JPH0512796A - Recording current mixing circuit - Google Patents

Abstract

(57) [Summary] [Configuration] FM audio signals and PCM audio signals are mixed,
Further, when superimposing a high frequency bias signal, the parallel resonance circuit 4 having a resonance point at the frequency of the high frequency bias signal is connected to the output side of the audio signal recording amplifier 3 and the output side of the high frequency bias signal recording amplifier 6 is A series resonance circuit 7 having a resonance point at the above frequency is connected to both circuits 4 and
The respective outputs of 7 are mixed and sent to the voice recording head 8. [Effect] By the parallel resonant circuit 4 and the series resonant circuit 7,
The current flowing from the high frequency bias signal recording amplifier 6 to the audio signal recording amplifier 3 side and the current flowing from the audio signal recording amplifier 3 to the high frequency bias signal recording amplifier 6 are suppressed, and the currents flowing in the audio recording head 8 are respectively reduced. To increase. As a result, power consumption can be reduced, and adverse effects such as interference with a video signal caused by flowing a large current can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording current mixing circuit, and more specifically, to an FM audio signal (Hi-Fi) on a recording medium such as a magnetic tape in a video tape recorder (hereinafter referred to as VTR). ) And a PCM audio signal by a high frequency bias method and the like.

[0002]

2. Description of the Related Art In recent years, also in a VTR, a method for recording an FM-modulated FM voice signal or a PCM-modulated PCM voice signal in order to improve sound quality has been developed. In addition to frequency-multiplexing with the above, a method of superposing a high-frequency bias signal on this to perform deep bias recording on the magnetic layer of the magnetic tape is under study.

The recording current mixing circuit in the high frequency bias recording system as described above, for example, as shown in FIG. 5, outputs a high frequency signal to the output line of the audio signal recording amplifier 21 to which the FM audio signal and the PCM audio signal are input. It can be configured by directly connecting the output line of the bias signal recording amplifier 22.

As a result, a composite audio signal of the FM audio signal and the PCM audio signal superimposed and amplified by the audio signal recording amplifier 21 is generated by the high frequency bias signal generating circuit 23 and amplified by the high frequency bias signal recording amplifier 22. The generated high frequency bias signal is superimposed and the superimposed signal is input to the voice recording head 24.

The frequency band of the FM audio signal is L-
ch is 1.3MHz ± 150kHz, R-ch is 1.7MH
z ± 150 kHz, and the frequency band of the PCM audio signal is 3.0 MHz ± 650 kHz. The frequency of the high frequency bias signal is, for example, 11 MHz.

[0006]

However, in the circuit configuration as described above, it is necessary to excessively amplify each of the amplifiers 21 and 22 in order to secure a sufficient signal level in the voice recording head 24. Is causing the problem. FIG. 6 shows an equivalent circuit of the circuit configuration of FIG. 5 viewed from the audio signal recording amplifier 21 side. In the figure, R ₂₁ is the internal impedance of the audio signal recording amplifier 21,
R ₂₂ is the internal impedance of the high frequency bias signal recording amplifier 22, and R ₂₃ is the impedance of the audio recording head 24. If R ₂₁ = R ₂₂ = 10Ω and the inductance of the audio recording head 24 is 14 μH at 3 MHz which is the signal band of PCM audio, then R
₂₃ becomes R ₂₃ = 2π × 3 MHz × 14 μH = 260Ω. That is, the current i flowing through the voice recording head 24
₂₃ is 1/26 of the current i ₂₂ flowing to the R ₂₂ (high frequency bias signal recording amplifier 22) side, and most of the current output from the audio signal recording amplifier 21 is to the high frequency bias signal recording amplifier 22 side. Flows. Therefore, in order for a sufficient recording current to flow through the audio recording head 24, the amplification in the audio signal recording amplifier 21 needs to be sufficiently large.

On the other hand, FIG. 7 shows an equivalent circuit in which the circuit configuration of FIG. 5 is viewed from the high frequency bias signal recording amplifier 22 side. In the figure, R ₂₄ is the impedance of the voice recording head 24 at 11 MHz, and if the inductance of this voice recording head 24 is 25 μH at 11 MHz, then R ₂₄ = 2π × 11 MHz × 25 μH = 1.7 kΩ. Therefore, the current i flowing through the voice recording head 24
₂₄ is 1/170 of the current i ₂₁ flowing to the R ₂₁ (audio signal recording amplifier 21) side, and most of the current output from the high frequency bias signal recording amplifier 22 is to the audio signal recording amplifier 21 side. Flows. Therefore, in order to allow a sufficient high frequency bias recording current to flow through the audio recording head 23, the high frequency bias signal recording amplifier 22 is also provided.
It is necessary to increase the amplification in the above.

As described above, in order to pass the proper recording currents for FM voice and PCM voice and the high frequency bias current, the currents which are 26 times and 170 times, respectively, are required as compared with the case where both recording currents are not mixed. Becomes For this reason, excessive power consumption occurs in each amplifier 21 and 22, and a high-frequency interference signal level due to the flow of a large current increases, which causes problems such as giving interference noise to an image.

[0009]

In order to solve the above-mentioned problems, the recording current mixing circuit of the present invention has an FM audio signal and a P audio signal.
An output line of an audio signal recording amplifier that mixes and amplifies a CM audio signal with an output line of a high frequency bias signal recording amplifier that amplifies a high frequency bias signal having a frequency higher than the frequency band of the audio signal. Connect,
A recording current mixing circuit that sends a mixed signal of the audio signal and a high-frequency bias signal from the interconnection point to the audio recording head, wherein an audio signal is provided between the audio signal recording amplifier and the interconnection point. The first directivity imparting means having frequency characteristics of low impedance in the signal frequency band and high impedance in the high frequency bias signal frequency band is provided, and between the high frequency bias signal recording amplifier and the interconnection point. In addition, a second directionality imparting means having a frequency characteristic of high impedance in the frequency band of the audio signal and low impedance in the frequency band of the high frequency bias signal is interposed.

[0010]

In the above structure, with respect to the audio signal output from the audio signal recording amplifier, the current flowing to the high frequency bias signal recording amplifier side is suppressed by the second directionality imparting means, and the audio recording head. The signal current flowing through the circuit increases. Further, for the high frequency bias signal output from the high frequency bias signal recording amplifier, the current flowing to the audio signal recording amplifier side is suppressed by the first directionality imparting means, and the signal current flowing to the audio recording head is reduced. To increase. In this way, the audio signal currents and high-frequency bias signals output from both amplifiers, respectively, flowing in the audio recording head can be increased more than before, so that the amplification factor of both amplifiers can be made smaller. As a result, the power consumption can be reduced and the adverse effects such as the interference of the high frequency component with the video signal due to the large current flowing can be suppressed.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe one embodiment of the present invention with reference to FIGS.

The FM audio signal and the PCM audio signal respectively output from the FM audio signal modulation circuit 1 and the PCM audio signal modulation circuit 2 are input to the audio signal recording amplifier 3. The FM audio signal and the PCM audio signal that have been superimposed in the audio signal recording amplifier 3 are mixed, and the mixed audio signal is further amplified and then input to the parallel resonance circuit 4 described later.

On the other hand, a high frequency bias signal is generated by the high frequency bias signal generation circuit 5, and this high frequency bias signal is amplified by a high frequency bias signal recording amplifier 6 and then input to a series resonance circuit 7 described later.

Then, the high frequency bias signal output from the series resonance circuit 7 is superimposed on the audio signal output from the parallel resonance circuit 4, and the superimposed signal flows to the audio recording head 8 and the magnetic recording tape 9 is inserted. Recorded in.

The frequency spectrum of the superimposed signal is shown in FIG.
As shown in (a), it is 1.3 MHz ± 150 kHz for the L-ch, 1.7 MHz ± 150 kHz for the R-ch, and 3.0 MHz for the PCM audio signal in the FM audio signal. Each frequency band of ± 650 kHz is set. The frequency of the high frequency bias signal is 11.0 MHz.

On the other hand, as shown in FIG. 1, the parallel resonance circuit 4 as the first directivity imparting means is formed by connecting a coil 4a and a capacitor 4b in parallel, and has a resonance frequency f ₁ , that is, f ₁ = 1 / [2 · π · (L ₁ · C ₁ ) ^1/2 ] where L ₁ : the inductance of the coil 4 a C ₁ : the capacity of the capacitor 4 b substantially matches the frequency of the high frequency bias signal of 11.0 MHz. Thus, the coil 4a and the capacitor 4b are selected. Therefore, this parallel resonant circuit 4
As shown in FIG. 2 (b), the impedance is sufficiently high near the frequency of 11.0 MHz, while the impedance is sufficiently low in the band of the audio signal.

As shown in FIG. 1, the series resonance circuit 7 as the second directivity imparting means is formed by connecting a coil 7a and a capacitor 7b in series, and the resonance frequency f ₂ in this case, that is, f ₂ = 1 / [2 · π · (L ₂ · C ₂ ) ^1/2 ] where L _{2 is} the inductance of the coil 7 a, C _{2 is} the capacity of the capacitor 7 b, and the frequency of the high frequency bias signal is approximately 11.0 MHz. The coil 7a and the capacitor 7b are selected so as to match each other. Therefore, this series resonance circuit 7
As shown in FIG. 2 (c), the impedance has a sufficiently low impedance near the frequency of 11.0 MHz, while the impedance has a sufficiently high frequency characteristic in the band of the audio signal.

FIG. 3 shows an equivalent circuit in which the circuit configuration of FIG. 1 is viewed from the output side of the audio signal recording amplifier 3. In the figure, R ₁ is the internal impedance of the audio signal recording amplifier 3, R ₂ is the internal impedance of the high frequency bias signal recording amplifier 6, and R ₃ is the audio signal frequency band (1.3 MHz, 1.7 MHz, 3.0 MHz). Is the impedance of the voice recording head 8. In addition, R ₅ and R ₆ are parallel resonance circuits 4 and 4 in the audio signal frequency band, respectively.
These are the impedances of the series resonance circuit 7.

Here, for example, the inductance of the voice recording head 8 is set to 3.0 MHz which is the frequency band of the PCM voice signal.
If z is 14 μH, R ₃ = 2π × 3.0 MHz × 14 μH = 260Ω. Further, since the audio signal recording amplifier 3 and the high frequency bias signal recording amplifier 6 are usually designed to have sufficiently small internal impedances as compared with the impedance of the audio recording head 8, respectively, for example, R ₁ = R ₂ = 10Ω. And in this case,
R ₅ connected in series with R ₁ and R ₆ connected in series with R ₂ are impedances at frequencies other than the resonance frequency in the parallel resonant circuit 4 and the series resonant circuit 7, respectively, in the vicinity of 3 MHz. Is R ₅ = 15Ω, R ₆
= Impedance of about 2.4 kΩ. This allows
The current i ₆ flowing from the audio signal recording amplifier 3 to the high frequency bias signal recording amplifier 6 side is about 1/10 of the current i ₃ flowing to the audio recording head 8, and the audio signal recording amplifier 3 outputs the current i _6. Most of the audio signal current of the current flows through the audio recording head 8.

On the other hand, FIG. 4 shows an equivalent circuit of the circuit configuration in FIG. 1 viewed from the high frequency bias signal recording amplifier 6 side. R ₁ and R ₂ are the same as in FIG. R ₄ is the impedance of the voice recording head 8. Since the audio recording head 8 is adapted to send a signal through a signal transmission path provided, for example, a rotary transformer (not shown), the inductance of the audio recording head 8 is included by including this signal transmission path. Is defined as
This inductance depends on the frequency. Therefore, assuming that the inductance is 25 μH at 11 MHz, the impedance R ₄ of the voice recording head 8 is R ₄ = 2π × 11 MHz × 25 μH = 970Ω. On the other hand, R ₈ is the resonance frequency 1 of the series resonance circuit 7.
The impedance at 1 MHz is sufficiently small, and R ₇ is sufficiently large at the resonance frequency of 11 MHz of the parallel resonant circuit 4. Therefore, most of the high frequency bias signal output from the high frequency bias signal recording amplifier 6 flows to the audio recording head 8.

As described above, most of the audio signal current output from the audio signal recording amplifier 3 and the high frequency bias signal output from the high frequency bias signal recording amplifier 6 flow to the audio recording head 8. , Both amplifiers 3
The output current from 6 is effectively used for recording on the magnetic recording tape 9. As a result, the power consumption of both amplifiers 3 and 6 can be reduced, and the adverse effects such as the interference of the high frequency component with the video signal due to the large current flowing can be eliminated.

In the above-described embodiment, the parallel resonance circuit 4 is provided with the first directivity imparting means having the frequency characteristic of low impedance in the frequency band of the audio signal and high impedance in the frequency of the high frequency bias signal.
In addition, the second resonance directing means having the frequency characteristics of high impedance in the frequency band of the audio signal and low impedance in the frequency of the high frequency bias signal has been described by using the series resonance circuit 7. However, other configurations such as a filter circuit having the above-mentioned frequency characteristic can be adopted.

[0023]

As described above, the recording current mixing circuit of the present invention includes the interconnection point between the output line of the audio signal recording amplifier and the output line of the high frequency bias signal recording amplifier, and the above audio signal recording amplifier. A first directivity imparting means having a frequency characteristic of low impedance in the frequency band of the audio signal and high impedance in the frequency band of the high frequency bias signal is interposed between the two, and the high frequency bias signal recording amplifier and the above-mentioned mutual amplifier are provided. A second directionality imparting means having a frequency characteristic of high impedance in the frequency band of the audio signal and low impedance in the frequency band of the high frequency bias signal is interposed between the connection point and the connection point.

Therefore, the audio signal current and the high frequency bias signal current, which are respectively output from the audio signal recording amplifier and the high frequency bias signal recording amplifier, flowing in the audio recording head are increased more than in the conventional case. It is possible to further reduce the amplification factor at, and as a result, it is possible to reduce the power consumption and suppress the adverse effects such as the interference of the high frequency component with the video signal due to the flow of a large current. Produce an effect.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing a configuration of a recording current mixing circuit in an embodiment of the present invention.

FIG. 2 is a graph showing frequency characteristics of the circuit, where (a) is a graph showing a frequency spectrum of a superimposed signal in which respective output signals from the parallel resonant circuit and the series resonant circuit in the circuit are superimposed, 7B is a graph showing the frequency characteristic of the parallel resonant circuit in the circuit, and FIG. 9C is a graph showing the frequency characteristic of the series resonant circuit in the circuit.

FIG. 3 is an equivalent circuit diagram seen from the audio signal recording amplifier side in the circuit.

FIG. 4 is an equivalent circuit diagram of the above circuit viewed from a high frequency bias signal recording amplifier side.

FIG. 5 is a circuit block diagram showing a configuration of a conventional recording current mixing circuit.

FIG. 6 is an equivalent circuit diagram seen from the audio signal recording amplifier side in the conventional circuit.

FIG. 7 is an equivalent circuit diagram viewed from the high frequency bias signal recording amplifier side in a conventional circuit.

[Explanation of symbols]

 3 Audio signal recording amplifier 4 Parallel resonance circuit (first directionality imparting means) 6 High frequency bias signal recording amplifier 7 Series resonance circuit (second directionality imparting means) 8 Audio recording head

Claims (1)

Claim: What is claimed is: 1. An output line of an audio signal recording amplifier for mixing and amplifying an FM audio signal and a PCM audio signal, and a high frequency bias signal having a frequency higher than the frequency band of the audio signal. A recording current mixing circuit that connects the output line of a high-frequency bias signal recording amplifier to be amplified to each other and sends a mixed signal of the audio signal and the high-frequency bias signal to the audio recording head from this interconnection point. And a first directionality imparting means having a frequency characteristic of low impedance in the frequency band of the audio signal and high impedance in the frequency band of the high frequency bias signal between the audio signal recording amplifier and the interconnection point. Along with the installation, between the high frequency bias signal recording amplifier and the interconnection point,
A recording current mixing circuit, wherein a second directionality imparting means having a frequency characteristic of high impedance in a frequency band of an audio signal and low impedance in a frequency band of a high frequency bias signal is interposed.