JP2597993B2 - Filter device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in the following order.

A Industrial Fields B Overview of the Invention C Prior Art D Problems to be Solved by the Invention E Means for Solving the Problems F Function G Example G-1 Configuration and Operation (FIGS. 1 to 4) Fig. G-2 Application example (Fig. 5) H Effect of the invention A Industrial application field The present invention extracts a component of a predetermined frequency band of an input signal, and has two delay times without changing frequency characteristics. The present invention relates to a filter device that can be switched to.

B SUMMARY OF THE INVENTION The present invention relates to a filter device for extracting a component of a predetermined frequency band of an input signal, a filter for extracting a component of a predetermined frequency band of a video signal through a delay unit, and one end connected to an output terminal of the filter. An impedance circuit having a resistance element and a capacitance element having one end connected to the other end of the resistance element; and being turned on or off in accordance with a control voltage, the impedance circuit is connected to the other end of the capacitance element by a reference potential. A switch for connecting or disconnecting a point, a signal obtained at a connection point between the resistance element and the capacitance element of the impedance circuit being doubled, and a filter for the filter from the amplified signal. An amplification and subtraction circuit for subtracting the signal obtained at the output terminal is provided. When the state in which the other end of a child is connected to a reference potential point, with the frequency characteristics are determined by the filter,
The delay time is determined by the filter and the impedance circuit, and when the switch causes the other end of the capacitive element to be not connected to the reference potential point, both the frequency characteristics and the delay time are determined by the filter. By using a simple configuration with a small number of elements, the delay time of the device can be switched in two ways without changing the frequency characteristics of the device. The signal is delayed by a time corresponding to one horizontal cycle.

C. Prior Art In a video tape recorder drop-out compensation system, a reproduced video signal composed of a demodulated luminance signal and a carrier chrominance signal converted to an original frequency is led out to a video signal output terminal. When the luminance signal in the signal is delayed by one horizontal cycle and a dropout exists in the signal reproduced from the magnetic tape, the luminance signal delayed by one horizontal cycle is derived to the video signal output terminal in place of the reproduced video signal. However, the luminance signal delayed by one horizontal period is supplied to, for example, a reproduction video signal to a delay CCD (charge coupled device: charge-coupled device), and a video signal obtained from the CCD is output. Is supplied to a low-pass filter having a predetermined cut-off frequency, and the delay time in the CCD is lower-passed than one horizontal period. By shortening by the amount of delay time in the filter can be obtained.

However, in a delay device using a CCD, it is difficult to completely set the delay time freely due to restrictions on the design of the CCD. Therefore, the delay time in the CCD in the above-described dropout compensation system is set as described above in the NTSC video tape recorder for recording and reproducing the NTSC video signal, and also in the PAL video tape recorder for recording and reproducing the PAL video signal. Difficult to do,
When one horizontal cycle of the NTSC video signal is Tnh, one horizontal cycle of the PAL video signal is Tph, and the delay time in the above low-pass filter with the cutoff frequency set to a predetermined frequency is τx, for example, an NTSC video tape recorder In the dropout compensation system, the delay time in the above CCD can be made exactly Tnh-τx, but in the dropout compensation system of the PAL video tape recorder, the delay time in the above CCD can be made exactly Tph−τx. Can not be.

Therefore, for example, in a drop-out compensation system of a PAL video tape recorder, the above-described low-pass filter having a delay time of τx while setting the delay time of the CCD to Tph-τy shorter than Tph-τx. Is delayed by τy-τx by a delay circuit to obtain a luminance signal delayed by one horizontal period. However, without providing a delay circuit for correcting the delay time in this way, the delay time in the low-pass filter is set to Tph and the delay time in the CCD, Tph-τ
It may be possible to use τy, which is the difference between y, but in such a case, the cutoff frequency of the low-pass filter will not be the predetermined frequency.

By the way, the above-mentioned CC of the signal delay selecting unit for obtaining the luminance signal delayed by one horizontal cycle in the above-described dropout compensation system.
It would be advantageous if all of D, including D, or a portion other than the above CCD could be configured to be used in both the NTSC video tape recorder dropout compensation system and the PAL video tape recorder dropout compensation system. In that case, the filter device including the above-mentioned low-pass filter other than the above-mentioned CCD of the signal delay selection unit that obtains the luminance signal delayed by one horizontal period is a low-pass filter in which the cutoff frequency is set to a predetermined frequency as described above. Assuming that τx is the delay time of the filter device, when this filter device is used in the NTSC video tape recorder dropout compensation system, the delay time of the device is only that in the low-pass filter. τx, and when this filter device is used in a drop-out compensation system of a PAL video tape recorder, the frequency characteristic of the device is set so that the delay time of the device is τy of τx and the sum of τy−τx described above. It is necessary to be able to switch the delay time of the device in two ways without changing it.

As described above, the low-pass filter that extracts a component of the input signal having a frequency equal to or lower than the predetermined frequency is provided. As a filter device which can be switched in two ways, as shown in FIG. 6, between an input terminal 91 and an output terminal 95, as shown in FIG.
A low-pass filter 92 having a delay time of τx for extracting a component of a predetermined frequency or less of the input signal Si, a delay circuit 93 for delaying the output signal of the low-pass filter 92 by τy-τx, and a low-pass filter It is conceivable that a switch 94 is inserted to switch one of the output signal of the output signal 92 and the output signal of the delay circuit 93 to the output terminal 95 as an output signal So of the device.

D Problems to be Solved by the Invention However, if two kinds of signals are switched by the switch as described above, a switch having a complicated structure having a large number of elements is required as a switch, and the structure of the device becomes complicated. is there.

In view of the above, the present invention provides a filter device for extracting a component of a predetermined frequency band of an input signal, with a simple configuration having a small number of elements, switching the delay time of the device in two ways without changing the frequency characteristics of the device. It is something that can be done.

E Means for Solving the Problems A filter device according to the present invention includes a filter for extracting a component of a predetermined frequency band of a video signal through a delay unit,
An impedance circuit having a resistance element having one end connected to the output terminal of the filter and a capacitance element having one end connected to the other end of the resistance element; and an impedance circuit which is turned on or off according to a control voltage. And a switch that sets the other end of the capacitive element to a state where the other end of the capacitive element is connected to or disconnected from the reference potential point, and amplifies the signal obtained at the connection point between the resistive element and the capacitive element of the impedance circuit by a factor of two. Amplifying and subtracting circuit for subtracting a signal obtained at the output terminal of the filter from the signal, wherein when the switch brings the impedance circuit into a state where the other end of the capacitive element is connected to the reference potential point, the frequency characteristic is determined by the filter. The delay time is determined by the filter and the impedance circuit, and the switch When the other end of the capacitive element is not connected to the reference potential point, both the frequency characteristic and the delay time are determined by the filter, and the delay means converts the component of the video signal into a predetermined frequency band of the video signal. It is configured to delay by a time corresponding to one horizontal cycle.

According to the filter device according to the present invention configured as described above, when the other end of the capacitive element is not connected to the reference potential point in the impedance circuit by turning off the switch, the resistance element of the impedance circuit The output signal of the filter is obtained as it is at the connection point between
The output signal of the filter is also obtained as it is at the output terminal of the amplification and subtraction circuit, which is the output terminal of the device. The frequency characteristics of the device are determined by the filter, and the delay time of the device is only that of the filter, and the switch is turned on. When the other end of the capacitive element is connected to the reference potential point in the impedance circuit, the resistance value of the resistive element of the impedance circuit is Ro, the capacitance of the capacitive element is Co,
When the angular frequency of the signal is ω, the transfer function of the impedance circuit is 1/1 + jwCoRo, and the transfer function between the output terminal of the filter and the output terminal of the amplification / subtraction circuit, which is the output terminal of the device, is 1−jwCoRo / 1 + jwCoRo. Therefore, the amplitude characteristic between the output terminal of the filter and the output terminal of the device, that is, the amplitude of the output signal of the device with reference to the output signal of the filter is always 1 irrespective of ω, Co, and Ro. The frequency characteristic is determined by the filter, and the phase characteristic between the output terminal of the filter and the output terminal of the device, that is, the phase angle of the output signal of the device based on the output signal of the filter is 0 to 180 in accordance with ω. Between the output terminal of the filter and the output terminal of the device, which has a delay time determined by Co and Ro, so that the delay time of the device is longer than that of the filter. It becomes as.

G Example G-1 Configuration and Operation (FIGS. 1 to 4) FIG. 1 shows an example of a filter device according to the present invention.

A low-pass filter 20 having a predetermined cut-off frequency and a delay time of τx is connected to the input terminal 11 of the device, and is supplied to the output terminal 20x of the low-pass filter 20 and the input terminal 11. A component having a frequency equal to or lower than a predetermined frequency of the input signal Si is extracted with a time delay of τx. Low pass filter 20
The output side is provided with an impedance circuit 30. The impedance circuit 30 includes a resistance element 31 and a capacitance element 32, and one end of the resistance element 31 is connected to an output terminal of the low-pass filter 20.
20x, one end of the capacitive element 32 is connected to the other end of the resistive element 31. The other end of the capacitive element 32 is connected to the collector of the transistor Qo configuring the switch 40,
The emitter of Qo is grounded, and the control voltage Vc is supplied from the terminal 13 to the base of the transistor Qo. The control voltage Vc is set to one of, for example, a ground potential for turning off the transistor Qo and a power supply voltage for turning on the transistor Qo. Resistance element 31 and capacitance element 32 of impedance circuit 30
And the output terminal 20x of the low-pass filter 20;
Between the output terminal 15 of the device, a resistance element 31 and a capacitance element 32
The signal obtained at the connection point is amplified by a factor of two, and the amplified signal is output from the output terminal 20 of the low-pass filter 20.
An amplification and subtraction circuit 50 for subtracting the signal obtained for x is provided.

In this example, the amplification and subtraction circuit 50 is configured such that the constant current source 61 is connected to the emitters of the transistors Q1 and Q2,
The load resistance element 62 is connected to the collector of Q2, the connection point between the resistance element 31 and the capacitance element 32 of the impedance circuit 30 is connected to the base of the transistor Q1, and the output terminal 20x of the low-pass filter 20 and the base of the transistor Q2. Resistance element 6 between
3, the collector of the transistor Q2 is connected to the base of the transistor Q3, the emitter of the transistor Q3 is connected to the constant current source 64, and the resistor 65 is connected between the emitter of the transistor Q3 and the base of the transistor Q2. The emitter of the transistor Q3 is connected to the output terminal 15 of the device. In this case, the resistance value of load resistance element 62 is made sufficiently larger than the emitter resistances of transistors Q1 and Q2, and the resistance value of resistance element 63 and resistance element 65
Are equalized.

In the circuit composed of the transistors Q1 to Q3, the resistor 63 connected between the base of the transistor Q2 and the ground as shown in FIG. 2 forms a so-called Burton amplifier circuit. The input voltage of this amplifier circuit is V1, the output voltage is V2, the gain of the differential amplifier circuit formed by the transistors Q1 and Q2 is A, and the resistance values of the resistance elements 63 and 65 are
Ra Therefore, the transfer function of this amplifier is Becomes Then, assuming that the emitter resistance of the transistors Q1 and Q2 is r _e and the resistance value of the load resistance element 62 is R _L , A = R _L
/ 2r _e , but R ₁ ≫r _e and A is very large as described above, Becomes

That is, the amplification and subtraction circuit 50 in the example of FIG. 1 is a common-mode amplification circuit having a gain of 2 with respect to a signal supplied to the base of the transistor Q1, and supplied to the base of the transistor Q2 via the resistance element 63. Gain of 1 for signal
As shown in FIG. 3, an amplifying circuit 51 having a gain of 2 equivalently amplifying a signal obtained at a connection point between the resistive element 31 and the capacitive element 32 of the impedance circuit 30 as shown in FIG.
And a subtraction circuit 52 for subtracting the signal obtained at the output terminal 20x of the low-pass filter 20 from the output signal of the amplification circuit 51.

When the control voltage Vc supplied to the terminal 13 is set to, for example, the ground potential, the transistor Qo configuring the switch 40 is turned off, and the other end of the capacitive element 32 of the impedance circuit 30 is connected to the collector of the transistor Qo. If not grounded via the emitter, a low-pass filter 20 is connected to the connection point between the resistance element 31 and the capacitance element 32 of the impedance circuit 30.
The signal obtained at the output terminal 20x, that is, the output signal of the low-pass filter 20 is obtained as it is, and the low-pass filter
The transfer function between the output terminal 20x of the device 20 and the output terminal 15 of the device is 2-1 = 1, and the output signal of the low-pass filter 20 is obtained as it is at the output terminal 15, ie, the output signal of the device. So becomes the same as the output signal of the low-pass filter 20, the frequency characteristics of the device are determined by the low-pass filter 20, and the delay time of the device is
Τx, which is that of

On the other hand, when the control voltage Vc supplied to the terminal 13 is, for example, a power supply voltage, the transistor Qo configuring the switch 40 is turned on, and the impedance circuit 30 is turned on.
If the other end of the capacitive element 32 is grounded via the collector / emitter of the transistor Qo, the impedance circuit 30
If the resistance value of the resistance element 31 is Ro, the capacitance of the capacitance element 32 is Co, and the angular frequency of the signal is ω, the transfer function of the impedance circuit 30 is 1/1 + jwCoRo, and the output terminal 20x of the low-pass filter 20 and the The transfer function between the output terminal 15 and The amplitude characteristic between the output terminal 20x of the low-pass filter 20 and the output terminal 15 of the device, that is, the amplitude of the output signal So of the device based on the output signal of the low-pass filter 20, As represented by ω, Co, Ro, it is always 1 and the phase characteristic between the output terminal 20x of the low-pass filter 20 and the output terminal 15 of the device, that is, the low-pass filter
The phase angle of the output signal So of the device based on the 20 output signals is represented by argT (jw) = − 2tan ⁻¹ ωCoRo, and as shown in FIG.
It changes in the range of degrees, and the delay time between the output terminal 20x of the low-pass filter 20 and the output terminal 15 of the device has τy−τx determined by Co and Ro. That is, in this case, the frequency characteristics of the device
And the delay time of the device is τ of the sum of τx and τy−τx which is that in the low-pass filter 20.
y, the output signal So of the device is a low-pass filter 20.
Τy-τx with respect to the output signal of
A time delay of y is obtained.

In the above-described filter device according to the present invention, the switch 40 can be constituted by one transistor, and the amplification / subtraction circuit
As shown in FIG. 1, the 50 can be composed of a small number of elements.
The whole device can be configured very simply.

G-2 Application Example (FIG. 5) FIG. 5 shows an example of a dropout compensation system in a video tape recorder using the filter device according to the present invention.

A reproduced video signal Vi composed of a demodulated luminance signal and a carrier chrominance signal converted to the original frequency is supplied to an input terminal 71 of the system, and the reproduced video signal Vi is connected to the terminal i and the terminal d by the terminal s. The signal is supplied to the terminal i of the switch 72 which is switched to either side. The switch 72 is supplied from the terminal 73 with a dropout detection signal Dd indicating whether or not there is a dropout in the signal reproduced from the magnetic tape, and when there is no dropout in the signal reproduced from the magnetic tape, , The terminal s is replaced by the terminal i, and the reproduced video signal Vi is led to the output terminal 74 of the system through the switch 72.

The output video signal Vo obtained at the output terminal 74 is supplied to a delay CCD (charge coupled device: charge-coupled device) 75, and a transfer clock Cl is supplied from the terminal 76 to the CCD 75. Is delayed. In this example, as will be described later, the dropout compensation system of the NTSC video tape recorder and the dropout compensation system of the PAL video tape recorder use a CCD75 having a different configuration, and the frequency of the transfer clock Cl is changed. This is the case when they are different. The delayed video signal Vd obtained from the CCD 75 is supplied to the input terminal 11 of the above-described filter device 10 according to the present invention, and the brightness of a predetermined frequency or less in the video signal Vd from the low-pass filter 20 is supplied to the filter device 10. The signal is extracted with a time delay of τx, and from the output terminal 15 of the filter device 10, the luminance signal obtained from the low-pass filter 20 has no time delay or τy− depending on the state of the switch 40. A luminance signal Yd delayed by time τx is obtained.

The luminance signal Yd obtained from the output terminal 15 of the filter device 10 is supplied to the terminal d of the switch 72, and when there is a dropout in the signal reproduced from the magnetic tape, the terminal s is switched to the terminal d. The luminance signal Yd
Is led to the output terminal 74 of the system through the switch 72.

Tnh one horizontal period of the NTSC video signal, the subcarrier frequency f _ns, Tph one horizontal period of the PAL video signal, when the subcarrier frequency is f _ps, Ie There is a relationship. The delay time in the low-pass filter 20 is, specifically, To be. Further, when the switch 40 is turned on, the delay time between the output terminal 20x of the low-pass filter 20 and the output terminal 15 of the filter device 10 is specifically, It is made shorter by the above τx.

Then, in the dropout compensation system NTSC video tape recorder, together with CCD75 is the construction of 905.5 bits, the frequency of the transfer clock Cl is a 4f _ns, the delay time in CCD75 It is said. In the NTSC video tape recorder dropout compensation system, the switch 40 is turned off, and the output terminal 20x of the low-pass filter 20 is turned off as described above.
And the delay time between the output terminal 15 of the filter device 10 is made zero. Therefore, the delay time in the signal delay selection unit including the CCD 75 and the filter device 10 is Tnh, which is one horizontal cycle of the NTSC video signal.

In dropout compensation system PAL video tape recorder, together with CCD75 is the construction of 846.5 bits, the frequency of the transfer clock Cl is the 3f _ps, C
Delay time in CD75 It is said. Also, in the drop-out compensation system of the PAL video tape recorder, the switch 40 is turned on, and the output terminal 20x of the low-pass filter 20 is turned on as described above.
The delay time between the filter and the output terminal 15 of the filter device 10 is set to τy−τx as described above. Therefore, the delay time in the signal delay selection unit including the CCD 75 and the filter device 10 is PA
This is Tph, which is one horizontal cycle of the L video signal.

H Advantageous Effects of the Invention In the filter device according to the present invention, when extracting and delaying a component of a predetermined frequency band of a video signal through the delay means, the number of elements is relatively small, so that the switch device has a simple configuration. A state in which the frequency characteristic is determined by the filter according to ON / OFF, and the delay time is determined by the filter and the impedance circuit;
A state is assumed in which both the frequency characteristic and the delay time are determined by the filter, whereby the delay time is switched in two ways without changing the frequency characteristic, for example, NTSC video signal and PAL
Regarding any video signal of a different format such as a video signal, the delay means can delay the component of the predetermined frequency band by a time corresponding to one horizontal cycle.

[Brief description of the drawings]

FIG. 1 is a connection diagram showing an example of a filter device according to the present invention, FIG. 2 is a connection diagram of a circuit for explaining an amplification / subtraction circuit, and FIG. 3 is a connection diagram showing a principle configuration of the filter device according to the present invention. FIG. 4 is a diagram showing phase characteristics of some circuits when a switch is turned on, and FIG. 5 is an example of a dropout compensation system in a video tape recorder using a filter device according to the present invention. FIG. 6 is a connection diagram showing a possible example of a filter device. In the figure, 20 is a low-pass filter, 30 is an impedance circuit, 40 is a switch, and 50 is an amplification and subtraction circuit.

Continuation of the front page (56) References JP-A-57-158614 (JP, A) JP-A-60-169213 (JP, A) JP-A-52-149458 (JP, A) Real opening 58-43032 (JP, A) , U) Japanese Utility Model Showa 61-322 (JP, U) Japanese Utility Model Showa 61-15847 (JP, U)

Claims (1)

(57) [Claims] 1. A filter for extracting a component of a video signal in a predetermined frequency band through a delay means, a resistance element having one end connected to an output terminal of the filter, and a capacitance element having one end connected to the other end of the resistance element. By turning on or off according to the control voltage,
A switch that sets the impedance circuit to a state in which the other end of the capacitance element is connected to or disconnected from a reference potential point; and a signal obtained at a connection point between the resistance element and the capacitance element in the impedance circuit is doubled. Amplifying and subtracting a signal obtained at the output terminal of the filter from the amplified signal, and an amplifier and subtraction circuit, wherein the switch is connected to the impedance circuit and the other end of the capacitive element is connected to a reference potential point. In the state, the frequency characteristic is determined by the filter, the delay time is determined by the filter and the impedance circuit, and the switch does not connect the impedance circuit to the other end of the capacitive element to the reference potential point. When entering the state, both the frequency characteristics and the delay time are determined by the above filter. Te, by the above delay means, the filter apparatus, wherein said video signal delaying by a time corresponding to one horizontal period of the video signal.