JPS6022819A - Ultrasonic wave delay circuit - Google Patents

Abstract

PURPOSE:To obtain a signal superimposed on an input terminal voltage of an ultrasonic wave delay line, reflected at an output terminal and delayed by double by subtracting a voltage corresponding to an input signal voltage from a voltage at the input terminal voltage of the ultrasonic wave delay line. CONSTITUTION:A signal voltage E1 at input terminals 16, 16' is a superimposed voltage of a signal voltage delayed by a time twice the one-way delay time of a delay line 8 and a voltage E0 at a signal input terminal, because the E1 is reflected at an output terminal of the ultrasonic wave delay line 8 and returned again. A signal voltage multiplying the voltage E0 at the input terminal by alpha is subtracted from a signal voltage multiplying the signal voltage E1 by beta at a subtractor 12. The term of the input signal voltage is eliminated from the superimposed voltage and only the reflected wave signal voltage is extracted by selecting the value alpha as alpha=betaXZi/(Z+Zi), where Zi is an input impedance of the ultrasonic wave delay line and Z is an impedace 9.

Description

[Detailed Description of the Invention] The present invention relates to an ultrasonic delay circuit using an ultrasonic delay line used for interference removal in NTSC color television receivers, cross color removal in video tape recorders, etc. In particular, the present invention provides an ultrasonic delay circuit using an ultrasonic delay line that can be significantly miniaturized compared to 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 1/100,000 of that of electromagnetic waves.
Focusing on this fact, the electric signal is first converted into an ultrasonic signal, and after obtaining a delay time of several 1Q 1iSCC or several 100μ of C9, it is converted again into an electric signal.

FIG. 1 shows the principle of a commonly used ultrasonic delay line. That is, on the end face of the glass delay medium 1, electrodes 2a, 2b and 2'a, 2'bf are provided/converting elements 3 and 3' having an electric-mechanical energy converting function are added. , '114 birth 2a and 2 of conversion element 3
When an electric signal Ei is applied between the time intervals b, 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 the path shown in FIG. , an electrical signal E according to its frequency. The electrode 2'a
It occurs between and 2'b.

As is well known, such an ultrasonic delay line is used as a comb-shaped 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 calculates the sine wave input signal EA(-α5ino)t) input to the input terminal 4, as shown in FIG. τ from the input signal EA, which is directly input to one input terminal 5a of the circuit 5 and obtained through the ultrasonic delay line 6 to the other input terminal 5b of the arithmetic circuit 5. The delayed signal EB (-β sin ω (-τ)) is inputted, and the above two types of signals EA and EB are added (subtracted) in the arithmetic circuit 5 and output from the output terminal 7. be.

In this way, when the input signal EA and the delayed signal EB obtained by passing this input signal through the ultrasonic delay line 6 are added,
The output signal Ec obtained from the output terminal is as follows.

E c = E p, + E B = α5111ωt + β5111ω (−τ.) = 72
aβcosωv.・5in(ωt+ψ)=As1n
(ωt+ψ) However, ψ=lan-1(βS'lnωr ./ (a
+βC03(IJ r )) Here, the maximum value to the amplitude is Amax, and the minimum value is A.

If the values of the frequency ω when the signal Ec takes these values are θmax and ω(n)mm, then the following equations are obtained.

Here, between the adjacent maximum values Amax, the distance is the minimum value A
, n is the frequency interval fH/, fH7/,
fH'= f (n+1)max fi-1-1n 1 τ0 τ0 τO fH''-f (n+1)min-f(n)mvL2n
+3 2n+1 2τ. 2τ.

It becomes τ0. In this way, the delay time τ. When the delayed signal EB and the original signal are added using an ultrasonic delay line of A peculiar phenomenon that repeatedly appears in
A so-called comb filter is obtained. Here fH',
fH'' is called the comb spacing in the characteristics of the comb filter.

In addition, when Fourier transform is used in the two-note calculation,
The results shown in FIG. 3 can be obtained very easily by using four unit impulse functions δ(
1), the delayed signal EB becomes δ(t-τ.), and the output signal Ec(t) becomes Ec(t)=EA+EB=δ(1)+δ(-τ).

When this is Fourier transformed, Ec(jω)=1+el″″0 Then, the frequency characteristic of the output signal Ec is Ec21
Ec(jω)1, and a comb-shaped waveform as shown in FIG. 3 is obtained.

Although such 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 present invention is a substantially compact ultrasonic delay circuit with good performance. It is an attempt to obtain.

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 ((a)) connected in series to the input end of this delay line 8, 1o is an amplifier with amplification factor a, 11゛ is an amplifier with amplification factor β, and 12 is an impedance connected in series to the input end of this delay line 8. The subtracter 16 is the output end of the delay signal extraction reservoir.

Here, as mentioned above, the impedance (Z
)9 are connected in series. This impedance (Z)
A line 13.14 is taken out from before and after 9 and connected to a subtracter 12 via an amplifier 10.11.

The ultrasonic delay line 8 has four terminals 16 on the input side and the output side.
, 16' and 17, 17', and when a signal is normally applied to the input terminals 16, 16', the output terminals 17, 17',
A predetermined delay time 1τ can be obtained from the input terminals 16 and 1 when configured as in the present invention.
6' has a reflected wave voltage E(2τ) with a delay time of 2τ.
appears. The impedance between the twisted input terminals 16 and 16' is Zl.

Now, sell it to the front stage of series impedance (Z) 9. Assuming that input signal No. 11 is applied, the voltage E1 between the terminals at the input end 16, 15' of the ultrasonic delay line 8 is expressed as follows. Also, the voltages on lines 13 and 14 are respectively σEo.

1i2= /but l/(Z+Zi) I! ,O ten/
It becomes 1E (2r). Then, in the subtracter 12, in order to extract only E(2τ) from this equation, (-a-+-βZi/(Z+Zi)) must be 0.

That is, it is sufficient to satisfy the relationship α/β=Zi/(Z−+−Zi). By adjusting each constant in this manner, a signal delayed by βE(2τ), that is, twice the predetermined delay time 1τ of the ultrasonic delay line 8, can be extracted from the output terminal 16.

As described above, according to the present invention, it is possible to obtain twice the signal delay time by utilizing the secondary unnecessary reflections 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 a and β may be varied, or even the series impedance Z may be varied. In this way, it is possible to obtain an ultrasonic delay circuit that is qualitatively small and has good performance.

[Brief explanation of the drawing]

Figure 1 is a front view of the structure and operation of the 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. FIG. 7012 shows an embodiment of the ultrasonic delay circuit according to the present invention. 8... Ultrasonic delay line, 9...-Series impedance (Z), 16.16'--Input end. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure 3 Figure 4

Claims (1)

[Claims] A series impedance (4) is connected to the input end (impedance Zi) of the ultrasonic delay line, and an input signal E is applied to the front stage of this series impedance Z. An ultrasonic delay circuit characterized in that the voltage βE1 obtained by amplifying the voltage E1 at the input terminal by an amplification factor β is configured such that the phases thereof are opposite to each other so that the voltage becomes a/β−Zi /(Z+Zi).