SU1762384A1 - Surface acoustic wave recursive filter - Google Patents

Abstract

The invention relates to acoustoelectronics and can be used as a bandpass filter, for example, in multichannel filters, adaptive filters, comb filters, intermediate frequency paths of radio receivers. The purpose of the invention is to reduce the distortion of the output waveforms. The recursive filter on surface acoustic waves contains interdigital transducers 1–3, amplifier 4, phase shifter 5, and piezoelectric transducer 6 2 Il.

Description

Fig 2

The invention relates to acoustoelectronics and can be used in radio information processing devices.

A recirculating device is known, which includes a piezoelectric acoustic conductor, on the surface of which interdigital transducers (IDT) are located.

The disadvantage of the device is a limited range of amplitude-frequency response (AFC) forms. In particular, in order to reduce the bandwidth of the device, it is necessary to increase the length of the IDT, which leads to an increase in its size.

Closest to the proposed device is a recursive filter on the surfactant containing three IDTs placed on the piezoelectric sound duct, the corresponding summation buses of which are connected to the common wire, the second summing tire of the first IDT is connected to the input of the device, the phase shifter whose input is connected to the input of the device and the output is connected to the amplifier input, the amplifier whose output is connected to the second summing bus of the second IDT, the second summing chinat the third IDT is connected to the output of the device.

The disadvantage of the prototype is a high level of spurious signals.

Analysis of the frequency response allows to establish that the device has a signal transmission from input to output (via the first to the third transducer), which does not depend on the parameters of the feedback circuit, and is parasitic for a recursive filter. At frequencies close to the resonance, the phase shifter introduces a constant phase shift in the output signal, which leads to distortions in the spectrum of the input signal, which is absent only in the case of a linear dependence of the phase shift on frequency (signal delay). In addition, part of the surfactant energy emitted by the first IDT is converted into electrical energy at the second IDP, which leads to the appearance of a parasitic signal at the output of the phase shifter. A portion of the surfactant energy emitted by the second IDT is converted into electrical energy at the first IDT, and a parasitic signal appears at the output of the input signal generator.

The aim of the invention is to reduce the distortion of the output waveform.

The goal is achieved by the fact that in a recursive filter on a surfactant containing three IDTs placed on a piezoelectric sound duct, the corresponding summation buses of which are connected to

the common wire, the second summing bus of the first IDT connected to the input of the device, the amplifier, phase shifter, provides the following differences: the second summing bus of the second IDT is connected to the input of the amplifier, the output of which is connected to the output of the device and the input of the phase shifter, the output of the phase shifter is connected to the second summing bus of the third The IDT, the first and the third IDT are placed in different acoustic flows, and the second IDT is made covering the acoustic flows of the first and third IDT.

FIG. 1 shows the graph of the proposed device; in fig. 2 is its structural scheme.

The recursive filter on the surfactant consists of a VSP 1-3, an amplifier 4, a phase shifter 5, a piezoelectric zvukoprovod 6. Corresponding summing buses VSP 1-3 are connected to the common wire of the device, the second summing bus VSP 1 is connected to the input of the device, VSP-2 with the amplifier input 4, the IDT is the 3rd output of the phase shifter 5. The output of the amplifier 4 is connected to the input of the phase shifter 5 and the output of the device.

The device works as follows.

The input signal is fed to the input IDT 1, where it is converted into surfactants, which are converted into an electrical signal at IDT 2. The electrical signal amplified by the amplifier 4 is fed to the output of the device and to the input of the phase shifter 5, where its phase changes. Then the signal goes to the IDT 3, where it is converted to surfactant that reaches the IDT 2. Thus, the signals are circulated through the IDT circuit 2 - amplifier 4 - phase shifter 5 - IDP 3.

The proposed device has the following advantages: the parasitic signal transmission circuit from the input to the output of the device is eliminated, there is no phase shift in the output signal of the device, the level of parasitic signals at the outputs of electronic elements is reduced, which significantly improves the characteristics of recursive filters on SAW.

Claims (1)

Invention Formula A recursive filter on surface acoustic waves (SAW) containing a piezoelectric acoustic duct and three counter-whip transducers (IDT) located on its surface. corresponding summing buses of which are connected to the common wire, as well as series-connected amplifier v a phase shifter, wherein the second summing bus of the first IDT is connected to the device input, characterized in that, in order to reduce distortion of the output signals, there the second summing bus of the second IDT is connected to the amplifier input, the device output is connected to the amplifier output, the output of the phase shifter is connected the second summing bus of the third IDT, the first and third IDT are placed in different acoustic channels, and the second IDT is made covering the acoustic channels of the first and third IDT. #i (ctdexp (-jwTfj) exp (-j & j (u) (j (r / HZ (M) G FIG. one