JPS6027480B2 - A processing circuit for input angle modulated wave signals in a demodulation circuit for angle modulated wave signals reproduced from a multi-channel disc record. - Google Patents

Description

[Detailed description of the invention] Frequency modulated wave signals (FM wave signals) and phase modulated wave signals (F
It is well known that a phase-locked loop (hereinafter sometimes abbreviated as PLL) can be used as a demodulation circuit for angle-modulated wave signals such as M-wave signals). When demodulating the sub-channel signal consisting of the angle-modulated wave signal reproduced from a multi-channel disc record in which the frequency-multiplexed signal and the sub-channel consisting of the angle-modulated wave signal are recorded in a frequency-multiplexed manner. Also, a PLL may be used.

Now, as is well known, the above-mentioned PLL has a locking range that varies widely depending on the signal level of the input angle modulated wave signal.
The frequency range of the demodulated signal from the angle modulated wave demodulation circuit configured by is determined depending on the lock range of the PLL. The occupied frequency band of the demodulated signal from the PLL is sufficiently wide.Contrary to the above case, when the signal level of the input angle modulated wave signal to the PLL is low, the occupied frequency band of the demodulated circuit from the PLL is wide enough. The lock range of the PLL automatically changes depending on the signal level of the angle modulated wave signal input to it, and the occupied frequency band of the demodulation circuit automatically changes accordingly. Therefore, a PLL with such characteristics can be used to play back a multi-channel disc record, for example, a CD-4 format disc record. When used as a means of demodulating a signal that is susceptible to interference by interference waves, such as an angle modulated wave signal in a demodulated signal, the signal level of the input signal decreases due to interference by the interference waves, and pulse-like signals are generated in the demodulated signal. At the moment when abnormal noise occurs, the lock range of the PLL becomes narrower, and the occupied frequency band of the demodulated signal becomes narrower, thereby making it possible to output a demodulated signal that causes less discomfort to the sense of intelligence. It is thought that the following advantages can be obtained.

By the way, the angle modulated wave signal in the signal reproduced from a CD-4 multi-channel disc record has a constant reproduction signal level due to the difference in sensitivity of the pickup cartridge used for reproduction. Moreover, even if the pickup cartridge used for playback is the same, the playback signal level will be different between the outer and inner circumferences of the disc record due to the existence of so-called tracing loss. Even if the pickup cartridge used for playback is the same and the playback position on the disc record is the same,
Due to the presence of various unstable factors, the signal level of the angle modulated wave signal in the playback signal is large, such as the playback signal level being different due to the difference in the state of friction due to the difference in the number of times the disc record is played. The problem is that the lock range of the PLL changes accordingly, and the sound quality of the demodulated signal also changes. In order to solve the above problems, attempts have been made in the past to provide a limiter 3 with a sufficiently high gain in the input signal circuit of the PLL, as shown in the first diagram. The illustrated device has various drawbacks as described below, and improvements have been desired.
Now, in Fig. 1, 1 is an input terminal for the angle modulated wave signal, 2 is an output terminal for the demodulated signal, and 3 is a limiter. Even under the worst conditions, the PLL
The angle modulated wave signal level input to the angular modulated wave signal is configured to be at a sufficiently high constant level.

In FIG. 1, the PLL is shown as being composed of a phase comparator 4, a loop filter 5, an amplifier 6, and a voltage controlled oscillator 7. If the angle modulated wave signal input to the PLL is always kept at a constant signal level by the limiter 3 having a sufficiently high gain, as in the circuit arrangement shown in the first diagram above, it may not be used. No matter what kind of cartridge it is, or what condition the disc record is in,
LL has the advantage that a demodulated signal with a wide frequency band can always be obtained, but on the other hand, the use of a limiter with sufficient amplification has the disadvantage of distorting the phase of the angle modulated wave signal. Even when the amplitude of the angle-modulated wave signal due to interference waves suddenly decreases, there is no significant decrease in the amplitude of the angle-modulated wave signal input to the PLL, so when abnormal noise is generated due to interference waves. Even in this case, the lock range of the PLL is not narrowed, and therefore, when the limiter 3 as described above is used, there is a drawback that the PLL's original suppressing effect on interference output is lost.

The baseband signal and the sub-channel signal based on the angle modulation wave signal recorded in the so-called CD-4 multi-channel disc record in the frequency multiplex format are located extremely close to each other on the frequency axis. Therefore, in the case of a program source where the baseband signal contains a large signal component in the high pitched part, for example, the sound of the s, such as s, s, s, c, or s, or the cymbal sound, etc. In the case of a program source that contains a large signal component in the Takagi part of the baseband signal, as in It appears as a disturbance wave with large energy within the frequency band of the channel signal, and when it is vectorially added to the angle modulated wave signal that constitutes the sub-channel signal, it causes the angle modulated wave signal to disappear, or This may cause the angle modulation wave signal to be extremely distorted, but as mentioned above, the angle modulation wave signal may be
When the amplitude is sufficiently limited and amplified by
Something near the female Hz crosstalks to the adjacent channel, causing interference distortion with the 3-channel Hz carrier wave of other channels,
Furthermore, the leakage of the large signal component present in the high pitched portion of the baseband signal mentioned above is amplified, resulting in various drawbacks such as abnormal locking of the PLL.

The present invention provides a multi-channel disc record in which an angle-modulated wave signal in a signal reproduced from a multi-channel disc record is demodulated by an angle-modulated wave signal demodulation circuit composed of a phase-locked loop. For input signals within such a low signal level range that it is acceptable and/or desirable to have a narrow locking range in the phase locked loop for the angle modulated wave signal in the signal reproduced from a disc record, The input signal is configured to obtain an output signal that follows the input/output characteristic curve in a state where no automatic gain control operation is performed on the input signal, and has a signal level exceeding the above-mentioned low signal level range. Regarding the signal, the signal is predetermined so that the signal level is higher than the signal level of the output signal when the low signal level signal is input by operating in an operating region that does not reach saturation. means for providing a demodulation circuit constituted by a phase-locked loop through an automatic gain control means configured to obtain an output signal of the angle; a means for determining the C/N of the angle modulated wave signal; C/ of modulated wave signal
Based on the output signal obtained from the above-mentioned C/N determination means of the angle modulated wave signal when the N deteriorates, the signal is supplied from the above-mentioned automatic gain control means to a demodulation circuit constituted by a phase-locked loop. Means for lowering the signal level of the angle modulated wave signal to be lower than a predetermined signal level so that the signal level is higher than the signal level of the output signal when the above-mentioned low signal level signal is input, etc. The present invention solves the above-mentioned conventional problems by providing a processing circuit for an input angle modulated wave signal in a demodulating circuit for an angle modulated wave signal reproduced from a multi-channel disc record, which is equipped with a multi-channel disc record. The specific contents will be explained in detail.

FIG. 2 is a block diagram of an embodiment of the input angle modulated wave signal processing circuit in the angle modulated wave signal demodulation circuit reproduced from a multi-channel disc record of the present invention. is an input terminal for the angle modulated wave signal, 2 is an output terminal for the demodulated signal, AGC is an automatic gain control circuit (automatic gain control means), SW is a switch circuit (switching means), and PLL is a phase-locked relay. An angle modulated wave signal demodulation circuit consisting of J
is a C/N determination circuit (C/N determination means).

The automatic gain control circuit AGC described above operates until the signal level of the angle modulated wave signal supplied to the input terminal 1 reaches a predetermined input signal level indicated by Via on the axis in FIG. That is, when the input angle modulated wave signal level is within the range of 0 to Via shown on the horizontal axis in Figure 3a, the signal level in Figure 3a is determined according to the signal level of the input angle modulated wave signal. The third curve defined by the input/output characteristic curve 1 of
An angle modulated wave signal having an output signal level in the range of 0 to Voa shown on the vertical axis in Figure a is supplied to the PLL', and
If the signal level of the angle modulated wave signal supplied to the input terminal 1 is higher than the predetermined input signal level indicated by Via at Yokoto in Figure 3a, the input signal level is angle having a predetermined constant output signal level Voa (illustrated in the vertical axis in FIG. PLL the modulated wave signal
supply to.

In Fig. 3a, the input/output characteristic curve 1, that is, 0
→The characteristic curve shown by A→B→C is the automatic gain control circuit AG.
C is the input/output characteristic curve of the automatic gain control circuit when automatic gain control operation is not performed, and the characteristic curve indicated by A→D→E in FIG. It is an input-output characteristic curve of automatic gain control circuit AGC when performing automatic gain control operation.

The entrusted automatic gain control circuit AGC changes the output signal level according to the fluctuation of the input signal level when the input angle modulated wave signal to it is of a signal level lower than a certain predetermined signal level Via. Since a fluctuating angle modulated wave signal is applied to the PLL, the loop gain of the PLL changes in accordance with the fluctuation in the signal level of the angle modulated wave signal from the automatic gain control circuit AGC, which causes the PLL to change its loop gain.
The lock range of L varies widely within the range of arrow Y in Figure 3b, which shows the relationship between the signal level of the angle modulated wave signal to be demodulated and the lock range (ln indicates an example of the lock range). Therefore, when the signal level of the angle modulated wave signal is low, the PLL operates to improve noise resistance.

The signal level of the angle modulated wave signal supplied to the PLL is determined when the input signal level to the automatic gain control circuit AGC is Vi.
a or more, the above-mentioned automatic gain control circuit AGC operates to maintain a predetermined constant signal level Vo, so the lock range of the PLL in this case is indicated by lw in Fig. 3b. It is maintained in the lock range shown in .

The automatic gain control circuit AGC is configured to operate in an operating region in which its gain control operation does not reach saturation. No phase distortion is introduced even by the intervention of PLL.
A demodulated signal without distortion can be obtained. In addition, as mentioned above, when the signal level of the angle modulated wave signal in the signal reproduced from the multi-channel disc record is higher than a predetermined signal level, the automatic gain control circuit AGC automatically controls the gain. During operation, an angle modulated wave signal with a constant signal level is supplied to the PLL, and as a result, the PPLL performs demodulation operation while maintaining a constant lock range. Even when interference waves are generated in the sub-channel signal area, the signal level of the angle modulated wave signal supplied to the PLL is kept constant, and the lock range of the PLL is also kept constant. Therefore, abnormal noise will not be generated in the demodulated signal due to the above causes, and furthermore, the automatic gain control circuit
Since the amount of C used is not large enough to cause problems,
By implementing the present invention, all the problems mentioned above can be satisfactorily solved.

Next, an example of the configuration of an automatic gain control circuit AGC that can perform the operation as described above is shown in FIGS. 2 and 3.
This will be explained with reference to Figure a.

The automatic gain control circuit AGC illustrated in FIG. 2 is composed of a variable attenuation network 8 and an automatic gain control amplifier 9. The variable attenuation network 8 includes a resistor 8a inserted and connected in series to the signal transmission path, and a resistor 8b connected in parallel to the signal transmission path.
and a variable resistance element 8c (in the illustrated example, a variable resistance element 8c is shown in which the resistance between the collector and emitter of the transistor is variably adjusted by the base voltage). The attenuation network 8 is a signal level detector L connected to the output side of the automatic gain control circuit AGC.
In response to the control signal V supplied from D, the signal level of the output angle modulated wave signal is changed according to a curve W shown by D→K→L in FIG. 3a.

In the illustrated example, the signal level detector LD includes a detector 10 that amplitude demodulates the angle modulated wave signal sent from the output side of the automatic gain control circuit AGC, a time constant circuit (integrator circuit) 11, and a level determination circuit. It is composed of circuits 12, 13, etc.

The level determination circuit 12 described above is an automatic gain control circuit AG.
The signal level of the output signal from C is Vo in Figure 3a.
a, a control signal is generated and is given to the automatic gain control amplifier 9 (described later) via the switch SW, and the level determination circuit 13 receives the output signal from the automatic gain control circuit AGC. When the signal level becomes equal to or higher than Vo in FIG. 3a, a control signal is generated and applied to the variable resistance element 8c in the variable attenuation network described above. Next, the automatic gain control amplifier 9 includes an amplifier 9a and resistors 9b to 9.
The transistor 9e is connected in parallel with the resistor 9d when a control signal is applied to the base of the transistor 9e by the signal level detector LD via the switch circuit SW.
The collector-emitter resistance of the amplifier changes to lower the negative feedback rate, thereby increasing the amplification factor.

That is, the automatic gain control amplifier 9 changes the signal level of the output angle modulated wave signal from ○ to A in FIG. 3a by changing the degree of amplification according to the control signal supplied from the signal level detector LD. → Change according to the curve m shown by D → F → G. Therefore, the input/output characteristics of the automatic gain control circuit AGC constituted by the variable attenuator 8 and the automatic gain control amplifier 9 follow the curve 0' shown by ○→A→D→E in FIG. 3a. becomes.

According to the description so far, the automatic gain control circuit AGC changes the output angle modulated wave signal depending on whether the input angle modulated wave signal applied thereto has reached the predetermined signal level Via. It is possible to supply V to the PLL as a signal whose signal level changes within the range of .about.Voa or a constant signal level indicated by Vo, thereby producing the effects described above.

By the way, the operation entrusted to the automatic gain control circuit AGC can also be applied to an angle modulated wave signal with a deteriorated C/N, such as an angle modulated wave signal in a signal reproduced from a worn disc record. If the same procedure is performed, abnormal noise is likely to occur in the demodulated signal. Therefore, in the present invention, in the case of an angle modulated wave signal with a deteriorated C/N, the input angle modulated wave signal is The signal level is as shown in Figure 3a.
Even if it is more than Via in the figure, the automatic gain control circuit AGC
By causing the automatic gain control circuit AGC to perform an operation that does not increase the amplification degree of the automatic gain control amplifier 9 in
/N degraded angle modulated wave signal has output signal level V
o, and the PLL is operated in such a state that its lock range becomes narrower than IW in Figure 3b, depending on the signal level of the angle modulated wave signal. This makes it possible to remove or reduce abnormal noise occurring in the demodulated signal.

That is, in FIG. 2, the C/N indicated by block J
The determination circuit outputs a control signal when the angle modulated wave signal output from the automatic gain control circuit AOC has a degraded C/N, and operates the switch circuit SW using the control signal. The control signal supplied from the level detector LD to the automatic gain control amplifier 9 is cut off to reduce the amplification degree of the automatic gain control amplifier 9, and the control signal is supplied from the automatic gain control circuit AGC to the PLL as described above. The signal level of the angle modulated wave signal is set to be lower than a predetermined constant output signal level Vo.

The C/N determination circuit J illustrated in FIG. It is composed of a 10K 500K, which has a normal band width of 1KHz), a level judgment circuit 16, etc., which detects a frequency around 1Hz in the signal reproduced from a worn record. The C/N judgment circuit J This was adopted during the construction of .

Further, the C/N determination circuit J may be constructed using a PLL and a synchronous detector SD as shown in FIG. That is, in FIG. 4, terminal 17 is a terminal to which an output signal from automatic gain control circuit AGC is supplied, and PLL is composed of phase comparator PC, loop filter LF, amplifier AMP, voltage controlled oscillator VCO, etc. is a phase-locked loop with this P
In LL, the voltage controlled oscillator VCO provided in the loop has a free-running oscillation frequency of around 30 KHz, and the loop gain is set to a large value. The synchronous detector SD to which the oscillation wave from the voltage controlled oscillator VCO described above is given as a reference wave is connected to the terminal 17.
Since an output signal is generated when the angle modulated wave signal supplied from the synchronous detector SD is reproduced from a worn record, etc., the output signal from the synchronous detector SD is passed through the integrating circuit TC and then the bell determiner 16. and sends out the required control signal from the output terminal 18. The control signal output from the C/N determination circuit J is added as a switching control signal to the switch circuit SW as described above and is used to change the characteristics of the automatic gain control circuit AGC. 2. In the circuit device shown in Figure 2, the C/N determination circuit J
The control signal output from the C/N determination circuit J is also applied to the variable resistance element 19c (transistor 19c in the illustrated example) of the loop gain control circuit 19 in the demodulation PLL, and the control signal output from the C/N determination circuit J is used to The loop gain of the demodulating PLL is lowered to narrow the lock range of the PLL, thereby further reducing the occurrence of abnormal noise when playing a worn record.

As is clear from the detailed explanation above, in the input angle modulated wave signal processing circuit in the demodulation circuit for angle modulated wave signals reproduced from a multi-channel disc record of the present invention, All of the above-mentioned problems that occur when demodulating an angle modulated wave signal in a signal using a demodulation circuit configured by a PLL can be satisfactorily resolved, and by employing the circuit of the present invention, abnormal noise is always avoided. A demodulated signal in which the occurrence of is suppressed can be obtained from the PLL.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional example, FIG. 2 is a block diagram of an embodiment of the input angle modulated wave signal processing circuit of the present invention, and FIGS. 3a and 3b are explanatory characteristic curve examples. , FIG. 4 is a block diagram showing an example of the configuration of the C/N determination circuit. 1, 17... Input terminal, 2, 18... Output terminal, 3...
...Limiter, 4, PC...Phase comparator,
5, LF...Loop filter, 6, AM circle...Amplifier, 7, VC○...Voltage controlled oscillator, 8...
... Variable attenuator, 9 ... Automatic gain control amplifier, 10, 14 ... Detector that performs amplitude demodulation, 1 1
, TC...Integrator circuit "12, 13, 16...
・...Level judgment circuit, 15...Obijo Kashihaki, 19・
...Loop gain control circuit, SW...
Switch circuit, PLL... Phase locked loop, AGC... Automatic gain control circuit, LD...
...Level detection circuit, J...C/N judgment circuit. Soft Figure 1 Figure 2 Figure 3 Collection Figure

Claims (1)

[Claims] 1. An angle modulated wave signal in a signal reproduced from a multi-channel disc record is demodulated by an angle modulated wave signal demodulation circuit composed of a phase locked loop. Input signals within a range of low signal levels such that it is permissible and/or desirable for the angle modulated wave signal in the signal reproduced from a multi-channel disc record to be locked in a narrow lock range in a phase locked loop. Regarding the signal, the output signal is designed to follow the input/output characteristic curve in a state where no automatic gain control operation is performed on the input signal, and the signal exceeding the above-mentioned low signal level range is For input signals that have a high level, the operation is performed in an operating region that does not reach the saturation region, so that the signal level of the output signal is higher than the signal level of the output signal when the low signal level signal is input. A means for supplying a demodulation circuit constituted by a phase-locked loop through an automatic gain control means such that an output signal of a predetermined signal level is obtained, and a C/N ratio of the angle modulated wave signal. and a phase locked loop from the automatic gain control means based on the output signal obtained from the above-described C/N determination means of the angle-modulated wave signal when the C/N of the angle-modulated wave signal deteriorates. A predetermined signal so that the signal level of the angle modulated wave signal supplied to the demodulation circuit composed of A processing circuit for an input angle modulated wave signal in a demodulation circuit for an angle modulated wave signal reproduced from a multi-channel disc record, the circuit comprising means for lowering the level below the level of the angle modulated wave signal. 2. A multichannel disc record in which the angle modulated wave signal in the signal reproduced from a multichannel disc record is demodulated by an angle modulated wave signal demodulation circuit composed of a phase locked loop. For input signals within a range of low signal levels where it is permissible and/or desired to lock the angle modulated wave signal in the signal reproduced from a record into a phase locked loop with a narrow lock range, Regarding an input signal that is configured to obtain an output signal that follows an input/output characteristic curve in a state where no automatic gain control means is applied to the signal, and has a signal level that exceeds the above-mentioned low signal level range. operates in an operating region that does not reach the saturation region, and maintains a predetermined signal level so that the signal level is higher than the signal level of the output signal when the low signal level signal is input. A means for supplying a demodulation circuit constituted by a phase locked loop through an automatic gain control means configured to obtain an output, and a C/
Based on the output signal obtained from the C/N determining means of the angle modulated wave signal and the C/N determining means of the angle modulated wave signal when the C/N of the angle modulated wave signal deteriorates, The signal level of the angle modulated wave signal supplied to the demodulation circuit configured as a locked loop is predetermined to be higher than the signal level of the output signal when the above-mentioned low signal level signal is input. Input angle modulation in a demodulation circuit for an angle modulated wave signal reproduced from a multi-channel disc record, with means for reducing the loop gain in the phase-locked loop. Wave signal processing circuit.