JPS6318282A - Chirp filter - Google Patents

Abstract

PURPOSE:To obtain an apparatus having a large delay time, by combining a plurality of chirp filter elements with characteristics of differing in the delay time range. CONSTITUTION:Chirp filters 11-1n (n is an integer of more than 1) different in the passage frequency band have all the same chirp rate, wherein the chirp rate gives a DELTAf/DELTAtau (tau represents delay time and (f) frequency). Delay elements 21-2n which have respective fixed delay times corresponding to the delay time of the chirp filters 11-1n are provided corresponding to the chirp filters 11-1n. A synthesization circuit 3 synthesizes all passage outputs of the chirp filters 11-1n and the delay elements 21-2n corresponding thereto to make filter outputs. Thus, chip filter elements with a smaller delay time range can be used to build an apparatus with a larger delay time.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a chirp filter device, and particularly to a chirp filter device that can obtain a large change in delay time.

Sarami-Nira I A chirp filter having a delay time corresponding to the frequency of an input signal can be constructed using a surface acoustic wave (SAW) element. In order to obtain a large delay time change in this chirp filter, it is necessary to use a large-sized substrate made of a material with a low elastic wave velocity. However, there are practical limits to the material and size of the substrate, and therefore there is a natural limit to the width of the delay time change.

An object of the present invention is to provide a chirp filter device having a large delay time width using a surface acoustic wave element having the same substrate material and size as conventional ones.

Structure of the Invention A chirp filter device according to the present invention includes a plurality of chirp filters having mutually different pass frequency bands and the same chirp rate, and delay time characteristics at adjacent boundaries of each pass frequency band of these chirp filters. It is characterized by having a delay time adjustment means that adjusts the delay time so that it changes continuously.

Example The present invention will be described in detail below using the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention, and 11
~1n (n is an integer of 2 or more) are chirp filters each having a different pass frequency band, and all of them have the same chirp rate. Here, the chirp rate indicates Δf/Δτ (τ is delay time and f is frequency).

Reference numerals 21 to 2n are delay elements that are provided corresponding to the above chirp filters 11 to 1, respectively, and have fixed delay times set respectively corresponding to the delay times of these corresponding chirp filters. 3 is a chirp filter 11 to 1n
and delay elements 21 to 2 corresponding to these chirp filters.
This is a synthesizing circuit that synthesizes all the outputs passed through n. That is, all the outputs of the series circuit of the chirp filter 1i (i is an integer from 1 to n) and the delay element 21 are combined to form a filter output.

Now, as a characteristic of the synthetic chirp filter device shown in FIG. 1, as shown in FIG. 3(d), the frequency f1 to f4 is
Consider the case where n=3 to obtain a characteristic in which the delay time changes from τ1 (seconds) to τ1+T (seconds).

In this case, three chirp filters 11, 12 and 13
Let the respective characteristics be as shown in FIGS. 3(a), (b), and (C). That is, the chirp filter 11 is as shown in FIG.
), the delay time width is from τ1 to τ2 in the frequency range f1 to f, and the chirp filter 2
As shown in (b), the delay time width is from τ to τ4 in the frequency range from f to f3. Further, as shown in (C), the chirp filter 13 has a frequency range from f to f4 and a delay time width from τ5 to τ6.

In this case, the chirp rates of each chirp filter are all the same and constant, and (f − f )/T = (f2 − f, )/(τ2 − τ
1) It is assumed that the settings are as follows: = (f3-f2'') / (τ4-τ3) = (f4-f3) / (τ6-τ5).

When the chirp filters 11, 12, and 13 are combined, the straight line of the frequency vs. delay time characteristic, which is the overall characteristic (the characteristic shown in FIG. 3(d)), must be continuous. Therefore, the delay time of each delay element 21, 22, 23 is selected so that τ2 and τ3 are equal at frequency f2, and τ4 and τ5 are equal at f3.

For example, in this embodiment, the delay time of the delay element 21 is O(
seconds), the delay time of the delay element 22 is adjusted to (τ2-τ3), and the delay time of the delay element 23 is adjusted to (τ2-τ3+τ4-τ5). If the delay time becomes negative, by selecting a large delay time for the delay element 21, it becomes possible to make the delay times of the other elements 22 and 23 positive.

If the outputs of all the chirp filters are combined by the synthesizer 3 under such conditions, a continuous delay time characteristic as shown in FIG. 3(d) can be obtained, and a constant value of the chirp rate can be obtained. Also, the frequency vs. amplitude characteristic is f
It can be seen that the characteristics are nearly flat in the entire range of −f4.

In FIG. 1, the structure is such that the chirp filters 11 to 1n are provided in the front stage, and the delay elements 21 to 2n are respectively provided in the subsequent stage, but it is clear that the arrangement may be reversed.

FIG. 2 is a block diagram showing another embodiment of the present invention,
Components equivalent to those in FIG. 1 are designated by the same reference numerals. In this example, n delay elements 41 to 4n are connected in series with each other, and the delayed outputs of each of these delay elements 41 to 4n are input to the corresponding chirp filters 11 to 1n. .

This has the advantage that the delay time of each delay element 41-4n can be made smaller than the delay time of delay elements 11-1n in the case of FIG.

By doing so, a chirp filter device with a large delay time width can be configured using a chirp filter element with a small delay time width. Therefore, conventional elements can be used without any restrictions regarding the material or size of the substrate of the surface acoustic wave element.

Effects of the Invention As described above, according to the present invention, a chirp filter device having a large delay time width is produced by combining a plurality of chirp filter elements each having a characteristic of a small delay time width.
It has the effect of being able to

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention, FIG. 2 is a block diagram of another embodiment of the present invention, and FIGS. 3(a) to (C) are diagrams of chirp filter elements of the embodiment of the present invention. The frequency vs. delay time and amplitude characteristic diagram, FIG. 3(d), is a diagram showing the overall characteristics of the apparatus according to the embodiment of the present invention. Explanation of symbols of main parts 3...Synthesis circuit

Claims (1)

[Claims] A plurality of chirp filters that have mutually different pass frequency bands and the same chirp rate, and a delay time that is adjusted so that the delay time characteristics change continuously at adjacent boundaries between the pass frequency bands of these chirp filters. A chirp filter device comprising: adjusting means.