JPH0516697B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a frequency characteristic variable circuit suitable for use in video contour correction, audio tone control, and the like.

BACKGROUND TECHNOLOGY AND PROBLEMS A conventional variable frequency characteristic circuit is configured as shown in FIG. In the figure, a signal from an input terminal 1 is supplied to a band pass filter 100 or a high pass filter, and a signal from this filter 100 is passed through a gain control amplifier 200 to an adder 300.
is supplied to Further, a signal from input terminal 1 or a signal obtained by passing this through a low-pass filter (not shown) is supplied to adder 300, and this added signal is taken out to output terminal 2.

However, this circuit has the following drawbacks.

1. If the gain change of the gain control amplifier 200 is generally linear, the change in boost or cut level will also be linear, so it will not match the log characteristic, which is the auditory/visual characteristic, and good control characteristics will not be obtained.

2. Similarly, changes from the flat state to the boost direction and the cut direction are preferably log symmetrical from an auditory and visual standpoint, but it is difficult to obtain such benefits.

3. If the above-mentioned characteristics were to be corrected, the circuit would become extremely complicated.

OBJECTS OF THE INVENTION In view of these points, the present invention is intended to provide good characteristics with a simple configuration.

Summary of the Invention The present invention connects integrators each having an adder at its output in series, feeds back the output of the adder in the latter stage 100% to the input of the earlier stage of the integrators,
The input signal is fed back to the input of the subsequent stage via an attenuator with an attenuation rate m, and the input signal is directly supplied to the input of the integrator of the previous stage and the input of the adder of the latter stage, and the input signal is fed back to the input of the previous stage and the input signal of the latter stage is fed back to the input of the latter stage. The sum or difference signal with the output signal of the adder is given a gain K
The output signal is supplied through the gain control circuit of m, and the output signal is taken out from the adder in the subsequent stage, and the m,
This variable frequency characteristic circuit is characterized in that the value of K is set to a value other than 0, and according to this, good characteristics can be obtained with a simple configuration.

Embodiment In FIG. 2, the signal from input terminal 1 is applied to the positive input terminal of integrator 3 ₁ . This integrator 3 ₁
The output of the adder 4 ₁ is supplied to the adder 4 _{1 , and the output of the adder 4 1} is supplied to the positive input terminal of the integrator 3 ₂ . The output of this integrator 3 ₂ is supplied to an adder 4 ₂ , and the signal from the input terminal 1 is supplied to the adder 4 ₂ . The output of this adder ₄₂ is taken out to the output terminal 2.
Further, the signal at the output terminal 2 is directly supplied to the negative input terminal of the integrator ₃₁ in the preceding stage, and is attenuated by m.
is supplied to the negative input terminal of the integrator 3 ₂ through the attenuator 5 ₂ .

Furthermore, the signal from the input terminal 1 and the signal taken out to the output terminal 2 are supplied to an adder 6, and this added signal is supplied to an adder ₄₁ through a gain control amplifier 7 with a gain of K.

The transfer function of this circuit is H(S)=S ² +Kω ₀ S+ω ₀ ² /S ² +(m−K)ω ₀ S+ω ₀ ² …
(1) However, S=jω. Here, if K=m/2+k, then H(S)=S ² +(m/2+k)ω ₀ S+ω ₀ ² /S ² +(m/2
−k) ω ₀ S+ω ₀ ² ……(2), and the level when ω=ω ₀ is m/2+k/m/2−k=H(jω ₀ ) ……(3).

In other words, the characteristic of equation (3) can be well controlled to match the auditory and visual characteristics by linearly changing k. Further, when k changes in the positive direction and in the negative direction, the boost or cut level changes log-symmetrically with respect to k, resulting in an extremely favorable change visually and audibly.

Furthermore, the Q of the filter is Q=1/m/2-k (4), and as k increases, Q also increases. This further improves the auditory and visual characteristics.

Further, FIG. 3 shows an example of application to a contour correction circuit. In the figure, among the signals supplied to the adder 6,
A signal from input terminal 1 is supplied with its phase inverted.

In this way, the phase of the output at ω=ω ₀ is reversed. The transfer function is H(S)=S ² −Kω ₀ S+ω ₀ ² /S ² +(m−K)ω ₀ S+ω ₀₂ …
…(5) becomes.

In this circuit, if we now consider the case of boosting, the output can be considered to be the sum of the original signal and the signal extracted only around ω ₀ . Therefore, in Figure 4, if there is an input like A,
A component near ω ₀ is extracted as shown in B, inverted as shown in C, and added to the original signal, thereby forming a contour-corrected signal as shown in D.

Furthermore, in the above-mentioned circuit, the circuit shown in FIG. 5 is used as the integrators 3 ₁ and 3 ₂ . In the figure, first and second terminals 11 and 12 are connected to the bases of differentially connected transistors 13 and 14.
The emitters of these transistors 13 and 14 are connected to each other, and a constant current source 1 with a current value of 2Ie is connected to this connection point.
5 is connected. Further, a constant current source 16 having a current value Ie is connected to the collector of the transistor 14, and the collector of this transistor 14 has a capacitance value C.
is connected to one end of the capacitor 17. The other end of this capacitor 17 is connected to a third terminal 18. In this circuit, a capacitor 17 with a current corresponding to the difference between the signals supplied to terminals 11 and 12
is driven, and the terminal 18 at the other end of this capacitor 17 is driven with a voltage, so that the signals supplied to this terminal 18 are added.

Therefore, by this circuit, the above-mentioned integrators 3 ₁ , 3 ₂
and one stage of adders 4 ₁ and 4 ₂ is formed, and terminal 1
1, 12 and 18 correspond to the positive and negative input terminals of the integrators 3 ₁ and 3 ₂ and the other input terminals of the adders 4 ₁ and 4 ₂ , respectively.

In this circuit, transistors 13,
14 emitter impedance as re, the integration time constant τ is τ=2re・C=2V _T /Ie・C However, V _T =k・T/q. Therefore, by changing the bias current Ie, the time constant τ can be controlled.

Furthermore, FIG. 6 shows a case where this integrator is used to construct an n-order filter device. Voltage in figure
An input signal source 21 biased to V ₀ is connected through the input terminal 1 to the base of the first stage transistor 13 ₁ . Further, the collector of the transistor 14 ₁ at the front stage is connected to the base of the transistor 13 ₂ at the rear stage. Further, the output terminal 2 is led out from the collector of the transistor 14 ₂ in the subsequent stage through the buffer transistor 22 .

Furthermore, the output terminal 2 is connected to the transistors 14 ₁ , 1
4 Connected to the base of ₂ . In this example, m=
It is 1.

Further, the other end of the capacitor 17 ₂ is connected to the input terminal 1 .

Further, input terminal 1 and output terminal 2 are connected to respective inputs of differential amplifier 23, and differential amplifier 2
The gain K is controlled by the control voltage Vc supplied to the terminal 25 of the current source 24 of the third emitter.
The collector of this differential amplifier 23 is connected through a current mirror circuit 26, and a signal (current) obtained by multiplying the difference between the input signal and the output signal by a gain K is formed. This current mirror circuit 26 is connected to the collector of the transistor 14 ₁ in the previous stage.

This provides the circuit of FIG. 3 described above.

In this way, a variable frequency characteristic circuit such as a contour correction circuit is constructed, and according to this circuit, the frequency characteristic can be varied satisfactorily with a simple configuration. This has been made possible by replacing the conventional LC filter with an active filter. Also, this circuit can be easily
Can be converted into an IC.

Further, according to the above-described circuit, the voltage-current conversion of the integrator is performed using the emitter impedance of the transistor, so the number of elements is extremely reduced. Further, the time constant can be controlled by the bias current, and in this case, the variations depend only on the bias current, so the variations can be easily corrected. Furthermore, since signals can be transmitted with minute voltage changes in the base-emitter voltage, the output circuit of the integrator can be extremely simplified.

Therefore, it is possible to realize a stable and highly accurate IC filter that is not affected by the temperature characteristics and variations of the elements.
Furthermore, the number of elements can be significantly reduced compared to conventional circuits.

This makes it possible to significantly reduce the number of peripheral IC components and integrate a wide variety of functions on a large scale, reducing product manufacturing costs and service costs, and increasing design freedom by reducing board area. It will be done.

Effects of the Invention According to the present invention, good characteristics can be obtained with a simple configuration.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional device, Fig. 2 is a block diagram of an example of the present invention, Fig. 3 is a block diagram of another example, and Fig. 4 is a block diagram of an example of the present invention.
6 to 6 are diagrams for explaining the same. 1 is an input terminal, 2 is an output terminal, 3 ₁ , 3 ₂ are integrators, 4 ₁ , 4 ₂ , 6 are adders, and 7 is a gain control circuit.

Claims (1)

[Claims] 1 Integrators each equipped with an adder are connected in series to the output, and the output of the adder in the latter stage is fed back 100% to the input of the earlier stage of the above-mentioned integrators, and the input of the latter stage is connected through an attenuator with an attenuation rate m. The input signal is directly supplied to the integrator input in the previous stage and the adder input in the latter stage, and the input signal is directly supplied to the input signal in the previous stage and the output signal of the adder in the latter stage. A variable frequency characteristic circuit, characterized in that a signal is supplied through a gain control circuit with a gain K, the output signal is taken out from the adder in a subsequent stage, and the values of m and K are set to other than 0.