JPS642291B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital filter with sharp frequency characteristics.

Conventionally, in order to sharpen the frequency characteristics of a receiver,
LC filters and ceramic filters have been used, but LC filters have frequency characteristics as shown in Figure 1, and it has not been easy to sharpen the frequency characteristics of these LC filters. Furthermore, the frequency characteristics of ceramic filters have been problematic due to harmonics, as shown in FIG.

Furthermore, these filters have the disadvantage that they cannot improve signal attenuation characteristics or be incorporated into equipment without adjustment during manufacturing.

In order to eliminate the drawbacks of the above-mentioned conventional example, the present invention provides a switch that blocks or passes an input signal;
an A/D converter that converts the input signal into a digital signal; an upper and lower limit pulse width setting device that sets a pulse width value of the upper or lower limit frequency of the input signal; a digital pulse width comparator that compares the pulse width of the input signal with the setting values set by the upper and lower limit pulse width setting devices, and the pulse width of the input signal from the A/D converter is the upper limit, When the pulse width is between the set values set by the lower limit pulse width setting device, the switch is opened by the signal from the comparator and the input signal is passed through. , provides a digital filter that can pass signals in any band. Hereinafter, embodiments will be described in detail with reference to the drawings.

FIG. 3 shows a block diagram of an embodiment of the present invention, in which 1 is a receiver for transmitting and receiving ultrasonic waves, 2 is a receiver for transmitting and receiving ultrasonic waves;
is a receiver, 3 is an A/D converter, 4 is a digital pulse width comparator, 5 is an upper limit and lower limit pulse width setting device,
6 is a switch that passes or cuts off the output of the receiver 2;

Next, the operation of this embodiment will be explained. First, a signal received by receiver 1 is converted into an electrical signal and sent to receiver 2, where it is amplified to a certain level and sent to A/D converter 3 and switch 6. The signal sent to the A/D converter 3 is converted into a digital signal and sent to the digital pulse width comparator 4. This digital pulse width comparator 4 has an upper limit,
The set value of the pulse width of the frequency whose upper limit is the lower limit from the lower limit pulse width setting device 5 is compared with the signal sent from the A/D converter 3. Here, specify the upper and lower frequency limits of the required receiver band, respectively.
Assuming _H and _L , the respective pulse widths t _H and t _L are t _H =1/ _H sec, t _L =1/ _L sec. Also, if the frequency of the received signal is the pulse width t, then t = 1/, and when t _H ≦t≦t _L , the signal is sent from the digital pulse width comparator 4 so that the switch 6 is turned on. If transmitted, the output signal of the receiver 2 is conveyed to the next stage only when _L ≦≦ _H . Therefore, as shown in Fig. 4, a filter with sharp frequency characteristics without adjustment is created, and the pulse width t H at the upper limit frequency _H and the pulse width _{t L at} the lower limit frequency _L are created.
By changing , it is possible to have an arbitrary frequency band.

In the above description of the embodiment, the digital filter is used in a fish finder, but it goes without saying that it can be used not only in the fish finder but also in other circuits. Furthermore, by using it in combination with an LC filter, the effect can be further increased.

As explained above, according to the present invention, there is provided a switch that blocks or passes an input signal, an A/D converter that converts the input signal into a digital signal, and a pulse width of the upper limit or lower limit frequency of the input signal. an upper and lower limit pulse width setting device for setting the value of
a digital pulse width comparator that compares the pulse width of the input signal from the A/D converter with the setting values set by the upper and lower limit pulse width setting devices; When the pulse width of the signal is between the set values set by the upper and lower limit pulse width setting devices, the signal from the comparator opens the switch and allows the input signal to pass, so that the frequency characteristics are It has the advantage of being sharp and allowing signals in any band to pass through.

[Brief explanation of drawings]

Fig. 1 shows the input/output frequency characteristics of a conventional LC filter, Fig. 2 shows the input/output frequency characteristics of a conventional ceramic filter, and Fig. 3 shows an example of the present invention. FIG. 4, a block diagram of the digital filter, is a diagram showing the input/output filter characteristics of the digital filter of the present invention. 1... Receiver, 2... Receiver, 3... A/D converter, 4... Digital pulse width comparator, 5... Upper and lower limit pulse width setting device, 6... Switch.

Claims (1)

[Claims] 1 A switch that cuts off or passes the input signal,
an A/D converter that converts the input signal into a digital signal; an upper and lower limit pulse width setting device that sets a pulse width value of the upper or lower limit frequency of the input signal; a digital pulse width comparator that compares the pulse width of the input signal with the setting values set by the upper and lower limit pulse width setting devices, and the pulse width of the input signal from the A/D converter is the upper limit, The digital filter opens the switch in response to a signal from the comparator to allow the input signal to pass when the pulse width is between the set values set by a lower limit pulse width setting device.