JPS6410965B2 - - Google Patents

Description

[Detailed description of the invention]

(Technical Field) The present invention relates to a frequency characteristic correction circuit (hereinafter referred to as a correction circuit). (Prior Art) As a conventional correction circuit, for example, a high frequency correction circuit as shown in FIG. 3 has been known. In the figure, 21 is an input terminal, 22 and 24 are resistors, 23 is a volume, 26 and 27 are capacitors, and 25 is an output terminal. In this case, the phase characteristic at the output terminal 25 is 0° at low and high frequencies, as shown in FIG. 2, but the phase changes significantly at mid-range frequencies depending on the setting position of the volume 23. Therefore, in an audio amplifier or the like having two left and right channels, if a correction circuit as described above is inserted for each channel, the phase difference will differ as shown in Fig. 2, depending on the characteristic setting state of each correction circuit.
At mid-range frequencies, the phase difference between the left and right channels becomes very large. (Objective) An object of the present invention is to provide a correction circuit that does not have the above-mentioned drawbacks, and will be described in detail below with reference to the drawings. (Example) FIG. 1 shows an example of the present invention. In the figure, an input signal applied to an input terminal 11 is branched into two, one being applied to an inverting input terminal 16 of a broadband amplifier 14 via a resistor 12, and the other being applied to a variable resistor 18.
is applied to the output terminal 15 via. The non-inverting input terminal 17 of the wideband amplifier 14 is grounded, and the output is branched into two, one being applied to the output terminal 15 via the capacitor 19, and the other being negatively fed back to the inverting input terminal 16 via the variable resistor 13. be done. The variable resistors 13 and 18 are variable in conjunction with each other. In this circuit, the resistance value of resistor 12 is R ₀ ,
The set resistance values of the variable resistors 13 and 18 are K・R ₀ and R, respectively, and the capacitance of the capacitor 19 is C.
Then, the transfer function G(jω) of this circuit is G(jω)=1−jωKCR/1+jωCR ……(1) Therefore, this phase characteristic arqG(jω) is arqG(jω)=−(tan ^-1 KωCR+tan ^-1 ωCR) ...(2) Now assuming that the phase is 90° at the point where the angular velocity ω becomes ω ₀ , the variable resistor 18 and capacitor 19
The time constant CR of the series circuit is given by equation (2). becomes. Now, by substituting equation (3) into equation (1) and finding the amplitude characteristic, And the phase characteristic in this case can be substituted into equation (3) as becomes. Therefore, if the time constant CR of the series circuit is changed in accordance with the change in K so as to maintain the relationship of equation (3), the amplitude characteristic will change according to each value of K according to equation (4). It can be seen that the result is as shown in Figure 4. Note that since the value of K is equal to the degree of amplification for the low frequency range, it is converted into decibels and shown in the figure. In addition, the phase characteristics change according to equation (5) depending on the value of K, as shown in Figure 5, and are approximately 0° in the low range of angular velocity, -90° at angular velocity ω ₀ , and -90° in the high range. is approximately -180°, and this relationship does not change even if the value of K is changed. In areas other than the three frequency points mentioned above, slight fluctuations in phase characteristics occur depending on the value of K, but there is no large fluctuation in phase as in the conventional example shown in Figure 2. . FIG. 6 shows that K is 3.16 (+10 dB) or 1/3.16 (-
10 dB) and K is 2 (+6 dB) or 1/2 (-
6dB), and it can be seen that in this case, only a maximum phase difference of about ±4.5° occurs. Therefore, in a multi-channel amplifier, if a correction circuit such as the one described above is used for each channel, the phase difference between each channel will be very small even if the adjustment states of these correction circuits are set independently of each other. Recognize. FIG. 7 shows an embodiment of the low frequency correction circuit according to the present invention. That is, in this embodiment, the connection between the capacitor 19 and the resistor 18 in the series circuit in the embodiment shown in FIG. A more detailed explanation of the configuration will be omitted. The transfer function G(jω) of such a circuit is G(jω)=−K−jωCR/1+jωCR ...(6), and the phase characteristic argG(jω) is arg(jω)=tan ^-1 ωCR/K+tan ^-1 ωCR ……(7) becomes. Therefore, if we assume that the phase becomes 90° at the point where the angular velocity ω becomes ω ₀ , the time constant CR of the series circuit is given by (7). Then, substituting equation (8) into equation (6), we get Also, substituting equation (8) into equation (7), we get becomes. Therefore, as in the embodiment of FIG. 3, the time constant CR of the series circuit can be adjusted according to the change in K.
If we change them in conjunction to maintain the relationship in equation (8), we get
The change in amplitude characteristics with respect to the value of K is as shown in FIG. The phase characteristics are as shown in Figure 9, approximately 180° in the low frequency range, 90° at angular velocity ω ₀ , and approximately 0° in the high range, and this relationship does not change even if the value of K is changed. do not have. In areas other than the three points mentioned above, a slight change in phase occurs depending on the value of K, but as in the embodiment of FIG. 1, this change is very small. Figure 10 shows that in this example, K is 3.16 (+10 dB) or 1/3.16 (-
10 dB) and K is 2 (+6 dB) or 1/2 (-
6dB). In the above embodiments, the capacitance C of the capacitor 19 is fixed, and the resistance value of the variable resistor 18 is inversely proportional to √ in the embodiment of FIG. 1, and directly proportional to √ in the embodiment of FIG. The resistance value R is fixed, and the capacitance C is inversely proportional to √ in the case of Fig. 1, and √ in the case of Fig. 7.
It may be set so that it is directly proportional to . For example, in the case of FIG. 3, the value of K of the resistor 13 K ₁ ,
Resistance values K ₁ R ₀ , K ₂ R ₀ ,…K _N corresponding to _K 2 ,…K _N
R ₀ is changed over by a changeover switch, and the changeover switch linked to this changes the resistance value R of the resistor 18.
of

【formula】

【formula】

It is also possible to switch as shown in [Formula]. The same applies to the case of FIG. Note that the angular velocity ω ₀ can be easily changed by changing the value of the capacitance C or the resistance R, which is fixed in the above. The value of K can also be changed by using a variable resistor as the input resistor 12. In this case, the input resistor 12 and, for example, the variable resistor 18 may be made variable in conjunction with each other. (Effects) As described above, according to the present invention, with an extremely simple configuration, the correction amount is changed so that one frequency band of the high frequency band or the low frequency band has attenuation or enhancement characteristics, As for the other frequency band, it is possible to obtain a frequency characteristic correction circuit having a correction characteristic that does not change the correction amount.
In addition, fluctuations in phase characteristics can also be reduced, so if applied when multiple frequency characteristic correction circuits are used in a stereo device, etc., each frequency characteristic correction can be performed by adjusting the adjustment state of each circuit differently. It is also possible to perform sound image localization well.

[Brief explanation of drawings]

Fig. 3 shows a conventional frequency characteristic correction circuit, Fig. 2 shows its phase characteristic diagram, Fig. 1 shows a circuit diagram of an embodiment of the present invention, and Figs. 4, 5, and 6 show its characteristics. FIG. 7 is a circuit diagram showing another embodiment of the present invention, and FIGS. 8, 9, and 10 are diagrams showing its characteristics. 13, 18...variable resistor, 14...wideband amplifier.

Claims (1)

[Claims] 1. An amplifier with variable amplification for amplifying an input signal applied to an external input terminal, a series circuit of a resistor and a capacitor that negatively feeds back the output of the amplifier to the input terminal, and a series circuit of the resistor and capacitor. 1. A frequency characteristic correction circuit, comprising an external output terminal provided at a series connection point, and wherein a time constant of the resistor and capacitor and an amplification degree of the amplifier are variable in conjunction with each other.