JPS6356071A - Frequency characteristic adjustment circuit - Google Patents

Abstract

PURPOSE:To keep the one of a center frequency and a sharpness to be a constant value with making the other of them variable by providing a frequency adjustment circuit and a sharpness adjustment circuit. CONSTITUTION:An input signal s1 is outputted from a buffer circuit 7 through amplification circuits 2, 3 and 4. When the current I0 of the variable constant- current source 23 of the frequency adjustment circuit 21 is made to be varied, the mutual conductance of the amplification circuits 214 alters keeping a specified ratio and the oscillation characteristic of the output signal 52 is emphasized(or supressed) by the value expressed as the sharpness Q, which is kept constant while the center frequency f0 alters. On the other hand, if the voltage V4 of the variable voltage source 31 of the sharpness adjustment circuit 22 is made to be varied, only mutual conductance of the amplification circuit 2 alters and the sharpness Q separately alters, while the center frequency f0 is kept to be the constant value.

Description

[Detailed description of the invention] The present invention will be explained in the following order.

A. Industrial field of application B. Overview of the invention C. Conventional technology Problems to be solved by the invention E. Means for solving the problems (Fig. 1) F. Effects (Fig. 1)
Figure) G Embodiment (Figures 1 to 9) H Effects of the invention A Industrial field of application The present invention relates to a frequency characteristic adjustment circuit,
This is suitable for application to the sharpness circuit of a video tape recorder.

B. Summary of the Invention The present invention provides a frequency characteristic adjustment circuit configured to change the amplitude characteristic of an output signal with respect to an input signal around a predetermined center frequency, in which mutual conductance of an amplifier circuit constituting the frequency characteristic adjustment circuit is changed. The center frequency is set to a desired value by varying it at a predetermined ratio, and the mutual conductance of a predetermined amplifier circuit among these amplifier circuits is independently varied to obtain an amplitude centered at the center frequency. By setting the sharpness of the characteristic to a desired value, one of the center frequency and sharpness is maintained at a constant value while the other is varied.

C. Prior Art Conventionally, in the sharpness circuit of a VTR, a frequency characteristic adjustment circuit has been used to emphasize the amplitude characteristics of frequency components near frequency 2 (IvHIz), thereby emphasizing the contours of the reproduced image. ing.

For such a frequency characteristic #A adjustment circuit, it is necessary to emphasize the amplitude characteristic with the above-mentioned frequency 2 (MHz) as the center frequency. What is disclosed in the specification and drawings of the application (filed on June 4, 1986, title of the invention is "Frequency Characteristic Adjustment Circuit", applicant is "Sony Corporation") has been proposed.

D Problems to be Solved by the Invention However, in the conventional frequency characteristic adjustment circuit, there is a problem in that when the center frequency for emphasizing the amplitude characteristic is changed, the level at which the amplitude characteristic is emphasized changes. Therefore, when contour correction is performed by varying both the center frequency and the enhancement level, there is a problem in that the adjustment work becomes extremely complicated.

Therefore, in conventional sharpening circuits and the like, the center frequency to be emphasized is fixed and the level of emphasis is varied to perform desired contour correction.

However, when the center frequency is fixed and only the emphasis level is varied in this way, the contour correction becomes monotonous, and there is a problem in that it is difficult to obtain the optimal contour correction desired by the user for the reproduced video.

The present invention has been made in consideration of the above points, and attempts to propose a frequency characteristic adjustment circuit that can maintain one of the emphasis level and center frequency at a constant value while setting the other to a desired value. It is something.

Means for Solving Problem E In order to solve this problem, the present invention includes a plurality of amplifier circuits 4.3.2 that can variably adjust the mutual conductances t/r+, t/rz, and i/r3. and the transfer function is the transconductance I/r+, 1/r
When z, 1/r:+ is variably adjusted, the first term represents an equalizing function in which the amplitude characteristic is constant and the phase characteristic changes, and the second term represents a filtering function in which the amplitude characteristic changes.
The output signal S for the input signal Sl is expressed as the sum of the terms
In the frequency characteristic adjustment circuit l in which the sharpness Q changes around a predetermined center frequency f6 in the amplitude characteristic of No. 2, the mutual conductance of the plurality of amplifier circuits 2.3.4 is 1/r1.1/r2. A frequency adjustment circuit 21 that selects the center frequency f0 to a predetermined value by variably adjusting .1/r at a predetermined ratio, and a plurality of amplifier circuits 2.
．． A sharpness adjustment circuit 22 that sets the sharpness Q to a predetermined value by variably adjusting the mutual conductance 1/r3 of the predetermined amplifier circuit 2 in 3.4, and adjusts the center frequency f0 or the sharpness Q to a predetermined value. Sharpness Q while keeping it at a predetermined value
Alternatively, the center frequency f0 may be changed.

When the mutual conductance 1/r1.1/r2.1/r1 of the amplifier circuit 2.3.4 constituting the F-effect frequency characteristic adjustment circuit 1 is varied while keeping it at a predetermined ratio, the sharpness Q is a constant value. The center frequency fo changes while being maintained at .

On the other hand, if only the mutual conductance 1/r of the predetermined amplifier circuit 2 is changed, the sharpness Q changes while the center frequency f0 is kept constant.

In this way, it is possible to realize a frequency characteristic adjustment circuit 1 that can maintain one of the emphasis level and the center frequency at a constant value while setting the other to a desired value.

G example An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, 1 indicates the frequency characteristic adjustment circuit as a whole, and amplifier circuits 2, 3 and 4 are composed of differential amplifier circuits.
has.

The amplifier circuit 2 constitutes a low-pass filter that feeds back an inverted output to a non-inverting input terminal via a capacitor 5, receives an input signal S1 in the form of a video signal at the non-inverting input terminal, and outputs its inverted output to a buffer circuit 7. .

On the other hand, together with the amplifier circuit 2, the amplifier circuit 3 receives the input signal S1 at its non-inverting input terminal, and provides a non-inverting output to the non-inverting input terminal of the amplifier circuit 4.

The amplifier circuit 4 has a capacitor 6 connected between its non-inverting input terminal and ground, and its non-inverting output terminal is connected to a buffer circuit 7 .

Further, the outputs of the amplifier circuits 2 and 4 connected to the buffer circuit 7 are fed back to the inverting input terminals of the amplifier circuits 2.3 and 4.

Here, if each mutual conductance of amplifier circuits 2.3 and 4 is set as gm=, gmg, and gm, each mutual conductance gm=~gffl+ is each emitter sum current 1i of each amplifier circuit 2.3 and 4, It changes in proportion to Iz and I, and can be expressed by the value of the following formula: %. However, here rl.

r! , r3 represent the emitter resistances of the respective differential amplifier circuits 4.3 and 2, and Kl, K2 and 2 represent proportionality constants.

Also, let the capacitances of capacitors 5 and 6 be CI and C2, and the angular frequency of input signal S1 be ω=2πf, and input signal S1,
Letting the output signal S2 and the voltage at the non-inverting input terminal of the amplifier circuit 4 to be V, , V, and v, respectively, in the frequency characteristic adjustment circuit 1 of FIG. It works.

If we eliminate V from equations (4) and (5) and find the transfer function T(ω) of the frequency characteristic adjustment circuit 1, we get: 1+jωCzrz(1-r+/r3)+(jω)”C
1rIC2rz (6) It can be expressed as follows.

Here, when (6) 2 is transformed into the form of a general quadratic transfer function, it is expressed in the form of the following equation (7), and the coefficients a, b, and C are calculated by comparing it with equation (6). and the following formula % formula % (8) r! b=□・・・・・・(9)r
, -r3 c=1...
... It can be expressed by the value of (10). Further, the resonance angular frequency ω0 (ω.==2πr,) is expressed by the following equation, and the sharpness Q is expressed by the value of the following equation.

Furthermore, equation (6) is transformed into the following equation T(ω) = 1-j ωczrz(1-r+/rs)+(j (d)
”C7rtCzrz1+j ωczrz(1-r+/r
i)+Uω)”C+rtCzrz.

The first term on the right side of equation (13) represents a transfer function that performs equalizing operation in which the gain is constant and only the phase characteristics change, and the second term on the right side represents a transfer function that represents filtering operation in which the amplitude characteristics change. ing.

This means that the frequency characteristic adjustment circuit 1 shown in FIG. 1 is represented by a functional block diagram as shown in FIG. 2, which includes an equalizing function block 10, a filtering function block 11, and an addition function block 12. It means.

Now, focusing on the numerator of the second term of equation (13) and setting the mutual conductances 1/r3 and 1/r to the values of the following equation % equation % (14), the second term of equation (13) becomes O This is the characteristic of only the equalizing function block in the first term. This means that even if the angular frequency (ω=2πf) of the input signal S1 changes, the amplitude characteristics of the output signal S2 with respect to the input signal S1 do not change.

On the other hand, the transconductances 1/r1 and 1/r,
When % is set to the value of the following equation (15), the second term of equation (13) takes a positive value.

This is the resonance angular frequency ω expressed by equation (11). This means that the amplitude characteristic of the output signal S2 with respect to the input signal S1 is suppressed by the sharpness Q expressed by (12)2, with the center frequency being .

On the contrary, the mutual conductances 1/r and 1/r,
When % is set to the value of the following equation (16), the second term of equation (13) takes a negative value.

This is the resonance angular frequency ω expressed by equation (II). This means that the amplitude characteristic of the output signal S2 with respect to the input signal S1 is emphasized by the sharpness Q expressed by equation (12) by setting the center frequency to .

Therefore, by changing the ratio of the mutual conductances 1/r1 and 1/r3, that is, the value of the proportionality constant B expressed by the following formula % formula % (17),
From equation (12), the sharpness Q expressed by the following equation can be changed.

At this time, from equation (11), the mutual conductance 1/r,
If 1/r2 is maintained at a constant value and the mutual conductance 1/r3 is changed to change the proportionality constant B, the resonant angular frequency ω. It is possible to change the sharpness Q while maintaining the value of -set.

In other words, by setting the ratio of mutual conductance 1/r and 1/r2 to the following formula using the proportionality constant A, the value of the following formula can be obtained from formulas (11) 2 and (17). .

Here, the mutual conductances 1/r and 1/r
If t is maintained at a constant value and the mutual conductance is changed by 1/r3, the proportionality constant B in equations (20) and (21)
Only the value of changes, resulting in the resonant angular frequency ω. It is possible to change the sharpness Q while keeping it at a constant value.

On the other hand, the resonance angular frequency ω is maintained while keeping the sharpness Q at a constant value. In order to change the resonant angular frequency ω. It can be seen that it is sufficient to change the mutual conductance 1/r, which is included in the equation (21) representing the sharpness Q and not included in the equation (20) representing the sharpness Q.

That is, the mutual conductance 1/r is changed while keeping the proportionality constants A and B mentioned above constant values (that is, the mutual conductances 1/rl, 1/rz, and 1/r are kept constant and the ratios of the mutual conductances 1/rl, 1/rz, and 1/r are kept constant) Conductance i/r+, t/rz and 1/r.

) by changing the resonance angular frequency ω while keeping the sharpness Q at a constant value. can be changed.

Based on this operating principle, the mutual conductance of the amplifier circuits 2, 3 and 4 is set to 1/rs while maintaining the above relationship.
, 1/rz and 1/r+,
The frequency characteristic adjustment circuit 1 in FIG.
and a sharpness adjustment circuit 22.

That is, the frequency adjustment circuit 21 constitutes a current mirror circuit composed of a variable constant current source 23, a diode 24, and transistors 25, 26, and 27, and currents It, It, and (2) 4 flows to transistors 25, 26 and 27;

The emitter sum currents of the amplifier circuits 3 and 4 flow through the transistors 25 and 26, respectively, and the adjusted output current I4 obtained by adjusting the emitter sum current 3 of the amplifier circuit 2 in the sharpness adjustment circuit 22 flows through the transistor 27. flows.

Furthermore, the emitter sizes ASI, Ag3, and Ag3 of the transistors 25.26 and 27 are selected using the proportionality constant C to have the following value: , 12 and ■4 are the values of the following formula % formula % (23). However, here L represents a proportionality constant.

Furthermore, the sharpness adjustment circuit 22 has a reference voltage source 3 at its base.
0 and a variable voltage source 31, and have resistors 34 and 35 connected to their emitters, respectively.
2 and 33 constitute a current shunt having a differential amplifier circuit configuration.

The sharpness adjustment circuit 22 receives the emitter sum current (3) of the amplifier circuit 2 at the collector of the transistor 33 and passes it through the resistor 35 to the transistor 27.

Therefore, the sum current of transistors 32 and 33 is always equal to the adjustment output current 4 flowing through transistor 27,
Moreover, the ratio of the currents of the transistors 32 and 33 changes depending on the voltages (1) and (2) of the reference voltage source 32 and the variable voltage source 31, and the difference voltages V and -V between the voltages (4).

Thus, when the current I4 of the transistor 27 changes, the current (2) of the transistor 33 changes proportionally, and when the voltage (4) of the variable voltage 11iX11 is further adjusted, the current (2) changes accordingly.

Therefore, the current of the transistor 33 can be expressed by the value of the following equation 1% (26) (D is the voltage v of the variable voltage source 31
4 and the variable that changes according to the potential difference V, -V between the voltage v3 of the reference voltage source 30), from equation (25), the following equation % equation % (27) At this time, the mutual conductance of each amplifier circuit 2.3 and 4 1/rs, 1/rz, and 1/r change in proportion to the emitter sum current and are expressed by equations (1) to (3), and in addition to this, equations (23), (24), and ( 27) Substituting the formula yields the value expressed by the following formula. However, here M,,M.

and M represent a constant of proportionality.

This means that by changing the current I0 of the variable constant current source 23, the ratio of the mutual conductances 1/rs, 1/r2 and 1/r of each amplifier circuit 2.3 and 4 can be expressed as follows: Each transconductance 1 while maintaining the value expressed.
This means that /r3.1/rt and 1/r1 can be varied to the values expressed by formulas (28) to (30).

As a result, as described above for equations (20) and (21), the mutual conductances 1/r2.1/rz and 1/
By changing the mutual conductances 1/rI, 1/rt and 1/r:1 while keeping the ratio of r, constant, the resonant angular frequency ω can be adjusted while keeping the sharpness Q at a constant value. can be changed.

On the other hand, from equation (27), the voltage of the variable voltage source 31 ■4
By changing the mutual conductance 1/r, it is possible to change the mutual conductance 1/r while keeping the ratio of mutual conductance 1/r2 and 1/r constant, and as mentioned above for (20) 2 and (21) 2. , resonance angular frequency ω
. It is possible to change the sharpness Q while keeping it at a constant value.

In the above configuration, the input signal S1 is output from the buffer circuit 7 via the amplifier circuits 2.3 and 4 having a transfer function T(ω) expressed by equation (6).

At this time, the current of the variable constant current source 23 is ■. By varying ,
Mutual conductance of amplifier circuits 2.3 and 4 1/r3.
1/rt and 1/rl change while maintaining a predetermined ratio, and as a result, the amplitude characteristic of the output signal S2 with respect to the input signal S1 is emphasized (or suppressed) by a value expressed by the sharpness Q, and this value is This center frequency f is maintained at a constant value,
(ω.

=2πf0) changes.

On the other hand, when the voltage 4 of the variable voltage source 31 is varied, only the mutual conductance 1/r of the amplifier circuit 2 changes, and as a result, the resonance angular frequency ω changes. The sharpness Q varies independently while the center frequency ro (ω.=2πro) expressed by is maintained at a constant value.

According to the above configuration, the sharpness Q and the resonance angular frequency ω. It is possible to obtain a frequency characteristic adjustment circuit that can freely set one of the two to a desired value while maintaining the other at a constant value.

In particular, as shown in the functional block diagram of FIG. 2, this frequency characteristic three-round adjustment circuit 1 can be expressed as a circuit connected in parallel with an equalizing function block 10 and a filtering function block 11 in which only the phase characteristics change.

At this time, from equation (13), the mutual conductance 1/r,
When the sharpness Q changes by changing , the change in the phase characteristic of the equalizing function block 10 changes in the opposite direction to the change in the phase characteristic of the filtering function block 11, and as a result, the phase of the output signal $2 changes. A state in which the characteristics hardly change can be obtained.

Specifically, for example, the resistances r2 and r, representing the mutual conductances 1/r and 1/r, respectively, are rz
” 31050 CΩ), r + =3468 (Ω
], the resonant frequency f a = 2 (Mtlz)
The value of the sharpness Q and the coefficient S shown in equation (9) is
As shown in Figure 3, the transconductance 1/rs
At this time, the phase characteristics change as shown in FIGS. 4 to 9.

As is clear from these characteristic curve diagrams, even if the mutual conductance gms (=1/rs) is changed and the sharpness Q is changed, the output signal S remains almost unchanged in the phase characteristics.
You can get 2. Moreover, the resonance angular frequency ω. Even if the phase characteristics are changed, the phase characteristics hardly change.

Therefore, the frequency characteristic iA adjusting circuit 1 according to the embodiment shown in FIG. 1 is particularly effective when applied to, for example, a frequency characteristic adjusting circuit for a video signal in which it is necessary to minimize the phase change of the output signal S2.

Further, in the above-described embodiments, a case has been described in which the frequency characteristics of a video signal are set to a predetermined value, but the input signal is not limited to this, and the present invention can be widely applied to, for example, an audio signal.

Furthermore, in the above embodiment, instead of the conventional AC control, the voltage 4 of the variable voltage source 31 and the variable constant current source 2
Current value of 3■. Since the frequency characteristics can be varied by controlling the DC value by varying the , it is possible to obtain a frequency characteristic adjustment circuit that is simpler than the conventional one and suitable for IC implementation, for example.

In addition, in the above-mentioned embodiment, 3 of the differential amplifier circuit configuration
Resonance angular frequency ω of a frequency characteristic adjustment circuit equipped with a signal processing system composed of two amplifier circuits 2.3 and 4. The present invention is not limited to this, but the point is that the present invention has a quadratic transfer function as shown in equation (7), and a phase adjustment as shown in equation (13). It can be widely applied to frequency characteristic adjustment circuits equipped with signal processing systems that can be represented in the form of a functional block diagram (FIG. 2) of an equalizing function block and a filtering function block in which only the characteristics change.

H Effects of the Invention As described above, according to the present invention, the amplitude characteristics of the output signal relative to the input signal can be emphasized or suppressed as necessary around the center frequency maintained at a predetermined frequency. By doing so, it is possible to easily obtain a frequency characteristic adjustment circuit that can set the sharpness to a desired value and can freely set the center frequency while maintaining the sharpness at a constant value. can.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the frequency characteristic adjustment circuit according to the present invention, FIG. 2 is a functional block diagram thereof, and FIG. 3 is the relationship between mutual conductance and sharpness of the frequency characteristic adjustment circuit of FIG. 1. 4 to 9 are characteristic curve diagrams of the frequency characteristic adjustment circuit of FIG. 1. ■・・・Frequency characteristic adjustment circuit, 2.3.4...
... Amplifier circuit, 5.6 ... Capacitor, 10
...Equalizing function block, 11...
...Filtering function block, 21...
Frequency adjustment circuit, 22... Sharpness adjustment circuit, 2
3...Variable constant current source, 25.26.27.32
．． 33...transistor, 31...variable voltage source.

Claims (1)

[Claims] The invention is comprised of a plurality of amplifier circuits capable of variably adjusting the mutual conductance, and the transfer function has an equalizing function in which the amplitude characteristic is constant and the phase characteristic changes when the mutual conductance is variably adjusted. It is expressed as the sum of the first term representing the filtering function and the second term representing the filtering function in which the amplitude characteristic changes, such that the sharpness changes around a predetermined center frequency in the amplitude characteristic of the output signal with respect to the input signal. The frequency characteristic adjustment circuit that has been made includes a frequency adjustment circuit that selects the center frequency to a predetermined value by variably adjusting the mutual conductance of the plurality of amplifier circuits while keeping them at a predetermined ratio; and a sharpness adjustment circuit that sets the sharpness to a predetermined value by variably adjusting the mutual conductance of a predetermined amplifier circuit, the sharpness adjusting circuit sets the sharpness to a predetermined value while maintaining the center frequency or the sharpness at a predetermined value. Alternatively, a frequency characteristic adjustment circuit characterized in that the center frequency is changed.