JPH10145741A - Output circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an output circuit simplified in circuit structure capable of minimizing a disturbance owing to a frequency-multiplexed sound signal. SOLUTION: Sound signals S1 and S2 are modulated into FM signals S11 and S13 having central frequencies f1 and f2 respectively by FM modulators 11 and 13 respectively. These FM signals are mixed by a mixer 15. The mixed signal S15 attenuates its harmonic components by a low-pass filter 20, and giving the component of frequency 3f1 an attenuation >=30.5 dB, so that respective filter processing to the FM signals S11 and S13 are omitted, restraint of harmonic component is realized only using one low-pass filter 20, its circuit structure is simplified, and disturbance owing to the harmonic components of a frequency- multiplexed sound signal is minimized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a video tape recorder (VTR).
The present invention relates to an output circuit that is used for a pe recorder, for example, and that frequency-multiplexes an audio signal and outputs it to a recording circuit together with a video signal.

[0002]

2. Description of the Related Art A video signal and an audio signal are recorded using a magnetic tape, and a V signal for reproducing the recorded signals is used.
In the TR, at the time of signal recording, the audio signal is frequency-multiplexed, recorded as a magnetic signal on a track of a magnetic tape by a rotary head together with a video signal, and at the time of reproduction, the magnetic signal recorded on the magnetic tape is read by the rotary head. Converts to electrical signals and outputs.

[0003] In this case, recording or reproduction processing is performed using a signal obtained by FM-modulating an audio signal. For example, 8mmVT
In R, when the audio signal is recorded as a stereo signal, the center frequency of the FM modulation is 1.
5 MHz and 1.7 MHz. FIG. 7 is a diagram showing a spectrum S (f) of an FM-modulated audio signal and video signal. As shown in FIG. 7, the center frequency f ₁ of the main channel of the FM-modulated audio signal is 1.5 MHz, the frequency shift is usually ± 60 kHz, and the maximum is ± 1 kHz.
00 kHz, center frequency f ₂ of sub-channel is 1.7 MH
z, and the frequency shift is slightly less than the main channel, typically ± 30 kHz and up to ± 50 kHz.

On the other hand, the carrier of an FM-modulated video signal has a frequency band from 4.2 MHz to 5.4 MHz in a normal mode, and from 5.7 MHz to 7.7 in a high band mode. It has a frequency band up to 7 MHz and each sideband extends below it. FIG. 8 shows the spectrum of an FM-modulated video signal in an 8 mm VTR. FIG. 8A shows the spectrum of a video signal in the normal mode. In FIG. 8A, f ₃ is 4.2 MHz, and f ₄ is 5.4.
MHz are shown. FIG. 8B shows the spectrum of a video signal in the high band mode. FIG.
In (b), f ₅ is 5.7MHz, f ₆ is 7.7M
Hz are shown. For reference, FIG.
₂ also shows the center frequencies f ₁ and f ₂ of the FM-modulated audio signal.

As described above, it is necessary to sufficiently attenuate the harmonic components of the FM-modulated audio signal so as not to interfere with the FM-modulated video signal existing on the high frequency side. Therefore, the conventional output circuit 10a has a configuration as shown in FIG. In FIG. 9, 11 and 13
Is an FM modulator, 12 and 14 are low-pass filters, 1
Reference numerals 5 and 16 denote mixers.

The center frequency of the FM modulator 11 is 1.5 MHz
z, and the center frequency of the FM modulator 13 is 1.7 MHz.
It is. A main audio signal S ₁ , for example, a sum signal (L + R) of a left channel L and a right channel R in a stereo signal is input from an input terminal T ₁ to an FM modulator 11, and is input to an FM modulator 13 from an input terminal T ₂ . The sub audio signal S ₂ , for example,
A difference signal (LR) between a left channel L and a right channel R in a stereo signal is input.

The FM modulator 11 uses the input main audio signal S ₁ as a modulation signal, with a center frequency of 1.5 MHz,
A frequency shift is normally ± 60 kHz, and a maximum frequency of ± 100 kHz is generated. An FM modulator 13 generates an FM-modulated signal S _{11. The} FM modulator 13 uses the input main audio signal S ₂ as a modulation signal and has a center frequency of 1.7 MHz and a frequency shift of 1.7 MHz. Normally ± 30 kh
z, FM modulated signal S ₁₃ of up to ± 50 kHz is generated.

[0010] The FM-modulated signal S ₁₁ is filtered through a low-pass filter 12 to remove harmonic components, and the FM signal S ₁₂
Is input to the mixer 15. Similarly, the FM-modulated signal S ₁₃ has its harmonic components removed via a low-pass filter 14 and is input to the mixer 15 as an FM signal S ₁₄ .

The low pass filter 12 is controlled by the mixer 15.
And FM signals S ₁₂ input from 14, mixed signal S ₁₅ as a mixture of S ₁₄ is generated. Thus, the mixer 15
Accordingly, the audio multiplex signal S ₁₅ which is FM frequency multiplexed is generated. Sound multiplex signal S ₁₅ is further input to the mixer 16, is mixed with the video signal S ₃ which is FM-modulated, mixed signal S ₁₆ of a frequency multiplexed audio and video is generated. The mixed signal S ₁₆ generated by the mixer 16 is recorded on a video tape by a rotating head.

[0010]

By the way, in the above-mentioned conventional output circuit, the FM-modulated audio signal generated by the FM modulators 11 and 13 converts the FM-modulated video signal existing on the high-frequency side thereof. High-frequency components are attenuated using low-pass filters 12 and 14 so as not to disturb the signal. For this reason, in the conventional output circuit, low-pass filters are provided at the outputs of the FM modulators of the main sound and the sub sound, respectively. Further, since these low-pass filters do not interfere with the FM-modulated video signal existing near the high-frequency side of the FM-modulated audio signal, a high-order, for example, a sixth-order low-pass filter is used. As a result, there is a problem that the number of circuit elements constituting the low-pass filter is increased, and the circuit configuration is complicated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an output circuit capable of simplifying a circuit configuration and minimizing interference by a frequency-multiplexed audio signal. It is in.

[0012]

According to the present invention, there is provided an output circuit for multiplexing a plurality of signals having different frequencies and outputting the multiplexed signals, wherein the first circuit has at least a first frequency component. Mixing means for mixing the second signal having the second frequency component and a second signal having a second frequency component, and a predetermined signal determined based on the first and second frequency components with respect to the signal mixed by the mixing means. A filter that attenuates frequency components and outputs the resulting signals.

In the present invention, preferably, the filter is constituted by a low-pass filter or a band-pass filter, and the pass band of the low-pass filter or the band-pass filter corresponds to the first and second frequency components. It is set according to.

Further, according to the present invention, there is provided an output circuit for outputting a frequency-multiplexed first sequence signal and a second sequence signal to a recording system circuit, wherein at least two signals having different frequency components are mixed. A first mixing means for generating the first sequence signal, and a predetermined signal determined based on frequency components of the two signals with respect to the first sequence signal generated by the first mixing means. And a second mixing means for mixing and outputting the output signal of the filter and the signal of the second series.

According to the present invention, a first signal having a first frequency component and a second signal having a second frequency component are mixed by a mixing means, and a frequency-multiplexed first sequence signal is mixed. Is generated. The first series of signals passes through a filter, and only signals in a band set according to the first and second frequencies pass therethrough, and other frequency components are attenuated. Further, the output signal of the filter is combined with the second series signal, and the combined signal is output to the recording system circuit.

Thus, for example, only necessary frequency components included in the first and second signals composed of frequency-modulated audio signals are left, and unnecessary components, for example,
Since the harmonic component is attenuated by the filter, the filtering process for each of the first and second signals is realized only by the filtering process for the frequency-multiplexed first series signal, so that the circuit configuration can be simplified, and the frequency multiplexing can be performed. Therefore, it is possible to minimize the interference with the video signal, which is the second series signal, due to the harmonic component of the converted audio signal.

[0017]

FIG. 1 is a circuit diagram showing an embodiment of an output circuit according to the present invention. In FIG. 1, reference numeral 10 denotes an output circuit, 11 and 13 denote FM modulators, 15 and 16 denote mixers, and 20 denotes a low-pass filter.

Input terminals T ₁ and T ₂ are connected to a main audio signal S ₁ and a sub audio signal S _{1 in the same} manner as in the conventional output circuit shown in FIG.
₂ is input respectively. Then, the FM modulators 11 and 13 generate FM-modulated audio signals S ₁₁ and S ₁₃ having a center frequency of 1.5 MHz and a center frequency of 1.7 MHz, respectively. These FM-modulated signals are input to the mixer 15.

The mixer 15 generates a frequency-multiplexed audio signal S ₁₅ and inputs it to the low-pass filter 20. By the low-pass filter 20, is the harmonic component is attenuated in the frequency multiplexed audio signal S ₁₅ from the mixer 15, as an audio signal S ₂₀ which is frequency multiplexed and outputted.

[0020] Incidentally, the audio signal S ₂₀ which is frequency multiplexed is generated by the low pass filter 20 is input to the mixer 16 at the next stage, is further mixed with the video signal S ₃ which is FM-modulated, the signal S ₁₆ Generated. Mixed signal S ₁₆ is outputted to the storage circuit, for example, by a rotary head, it is recorded on the magnetic tape.

Hereinafter, the operation of the output circuit of the present invention will be described with reference to FIG. In FIG. 1, an output signal S ₁₁ from the FM modulator ₁₁ has, for example, a center frequency of 1.
5MHz, frequency shift is usually 60kHz, maximum 100k
Hz FM-modulated signal, and the output signal S ₁₃ from the FM modulator ₁₃ has, for example, a center frequency of 1.7 MHz,
Frequency deviation is usually ± 30 kHz, F ± 50 kHz maximum
This is an M-modulated signal.

The FM-modulated signals S ₁₁ and S ₁₃ are both input to a mixer 15, which generates a sum signal S ₁₅ of these signals. Sum signal S ₁₅ is a so-called frequency multiplexed audio signal. Some frequency multiplexed audio signal S _15, in addition to 1.5MHz and 1.7MHz frequency component is a fundamental wave of the signal S ₁₁ and the signal S _13, also mixed harmonic components of these frequency components ing. That is, the spectrum of the signal S ₁₅ is as shown in FIG.

Here, since the frequency component of the FM-modulated video signal S ₃ exists in the high frequency range of the FM-modulated audio signal as described above with reference to FIG. May interfere with the FM-modulated video signal. To suppress this, the low-pass filter 20, it is necessary to sufficiently attenuate these harmonic components in the signal S _15.

Here, the FM modulator 11 and the FM modulator 11
The modulator 13 becomes an output signal of a voltage controlled oscillator (VCO) and has, for example, a cycle of the audio signal S ₁ or the audio signal S _2.
Is a rectangular wave that changes in accordance with. The Fourier series of such a square wave is represented by the following equation.

[0025]

S (t) = 4 (sinωt + sin3ωt / 3 + sin5ωt / 5 + ...) / πω = 2πf (1)

In the equation (1), the sin ωt component is used as a fundamental wave, for example, the above-described FM-modulated audio signal S _11.
And the center frequency f _1, f ₂ of S _13. According to the equation (1), the amplitude of the third harmonic of the center frequency is 1/3 of the amplitude of the fundamental wave, that is, 9.5 dB lower than the fundamental wave. For this reason, it is particularly necessary to sufficiently attenuate the third harmonic component of the component obtained by FM-modulating the audio signal. In order to suppress the influence on the FM-modulated video signal, it is necessary to attenuate the third harmonic component of the FM-modulated audio signal mixed with the video signal to, for example, -40 dB or less with respect to the fundamental wave. If so, the low-pass filter 20 connected downstream of the mixer 15 needs to attenuate the third harmonic component of the FM-modulated video signal by 30.5 dB.

FIG. 3 is a graph showing an example of the transfer characteristic of the low-pass filter 20 satisfying such conditions.
Of the output signals of the mixer 15, the center frequencies f ₁ and f ₂
Of the third harmonic component are 4.5 MHz and 5.1 MHz, respectively. In the example of the low-pass filter shown in FIG. 3, the cut-off frequency f _C is 2.8 MHz,
At 4.5 MHz, it has a transfer characteristic of attenuating 30.5 dB.

FIG. 4 shows an example of a circuit of the low-pass filter having the above-described transfer characteristics. FIG. 4 shows a sixth-order active low-pass filter including a resistance element, a capacitor, and an amplifier. In FIG. 4, two-stage low-pass filters LPF ₀₁ and LPF ₀₂ are connected in series. Since the low-pass filter of each stage has a similar configuration, the low-pass filter LP
A description will be given using only _F01 as an example.

As shown in FIG. 4, the front stage of the low-pass filter LPF _01, the resistance element _{R 1, R 2, R 3} , it is constituted by a capacitor C _1, C _2, C ₃ and the amplifier AMP _1. As shown, the resistance elements R ₁ , R ₂ , R ₃ and the amplifier AMP ₁ are connected in series. Resistance element R
₁ is connected to the input terminal T _IN, the output terminal of the amplifier AMP ₁ constitutes the output terminal of the low pass filter LPF _01, and is further connected to an input terminal of the next stage of the low pass filter LPF _02. Between the resistor element R ₁ and the connection point of the resistance element R ₂ and the ground line, the capacitor C ₁ is connected. Capacitor C ₃ is connected between the resistance element R ₂ and the output terminal of the connection point between the amplifier AMP ₁ of the resistance element R _3. Between the connection point of the input terminal of the resistor R ₃ and the amplifier AMP ₁ and the ground line, the capacitor C ₂ is connected.

In this example, the resistance elements R ₁ , R ₂ ,
The resistance value of R ₃ is 5 kΩ, 4 kΩ, 4 kΩ, respectively, and the capacitance value of capacitors C ₁ , C ₂ , C ₃ is 2.5 p each.
F, 3 pF, and 15 pF. Amplifier A
The amplification factor of MP ₁ is 1.

The structure of the low-pass filter LPF ₀₂ is the same as that of the low-pass filter LPF ₀₁ as described above, will not be described here in its detail. Thus, the low-pass filters LPF ₀₁ and LPF ₀₂ connected in series provide:
A low-pass filter having the transfer characteristics shown in FIG. 3 is realized.

In FIG. 1, the low-pass filter 2
High pass filter (HPF) before or after 0
Is connected, the effect of the low-frequency signal included in the output signal of the mixer 15 can be suppressed. In this case,
The transfer characteristic of the high-pass filter is shown by a dotted line in FIG.

The output signal S ₂₀ of the low-pass filter 20 is further mixed by the mixer 16 with the FM-modulated video signal S ₃ to output a mixed signal S ₁₆ . This mixed signal S
₁₆ is recorded on the magnetic tape, for example, by the recording circuit. As described above, the third FM modulated audio signal contained in the output signal S ₂₀ of the low-pass filter 20
The second harmonic component is sufficiently attenuated with respect to the fundamental component, and the influence of these harmonic components on the FM-modulated video signal is suppressed to a negligible level.

As described above, according to the present embodiment, the audio signals S ₁ and S ₂ are converted by the FM modulators 11 and 13 into the FM signals S ₁₁ and S _{2 having} the center frequencies f ₁ and f ₂ , respectively.
₁₃ is modulated into, these FM signals after being mixed by the mixer 15, a mixed signal S ₁₅ is a low-pass filter 20 to remove harmonic components, for example, gives an attenuation of 30.5dB the component of the frequency 3f ₁ Therefore, the FM signals S ₁₁ and S
₁₃ can be implemented by the low-pass filter 20, the circuit configuration can be simplified, and interference by harmonic components of the frequency-multiplexed audio signal can be suppressed to a minimum.

Further, the low-pass filter 20 shown in FIG.
Instead of, as shown in FIG. 5, it is also possible to use a band-pass filter BPF ₁ downstream of the mixer 15. In this case, transfer characteristics of the band-pass filter BPF ₁ is 6
Is shown in That is, the characteristics obtained even when the band-pass filter BPF ₁ is used are the same as the transfer characteristics when both the low-pass filter and the high-pass filter shown in FIG. 3 are used. The band-pass filter BPF _1, the output signal S ₁₅ of the mixer 15 shown in FIG. 1,
The frequency components of 1.5 MHz and 1.7 MHz are passed without attenuation, and the frequency components of 4.5 MHz or more are attenuated, for example, 30.5 dB or more so as not to affect the FM-modulated video signal. .

As described above, according to the present invention, the mixer 1
As shown in FIG. 3, the filter used at the subsequent stage of FIG. 5 passes the frequency components of the center frequencies 1.5 MHz and 1.7 MHz without attenuating, and is necessary for the frequency components of the frequency of 4.5 MHz or more. What is necessary is just to have the transfer characteristic which fully attenuates, and is not limited to a low-pass filter. Further, when configuring the filter, any of the configuration methods such as Butterworth and Chebyshev may be used, and it goes without saying that the configuration method of the filter is not particularly limited. Also, in this case, the attenuation amount is described for convenience of explanation, but this is not specified.

[0037]

As described above, according to the output circuit of the present invention, there is an advantage that the circuit configuration can be simplified and interference due to frequency-multiplexed audio signals can be suppressed to a minimum.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating an embodiment of an output circuit according to the present invention.

FIG. 2 is a graph showing a spectrum of a mixer output signal.

FIG. 3 is a graph showing a transfer characteristic of a filter.

FIG. 4 is a circuit diagram illustrating a configuration example of a filter.

FIG. 5 is a circuit diagram showing another configuration example of the present invention.

FIG. 6 is a graph showing transfer characteristics of a bandpass filter.

FIG. 7 is a graph showing a spectrum of a frequency multiplexed audio signal and a video signal.

FIG. 8 is a graph showing a video signal and its spectrum.

FIG. 9 is a circuit diagram illustrating a configuration example of a conventional output circuit.

[Explanation of symbols]

11, 13 ... FM modulator, 12, 14, 20 ... low-pass filter, 15, 16 ... mixer, 22 ... band-pass _{filter, R 1, R 2, R} 3, R 4, R 5, R 6 ... resistance element, _{C 1, C 2, C 3} , C 4, C 5, C 6 ... capacitors, AMP _1, AMP ₂ ... amplifier, V _CC ... power supply voltage, G
ND: Set potential.

Claims (8)

[Claims] An output circuit for frequency-multiplexing and outputting a plurality of signals having different frequencies, comprising: a first signal having at least a first frequency component;
Mixing means for mixing a second signal having the following frequency component, and a first signal for the signal mixed by the mixing means.
And a filter for attenuating and outputting a predetermined frequency component determined based on the second frequency component. 2. The output circuit according to claim 1, wherein said first signal and said second signal are frequency-modulated audio signals. 3. The output circuit according to claim 1, wherein said filter is a low-pass filter. 4. The output circuit according to claim 3, wherein a pass bandwidth of said low-pass filter is set according to frequencies of said first and second signals. 5. The output circuit according to claim 1, wherein said filter is a band pass filter. 6. The pass band width of said band pass filter is:
6. The output circuit according to claim 5, wherein the output circuit is set according to the frequencies of the first and second signals. 7. An output circuit for outputting a second sequence signal together with a frequency-multiplexed first sequence signal to a recording system circuit, wherein at least two signals having different frequency components are mixed,
First mixing means for generating the first series of signals; and a predetermined signal determined based on frequency components of the two signals with respect to the first series of signals generated by the first mixing means. An output circuit comprising: a filter for attenuating a frequency component; and second mixing means for mixing and outputting the output signal of the filter and the second series of signals. 8. The output circuit according to claim 7, wherein said first sequence signal is a frequency-multiplexed audio signal, and said second sequence signal is a frequency-modulated video signal.