JP2885374B2 - Hold circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to the removal of pulse noise superimposed on an audio signal in an audio device, a video tape recorder, a video disc player, and the like, and a signal loss occurring in the audio signal. The present invention relates to a hold circuit that compensates and complements an audio signal waveform.

[Conventional technology]

Conventionally, in a HiFi audio system of the video tape recorder, when switching heads, or, such as during dropout reproduced FM signal is missing, is superimposed pulse noise in the audio signal S _i, the waveform distortion in the audio signal S _i It is known to occur. Therefore, the removal measures this noise, for example, the fourth differentiating the audio signal S _i by a head switching section or the signal missing section with a hold circuit shown in FIG., The differential signal differential hold correction to complement the audio signal S _i with a Has been done.

An audio signal S _i to be reduced in noise from a signal source such as a reproducing head is applied to the input terminal 2. The audio signal S _i passes through a buffer amplifier 4 and a switch 6 and is applied to an amplifier 8 on the subsequent stage. Have been. Amplifier 8
Is constituted by, for example, a non-inverting amplifier.
It is installed in the reproduction signal processing system of the audio system. A series circuit including a resistor 10 and a first capacitor 12 is connected in parallel between the input and output units of the amplifier 8,
Further, a second capacitor 14 is provided at an input portion of the amplifier 8.

In such a configuration, the switch 6 is configured by an analog switch or the like, and in the head switching section,
It is assumed to be controlled to the off state shown by the broken line. That is, the switch 6 is turned on, the audio signal S _i which has passed through the buffer amplifier 4 through the switch 6 capacitor
Was added to 14, the instantaneous value level of the audio signal S _i which constantly amplitude level in the capacitor 14 is changing are retained while being updated.

Therefore, when the switch 6 is on, if that output impedance of the buffer amplifier 4 is set extremely low, the terminal voltage of the capacitor 14 is equal to the signal voltage of the audio signal S _i applied through a buffer amplifier 4 Become. Holding voltage by the capacitor 14 is applied to the amplifier 8 is extracted from the output terminal 16 as the output audio signal S _0.

In this case, the input of the amplifier 8 is placed via the switch 6 at the output of the buffer amplifier 4 with a very low output impedance, and thus comprises the resistor 10 and the capacitor 12 in a series circuit added to the amplifier 8. The differentiating operation of the differentiating circuit is stopped. As a result, the audio signal _Si is not affected by the feedback circuit of the amplifier 8,
Will be taken from the output terminal 16 as the output audio signal S _0.

When the switch 6 is turned off, the signal voltage held in the capacitor 14 is applied to the amplifier 8 in place of the audio signal S _i, at this time, the output of the amplifier 8, the feedback circuit side resistor 10 and a capacitor 12 The signal is then fed back to the input side of the amplifier 8. In this case, the output voltage of the amplifier 8 is divided by the capacitors 12 and 14, and the divided voltage is accumulated in the capacitor 14. In such a feedback operation, a differential operation is performed by the resistor 10 and the capacitors 12, 14, and a differential hold correction output is obtained from the output terminal 16.

The switch 6 is synchronously opened and closed in FIG. 5 hold pulses shown in A (the head switching section pulses) P _H,
Hold pulse P _H is switched to the OFF state by the head switching section T _H represented, since the differential hold correction operation is performed in the interval T _H, as shown in FIG. 5 of B, and the differential hold the correction signal V _H1 facilities Output audio signal S ₀ is output to output terminal 1
Taken out of 6.

[Problems to be Solved] However, in such differential hold correction, as shown in B of FIG. 5, in the vicinity of the middle level of the waveform, the shape of the correction signal component along the waveform of the audio signal S _i So
Although the waveform correction effect is good, in the vicinity of the peak level of the waveform, the differential hold the correction signal V _H1 is significantly deviate from the original waveform, causing waveform distortion in the audio signal S _i for projecting impulse, this is, switching There was a drawback that it was output as noise.

Therefore, an object of the present invention is to realize a hold circuit that reduces waveform distortion due to differential hold correction at the peak level of a waveform, and optimizes waveform supplement processing.

[Means for solving the problem]

A hold circuit according to the present invention is connected to a switch installed at an input section of an amplifier to interrupt an input to the amplifier in a specific section of an audio signal, and is connected via a first resistor between an input / output section of the amplifier. A differential hold circuit including a first capacitor and a second capacitor installed on the input side of the amplifier and holding an audio signal passing through the switch, and a second resistor in parallel with the second capacitor. And a time constant circuit comprising a third capacitor connected to the time constant circuit.

[Action]

The amplifier is, for example, a reproduction head of a HiFi audio system of a video tape recorder as a signal source, and is installed in a circuit system for transmitting an audio signal obtained from the signal source to an FM reproduction system. The signal is amplified and transmitted to the next processing system.

A switch for passing or blocking an audio signal is provided at the input of such an amplifier. The switch is arbitrarily opened and closed, and when the switch is closed, the second capacitor and the third capacitor are output by the audio signal. Is charged, and the switch is opened in a noise section or a signal missing section to prohibit the passage of the audio signal and cut off the input of the audio signal to the amplifier.

When the switch is opened, the charging voltage of the second capacitor is applied to the amplifier, and the output of the amplifier is fed back to the input side through the first resistor and the first capacitor provided on the feedback circuit side, and And a second resistor, the first,
Differentiation is performed using a double time constant set in the differential hold circuit and the time constant circuit including the second and third capacitors, and the differentiated output is taken out through the amplifier as a hold correction output.

Therefore, the differential hold correction near the peak level of the waveform is less gradual than in the conventional case where a differentiating circuit having a single time constant consisting of one resistor and two capacitors is used. Is prevented, the waveform correction approximating the ideal original waveform is performed, and the effect of suppressing the waveform distortion in the differential hold correction is obtained.

〔Example〕

 FIG. 1 shows an embodiment of a hold circuit according to the present invention.

The input terminal 2, the audio signal S _i to be reduce noise from a signal source such as a reproducing head is applied. The audio signal S _i is applied to a subsequent amplifier 8 via a buffer amplifier 4 and a switch 6 installed in a previous stage.
Amplifier 8 is configured with, for example, a non-inverting amplifier. The buffer amplifier 4 and the amplifier 8 are installed in a reproduction signal processing system in a HiFi audio system of a video tape recorder, for example, and are configured as a part of a signal processing IC.

The switch 6 can be configured with a switch element such as a transistor on the IC or, in some cases, a switch outside the IC. Then, the hold pulse generating circuit 18 as a switching control unit for opening and closing the switch 6 is installed, in the hold pulse generator circuit 18, the audio head switching signal S _W from a predetermined section, e.g., 5-10
hold pulse P _H having a pulse width of about μsec is obtained, the hold pulse P _H is applied to the switch 6 as the switching control signal. Therefore, the head switching section T _H represented by this hold pulse P _H, the switch 6
Is controlled to the open state.

The amplifier 8 has a first resistor between its input and output sections.
A series circuit composed of a first capacitor 12 and a first capacitor 12 is provided, and a second capacitor 14 is provided at an input of the series circuit. Further, a second resistor 20 and a third capacitor 22 Are added in parallel. That is, the resistor 10 and the capacitor
A time constant circuit 26 is constituted by the differential hold circuit 24 and the resistor 20 and the capacitor 22 by 12 and 14. Different time constants are set in the differential hold circuit 24 and the time constant circuit 26 depending on the constant of each element.

Since it is configured as described above, the switch 6 is opened and closed by a hold pulse P _H shown in the second view taken from the hold pulse generating circuit 18 A, a high (H) level and becomes off at the head switching section T _H It is controlled to an (open) state and an on (closed) state at a low (L) level.

Therefore, when the switch 6 is ON, the capacitor 14, 22 is charged by the audio signal S _i, the charging voltage is obtained by charging current increases and decreases in response to the tangent of the audio signal S _i, the buffer amplifier 4 has an extremely low output impedance.
Terminal voltage of 14 and 22 becomes equal to the signal voltage of the audio signal S _i applied through a buffer amplifier 4. Holding voltage of the capacitor 14 is applied to the amplifier 8 is extracted from the output terminal 16 as the output audio signal S _0. In this case, since the input section of the amplifier 8 is placed via the switch 6 on the output side of the buffer amplifier 4 having an extremely low output impedance, the resistor 10 and the capacitor 10 provided on the feedback circuit side added to the amplifier 8 are provided. Differentiating operations such as 12 and 14 are stopped. As a result, the audio signal _Si is output from the output terminal without being affected by the feedback circuit system of the amplifier 8.
16 will be taken out as an output audio signal S ₀ from.

Further, the switch 6 is turned off, blocked the audio signal S _i from the buffer amplifier 4, the signal voltage is charged to the cut-off immediately before is held in the capacitor 14 is applied to the amplifier 8. At this time, the output of the amplifier 8 is fed back to the input side of the amplifier 8 through the feedback circuit, and the output signal voltage of the amplifier 8 is divided by the capacitors 12, 14 and the capacitor 22, and the divided voltage is supplied to the capacitors 14, 22. The partial pressure is accumulated. That is, the differential operation is performed by the differential hold circuit 24 including the resistor 10 and the capacitors 12 and 14, and the time constant circuit 26 including the resistor 20 and the capacitor 22. In this case, the time constant circuit 26 acts against a relatively high frequency in accordance with a constant, and its potential V _N is high frequency waveform midpoint level.

Such differentiation hold the corrected output from the amplifier 8 is obtained by differentiating operation, as shown in B of FIG. 2, the head switching section T _H in the differential hold the correction signal V _H2 is the output audio signal S ₀ which is added the output It is taken out from the terminal 16.

Incidentally, the relationship between the voltage V _M at the potential V _N and the capacitor 14 of the waveform midpoint of the time constant circuit 26, the resistance value of the resistor 20 R
Then, the current I = (V _M −V _N ) / R flows through the resistor 20, and the voltages of the capacitors 14 and 22 are averaged. Therefore, the differential hold correction signal V _H1 in the case of only the differential hold circuit 24 is By comparison, the peak value of the waveform of the fine powder hold correction signal _VH2 is suppressed, and the protrusion of the waveform is suppressed. Such a suppression effect becomes remarkable near the peak level of the audio signal waveform where the difference between the voltages V _M and V _N is large, and is small at the midpoint level of the audio signal waveform where the difference between the voltages V _M and V _N is small. The suppression effect is reduced, and effective differential hold correction is performed.
As a result, differential hold correction with small waveform distortion can be realized.

For example, as shown in FIG. 3, the audio signal S _i as a high-frequency component S _iH is superimposed on the low frequency components S _iL, when performing differential hold correction process, the only differentiating hold circuit 24 differential hold correction In contrast to the signal V _H1 , the addition of the time constant circuit 26 results in a differential hold correction signal V _H2 as shown by the solid line, and differential hold correction with small waveform distortion is performed. As a result, it is possible to suppress the waveform distortion and noise of the audio signal S _i during head switching to a minimum.

In the embodiment, one signal system has been described as an example. However, when a signal system of a plurality of channels is used for stereo reproduction or the like, a hold circuit may be provided for each channel.

Further, in the embodiments, the audio signal system in the HiFi audio system of the video tape recorder has been described as an example. However, the present invention is applicable to audio equipment, radio receivers, television receivers, video disc players, other playback equipment, and the like. And is not limited to video tape recorders.

〔The invention's effect〕

As described above, according to the present invention, by providing the differential hold circuit and the time constant circuit, the differential hold correction is performed with a double time constant with a very simple configuration, so that the head is switched and the signal is lost. In this case, abnormal waveform protrusion can be suppressed, differential hold correction with small waveform distortion can be performed, and noise due to waveform correction can be minimized. Waveform distortion of an audio signal at a frequency can be reduced as much as possible, and the fidelity of a music signal containing many high-frequency components can be increased.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a hold circuit of the present invention, FIGS. 2 and 3 are diagrams showing operation waveforms of the hold circuit shown in FIG. 1, and FIG. 4 is a diagram showing a conventional hold circuit. FIG. 5 is a circuit diagram, and FIG. 5 is a diagram showing the operation of the hold circuit shown in FIG. 6 Switch 8 Amplifier 10 First resistor 12 First capacitor 14 Second capacitor 20 Second resistor 22 Third capacitor 24 Differential hold circuit 26 …… Time constant circuit

Claims (1)

(57) [Claims] A switch disposed at an input of the amplifier for interrupting an input to the amplifier during a specific section of the audio signal; a first resistor connected between the input and output of the amplifier via a first resistor; A differential hold circuit, which is provided on the input side of the amplifier and holds an audio signal passing through the switch, together with the capacitor of the amplifier, and is connected to the second capacitor via a second resistor in parallel with the second capacitor. And a time constant circuit comprising a third capacitor.