JPS5934004B2 - Unwanted signal removal device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an unnecessary signal removal device, and an object of the present invention is to provide an apparatus that can effectively remove interference signals appearing outside the band of a desired input signal.

In various audio playback devices and audio recording devices such as F, M, receivers, etc., if an interference signal that appears outside the band of the desired input signal mixes with the desired input signal, unnecessary audio will be reproduced. This is inconvenient as it may be recorded.

Therefore, for example, an FM-intermediate frequency filter that has a band that eliminates the interference signal is naturally required.

However, as is well known, in order to obtain high-quality audio with a high S/N ratio, a filter with a pass band as wide as possible is desired.

Inevitably, only when an interfering signal comes in, use a narrow band filter like the one above to prevent the interference! When no signal is coming in, it becomes more desirable to use a wideband filter.

Currently, as a method to meet these demands, it is known to configure the above two types of filters individually and switch between them mechanically, but this method has the disadvantage that the configuration becomes complicated and large in practical use. Another problem remains that since the switching described above is manual, it is desirable to automate it.

The present invention eliminates the drawbacks or problems of the conventional example,
The present invention provides a device that can effectively remove unnecessary signals.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to drawings showing embodiments.

FIG. 1 is a basic configuration diagram of an unnecessary signal removal device based on an embodiment of the present invention, and 1 to 3 are respectively passbands (W
interdigital electrodes provided on the piezoelectric body having 1 to W3;
4 is a mixer, 5 is a switching circuit, 10 is an input signal,
20 means an output signal.

Next, the functions of this device will be explained based on FIG.

The center frequency of the signal 10 is fW, and the desired band wider than the occupied frequency band and where a sufficiently high S/N ratio can be obtained is W. The center frequency is determined by the electrode pinch of electrodes 1 to 3 and the surface wave velocity of the piezoelectric body. Frequencies f1 to f3 and their passbands W1 to
W3 has the following relationship.

That is, fw""=f2; f3 --(1) W<1ni!
t(W□, W2.W3) (2) However, the meaning of the right side of equation (2) refers to the minimum of W1 to W3.

If the frequency of the interference signal is fn, the mixer M catches fn and generates a beat signal of Δf=1fn-fw1.

The switch output circuit S forms an electrically isolated state when no beat signal is input, and forms an electrically conductive state when a beat signal Δf is input, and in the case of Fig. 1, the output side is interdigitated. The electrodes 2 and 3 operate as if they were acoustically connected in cascade and electrically connected in parallel.

At this time, the effective band of 2 and 3 connected in parallel is f
.

It works as a transducer for receiving or transmitting a set of surface acoustic waves without reducing the signal-to-noise ratio (S/N), and in accordance with the basic principle of surface acoustic waves (2).
It is fully possible to select configurations 1 to 3 in advance so as to satisfy the formula.

Now, when a signal 10 containing an interference signal enters the apparatus configured as described above, the surface acoustic wave generated at 1 is received in series by 2 and 3 in the configuration shown in FIG. 1a. A signal within the desired frequency band of the desired input signal while effectively eliminating the interfering signal is extracted from 20.

FIG. 2 shows a different embodiment of the present invention, and since all of the elements are common to those in FIG. 1, the same numbers are given.

In this case, at the stage of generating surface acoustic waves, the interfering signal is effectively removed, and only the signals within the frequency band occupied by the desired signal are domained as surface acoustic waves. This means that it is reconverted into a signal and extracted from 20.

If the interference signal does not come in, the input signal is the first
In the case of Figure A, the waves are converted into surface acoustic waves and transmitted and received between the electrodes 1 and 2, and in the case of Figure 1, between the electrodes 2 and 3.

At this time, since Equation 2 is satisfied, the band of the input signal is not effectively narrowed, and therefore the output signal can be extracted without reducing the S/N ratio.

The specific structure of S can be easily constructed using conventionally well-known transistors, diodes, photoconductors, etc. When using a piezoelectric thin film on a substrate, it is also possible to incorporate transistors and diodes as 1,C (integrated circuit) elements on the substrate, and when the switching action is performed by light, a photo sensor can be used as a piezoelectric thin film. It is also possible to wear it on the body.

As described above, the present invention lies not in the structure or composition of the surface acoustic wave filter itself, but in the mixer that generates a beat signal based on the difference between a desired input signal and an unnecessary signal, and the beat signal generated from the mixer. It is equipped with a switching circuit that has a switching function that performs electrical continuity when no beat signal is received, and electrical isolation when no beat signal is received, and a piezoelectric body that is provided with three pairs of interdigital electrodes that function as a surface acoustic wave filter. It is composed of
There are no restrictions on the type of piezoelectric body, the mode of surface acoustic waves used, or the specific configuration of the switching circuit.

Therefore, the unnecessary signal removing device constructed based on the present invention can effectively and automatically remove unnecessary signals without reducing the S/N ratio of the desired input signal.

[Brief explanation of drawings]

FIGS. 1 and 2 are basic configuration diagrams of unnecessary signal removing devices according to different embodiments of the present invention. 1 to 3...Cross-fingered mold t4...Mixer, 5...°Switching circuit, 10...
・Input signal, 20... Output signal.

Claims (1)

[Claims] 1 A piezoelectric body provided with three pairs of interdigital electrodes having a band sufficiently wider than the occupied frequency band of a desired input signal, and with electrode spacing arranged such that the center frequency is near the center frequency of the input signal. Then, a beat signal between the desired input signal and the interference signal appearing outside the band of the desired input signal is generated. : a mixer, and a switching circuit capable of electrically connecting two adjacent interdigital electrodes in parallel according to the beat signal, the two adjacent electrodes being output terminals, and the remaining one electrode being an output terminal. is used as an exit terminal, and the two adjacent electrodes are acoustically connected in cascade and electrically connected in parallel to make the passband equal to the frequency band occupied by the desired input signal to eliminate the interference signal. An unnecessary signal removal device characterized by: