain at this frequency F4 is attenuated by PdB compared to the gain of a conventional loop filter.

As a result, compared to the conventional PLL, the loop filter 3
The amount of input signal to the next stage decreases, so the loop gain decreases, and as a result, the lock range narrows around frequency F4, as shown by the broken line in FIG. Therefore, the PLL of the present invention can prevent abnormal noise from occurring due to the overmodulation phenomenon by setting a wide lock range that satisfies the shift frequency of the modulation signal in the middle and low frequencies, and narrow the lock range in the high frequencies. By setting this, it is possible to attenuate the high frequency demodulated signal and reduce the apparent noise level, while at the same time preventing interference from the direct wave signal band to the angle modulated wave signal band.

Furthermore, since the loop gain at high frequencies is small and the demodulation frequency characteristics also deteriorate at high frequencies, the amount of angle-modulated wave frequency components and twice their harmonic components included in the output demodulated signal of the PLL is small. Less is. Therefore, the configuration of the low-pass filter that extracts only the demodulated signal from the output of the PLL can be simplified. In addition, in FIG. 7, the frequency f1 is determined by the resistance value of the loop filter resistor R1 and the capacitor C shown in FIG.
1, the frequency F2 is determined mainly by the resistance value of the resistor R2 and the capacitance value of the capacitor C1, and the frequency f'3 is determined mainly by the capacitance values of the resistor R2 and the capacitor C2.
FIG. 9 shows a specific circuit of a second embodiment of the loop filter applied to the PLL of the present invention, and FIG. 10 shows a specific circuit of the third embodiment of the loop filter applied to the PLL of the present invention.

In FIGS. 9 and 10, the same parts as in FIG. 6 are designated by the same reference numerals, and their explanations will be omitted. Figure 9 shows the capacitor C1 and resistor R2 of the conventional lag lead filter shown in Figure 2.
The feature is that a capacitor C4 is connected in parallel to the .

As a result, this loop filter has frequency characteristics as shown in FIG. 7, and the frequency Fl3 is determined by the capacitance value of the capacitor C4 and the resistance value of the resistor R2. Therefore, similarly to the first embodiment, the PLL using the loop filter of this embodiment has lock range characteristics as shown by the dashed line and dashed line in FIG. 8, respectively. Figure 10 shows the above capacitor C.
1 and resistor R2 are connected in parallel with a series circuit consisting of capacitor C5 and resistor R4.

The frequency characteristics of this loop filter are as follows:
As in the embodiment, the result is as shown in FIG. 7, and the frequency f'3
is mainly determined by the resistance value of resistor R2 and the capacitance value of capacitor C5. As a result, the PLL using the loop filter of this embodiment has lock range characteristics as shown by the dashed line and dashed line in FIG. 8, respectively, as described above.
In each of the above embodiments, for convenience of explanation, the loop filter 3 was explained to have a structure having frequency characteristics as shown in FIG. Of course, it is also possible to vary the characteristics of the loop configuration circuit, such as the conversion gain of the VCO 5, so that the loop gain of the PLL is large in the middle and low frequencies and small in the high frequencies. .

In addition, in the frequency characteristics of the loop filter shown in FIG. 7, the characteristics are approximately flat in the middle and low frequencies from frequency F2 to f'3, but the characteristics have a peak at frequencies near the middle frequency F3. It may be set as a characteristic.
As described above, the phase-locked loop for demodulating multi-channel records according to the present invention can reproduce 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 loop gain in the middle and low frequencies of the modulation signal is set to be larger than a predetermined value of the loop gain that should have lock range characteristics in the maximum deviation frequency range that is approximately equal to the maximum deviation frequency of the modulation signal, and Since the loop gain at the range frequency is made smaller than the predetermined value, it is possible to obtain a lock range characteristic that corresponds to the frequency of the error voltage (demodulated signal) from the phase comparator forming the phase-locked loop. Since the lock range characteristics can be controlled by the information of the demodulated signal, the apparent overmodulation phenomenon of the above modulation signal, where energy is particularly distributed in the middle and low frequencies, such as a trumpet sound, can be prevented and eliminated by widening the lock range. For example, for the above modulated signal where a lot of energy is distributed in the high frequency range, such as a cymbal sound, by narrowing the lock range, the transient response of the phase locked loop is slowed down and the high frequency demodulated signal is attenuated. This reduces the apparent noise level and at the same time prevents interference from the direct wave signal band to the angle modulated wave signal band.Furthermore, since the frequency characteristics of the phase-locked loop demodulated signal have high-frequency attenuation characteristics, It has the advantage of being able to reduce the leakage of the carrier frequency component and its double harmonic component, and therefore simplifying the design of a reduction filter that extracts only the demodulated signal from the output of the phase-locked loop. .

[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-locked loop.
FIGS. 5A and 5B are demodulated signal waveform diagrams in the high and mid-low ranges of a conventional phase-locked loop, respectively, and FIG. 6 is a specific example of the first embodiment of the loop filter applied to the phase-locked loop of the present invention. 7 is a diagram showing the frequency characteristics of FIG. 6, FIG. 8 is a diagram showing the lock range characteristics of the phase-locked loop of the present invention, and FIGS. 9 and 10 are diagrams of the phase-locked loop of the present invention. FIG. 6 is a diagram showing specific circuits of second and third embodiments of the locked loop. 1... Angle modulated wave signal input terminal, 2...
...Phase comparator, 3...Loop filter, 5.
...Voltage controlled oscillator (VCO), 6...
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 modulation signal of the angle-modulated wave signal is The loop gain at low frequencies is larger than the loop gain of a 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, and the loop gain at the high frequencies of the modulation signal is A phase-locked loop for demodulating multi-channel records, characterized in that the loop gain is smaller than the predetermined value.