JPS5929968B2 - Frequency characteristic adjustment circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frequency characteristic adjustment circuit used, for example, in a sound quality adjustment circuit of an audio amplifier, and is capable of mutually changing the output of a circuit having a flat frequency characteristic and the output of a circuit having a secondary high-frequency cutoff characteristic. In addition, a correction signal obtained through a secondary resonance circuit is added to the output having the staircase characteristic to obtain the flat frequency characteristic and the high-frequency cut-off characteristic. By removing valleys in the frequency characteristics that occur near the intersection of purpose.

Figure 1 shows an example of a conventionally used frequency characteristic adjustment circuit composed of two resistors R1 and R2 and a capacitor C. Assuming that the input level is constant over the entire frequency band, The frequency characteristics are as shown in FIG.

That is, since the slope of the change in frequency characteristics in this case is gentle, at most 6 dB/octave, there is a drawback that the characteristics change not only in the desired frequency band but also in unnecessary bands.

The present invention provides a frequency characteristic adjustment circuit that eliminates such conventional drawbacks.

That is, the present invention is configured so that an input signal is applied to a circuit having flat frequency characteristics and a circuit having secondary high frequency cutoff characteristics, and the outputs of the respective circuits are added together to obtain a staircase characteristic. By adding a correction signal obtained by passing the input signal through a secondary resonance circuit to the output having the stepwise characteristic, the flat frequency characteristic and the secondary high-frequency cut-off characteristic intersect. It is configured to remove valleys in frequency characteristics that occur nearby.

First, the principle of the present invention will be explained according to FIGS. 3, 4, and 4.

In FIG. 3, 1 is a transmission circuit having flat frequency characteristics, 2 is a secondary high-frequency cutoff circuit, and 3 is a mixing circuit that adds the outputs of both these circuits.

Here, if the transfer function of the transmission circuit 1 is T1, and the transfer function of the high-frequency cutoff circuit 2 is T2, the input signal ei applied to the input terminal a is e I T1 in both circuits 1 and 2, respectively.
, e I T2, which is further added in the mixing circuit 3, and sent to the output terminal as an output signal e (T1+T2).

appears. At this time, since the transfer function T1 of the transmission circuit 1 has a flat characteristic, it is expressed as equation (1).

T1-A1 (constant) ・・・・・・・・・・・・・・・・・・
(1) On the other hand, the transfer function T2 of the secondary high-frequency cutoff circuit 2 is expressed as in equation (2).

However, ω.

: cutoff angular frequency, ω : angular frequency Q: Determine the shoulder characteristics of the cutoff frequency constant, A2: Gain at ω-0, Therefore, the transfer function at the output terminal of mixing circuit 3 is becomes.

Therefore, 201og, olTl=207ogtolAtl.

These 20 loglTll + 20 log
The relationship between 101T21 is shown in FIG. 4, and the slope of the transfer function T is as steep as 12 dB/octave.

However, in this case, the cutoff frequency ω.

In the following frequency bands, the input signal and output signal have the same phase, but the cutoff frequency ω.

In higher frequency bands, the phase of the output signal is delayed by about 90 degrees with respect to the input signal, and furthermore, both transfer functions T1. Around the frequency where the output levels of T2 are equal, there is a delay of approximately 180 degrees, so the transfer function T of the signal appearing at the output terminal is different from the two transfer functions T1.T2 as shown in FIG. This results in a staircase characteristic with a valley near the frequency where the output levels of T2 become equal, and this is not practical as it is.

Therefore, as shown in FIG. 5, the present invention provides a secondary resonant circuit 4 in addition to the transmission circuit 1 and the secondary high frequency cutoff circuit 2 shown in FIG.
is added, and the secondary resonance characteristics, which are the outputs of the secondary resonance circuit 4, are synthesized by the mixing circuit 3, thereby eliminating the valley in the frequency characteristics shown in FIG.

That is, the transfer function T1. of the transmission circuit 1 and the secondary high-frequency cutoff circuit 2. T2 as mentioned above, T1=A1 ・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・If (1),
The transfer function T3 of the secondary resonance circuit 4 is expressed by the following equation (4).

Therefore, the entire transfer function can be calculated using equation (3) as follows: Because it is, and becomes.

As is clear from equation (5), the overall transfer function (T1 + T
2+T3), by changing the level A3 of the secondary resonant circuit 4, only the characteristics near the valley of the frequency characteristics change.

Therefore, by appropriately changing the output of the secondary resonant circuit 4, it is possible to obtain a desired staircase characteristic without valleys as shown in FIG.

As described above, according to the present invention, it is possible to easily obtain a staircase characteristic without valleys in the secondary frequency characteristic, and it is possible to enhance only the level of a necessary band. Can be used.

When used as a sound quality adjustment circuit, smooth frequency characteristics without valleys can be obtained in any case by configuring the high-frequency cutoff circuit to adjust l/bell in conjunction with each other.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing a conventional frequency characteristic adjustment circuit;
3 is a circuit diagram for explaining the present invention in detail, FIG. 4 is a frequency characteristic diagram thereof, and FIG. 5 is a frequency characteristic adjustment circuit according to an embodiment of the present invention.
177 and 6 are frequency characteristic diagrams thereof. 1 transmission circuit, 2...secondary high frequency cutoff circuit, 3.
...Mixed circuit, 4...Secondary resonant circuit, a
・・・・・Input terminal, b・・・・・・Output terminal

Claims (1)

[Claims] 1. A human signal is applied to a circuit having a flat frequency characteristic and a circuit having a secondary high-frequency cutoff characteristic, and the outputs of each of the circuits are added together to obtain a staircase characteristic, and the staircase characteristic is By adding the correction signal obtained from the above input signal via a secondary resonance circuit to the output with
A frequency characteristic adjustment circuit characterized in that it is configured to remove a valley in the frequency characteristic that occurs near the intersection of the flat frequency characteristic and the second-order high-frequency cutoff characteristic.