JPS643087B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic delay circuit using an ultrasonic delay line used for removing dot interference in NTSC color television receivers, cross color removal in video tape recorders, etc. The present invention provides an ultrasonic delay circuit using an ultrasonic delay line that can be significantly smaller than conventional ultrasonic delay lines.

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.

FIG. 1 shows the principle of a commonly used ultrasonic delay line. That is, glass retardation medium 1
Conversion elements 3 and 3', which have electrodes 2a, 2b and 2'a, 2'b and have an electro-mechanical energy conversion function, are attached to the end faces of the conversion elements 3 and 3'.
When an electric signal Ei is applied between the electrodes 2a and 2b, the conversion element 3 mechanically vibrates according to the frequency of the signal, and ultrasonic waves are emitted into the delay medium 1. This ultrasonic wave is reflected many times within the delay medium 1 as shown in FIG. Then, an electric signal E ₀ corresponding to the frequency is generated between the electrodes 2'a and 2'b.

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

Next, the configuration of a conventional comb filter using such an ultrasonic delay line is as shown in FIG _.
(=αsinωt) at one input terminal 5a of the arithmetic circuit 5
A delayed _signal E _B ( ₌ βsinω
(t−τ ₀ )) and the above two types of signals E _A and
E _B is added (or subtracted) by the arithmetic circuit 5 and outputted from the output terminal 7.

In this way, when the input signal E _A and the delayed signal E _B obtained by passing this input signal through the ultrasonic delay line 6 are added, the output signal obtained from the output terminal 7 is
Ec becomes as follows.

Ec=E _A +E _B = αsinωt+βsinω(t-τ ₀ ) =√ ² + ² +2 ₀・(+) = Asin(ωt+) However, = tan ^-1 {βsinωτ ₀ /α+βcosωτ)} A=√ ² + ² +2 _0Here , the maximum value of amplitude A is Amax, the minimum value Amin,
If the values of the frequency ω when the signal Ec takes these values are ω(n)max and ω(n)min, then Amax=α+β;ω(n)max=2nπ/2ω(n=0, 1, 2,...) Amin=α-β;ω(n)min=(2n+1)π/2ω(n=0, 1, 2,...).

Here, if the frequency interval between adjacent maximum values Amax or minimum values Amin is H', H'', then H'=(n+1)max =n+1/τ ₀ -n/τ ₀ =1/τ ₀ H ″=(n+1)min−(n)min=2n+3/2τ ₀ −2n+1/2τ ₀ =1/τ ₀ . In this way, using an ultrasonic delay line with a delay time τ ₀ 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 ₀ , a unique so-called comb filter is obtained in which the pass band and attenuation band appear alternately, as shown in FIG. Here, H' and H'' are called the comb spacing in the characteristics of the comb filter.

In addition, in the above calculation, if Fourier transform is used, the results shown in FIG. 3 can be obtained very easily.

In other words, if the unit impulse function δ(t) is used as the input signal E _A , the delayed signal E _B becomes δ(t−
τ ₀ ), and the output signal Ec(t) is Ec(t)=E _A +E _B =δ(t)+δ(t−τ ₀ ).

When this is Fourier transformed, Ec(jω)=1+e ^-j 〓〓 ₀ Therefore, the frequency characteristic of the output signal Ec is Ec=|Ec(jω)| =√(1+ ₀ ) ² + ² ₀ =√2( 1+ ₀ ) = |2cosω·τ ₀ /2|, and a comb-shaped waveform as shown in FIG. 3 is obtained.

Although comb-shaped filters using ultrasonic delay lines have been known for a long time, the purpose of the present invention is to extract only delayed signals, and the purpose of this invention is to create an ultrasonic delay circuit that is essentially small and has good performance. It is what you are trying to get.

An embodiment of the present invention will be described below with reference to FIG. In the figure, 8 is an ultrasonic delay line, 9 is an impedance (Z) connected in series to the input end of this delay line 8, 10 is an amplifier with amplification factor α, 11 is an amplifier with amplification factor β, and 12 is a subtracter. , 15 are output terminals for extracting delayed signals.

Here, as described above, the impedance (Z) 9 is connected in series with the two terminals 16 and 16' on the input side of the ultrasonic delay line 8. Lines 13 and 14 are taken out from before and after this impedance (Z) 9, and are connected to a subtracter 12 via amplifiers 10 and 11.

The ultrasonic delay line 8 has four channels on the input side and the output side.
It has terminals 16, 16' and 17, 17',
Normally, when a signal is applied to the input terminals 16, 16', a predetermined delay time 1τ is obtained from the output terminals 17, 17', and when configured as in the present invention,
A reflected wave voltage E〓(2τ) having a delay time of 2τ appears at the input terminals 16, 16'. Also,
The impedance between the input terminals 16 and 16' is Zi
shall be.

Now, if an input signal that becomes E〓 ₀ is applied to the front stage of the series impedance Z9, the voltage E〓 ₁ between the input terminals 16 and 16' of the ultrasonic delay line 8 is E〓 ₁ = Zi / (Z + Zi )E〓 ₀ +E〓(2τ). Further, the voltages of the lines 13 and 14 are respectively αE〓 ₀ and βE〓 ₁ =βZi/(Z+Zi)E〓 ₀ +βE〓(2τ). Then, in the subtracter 12, −αE〓 ₀ +βE〓 ₁ = {−α+βZi/(Z+Zi)}+βE
〓(2τ), and in order to extract only E(2τ) from this equation, it must be {-α+βZi/(Z+Zi)}=0.

That is, it is sufficient to satisfy the relationship α/β=Zi (Z+Zi). By adjusting each constant in this way, βE〓(2τ),
That is, 2 of the predetermined delay time 1τ of the ultrasonic delay line 8
A signal delayed by twice the delay time can be extracted.

As described above, according to the present invention, it is possible to obtain twice the signal delay time by utilizing the secondary unnecessary reflection of the ultrasonic delay line, and therefore it is possible to obtain an extremely compact ultrasonic delay circuit. . Moreover, the adjustment of the circuit of the present invention is very simple, and either one of the above α and β may be varied, or the series impedance (Z) may be varied. In this way, the present invention makes it possible to obtain an ultrasonic delay circuit that is substantially compact and has good performance.

[Brief explanation of drawings]

Figure 1 is a front view for explaining the configuration and operation of an ultrasonic delay line, Figure 2 is a block diagram of a conventional comb filter, Figure 3 is a frequency characteristic diagram of the comb filter, and Figure 4 is a diagram of the frequency characteristics of the comb filter. 1 is a block diagram showing an embodiment of an ultrasonic delay circuit according to the present invention. FIG. 8... Ultrasonic delay line, 9... Series impedance (Z), 16, 16'... Input end.

Claims (1)

[Claims] 1. An ultrasonic delay line with a structure in which a conversion element having an electro-mechanical energy conversion function is attached to a glass delay medium, and a second-order delay time appears at the input end of the ultrasonic delay line, and the input end (impedance A first amplifier that amplifies the input signal E〓 ₀ applied to the front stage of the series impedance Z with an amplification factor α, and an input terminal of the ultrasonic delay line. A second amplifier that amplifies the voltage E〓 ₁ with an amplification factor β, and voltages αE〓 ₀ and βE〓 ₁ output from these first and second amplifiers.
are opposite in phase, and α/β=Zi/(Z+
1. An ultrasonic delay circuit comprising: a subtracter into which the input signal is input as shown in FIG.