JPS5919641B2 - Frequency characteristic adjustment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frequency characteristic adjustment device for an audio amplifier or the like.

The frequency characteristic adjusting device is, for example, a device having variable frequency characteristics for increasing or decreasing bass and treble tones as desired.

Conventional frequency characteristic adjustment devices have used variable resistors to achieve this variable frequency characteristic.

FIG. 1 shows an example of this conventional frequency characteristic adjusting device, in which 11 is an input terminal, 12 is an output terminal, and 13 is an amplifier. Resistor and capacitor connected.

Of these, the resistors 14 and 15 are variable resistors in order to make the frequency characteristics variable;
The frequency characteristics can be changed by manipulating the .

However, such conventional frequency characteristic adjusting devices have the disadvantage that they are not suitable for remote control.

In other words, in order to enable remote control of the device shown in Fig. 1, the variable resistor 14.15 is placed in a hand-held operating section separate from the main body of the device, and the variable resistor 14.15 and the main body of the device are connected by a transmission line. The configuration must be such that the connection is made through the .

In this case, since the frequency-adjusted signal flows through the transmission line, the transmission line must be shielded to prevent noise and induction, which adds extra capacitance and inductance9 to obtain sufficient performance. The problem is that it is not possible.

Also, recent audio equipment is stereo (2 channels).
In many cases, it is necessary to use one more set of the above-mentioned transmission lines.

Therefore, the conventional tone circuit is extremely inconvenient when remote control is desired.

The present invention has been made in view of the above, and an object of the present invention is to provide a frequency characteristic adjustment device suitable for remote control and further suitable for integrated circuits.

That is, the present invention provides a filter circuit that generates p-waves in a predetermined frequency band of an input signal, amplifies the output of this filter circuit and signals between input and output of the filter circuit with different amplifiers, and adds the outputs of the amplifiers to obtain the output. At the same time, the present invention provides a frequency characteristic adjusting device in which at least one of the amplifiers is a variable gain amplifier, and by arbitrarily changing the gain thereof, the frequency characteristic of the addition output can be arbitrarily changed.

The present invention will be explained in detail below with reference to the drawings.

FIG. 2 shows an embodiment of the present invention, in which the input terminal 2
1 is applied to a non-inverting input terminal of a first variable gain amplifier (hereinafter referred to as VCA) 22.

This first VCA 22 constitutes a feedback amplifier in which an inverting input terminal and an output terminal are commonly connected, and a first capacitor C123 is connected between the output terminal and ground.

The output of the first VCA 22 is supplied to the non-inverting input of the second VCA 24.

This second VCA 24 also constitutes a feedback amplifier in which an inverting input terminal and an output terminal are commonly connected, and a second capacitor C225 is connected between the output terminal and ground.

On the other hand, the voltage between the non-inverting input terminal and the output terminal of the first VCA 22 is applied between the non-inverting input terminal and the inverting input terminal of the third VCA 26.

Further, the voltage between the non-inverting input terminal and the output terminal of the second VCA 24 is applied between the non-inverting input terminal and the inverting input terminal of the fourth VCA 27.

Further, the voltage between the output terminal of the second VCA 24 and ground is applied between the non-inverting input terminal and the inverting input terminal of the fifth VCA 28.

The outputs of the third to fifth VCAs 26 to 28 are each led to an adder 29 and added together, and the output thereof is led to an output terminal 30.

Note that the first to fifth (7) VCAs 22, 24, 26 to
28 is of a voltage input/current output type, for example, and has sufficiently high input impedance and output impedance.

Next, the operation of this circuit will be explained.

First, a circuit including the first VCA 22 and the first capacitor 23 constitutes a first low pass filter (LPE) as shown at 31 in FIG. 3 in an equal and economical manner.

This is because when the frequency of the input vi of the VCA 22 is lower than the frequency at which the capacitor 23 conducts, an output v1 corresponding to the gain of the VCA 22 is obtained at the output of the VCA 22, but as the frequency of the input vi increases, the capacitor 23 becomes conductive. Then, the output terminal of VCA22 becomes the ground potential, so the output v1
becomes zero.

Therefore, the LPF is configured to be equally economical.

On the other hand, in this case, the signal between the input and output of this LPF (vi-v
Since l) is the input signal (vi) minus its low frequency component, it can be expressed as - as shown in 32 in Figure 3 for equal economy.
・Equivalent to the output of an i-pass filter (HPF).

Therefore, the third VCA 26 to which this differential voltage is applied is HP
This is a VCA for F output.

Here, if the above relationship is expressed using a relational expression, VCA2
2 input is v i (s), output is V, (S), VCA
When the gain of 22 is gml.

On the other hand, the second VCA 24 and the second capacitor 25 also constitute a second LPF.

Therefore, here, the cutoff frequency of this second LPF is the same as that of the first LPF.
If the time constant is set to be lower than the cutoff frequency of the LPF of - Equivalent to the output of a pass filter (BPF).

That is, since the output of the second LPF is a lower frequency component of the output of the first LPF, the output of the first LPF minus the output of the second LPF is equivalent to the output of the BPF.

Therefore, the fourth VCA 27 to which this differential voltage is applied is BP
This is a VCA for F output.

Here, if the above relationship is similarly expressed by a relational expression, VCA2
This is when the 4 outputs are v2(s) and the VCA gain is 9m2.

Furthermore, on the other hand, the voltage between the output terminal of the second VCA 24 and the ground is the output v2 of the second LPF itself, and its frequency characteristic is as shown at 33 in FIG.

Therefore, if this is expressed as a relational expression, it becomes the above-mentioned equation (2).

Therefore, the fifth VCA 2B to which this voltage is applied is L
This is a PF output VCA.

Now, the outputs of the third to fifth VCAs 26 to 28 are supplied to the adder 29 and added together as described above.

In this case, the addition output i. (s) is (2) when the gains of VCA26 to 28 are gm32gm4 and 9m5, respectively.
From equations (3) and (4), io=gm3(v 1(s)-v 1(s))−+−
gm4(vt(8)-V2(8))-1-9m5(
v 2(s)) ...(5).

Therefore, the gain G(s) from input terminal 21 to output terminal 30
-io(s)/v1(s) is expressed by equation (5) and (2), (3).

(4) Eq. becomes.

It can be seen from equation (6) that by adjusting the gains gm3 to gm of each VCA 26 to 28 as shown, the frequency characteristics of the gain G(s) can be set arbitrarily.

That is, for example, the gain of each VCA26-28 is 9m3-9
When m4-9m5, the gain G (s) is G(s)J
'm3, which is constant with respect to frequency.

The rounded frequency characteristic becomes exactly flat. Also, the third VC
Increasing the gain gm3 of A26 emphasizes the high range, increasing the gain gm4 of the fourth VCA 27 emphasizes the middle range, and further increasing the gain gm of the fifth VCA 28 emphasizes the low range. I understand that.

In this way, according to the present invention, the third to fifth VCAs
Any frequency characteristic can be obtained by changing the gain 9m3 to gm5.

However, if only the gains gm3 to gm5 of the third to fifth VCAs are changed as described above, the characteristics become asymmetrical when the gains are increased and decreased, as explained below, and the acoustic This may be undesirable when applied to a tone circuit or the like.

For example, if we consider the low frequency region as C1 (C2) It can be approximated as

Therefore, the absolute value of the gain at low frequencies is becomes.

Therefore, if we keep 9m25gm4 constant and change 9m5 to change the low-frequency characteristics, the gain g is as shown in Figure 4.
When m5 is increased, the frequency characteristic of the output of VCA28 becomes 33', and the overall characteristic becomes 41, whereas when the gain gm5 is decreased, the frequency characteristic of the output of VCA28 becomes 3f, and the overall characteristic becomes 42. It will be like this.

In other words, the frequency characteristics 41 and 42 become asymmetrical.

However, according to this invention, the gain g of the fifth VCA 28
When changing m5, the benefit of the second VCA 24 is changed at the same time.
By changing the cut-off frequency of the filter by changing 49 m2, the frequency characteristics can be made symmetrical.

That is, when increasing the gain gm5 of the fifth VCA 28, the gain gm2 of the second VCA 24 is simultaneously decreased to lower the cut-off frequency of the LPF as shown in the frequency characteristic 51 of FIG.

In this case, the overall characteristic is as shown in 52.

On the other hand, when the gain gm5 of the VCA 28 is to be made smaller, the gain gm2 of the second VCA 24 is increased to raise the cut-off frequency of the LPF as shown in the frequency characteristic 53 of FIG.

Then, the overall frequency characteristic becomes as shown in 54, which can be made symmetrical to the frequency characteristic 52.

Therefore, specifically, 9 m2 is set in the above equation (8).

In this case, if 9m4 is 1 (constant) and β is constant, α
When changing (that is, changing gm), equation (8) becomes.

Therefore, the relationship between the absolute value of this gain and the frequency is shown in FIG. 6.

This figure shows the characteristics of the so-called bass control on the low frequency side.

As can be seen from the figure, <9m4゜gm 5,j
It can be seen that if the relationship of im 2 is defined, frequency characteristics that are symmetrical with respect to changes in α (ie, 9m5) can be obtained, and that the circuit has optimal characteristics as a tone circuit.

The same thing holds true for the high frequency side, for example α−
When the relationship 9m s /gm45gm1-αiβ holds, as shown in Figure 7, symmetrical frequency characteristics can be obtained with respect to changes in α (i.e., 9m3), and optimal characteristics can be obtained for the tone circuit on the high frequency side. have

Note that tone circuits often adjust both the low and high frequencies, so an example of the frequency characteristics of the gain in that case is shown in Part 8.
As shown in the figure.

In this way, according to the present invention, the gain g of VCAs 26 to 28 is
By appropriately controlling m3 to gm5, the frequency characteristics can be changed arbitrarily, and the 1st to 2nd (7)
Gain gm1 of VCA22,24. By changing gm2, the cut-off frequency of each LPF can be changed, so this gain gm1. gm2 to gm.

It is also possible to obtain symmetrical frequency characteristics by changing it simultaneously with the change of ~9m7.

It goes without saying that the gain of the VCA can be controlled by controlling the DC control voltage.

Therefore, according to the frequency characteristic adjustment device of the present invention, in the case of remote control, it is possible to obtain excellent performance by simply providing only the DC control voltage generation section in the handheld operation section and connecting this and the VCA with a transmission line. can.

In other words, in conventional frequency characteristic adjustment devices, the signal that controls the frequency characteristics flows through the variable resistor and the transmission line that connects it to the circuit body, so the transmission line had to be shielded. On the other hand, in the present invention, the gain of the VCA is changed using a DC control voltage instead of directly adjusting the signal level whose frequency characteristics are controlled, so no signal whose frequency characteristics are controlled is flowing through the transmission line. There is no need to shield transmission lines to prevent noise or induction.

In addition, when the circuit of this invention is integrated into an integrated circuit, the only external connection point required in addition to the input/output is a connection point 3 with a capacitance of 23°25.
Since it is L32, the number of pins can be reduced.

This shows that the present invention is particularly suitable for integrated circuit implementation.

FIG. 9 shows another embodiment of the invention.

The difference between this embodiment and the embodiment shown in FIG. 2 is that the first and second VCAs in FIG. 2 each have a fixed resistance of 6L6.
This point is that it has been replaced by 2.

The rest of the structure is the same as in FIG. 2, so the same parts are given the same numbers.

In this embodiment, as in the circuit shown in FIG.
Since it is not possible to change the cut-off frequency of each filter by adjusting the gain of the second VCA, VCAZ6
Although it is not possible to obtain symmetrical frequency characteristics for a gain change of ~28, it is possible to obtain sufficient characteristics when symmetrical frequency characteristics are not particularly required, and the circuit configuration is extremely simple. It has the following characteristics.

Note that in a normal tone circuit, there is no particular need for the VCA 27 to have a variable gain, so a normal amplifier may be used instead of the VCA, and in this case, the circuit is further simplified.

Although this invention has been described above with reference to the embodiments shown in FIGS. 2 and 9, the invention is not limited to these embodiments.

That is, in the above embodiment, a case has been described in which the frequency band is divided into three and controlled, but it is also possible to control the frequency band divided into two bands.

In this case, the VC constituting the second LPF in FIG.
A24, capacitor 25 and fourth (7) VCA 27 are removed, and the first (7) LPF (first (7) VCA 22) (7
) output and the input of the fifth VCA 28 may be connected.

It is also possible to control the frequency band by dividing it into four or more.

In this case, LPFs and amplifiers that amplify signals between their input and output may be connected in multiple stages.

In addition, as mentioned above, the signals between the input and output of each LPF and the LP
All the amplifiers that amplify the output of F do not necessarily have to be VCAs, and at least one amplifier corresponding to a band whose frequency characteristics need to be variably controlled may be a VCA.

Furthermore, in the embodiment, a case is shown in which an LPF is used as the filter circuit network, but even if an HPF is used, exactly the same effect can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a conventional frequency characteristic adjustment device, FIG. 2 is a diagram showing an embodiment of the device of the present invention, and FIG. 3 is a diagram showing the frequency band of an input signal divided by the device of the present invention. Figures 4 and 5 are diagrams for explaining changes in the overall low frequency characteristics with respect to changes in gain, Figure 6 is a frequency characteristic diagram of the gain on the low frequency side of the device of the present invention, and Figure 7
FIG. 8 is a diagram showing the frequency characteristic of the gain on the high frequency side of the device of the present invention, FIG. 8 is a diagram showing an example of the frequency characteristic of the gain of the device of the invention, and FIG. 9 is a diagram showing another embodiment of the invention. 22.24,26,27,28-VCA, 23°25・
... Capacity, 29... Adder.

Claims (1)

[Scope of Claims] 1. A filter network formed by connecting in series a plurality of filter circuits having mutually different characteristics that transmit a predetermined frequency band of a human signal, an output signal of this filter network, and each of the filter circuits. and means for adding the outputs of these amplifiers, and at least one of the amplifiers is a variable gain control amplifier, and by changing the gain of the variable gain amplifier, the frequency characteristics can be adjusted. A frequency characteristic adjustment device characterized by adjusting. 2. The frequency characteristic adjustment device according to claim 1, wherein the filter circuit is a low pass filter.