JPS6337968B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic delay circuit formed by cascading ultrasonic delay lines for use in color television receivers of NTSC system, PAL system, etc., and particularly to improve the frequency characteristics thereof. With the goal.

Ultrasonic delay lines are used to delay electrical signals for a certain period of time, and the speed of sound waves is approximately equal to that of electromagnetic waves.
Focusing on the fact that it is 1/100,000th, we convert electrical signals into ultrasonic signals and convert them from several tens of microseconds to several tens of microseconds.
After obtaining a delay time of 100 μsec, it is converted back into an electrical signal.

Figure 1 shows the principle. The end face of the delay medium 1 is provided with electrodes 2a, 2b and 2'a, 2'b.
Conversion elements 3 and 3' with mechanical energy conversion function
is installed. Now, when an electric signal E _i is applied between the electrodes 2a and 2b of the conversion element 3, the conversion element 3 mechanically vibrates according to the frequency of the signal.
Ultrasonic waves are emitted into the delay medium 1. This ultrasonic wave is reflected many times within the delay medium 1 as shown in the path 4 shown in FIG. 1, and reaches the conversion element 3' at the other end.
This causes the conversion element 3' to vibrate mechanically,
An electric signal E _p corresponding to the frequency is generated between electrodes 2'a and 2'b. In this way, the time required for the signal applied to the input end of the ultrasonic delay line to arrive at the output end, that is, the delay time, is the horizontal scanning period of the television signal (referred to as 1H, 63.556 μsec in the NTSC system). Based on 1/4~2H
An ultrasonic delay line with a value of .

The delay time determined from the phase difference between input and output when a sine wave signal is applied to an ultrasonic delay line is called phase delay. As shown in FIG. 2, if the input signal E _A input to the input side 6 of the ultrasonic delay line 5 is E _A =αsinωt, the output signal taken out from the output end 7 is
E _B becomes E _B =βsinω(t−τ _p ). The input signal E _A and the output signal E _B are shown in Figure 3a,
Shown in b. Note that τ _p is phase delay, α, β
are the amplitudes of the input and output signals, respectively. In actual measurement, find the frequency that has elapsed in the input signal E _A until the signal E _B delayed by the ultrasonic delay line 5 rises, and calculate the delay time τ _p using the following equation (1). obtain.

m=τ _p /T=τ _p · _p (1) Here, m _p is the transition frequency, T is the period of the input/output signal, and _p is the frequency.

Let m _p be the integer part of m, and let the phase of the output signal E _B with respect to the input signal E _A be, the following equation (2) is obtained: τ _p = (m _p −/360)・T = (m _p −/ 360)・1/ _p …(2). Phase delay is mainly used when it is necessary to specify the delay time of a sine wave signal as well as the phase difference between input and output signals.

As is well known, such an ultrasonic delay line is used as a comb filter to remove dot interference in NTSC color television receivers and to remove cross color in video tape recorders.

That is, in FIG. 2, when the voltage E _A at the terminal 8 where the input signal appears and the voltage E _B at the output terminal 7 are added, the signal E _C becomes as follows.

E _C = E _A + E _B = αsinωt+βsinω(t−τ _p ) =√ ² + ² +2 _p・sin(ωt+)=Asin(ωt+) However, = tan ^-1 {βsinωτ _p /(α+βcosωτ)} A=√ ² + ² + 2 _p , that is, the maximum value A _nax , the minimum value A _nio of the amplitude A,
And if the values of the frequency ω when the signal E _C takes these values are respectively ω(n) _nax and ω(n) _nio , then A _nax = α + β; ω(n) _nax = 2nπ/2ω (n = 0 , 1, 2, ...) A _nio = α-β; ω (n) _nio = (2n + 1) π/2ω (n = 0, 1, 2, ...).

Here, if the frequency interval between adjacent maximum values A _nax or minimum values A _nio is _H ′, _H ″, then _H ′=(n+1) _nax −(n) _nax = n+1/τ _p −n/τ _p =1/τ _{p H} ″=(n+1) _nio −(n) _nio =2n+3/2τ _p −2n+1/2τ _p =1/τ _p . In this way, using an ultrasonic delay line with delay time τ _p and adding the delayed signal E _B and the original signal, we get
Since the output signals exhibit the same phase with a period of 1/τ _p , a unique so-called comb filter is obtained in which a pass band and an attenuation band appear alternately. In addition,
_H ′ and _H ″ are called comb spacings in the characteristics of a comb filter.

In the NTSC system, the chrominance signal and the luminance signal are interleaved and transmitted, and the above-mentioned comb filter is used to separate them within the television receiver and remove dot interference. At this time, the comb spacing (1/τ _p = _H ′ = _H ″) must match the horizontal synchronization frequency _H determined by the color signal system, so it is necessary to flatten the delay characteristics with respect to frequency. At the same time, the input and output phase difference must be 180° (or 0°) at carrier frequency _p .

Therefore, conventionally, ultrasonic delay lines are designed so that the delay time τ _p corresponds to one scanning period of 63.5 to 64.0 μs defined by 1/ _H = 1H ( _H is the horizontal synchronization frequency).

However, even when designed in this way, the phase characteristics of the ultrasonic delay line are not actually flat as shown in FIG. 4 due to the characteristics of the piezoelectric transducer, the relationship with the matching circuit, etc.

In FIG. 4, _p is the carrier frequency of the circuit using the ultrasonic delay line, and _H is the horizontal synchronization frequency.

The horizontal axis represents the frequency centered on the carrier frequency _p , and the vertical axis represents the delay phase deviation when the delay phase at the carrier frequency _p is set to 0.

In Figure 4, the frequency is below _-5H and +
In the region of 10 _H or more, the delay phase deviation becomes large.

Conventionally, multiple ultrasonic delay lines like this,
In the cascaded ultrasonic delay circuits, the delay phase difference described above is added, and as shown in FIG. 5, the phase characteristics of the output signal are greatly distorted when the signal deviates from the carrier frequency _p . Therefore, when an ultrasonic delay circuit including a plurality of ultrasonic delay lines is used as a comb filter, there is a drawback that the intervals between the combs are not uniform.

The present invention eliminates the above conventional drawbacks and provides an ultrasonic delay circuit with flat frequency characteristics.

An embodiment of the present invention will be described below.

FIG. 6 shows an ultrasonic delay circuit in which ultrasonic delay lines are connected in cascade according to an embodiment of the present invention. The deviation is changing upward to the right. On the other hand, the ultrasonic delay line 10 in the latter stage
As shown in FIG. 8, the phase deviation changes downward to the right as the frequency increases. Figure 9 shows the frequency characteristics of the ultrasonic _delay circuit 11 obtained by cascading the ultrasonic delay lines 9 and 10 in the front and _rear stages. The results were obtained. This is because the upward-to-the-right characteristic of the ultrasonic delay line 9 in the preceding stage and the downward-rightward characteristic of the latter-stage ultrasonic delay line 10 are superimposed, and their delay phase deviations with different signs cancel each other out. In order to obtain the characteristics shown in FIG. 7 in the ultrasonic delay line 9 in the previous stage, for the horizontal synchronization frequency _H ,
The delay time τ ₁ of the ultrasonic delay line 9 may be determined as follows.

1/τ ₁ < _H In other words, if the delay time τ ₁ is determined to satisfy the relationship 1/τ ₁ = _H with respect to the horizontal synchronization frequency _H , then _H
When a signal with a frequency that is an integer multiple of Connect the delay line 9 as shown in Figure 7.
In order to make the delay phase shift at a constant rate for frequencies that are integral multiples of _H , especially the horizontal synchronization frequency.
1/τ ₁ is made small for _H.

On the other hand, the ultrasonic delay line 10 in the latter stage is designed so that its delay time τ ₂ satisfies the condition 1/τ ₂ > _H , and obtains the downward-sloping characteristic shown in FIG.

In addition, in the above embodiment, as shown in FIG.
Although a case is shown in which a matching coil 11 is provided between two ultrasonic delay lines 9 and 10, as shown in FIG.
The present invention is also applicable to cases where

As explained above, the present invention is based on the horizontal synchronization frequency.
The present invention provides an ultrasonic delay circuit formed by cascading a plurality of ultrasonic delay lines having different phase characteristics for frequencies that are integral multiples of _H. This has the effect of providing an ultrasonic delay circuit with flat frequency characteristics. As mentioned above, this ultrasonic delay circuit can obtain output signals with the same phase for frequencies that are integral multiples of the horizontal synchronization frequency _H , so even when used in a comb filter, the intervals between all combs can be adjusted to the horizontal synchronization signal. _H
It is possible to accurately match the , and its practical value is great.

[Brief explanation of the drawing]

Figure 1 is a front view to explain the operation of the ultrasonic delay line, Figure 2 is a diagram to explain the delay characteristics of the input and output signals of the ultrasonic delay line, and Figures 3a and b are the same ultrasonic waves. A diagram of the input signal to the delay line and its output signal, FIG. 4 is a frequency characteristic diagram of a single ultrasonic delay line, FIG. 5 is a frequency characteristic diagram of a conventional ultrasonic delay circuit, and FIG. 6 is a diagram of the present invention. A circuit diagram of an ultrasonic delay circuit in one embodiment, FIG. 7 and FIG. 8 are frequency characteristic diagrams of the front and rear ultrasonic delay lines constituting the same ultrasonic delay circuit, respectively, and FIG. FIG. 10, a frequency characteristic diagram of the delay circuit, is a circuit diagram of an ultrasonic delay circuit in another embodiment of the present invention. 9,10...Ultrasonic delay line.

Claims (1)

[Claims] 1. In an ultrasonic delay circuit formed by cascading two or more ultrasonic delay lines, delay phase deviation is achieved by varying the phase characteristics of the two or more ultrasonic delay lines for frequencies that are integral multiples of the horizontal synchronization frequency _H. Ultrasonic delay circuit that cancels out each other.