JPS5929009B2 - signal expansion device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a signal expansion device whose input/output transfer characteristic is an exponential function.

BACKGROUND TECHNOLOGY AND PROBLEMS Conventionally, as a noise reduction method for improving the S/N ratio in a recording/playback system, dbx Corporation has proposed a method called a desilinear method as shown in FIG. 1.

In this method, during recording, the input signal Vin is applied to a compressor 1 having an output level proportional to the 1/2 power of the input level, the dynamic range is compressed to 1/2 in dB, and this compressed output V1 is In addition to an expander 3 that records on a recording medium 2 such as a magnetic tape or a record, and has an output proportional to the square of the input level, the playback output V2 during playback is added to an output Vout that doubles the dynamic range in dB. I'm trying to get it.

In this way, the dynamic range of the input signal Vin is reduced to 1/
By compressing the signal to 2 and expanding it to 2 during playback, the level of noise such as hiss and noise on the magnetic tape is substantially reduced without changing the signal level of the output Vout. . The compressor 1 and expander 3 shown in FIGS. 2A and 2B are conventionally known.

In the case of A in the same figure, the gain A is set to A=A by the control voltage Vc.
, eC1Vc (where Ao: reference gain, C: constant) A gain control circuit (hereinafter abbreviated as VCA) 4 that changes with an exponential function, the input Vi of this VCA 4 is input, and the output Vc is Vc=C2' 11nkVl (however, C2 and C2 are constants) and a logarithmic variable circuit 5a.

Also, what is shown in figure B is the above-mentioned VCA4 and this VCA.
4 output. As input, output Vc is Vc=Ci11nk
It is constituted by a logarithmic conversion circuit 5b that changes with V0. The circuit in A of the figure becomes a 1/2 power compressor by setting C2-2, and becomes a 2 power expander by setting C2=D. Further, the circuit shown in FIG. 2B becomes a 1/2 power compressor by setting C2=2, and becomes a 2 power expander by setting C2 -. The circuits shown in FIGS. 2A and 2B have the characteristic that arbitrary power transfer characteristics can be obtained by changing the ratio of C1 and C2.

However, deviations from the ideal characteristics of the VCA 4 and logarithmic conversion circuits 5a and 5b, temperature characteristics, variations in circuit elements, etc. directly affect the intended transfer characteristics.
It was difficult to obtain the /square characteristic and the square characteristic. In particular, variations in circuit elements must be suppressed with extremely high precision, making actual circuit design difficult. OBJECTS OF THE INVENTION The present invention solves the above problems and provides a signal expansion device that can easily obtain desired power characteristics.

Summary of the Invention The present invention provides first, second, third, and fourth series circuits each comprising m, n, k, and one VCAs connected in series; is connected between the input terminal and the output terminal, and the second, third, and fourth series circuits are connected in series, and the first stage of the second series circuit is connected to the input terminal, and the final stage is connected between the input terminal and the output terminal. The VCA of the second and third series circuits is controlled by a first control voltage obtained by adding the output voltage of the output voltage and a first bias voltage that is sufficiently larger than the output voltage. The output voltage of the final stage of the fourth series circuit and the second stage which is sufficiently larger than this output voltage.
The VCA of the first and fourth series circuits is controlled by a second control voltage obtained by adding the bias voltage of the first and fourth series circuits.

With this configuration, a particularly high-precision VC
A signal expansion device having desired power-law transfer characteristics can be easily obtained without using A. In the embodiment shown in FIG. 3, the input signal Vin is applied to m VCAs 6 connected in series, and the final stage VCA 6 outputs the output signal V.
.

It is designed to obtain ut. Each VCA6 has a control voltage V. The gain A (VG) is controlled by. On the other hand, a part of the input signal ViO is applied to n VCAs 7 connected in series, and the output V3 of the final stage VCA 7 is further applied to k VCAs 8 connected in series.

These VCAs 7 and 8 have their gain A controlled by the control voltage V.
(is controlled. A part of the output V3 is added to four points, and by adding the bias voltage -VBl at these five points, the control voltage V=V3-VBl is obtained. The output V4 of the final stage of the VCA 8 is further added to one VCA 9 connected in series to obtain an output V5.
The gain A (VG) of this VCA9 is controlled by the control voltage VG together with the VCA6. Further, the control voltage V is obtained by adding the output V5 and the bias voltage -VB2 at five points. -V5-VB2. The input/output of the VCA 6 is an AC signal, and the input/output of the VCAs 7, 8, and 9 are DC signals based on a rectified signal of the input signal Vin. Next, the input/output characteristics of the circuit with the above configuration will be explained.

In the circuit of FIG. 3, the following equation holds.

▼ JVDl assault 1▼' ▼ l[l A D
1 ζ-' From equations 1), (2), and (3), in equation (3), the power (1+button) that depends on the input Vin is determined if K, l, m, and n are each positive. (1 + 0)≧1 on the condition that it is an integer.

Bias voltages VBl and VB2 are DC voltages so that fluctuations in V and VG can be ignored, respectively, and by making these VBl and VB2 sufficiently large, the change in the term +VB2)l can be made small, and these can be regarded as approximately constant. Therefore, the above equation (8) is the output V. ut is input Vi
This indicates that the power function transfer characteristic is O. That is, by selecting K, l, m, and n, the circuit of FIG.
It becomes an expander with a power greater than 1. The circuit in Figure 3 is
In order to use it as the decompressor 3 whose exponent is 2 in Fig. 1,
From equation (8)? It suffices to set y=1, and to configure a circuit with the minimum gain, it suffices to set k-l-m=n=1.

VCAs 6, 7, 8, used in the circuit shown in FIG.
9, there is no need to use one whose input/output transfer characteristics change exponentially depending on the control voltage, and there is almost no influence from variations in circuit elements or temperature characteristics.
It is sufficient to simply use VCAs having substantially the same various characteristics.

Further, in FIG. 3, the VCA 6 is described as an AC system, and the VCAs 7, 8, and 9 are described as a DC system, but the VCA 6 may be a DC system. Effects of the Invention Each VCA does not need to have an exponential output characteristic, and the logarithmic conversion circuits 5a and 5b in FIGS. 2A and 2B are also not required.

Furthermore, there is almost no influence from variations in circuit elements, temperature characteristics, etc. Therefore, an expander having a desired expansion ratio can be easily obtained. In particular, when used in a noise reduction circuit, high quality audio processing can be performed.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of a conventional noise reduction device, Figs. 2 A and B are block diagrams showing an example of a conventional compressor and decompressor, and Fig. 3 is a block diagram showing an embodiment of the present invention. It is a diagram. In addition, in the symbols used in the drawings, 6, 7, 8,
9...VCA, Vin...input signal,
VOul...Output signal, -VBl, -VB2.
...It is voltage.

Claims (1)

[Claims] 1. Provide first, second, third, and fourth series circuits each consisting of m, n, k, and l voltage-controlled amplifiers connected in series, and The second, third, and fourth series circuits are connected in series between the input terminal and the output terminal, and the first stage of the second series circuit is connected to the input terminal, and the output of the final stage is connected between the input terminal and the output terminal. A first control voltage is obtained by adding the voltage and a first bias voltage that is sufficiently larger than the output voltage, and the amplifier constitutes the second and third series circuits using the first control voltage. A second control voltage is obtained by adding the output voltage of the final stage of the fourth series circuit and a second bias voltage that is sufficiently larger than this output voltage. By controlling the amplifiers constituting the first and fourth series circuits using the control voltage, the input signal applied to the input terminal is changed to [1+
(mk/nl)] is obtained from the output terminal.