JPS6057243B2 - Demodulation method of angle modulated wave signal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention addresses noise (and/or interference waves and interference noise) that exists or occurs in a frequency band occupied by an angle-modulated wave signal to be demodulated and/or in a frequency band close to it. Therefore, the noise generated in the demodulated signal is effectively suppressed, and the loop gain of the phase tracking loop is automatically controlled in accordance with the signal level of the input angle-modulated wave signal, so that the optimal tracking range is always maintained. The purpose of this invention is to provide a method for demodulating an angle-modulated wave signal, which has a good S/N ratio and can greatly improve the perceptual sound quality.

FIG. 1 is a block diagram of a demodulation circuit for an angle-modulated wave signal composed of a single round phase tracking loop previously proposed by the applicant company.
is an input terminal for an angle-modulated wave signal to be demodulated, and the angle-modulated wave signal supplied to the input terminal 1 is applied to a variable bandpass filter 2 and a second order differentiator 5. The variable bandpass filter 2 is configured such that the center frequency in its pass frequency band (hereinafter referred to as passband) is variably controlled by a control signal supplied to the control terminal 2c. An example of the configuration is shown in FIG.

That is, in FIG. 2, 2a is an input terminal, 2b is an output terminal, and 2c is a control terminal. Between the input terminal 2a and the inverting terminal of the amplifier A, a resistor Rll and a capacitor Cl are connected.
2 is connected to the amplifier A, and the non-inverting terminal of the amplifier A is grounded, and the output side of the amplifier A, which is connected to the terminal 2b, is connected to its inverting terminal via a resistor Rl3. and a resistor Rl via a capacitor Cll.
A field effect transistor F whose source is grounded is connected to the connection point between the resistor Rll and the capacitor Cl2.
The drain of ET is connected, and the control terminal 2c is connected to the gate of the field effect transistor FET.

The variable bandpass filter 2 shown in FIG. 2 includes a field effect transistor FET used as a control element.
By changing the channel resistance Rl2 between the drain and the source of L in accordance with a control signal supplied to the control terminal 2c, the center frequency in the passband is variably controlled in accordance with the control signal.

This will be explained in detail as follows. The center frequency FO in the passband of the variable bandpass filter 2 shown in FIG.
The capacitance values Cll and Cl2 of lJ2 are expressed by the following equation. Here, resistor Rll and resistor Rl2 are Rll
〉If selected so that the relationship is Rl2, the above (1)
The equation is as shown in equation (2) below.

From the above equation (2), the resistance Rl2 of the control element, that is, the channel resistance R of the field effect transistor FETl
It can be seen that if the resistance value of l2 is changed by the control signal, the center frequency FO in the passband of the variable bandpass filter 2 can be variably controlled.

The angle-modulated wave signal sent from the output terminal 2b of the variable bandpass filter 2 is applied to the first-order differentiator 3, where it is first-order differentiated. The phase characteristics between the angle modulated wave signals are kept constant at approximately 90 within the frequency band occupied by the angle modulated wave signal. The output signal from the first-order differentiating circuit 3 is waveform-shaped by an amplitude limiting amplifier 4 and then supplied to a phase comparator 7.

Further, the angle-modulated wave signal which has been second-order differentiated by the second-order differentiator 5 is waveform-shaped by the amplitude-limiting amplifier 6 and then given to the phase comparator 7. No. 5 has such a characteristic that the phase characteristic between its input and output is kept constant at approximately 1800 within the frequency band occupied by the angle-modulated wave signal.

The error signal voltage from the phase comparator 7 described above is subjected to high frequency components removed by a low-pass filter 8 serving as a loop filter, and then amplified by an amplifier 9, and then sent to the loop gain controller 13 as an input signal. It is also supplied as one input signal to the arithmetic circuit 10.

A signal obtained by detecting the input angle-modulated wave signal by the envelope detector 15 is applied to the loop gain controller 13 as a loop gain control signal. The output from the loop gain controller 13 is applied as a control signal to the control terminal 2c of the variable bandpass filter 2 via the amplifier 14, and is also supplied to the arithmetic circuit 10 as an input signal.

The above-mentioned arithmetic circuit 10 operates when the input side signal voltage E1 and the output side signal voltage E2 of the loop gain controller 13 are controlled when the loop gain is controlled for one round of the phase tracking loop. , change as shown in curves El and E2 shown in Figure 3, respectively, with respect to the loop gain, and as a result, as shown in Figure 4, the frequency band of the demodulated signal changes widely and narrowly depending on the magnitude of the loop gain. , is provided to prevent the signal level of the demodulated signal from changing high or low, and in this arithmetic circuit 10, the signal voltage E1 on the input side and the signal voltage E2 on the output side of the loop gain controller 13 are By adding, arithmetic circuit 1
The output signal of the demodulation circuit that appears at the output terminal 12 when the output of 0 is passed through the low-pass filter 11 has its frequency band widened or narrowed by changing the loop gain.
The signal level remains constant regardless of changes in loop gain.

In the previously proposed demodulation circuit for angle-modulated wave signals configured in this way, a variable bandpass filter 2, a first-order differentiator circuit 3,
Amplitude limiting amplifier 4, second-order differentiator circuit 5, amplitude limiting amplifier 6
, a phase comparator 7, a low-pass filter 8 serving as a loop filter, an amplifier 9, a loop gain controller 13, an amplifier 14, etc., form a single round phase tracking loop, and during tracking, The variable bandpass filter 2 has a center frequency FO in its passband that automatically follows the frequency of the input angle-modulated wave signal and changes within the range fl-Fh as shown by curves Gl and G2 in Figure 5. In addition, the first-order differentiating circuit 3 and the second-order differentiating circuit 5 in the above-described one-round phase tracking loop convert the phase difference between the two input signals applied to the phase comparator 7 into angle-modulated waves. When the signal is in an unmodulated state, the signal becomes zero, and by appropriately setting the passband width of the variable bandpass filter 2 and the gains of the amplitude limiting amplifiers 4 and 6, the differentiation circuit can be Even if noise exists in the occupied frequency band of the angle modulated wave signal and the frequency band adjacent to it due to the fact that the well-known PLJ. In addition to being able to perform more stable operation than the demodulation circuit for angle modulated wave signals,
One round phase - By adding a loop gain control signal corresponding to the envelope of the input angle modulated wave signal to the loop gain controller installed in the tracking loop,
It is intended that the loop gain of the phase tracking loop is reduced every time the amplitude of the angle-modulated wave signal is reduced to narrow the tracking range and improve the S/N ratio.

By the way, the angle-modulated wave signal to be demodulated is, for example, the angle-modulated wave signal in the reproduction signal from a disc record of the so-called CD-4 (registered trademark) system, that is, the signal in the audio frequency range (hereinafter referred to as , is an angle modulated wave signal in the ultra-audio frequency range that is frequency-multiplexed with respect to the baseband signal so that it occupies a frequency band adjacent to the occupied frequency band of the baseband signal (described as a baseband signal). Since there is not necessarily a strong correlation between the decrease in the amplitude of the angle-modulated wave signal and the generation of abnormal noise, it is not possible to use a disc record as in the previously proposed demodulation circuit. If the tracking range of the phase tracking loop is narrowed every time the amplitude of the angle-modulated wave signal decreases, which often occurs in the reproduced signal in a worn state, the reproduction signal in a state where no abnormal noise occurs will be This would result in the frequency band being needlessly narrowed, so improvements were requested.

The present invention can satisfactorily solve the problems in the previously proposed circuits described above, and also improve the signal level of the angle-modulated wave signal in the reproduced signal due to the difference in sensitivity of the pickup cartridge used in the reproduction 7 of a disc record. An angle modulated wave that can suppress noise well without causing malfunctions due to changes in the angle modulated wave signal as well as changes in the signal level of the angle modulated wave signal in the playback signal in the radial direction of a disc record. It provides a signal demodulation method, and is described below.
The contents will be explained in detail with reference to the accompanying drawings.

FIG. 6 is a block circuit diagram of an embodiment of the demodulation method for angle-modulated wave signals of the present invention. In FIG. 6, the components corresponding to the circuit arrangement shown in FIG. The same drawing symbols as those used in FIG. 1 are given.

In FIG. 6, 16 is a signal level detection circuit of the input angle-modulated wave signal, 17 is a low-pass filter (or smoothing circuit,
18 is a differentiation circuit, 19 is a pulse peak value determination circuit, 20 is an adder, and 21 is a pulse density detection circuit.

The signal level detection circuit 16 of the input angle modulated wave signal includes:
A smoothing circuit consisting of a buffer amplifier A1 that amplifies the input angle modulated wave signal supplied to the input terminal 1, a coupling capacitor C1, detection diodes Dl and D2, a resistor R1 and a capacitor C2, and limits the signal level of the output signal. Diode D3, which operates as a limiter, and variable resistor V
Rl, etc., and a transmitter diode D3 (
Although only one diode symbol is shown in the figure, in practice any desired number of diodes connected in cascade may be used).

The smoothing circuit made up of the resistor R1 and the capacitor C2 has a time constant that is sufficiently large compared to the period length of the instantaneous amplitude drop in the input angle-modulated wave signal.

FIG. 7a is a waveform diagram of an input angle-modulated wave signal having an instantaneous amplitude drop portion, and in this diagram, at time t1
to time T2 and . The period from time T5 to T6 shows an instantaneous and large amplitude drop, and the period from time T3 to time ζ shows a small amplitude drop for reference. It is. FIG. 7b shows the signal level appearing across the variable resistor VRl on the time axis of the output voltage of the detection circuit 16 when the input angle modulated wave signal is as shown in FIG. 7Sa. Curve 1 shown as an imaginary line in the figure shows the temporal change in the output voltage of the signal level detection circuit 16 when the diode D3 is not provided in the signal level detection circuit 16. In addition, the solid curve (■) in the figure represents the change in the output voltage of the signal level detection circuit 16 on the time axis when a limiter using the diode D3 is provided in the signal level detection circuit 16. In addition, the curve ■ shown by the dashed-dotted line in the figure is based on the assumption that instantaneous amplitude decrease portions frequently appear in the input angle-modulated wave signal between the time of the hour and the time of the hour. 2 is an example of how the output voltage of the signal level detection circuit 16 changes over time.

Further, FIG. 7c shows a temporal change in the control voltage VCl obtained by adjusting the slider of the variable resistor VRl in the signal level detection circuit 16.

In addition, ■A, ■0, ■a/n in Figure 7 B and c
etc. are indications of voltage values, and n has a value corresponding to the adjustment state of the slider of the variable resistor VRl. 7 Figure 7a-
As can be seen from figure c, since the output voltage Va of the signal level detection circuit 16 and the control voltage VCl set by the variable resistor VRl have a large time constant of the smoothing circuit in the circuit, the input angle modulated wave Even in the instantaneous amplitude drop portion that appears in the signal, it only shows a gradual change on the time axis, and the output voltage ■a and control voltage VCl are dependent on the signal level of the input angle-modulated wave signal. When the input angle-modulated wave signal has a signal level equal to or higher than a predetermined signal level, the voltage value is suppressed to a constant voltage value.

As mentioned above, when the signal level detection circuit 16 is provided with a limiter means, from the outer circumference to the inner circumference of the disc record,
The amplitude of the angle-modulated wave signal in the reproduced signal may gradually decrease, or the amplitude of the angle-modulated wave signal in the reproduced signal may decrease when a disc record is played several times. However, it is considered that the degree of decrease in the amplitude of the angle-modulated wave signal described above does not have a significant effect on the deterioration of the S/N ratio, and the voltage value of the control voltage VCl is set to the range of the amplitude of the angle-modulated wave signal. Since it is possible to maintain a constant value Va/n regardless of changes in the amplitude of In addition, even if pickup cartridges with different sensitivities are used, the variable resistor VRl can be adjusted every time the cartridge used is changed. This eliminates the extra effort required to process the product, resulting in advantages such as easier manufacturing and adjustment work at the factory.

In one embodiment of the present invention shown in the block diagram of FIG. 6, a diode D,
If the input angle modulated wave signal has a signal level higher than a predetermined signal level, a control voltage C1 suppressed to a constant voltage value is obtained from the signal level detection circuit 16. However, when implementing the method of the present invention, a signal level detection circuit 16 having a configuration in which the diode D3 in the signal level detection circuit 16 is omitted may be used, and in this case, the signal level detection circuit 16 may be The control voltage output from the level detection circuit 16 fluctuates on the time axis, as shown by curve 1 in FIG. Due to the time constant, even the instantaneous amplitude drop portion that appears in the input angle-modulated wave signal only shows a gradual change on the time axis, and in this case, the signal level detection circuit 16 obtains a gradual change. The control voltage that is output corresponds to the level of the input angle-modulated wave signal, so even if there is an instantaneous amplitude change in the input angle-modulated wave signal, it will respond sensitively to it and complete the cycle. ● The tracking range of the tracking loop does not change, and even if there is a momentary amplitude drop part in the input angle-modulated wave signal, it operates so that the playback quality will not deteriorate due to it. can do.

Control voltage VCl obtained from signal level detection circuit 16
is given to the adder 20 as one input.

In the illustrated example, the adder 20 is composed of an operational amplifier 20a and resistors R2 and R3, and the control voltage C1 output from the signal level detection circuit 16 is applied to the non-inverting input terminal of the operational amplifier 20a. Further, an output signal from a pulse peak value determining circuit 19, which will be described later, is applied to the inverting input terminal of the operational amplifier 20a via a resistor R2. The error signal obtained at the output side of the phase comparator 7 is converted into a demodulated signal for pulse noise detection by a low-pass filter 17 composed of resistors R4 and R5 and capacitors C3 and C4, and then sent to a differentiating circuit. given to 18.

In the differentiating circuit 18, after amplifying the demodulated signal using the buffer amplifier 18a, the signal is differentiated using a circuit including a capacitor C5 and a variable resistor VR2.

The output signal from the differentiating circuit 18 is given to the pulse peak value determination circuit 19 from the slider of the variable resistor VR2. In the illustrated example, the pulse peak value determination circuit 19 is a diode D.
4 to D6, a capacitor C6, etc., and among the negative pulses present in the output signal of the differentiating circuit 18, only those having a predetermined peak value or more are supplied to the adder 20 as addition inputs.

The adder 20 adds and superimposes the control voltage ■C1 obtained from the signal level detection circuit 16 and the signal obtained from the pulse peak value determination circuit 19, and provides the result to the pulse density detection circuit 21.

The pulse density detection circuit 21 is configured such that a capacitor C7 is charged by a negative control voltage VCl via a resistor R6, and a capacitor C8 is further charged via a resistor R7, and also includes a pulse peak value determination circuit. The output signal (negative pulse) from 19 is inverted in polarity by the operational amplifier 20a, and when the positive pulse passes through the diode D7, the capacitor C8 is discharged, thereby producing an output signal corresponding to the density of the input pulse. . FIG. 8a is a waveform diagram showing an example of a pulse train given from the pulse peak value determining circuit 19 to the adder 20, and the pulses P1 to P7 shown in the figure are processed by the pulse peak value determining circuit 19 among the pulse noise. A pulse that exceeds a set predetermined level.

8b shows that the control voltage VCl obtained from the signal level detection circuit 16 and the pulse train obtained from the pulse peak value determination circuit 19 are superimposed by an adder 20, and the resulting product is applied to the pulse density detection circuit 21. , which shows an example of the waveform of the loop gain control signal S obtained as the output of the pulse density detection circuit 21. FIG. An example is given for the case where it is something like this. The loop j gain control signal S sent out from the pulse density detection circuit 21 is given to the control element FET in the loop gain controller 13,
By changing the channel resistance, the loop gain of the one-round phase tracking loop is variably controlled. In the illustrated example, the loop gain controller 13 uses a field effect transistor FET as a variable resistance element, and a resistance R
8 and a coupling capacitor C9, it will be appreciated that other configurations may be used as the loop gain controller 13.

In the demodulation method of the angle modulated wave signal of the present invention configured as described above, the loop gain control signal given to the loop gain controller 13 corresponds to the signal level of the input angle modulated wave signal and Among the noise pulses that appear in the signal whose maximum value is set to a predetermined level and the demodulated signal, there are those with high peak values that are audible to the ears, and those with peak values that are not very high. The method of the present invention can be applied to, for example, C
When adopted in a playback device for D-4 type stereophonic disc records, the problems with the conventional devices mentioned above are successfully solved, and playback signals with high fidelity and good S/N can be easily produced. In addition, there are advantages such as ease of manufacturing and preparation work for the device.

That is, in the demodulation method of the angle-modulated wave signal of the present invention, the pulse noise that appears in the demodulated signal corresponding to the state in which abnormal noise occurs in the reproduced sound is detected, and the peak value and pulse density are determined. Since the loop gain controller 13 is controlled by generating a corresponding loop gain control signal, for example, even if the amplitude of the angle-modulated wave signal decreases to some extent,
If abnormal noise does not occur in the reproduced sound, the loop gain is not controlled, and therefore, the phase of one cycle ●The tracking loop is in a wideband state, and the demodulated signal has a wide frequency range. It is designed to have a wide range of frequencies, and can reproduce sound with good quality.
In addition, if abnormal noise occurs in the reproduced sound, the loop gain can be reliably controlled to ensure that the phase and
By setting the tracking loop in a narrowband state and effectively suppressing the occurrence of abnormal noise, furthermore, by controlling the loop gain using the loop gain control signal of the portion corresponding to the signal level of the input angle-modulated wave signal, it is possible to prevent wear from progressing. When playing a disc record where the signal level of the angle-modulated wave signal is extremely low, the phase tracking loop is automatically set to the necessary minimum narrowband state to effectively suppress abnormal noise. In addition, by providing a transmitter means, the loop gain control signal does not fluctuate even when the signal level of the input angle-modulated wave signal changes to a certain extent. By doing so, you can prevent inconveniences such as changes in the quality of the reproduced sound, and even if there are differences in sensitivity between the pickup cartridges used, the noise suppression setting level of the device can be adjusted. Since there is no need for extra effort such as re-adjustment, the production and adjustment work of the device becomes easier.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a demodulation circuit for angle-modulated wave signals according to an existing proposal, FIG. 2 is a circuit diagram of an example configuration of a variable band filter, and FIGS. 3 to 5 are explanatory characteristic curve diagrams. FIG. 6 is a block circuit diagram of an embodiment of the demodulation method for angle-modulated wave signals of the present invention, FIGS. 7 a-c and 8 A,
Figure b is an explanatory waveform diagram. 1, 2a... Input terminal, 2... Variable bandpass filter, 3... First-order differentiator circuit, 4, 6...
... Amplitude limiting amplifier, 5... Second order differential circuit,
7...Phase comparator, 8...Low pass filter serving as a loop filter, 9,14...Amplifier,
10... Arithmetic circuit, 11, 17... Low pass filter, 12... Output terminal, 13... Loop gain controller, 15... Envelope detector, 16.
・Signal level detector, 18...differentiation circuit, 19
...Pulse wave height value judgment circuit, 20...Adder,
21...Pulse density detection circuit.

Claims (1)

[Claims] 1. An angle modulated wave signal to be demodulated is applied to a variable bandpass filter and a second order differentiator whose center frequency of a pass frequency band is variably controlled by a control signal. , the output signal from the variable bandpass filter is applied as one input to the phase comparator through a series connection circuit of a first-order differentiator and an amplitude-limiting amplifier;
The output from the differential differential circuit is given as the other input to the phase comparator through an amplitude limiting amplifier, and the error signal obtained from the phase comparator is sent to a low pass filter serving as a loop filter, an amplifier and a loop. It is applied as a control signal to the above-mentioned variable bandpass filter through a circuit including a gain controller, etc., and after calculating the input side signal and output side signal of the above-mentioned loop gain controller, it is applied to the low-pass filter. In the demodulation method for angle-modulated wave signals, which consists of a single round phase tracking loop in which the demodulated signal is obtained from the output side of the phase comparator, the low-pass filter obtained from the output side of the phase comparator is A signal obtained by differentiating the pulse through a pulse generator and then feeding it to a pulse peak value determination circuit to obtain only pulses exceeding a predetermined level;
A superimposed signal with a signal obtained by applying the input angle modulated wave signal to a signal level detection circuit, and a signal obtained through the pulse density detection circuit are supplied as a loop gain control signal to the loop gain controller. A demodulation method for angle-modulated wave signals. 2. An angle modulated wave signal to be demodulated is applied to a variable bandpass filter and a second order differentiator whose center frequency of the pass frequency band is variably controlled by a control signal; The output signal from the bandpass filter is applied as one input to the phase comparator through a series connection circuit of a first-order differentiating circuit and an amplitude limiting amplifier, and
The output from the differential differential circuit is given as the other input to the phase comparator through an amplitude limiting amplifier, and the error signal obtained from the phase comparator is sent to a low pass filter serving as a loop filter, an amplifier and a loop. It is applied as a control signal to the above-mentioned variable bandpass filter through a circuit including a gain controller, etc., and after calculating the input side signal and output side signal of the above-mentioned loop gain controller, it is applied to the low-pass filter. to obtain a demodulated signal, and
The signal obtained from the output side of the phase comparator described above is differentiated after passing through a low-pass filter, and the obtained signal is applied to a pulse wave height value determination circuit. In a demodulation method of an angle modulated wave signal, a signal superimposed with a signal obtained by applying the signal to the pulse density detection circuit is further supplied as a loop gain control signal to the loop gain controller described above, A demodulation method for an angle modulated wave signal in which a signal from a signal level detection circuit is limited to a constant value when the signal level is higher than a predetermined signal level of an input angle modulated wave signal.