JPH0422568Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a comb filter using an ultrasonic delay element.

[Prior Art] Conventionally, the comb shape of a comb filter is not particularly defined, and is determined from the characteristic impedance of the input and output side circuits of the comb filter, and the comb shape is determined from the characteristic impedance of the input and output side circuits of the comb filter. In a measurement circuit that is combined with a circuit, various characteristics of the comb filter, such as delay time characteristics, frequency band characteristics, insertion loss characteristics, spurious characteristics, etc., are measured.

The comb shape of the comb filter is not particularly defined, and for example, the comb depth at the center frequency is defined by a specific numerical value, for example, the comb depth at ±500 KHz of the center frequency.

The comb shape of the comb filter has spurious characteristics of 2τ.
It is a well-known fact that an unnecessary reflected signal called spurious has a large influence.The 2τ spurious means that the ultrasonic signal propagates in the ultrasonic delay element in a specified time, but the This is a signal that is output with a delay of twice as much time. Therefore, it can be said that although the comb shape of the comb filter has not been defined in the past, it has been constrained by the 2τ spurious definition instead.

Furthermore, the 2τ spurious is required to be as small as possible, and ultrasonic delay elements have been designed to reduce the 2τ spurious while comparing other characteristics. Conventionally, the study of such 2τ spurious has focused on the structure and material design of the ultrasonic delay element, and conditions such as matching of peripheral circuit conditions have been determined in advance.

In addition, in order to minimize the insertion loss of the comb filter, the impedance element value of the matching circuit is usually
It was chosen to match the front and rear circuits.

[Problems to be solved by the invention] Recently, demands for higher image quality of video equipment such as video tape recorders have increased, and in response to these demands,
Various high-quality circuit systems have been invented and are in actual use. Among these measures, there are new regulations and requirements regarding the characteristics of the comb filter regarding the comb shape, which were not available in the past. However, the conventional design changes for improving and modifying ultrasonic delay elements take a long time to manufacture, are structurally difficult, and are difficult to quantitatively design. There was a problem in that it was difficult to respond to the characteristics and performance that were being developed.

The present invention was made to solve the above-mentioned problem, and by changing the matching of the front and rear matching circuits without changing the ultrasonic delay element, the comb-shaped filter, that is, the 2τ spurious signal It is an object of the present invention to provide a comb-shaped filter that can increase the amount of filter.

[Means for Solving the Problems] The present invention includes an ultrasonic delay element, a branch path for applying a part of the input of the ultrasonic delay element to the output without going through the ultrasonic delay element, and an ultrasonic delay element. A comb-shaped filter having a matching circuit that performs impedance matching with a circuit before or after a sound wave delay element,
By connecting one impedance element between the ground and the output end of the ultrasonic delay element, an output-side matching circuit is created, or by opening the output end, an output-side matching circuit is created. An input side matching circuit is created by connecting one series impedance element to the input end of the delay element, and when the impedance value of the output side matching circuit and the impedance value of the input side matching circuit are in an optimal matching state. By setting the impedance value of the output side matching circuit and the impedance value of the input side matching circuit to impedance values other than the optimum matching state, the amount of signal passing through the 2τ spurious is made larger than the magnitude of the 2τ spurious, The magnitude of the change is 3~
It is characterized by being 5 dB.

FIG. 1 is a circuit diagram showing a typical configuration of a comb filter according to the present invention. In the figure, a capacitor 4 is connected to the input and output ends of the ultrasonic delay element 1 in parallel with the ultrasonic delay element 1 to form a comb filter. A resistor 2 is connected to the input terminal of the ultrasonic delay element 1, forming an input side matching circuit. The other end of the resistor 2 is connected to the input terminal 5 of the present comb filter. In addition, the ultrasonic delay element 1
A resistor 3 is connected to the output terminal of and grounded.
Configure the output side matching circuit. At the same time, the output terminal 6 of this comb filter and the output terminal of the ultrasonic delay element 1 are connected. Note that resistor 3 may not be connected if necessary, and resistor 2 and resistor 3 are
Instead of using a resistor, other impedance elements such as a capacitor or a coil may be used. Further, the capacitor 4 may also be another impedance element such as a coil, or a level adjustment resistor or the like may be connected in the branch path including the capacitor 4.

[Function] The signal input from the video signal input terminal 5 is branched into a signal that passes through the resistor 2 and is delayed via the ultrasonic delay element 1, and a signal that passes through the capacitor 4. The signal is output depending on the frequency of the signal. It is added or subtracted on the terminal side 6 and output.

In FIG. 1, by changing the values of resistors 2 and 3, the comb shape of the comb filter can be changed. FIG. 2 shows the curves. Curve 11 is the comb shape when the values of resistors 2 and 3 are optimally matched with the circuits in the front and rear stages of this comb filter, and curve 12 ,1
3 is a comb shape when the values of resistors 2 and 3 are changed from the above-mentioned optimal matching state. Here curve 12
is a comb shape when the amount of the 2τ spurious signal included in the signal output from the output terminal 6 is increased.

That is, based on the well-known fact that the comb shape of the comb-shaped filter changes with changes in the 2τ spurious, the present invention allows the element values of the peripheral circuit of the ultrasonic delay line, that is, the matching circuit, to be changed without changing the design of the ultrasonic delay line. By changing from the optimal matching state, the amount of 2τ spurious signal passing through is increased, and the comb shape of the comb filter is changed.

[Example] FIG. 3 shows the measured values when the resistance values of the resistors 2 and 3 were variously changed in the circuit configuration shown in FIG. 1.

In the figure, matching No. 1 has the resistance value of resistor 2
The resistance value of the resistor 3 is 680Ω, and the characteristic corresponds to curve 11 in FIG. The following examples are examined and evaluated based on the matching No. 1. Matching No. 2 uses resistor 2.
When 1000Ω and resistor 3 are 4700Ω, the insertion loss is the same as matching No. 1, but only 2τ spurious
It has gotten worse by about 3dB. Matching No. 3 uses resistor 2
This is an example of 1300Ω with resistor 3 open, matching No.
1 and the insertion loss is the same, but only the 2τ spurious
It has gotten worse by about 5dB. Matching No. 2 and No. 3 correspond to curve 12 in FIG. 2 as the direction of change in comb shape. In the case of matching No. 2, the 2τ spurious is 3 dB worse than the characteristic value in the optimum state described above. In other words, the amount of 2τ spurious signal passing through is
It is relatively larger by an amount equivalent to 3 dB. At this time, no change in insertion loss is observed. similarly aligned
In No. 3, the amount of 2τ spurious signal passing through is relatively large by an amount equivalent to 5 dB. Also, consistency No. 4
For No. 2, No. 3 and comb shape, curve 1 in Figure 2
The values of the resistors are chosen so that they are reversed as shown in 3.

As described above, the comb shape can be changed by appropriately selecting the matching impedance element values on the input and output sides.

It is also possible to change the comb shape without changing the insertion loss.

[Effect of the invention] In the comb filter of the invention, by setting the value of the impedance element of the matching circuit to a value other than the optimum matching state, the comb shape of the comb filter can be changed without changing the structure of the ultrasonic delay element. It is economical in that it can be changed and various required comb shapes can be obtained without increasing the types of ultrasonic delay elements.

Further, for example, when the comb shape 12 shown in FIG. 2 is desired, the matching impedance element on the output side can be eliminated, further increasing economic efficiency. By using the characteristics of this comb shape 12, the signal separation characteristics of the comb filter can be improved.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a typical example of the comb filter of the present invention, Fig. 2 is a frequency characteristic diagram when the impedance element value of the circuit of Fig. 1 is changed, and Fig. 3 is an embodiment of the present invention. It is a table showing actual measurement data. 1... Ultrasonic delay element, 2, 3... Resistor, 4
... Capacitor, 5 ... Input terminal, 6 ... Output terminal.

Claims (1)

[Claims for Utility Model Registration] An ultrasonic delay element, a branch path for applying a part of the input of the ultrasonic delay element to the output without going through the ultrasonic delay element, and a stage before or after the ultrasonic delay element. In a comb filter having a matching circuit that performs impedance matching with the subsequent circuit, the output side matching circuit can be formed by connecting one impedance element between the ground and the output terminal of the ultrasonic delay element. , or an output side matching circuit is created by opening the output end, and an input side matching circuit is created by connecting one series impedance element to the input end of the ultrasonic delay element, and the impedance value of the output side matching circuit is The magnitude of the 2τ spurious when the impedance value of the output side matching circuit and the impedance value of the input side matching circuit are in the optimal matching state is greater than the magnitude of the 2τ spurious when the impedance value of the output side matching circuit and the impedance value of the input side matching circuit are in the optimal matching state. By setting an impedance value other than 2τ
A comb-shaped filter that increases the amount of spurious signal passing, and is characterized in that the magnitude of the change is 3 to 5 dB.