SU1663746A1 - Suface-acoustic-wave frequency discriminator - Google Patents

Abstract

The invention relates to radio engineering. The purpose of the invention is to improve the accuracy of determining the instantaneous frequency. The surface acoustic wave frequency discriminator (SAW) contains a piezoelectric acoustic duct 1, on the surface of which an input interdigital transducer / IDT / 2 and two receiving IDT 3 and 4 are located. To improve the accuracy of determining the instantaneous IDT frequency 2, 3 and 4 are performed as unidirectional converters of group type. In addition, each of them has an average square-wave electrode and inductive phase-shifting elements 5 located between the upper 7 and lower 6 groups of 6 and 7 electrodes of the corresponding converter. The property of such converters to change the direction of emission of the SAW, depending on which frequency interval the frequency of the input signal belongs to, makes it possible to increase the accuracy of determining the instantaneous frequency value. 8 il.

Description

The invention relates to radio engineering and can be used in various radio engineering devices for detecting frequency modulated signals.

The purpose of the invention is to improve the accuracy of determining the instantaneous frequency

Fig. 1 shows the functional electrical circuit of the frequency discriminator on surface acoustic waves (SAW), Fig. 2 shows the amplitude-frequency characteristics (AFC) of unidirectional group-type converters (OPGT), Fig. 3 shows the discriminatory characteristic (HF) of the frequency discriminator (PR). on surfactant; 4 is an equivalent circuit of a circuit formed by an inductive phase-shifting element and a static capacitance.

OPGT in Fig. 5 is the phase-frequency characteristic (PFC) of the circuit formed by an inductive phase-shifting element and static capacitance (OPGT). Figure 6a shows the input converter of the OPGT. Figure 66 shows the spatial position of elementary sources of surfactant within the same period of groups of electrodes of the input OPGT. the formation pattern of the surfactant emitted towards the output OPGT in FIG. 8 is a diagram of the formation of the emitted surfactant towards the output OPGT

The SAW frequency discriminator contains a piezoelectric acoustic duct 1 on the surface of which input 2 and two receiving IDT 3 and 4 are located in the form of unidirectional transducer converters

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ABOUT

each with a middle meander electrode and phase-shifting (inductive) elements 5, respectively, located between the lower 6 and upper 7 groups of electrodes of the corresponding OPGT, the width of the electrodes of OPGT 2 is equal to the interelectrode distance Ao / 8, and the spatial period of the group electrodes is equal to 2 AO, where AO is the length of the surfactant, and AO 0 EFF,, where / Eff 2 LO) ®

surfactant speed; a) 0 is the average frequency of the amplitude-frequency characteristic (AFC) of the OPGT 2. The output transducers are located in the input aperture and at equal distances from it: OPGT 3 - to the right, OPGT 4 - to the left. OCGT 3 has an average frequency response of an og, the width of the electrodes is equal to the interelectrode distance of L2 / 8, and the spatial period of the group of electrodes is 2

Kg, and R2 EFF-. OPGT 4 has the average frequency response 0) 1, the width of its electrodes is equal to the interelectrode distance Ai / 8, and the spatial period of the group

electrodes is equal to 2 AI, and AI.

Ј. t / lr uj

Entrance. OGT 2 is the input of the frequency discriminator to the surfactant.

Output converters 3, 4 are anodized along the length of the electrodes in accordance

with the law (), resulting in their frequency response

X

takes a triangular shape (figure 2), and their length is twice the length of the input converter 2. The outputs of OPGT 3 and OPGT 4 are each connected to its detector unit 8, which performs detection and filtering using detector diodes 9, 10 and parallel RC - chains 11, 12. Diodes 13, 14 - damping.

The frequency discriminator works as follows.

Let the input on OPGT 2 signal at the frequency w. Since between the lower 6 and upper 7 groups of electrodes, inductive phase-shifting elements 5 are included, which with a static capacitance of the converter 2 form a parallel oscillating circuit (the equivalent circuit of this circuit is shown in Fig. 4), the phase-response characteristic (PFC) of which looks like 5, the electrical phase shift ipsn generated by this element 5 depends on the frequency a) of the input signal. If the frequency of the input signal w is such that one wi ak,

then the phase shift will be + (see FIG. 7),

if the frequency of the input signal will lie in a different frequency interval

Shaw and w. then the phase shift will be - (see FIG. 8). Transducer 2 excites surfactants that propagate either toward OPGT 3 or toward OPGT 4.

0 Elementary surfactant sources located in the interelectrode gaps of the transducer 2 (see Fig. 6) excite acoustic waves, the phases of which (acoustic phases ak) are determined by the spatial positions of these sources. Figure 2 shows the spatial position of elementary sources of surfactants, within one period of groups of electrodes OPGT 2, taking into account their signs and shows

0 values of acoustic and electrical phases of each source.

Let the frequency of the input signal be such that the phase shift created by element 5 is -, i.e. OJ2 & "B in this

In case of this, acoustic waves generated by each elementary source will be added in phase for surfactants propagating to the right of transducer 2 and out of phase for surfactants propagating in the opposite direction (see Fig. 2), i.e. the radiation is directed in the frequency band (w0), and the velocity vector of these waves is directed towards the output OPGT 3. If the frequency w of the input signal is such that the phase shift,

given by the phase shifter, (- -4-), i.e.

Odo to it. The acoustic waves excited by elementary sources are added in phase for surfactants propagating to the left of transducer 2 and out of phase for surfactants propagating to the right of it (see Fig. 8), i.e. radiation

5 is directed in the frequency band (a) 0; g / l), and the surfactant velocity vector, in this case, is directed toward the output OPGT 4, i.e. input OPGT 2 performs frequency-spatial selection of the input signal

0 and at the same time it operates in the mode of unidirectional emission of the surfactant. Thus, a signal whose frequency lies in the interval (OOD) is converted by the OPGT 2 to the surfactant, which propagates to the right of the converter 5 and is converted by the output OPGT 3, operating in the unidirectional reception mode frequency band, into an electrical signal, which, after detection and filtering, has an amplitude

Uv2 (see FIG. 3), and the signal whose frequency belongs to the frequency domain (oA; a) is converted to a SAW propagating to the left of OPGT 2 and converted by output OPGT 4 operating in unidirectional reception in a band (ftfe; wi) into an electrical signal, which, after detection and filtering, has an amplitude of UBbix-i (cM. FIG. 3). OPGT 2 and output OPGT 3 form a filter having a bandwidth up to Ј 2 (soo) - the right channel of the BH, the frequency response of which is shown in Fig.2. OPGT 2 and output OPGT 4 form a filter having a bandwidth of Dan 2 (cot - ob) - the left channel of the BH, the frequency response of which is shown in Fig.2.

From the above it can be seen that the frequency discriminator converts the input signal, the frequency of which belongs to the frequency interval (ohm: hell), into an electrical signal, the amplitude of which is 1) The output is directly proportional to the frequency of the input signal and varies within (andout: ioutmax) equivalent circuits of all OGTs are different, hence the inductive phase-shifting elements are different. The criterion for choosing such an element is the specified phase response of the circuit formed by the inductance and static capacitance of the converter, and the minimum phase angle in (see Fig. 1), the value of which is determined by the quality factor of this circuit.

The OPGT property to change the direction of emission of the surfactant depending on which frequency interval (hell;) or

0

five

0

five

Claims (1)

((No;) belongs to the frequency of the input signal (i.e., frequency-spatial selection of signals), allowed the use of unidirectional transducers in this BH circuit, which reduces the insertion loss by four times and decreases the frequency response pulsations (by 10-12 dB) due to triple-pass signals and surfactant re-reflections from the transducer electrodes, as a result, allows to extend the linear section of the DF, to increase its linearity and accuracy in determining the instantaneous frequency value. surface acoustic wave discriminator, containing a piezoelectric acoustic conduit, on the surface of which are located an input meeting-pin converter (IDT) with an average frequency WQ, from two sides at equal distances from it - the first and second receiving IDT with an average frequency a) 0 + Lo and w0 - A WQ, respectively, whose electrodes are apodized in length in accordance with the law 51PHh2 h / / and exits connected, respectively, with the first and second detector units, characterized in that, in order to improve the accuracy of the instantaneous frequency, the input first and second transducer IDTs are made in the form of unidirectional group-type converters (OPGT) with the meander meander electrode, and between the upper and lower groups The electrodes of each OPGT included phase-shifting elements. sh Ujo FIG. 2 idi max U, ffblXi ffd / xi Usbtx.min 4 one sy sh one si FIG. five “§F § n- n- % ( s   Sf To the right of the OPPly to the OPP ь, -Кк + Ч, -L-b- - - e- y-if g 7 To the right of Oppvlevo from OPGT w  Jl. z / 4 /; j Fm.d