JPS63214014A - Filter circuit - Google Patents

Abstract

PURPOSE:To obtain a filter circuit with ease of manufacture and the less number of components by constituting the filter circuit by a couple of input terminals receiving respectively signals with different phase, 1st and 2nd impedance circuits each comprising a capacitor and a coil and a 3rd impedance circuit comprising a resistor. CONSTITUTION:Signals different in phase by 180 deg. are supplied to a couple of input terminals 10A, 10B. The input terminal 10A is connected to an output terminal 20A via the impedance circuit 1 and the input terminal 10B is connected to the output terminal 20A via the impedance circuit 2. Moreover, the output terminal 20A is connected to ground via an impedance circuit 3. The filter circuit 30 is a 3rd-order filter circuit. Since the mutual inductance by a coil is not required in the filter circuit 30, the manufacture is facilitated. Moreover, a component for the connection is not required and the number of components is decreased. Then the filter is suitable as an all pass filter.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a filter circuit for analog signals, in particular:
This invention relates to a third-order filter circuit.

B0 Summary of the Invention The present invention skillfully combines a resistor, a coil, and a capacitor in a third-order filter circuit for analog signals, has no mutual inductance structure, and has an hThi-like structure for each of the first-order and second-order filter circuits. The circuit configuration is fundamentally different from the conventional third-order filter circuit that connects to the
This allows the number of elements to be reduced.

BACKGROUND OF THE INVENTION For example, in a video tape recorder, a phase shift circuit (phase shift filter) is used to reduce moiré by providing two outputs having a phase difference of 90' from each other within a predetermined frequency range. This 90° phase shift circuit generally includes a set of all-pass filters. As shown in FIG. 6, for example, the circuit configuration of the all-pass filter includes a first-order filter circuit 101 having a mutual inductance structure including coils La and Lm, and coils Lc and Lm.
L.

The second-order filter circuit 102 having a mutual inductance structure is 4! A third-order filter circuit that is connected in series is conventionally known. In addition, as shown in FIG. 7, a first-order filter circuit 1 consisting of a resistor and a capacitor
03 and the second-order filter circuit 104, which also consists of a resistor and a capacitor, are transistors Q,,Q! A third-order filter circuit is also known, in which the filter circuit is connected in series through the filter circuit.

D1 Problems to be Solved by the Invention However, since the filter circuit shown in FIG. 6 has a mutual inductance structure, it is difficult to manufacture. The filter circuit shown in Figure 7 is a transistor. There was a point where an extra element such as 1°Q2 was required, resulting in an increase in the number of elements.

Therefore, the present invention was proposed in view of the above-mentioned problems, is easy to manufacture, does not require any extra elements, and can be used as an all-pass filter constituting, for example, a 90° phase shift circuit. We are committed to providing a suitable third-order filter circuit.

Means for Solving Problem E9 In order to solve the above-mentioned problem, the filter circuit according to the present invention includes a pair of input terminals to which signals having different phases from each other are supplied, and a capacitor and a coil connected in parallel. a first impedance circuit including a coil and a resistor connected in series; a series connection of the coil and a capacitor;
a second impedance circuit consisting of a capacitor connected in parallel and a resistor connected in series; a third impedance circuit consisting of a resistor; and an output terminal, one of the input terminals being The other of the input terminals is connected to the output terminal via the second impedance circuit, and the output terminal is grounded via the third impedance circuit. It is characterized by the fact that

F0 Effect According to the present invention, since there is no mutual inductance structure, manufacturing becomes easy. Furthermore, the circuit configuration is fundamentally different from the conventional third-order filter circuit in which the first-order and second-order filter circuits are connected in series, and no element is required for connection.

G. Example Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of a filter circuit according to the present invention.
! ! It is a road map. In FIG. 1, signals having mutually different phases are supplied to a pair of input terminals 10A and IOB, respectively. The phase difference between them is, for example, 180°. The first impedance circuit 1 includes a capacitor C1 and a coil L connected in parallel, and a coil Lt and a resistor R connected in series. The second impedance circuit 2 has a series connection of a coil L3 and a capacitor c2, and a parallel connection of a capacitor C3, and a resistor R.
2 are connected in series. Further, the third impedance circuit 3 is made up of a resistor R3.

The input terminal 10A is connected to the output terminal 20A via the impedance circuit 1, and the input terminal 10B is connected to the output terminal 20A via the impedance circuit 2. In addition, the above output terminal 20A
is grounded via the impedance circuit 3.

The filter circuit 3o of this embodiment having such a configuration is a third-order filter circuit.

By the way, it is assumed that signals having phases different from each other by 180 degrees are supplied to the input terminals 10A and IOB, respectively. Then, the input voltage at the input terminal 10A is VIN, the input voltage at the input terminal 10B is -VIN, and the output terminal 2
The output voltage at 0A is vout, and each impedance of impedance circuits 1, 2.3 is z, z, z,
Expressing Vout/VIN, the following equation is given.On the other hand, the transfer function of the third-order all-bus filter is given to -m by the following equation.

Here, K, α, β, and T are constants, and S is a complex frequency. The above formula (2) is expressed as K −1/(1+ 1 /R
) can be transformed as shown below.

(3) By comparing the above equation (11) and equation (3), each impedance ZI, Zt, and Z3 is expressed as follows.

...(4) Zs-R...(7) In the above equation (4), the first term corresponds to the resistance R+, the second term corresponds to the coil L2, and the third term is This corresponds to parallel connection of capacitor C1 and coil Ll. In addition, in the above equation (5), the first term corresponds to the resistor R2, and the second term corresponds to the series connection of the coil L3 and the capacitor Ct, and the parallel connection of the capacitor C3. . Further, the above equation (7) corresponds to the resistor R8. In this way, each impedance circuit 1.2.3
In other words, the configuration of the filter circuit 30 has been determined. In FIG. 1, the numerical values or symbols shown in parentheses correspond to the values of each element.

The filter circuit 30 as described above is easy to manufacture because it does not have a mutual inductance structure using coils. Furthermore, since this is fundamentally different from the conventional configuration in which a first-order filter circuit and a second-order filter circuit are connected in series, an element for connection is not required, and the number of elements can be reduced.

Incidentally, by symmetrically combining the filter circuits 30 described above, a phase shift circuit as shown in FIG. 2, for example, can be constructed. That is, this phase shift circuit includes resistors Ra and Rs in addition to the configuration of the filter circuit 30 described above.

R6, coils Lm, Ls, Lh, and capacitor Ca
.

It has a configuration in which Cs, Ci, and an output terminal 20B are added. When signals having phases different by 180 degrees from each other are supplied to the input terminals 10A and IOB, signals having phases different by 90 degrees from each other are outputted from the output terminals 20A and 20B, respectively.

Here, assuming that the number of transmission lines is cubic, the phase difference between the two output signals is 90°, and the pole that minimizes the maximum error is selected.
) and zero point (zero) values were determined. The results are shown in Table 1.

Table 1 The above constants α and β are determined from the values of these poles and zeros.

The value of T is calculated, and the value of each element is determined, for example, as shown in parentheses in FIG. The frequency characteristics of the phase and phase difference in this case are shown in FIG. In FIG. 3, A indicates the phase of the signal output from the output terminal 20A, B indicates the phase of the signal output from the output terminal 20B, and C indicates the phase difference between these. The above phase difference is approximated by Chebyshev, and is 0.5? IH
z~18M)! 2, it is 90° ±0.59° (equal ripple pull), and it can be seen that the conditions for a 90° phase shift circuit are satisfied.

Further, the frequency characteristics of the group delay time and attenuation amount for the signal output from the output terminal 2OA are shown in FIG. 4, and the frequency characteristics of the group delay time and attenuation amount for the signal output from the output terminal 20B are shown in FIG. In FIGS. 4 and 5, A represents the group delay time, and B represents the attenuation amount (amplitude characteristics). In any case, the above attenuation varies only by the last digit of the numerical value in the figure in the range of 0.5 MHz to 18 MHz,
It can be seen that it can be regarded as constant and satisfies the conditions for an all-bus filter.

In this way, the phase shift circuit shown in FIG.
It can operate as a 90° phase shift circuit in the range of ~18 MHz, and is suitable for use as a phase shift circuit for moiré reduction in video tape recorders.

Note that the output resistances Rx and Rh are each 10
kΩ, but any ohm may be used. Also, the input resistance RI
+Rz, Ra, and Rs are each set to 1 and Ω, but if they are set to a value of 1/10, for example, the value of the capacitor may be set to 10 times the value, and the value of the coil may be set to 0.1 times.

H0 Effects of the Invention As is clear from the description of the embodiments described above, the filter circuit of the present invention is easy to manufacture because it has a circuit configuration without a mutual inductance structure. In addition, by adopting a circuit configuration that is fundamentally different from the conventional configuration in which a primary filter circuit and a secondary filter circuit are connected in series, no elements are required for connection, and the number of elements can be reduced. be able to. Therefore, it is suitable for use as an all-pass filter constituting a 90° phase shift circuit, for example.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a filter circuit according to the present invention, FIG. 2 is a circuit diagram showing a phase shift circuit configured by symmetrically combining the filter circuits of the above embodiments, and FIG. FIG. 4 is a diagram showing the frequency characteristics of each phase of each output signal of the phase shift circuit and the phase difference between them, and FIG. 4 is a diagram showing the frequency characteristics of the group delay time and attenuation amount for one output signal of the phase shift circuit. , FIG. 5 is a diagram showing the frequency characteristics of the group delay time and the amount of attenuation for the other output signal of the phase shift circuit. FIG. 6 is a circuit diagram showing a conventional example of a filter circuit, and FIG. 7 is a circuit diagram showing another conventional example of a filter circuit. 1.2.3...Impedance circuit R1
, Rz, Rz...Resistance LI+ LX, L3-Coil CI, Cz, C3...Capacitor 10A, IO
B...Input terminal 20A...
... Output terminal 30 ... Filter circuit

Claims (1)

[Claims] A pair of input terminals to which signals having mutually different phases are supplied, a first impedance circuit including a capacitor and a coil connected in parallel, a coil and a resistor connected in series, and a coil. and a capacitor connected in series, a second impedance circuit including a capacitor and a resistor connected in series, a third impedance circuit including a resistor, and an output terminal, One of the input terminals is connected to the output terminal via the first impedance circuit, the other input terminal is connected to the output terminal via the second impedance circuit, and the output terminal is connected to the third impedance circuit. A filter circuit characterized in that the filter circuit is grounded through an impedance circuit.