JPS6212701B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tone signal detector using an N-way filter that sequentially receives and passes a plurality of tone signals.

A conventional tone signal detector of this type includes an active filter, a circuit element for changing the center frequency and bandwidth of the filter, and switching means, as disclosed in Japanese Patent Laid-Open No. 49-79653. However, this circuit has the disadvantage that since the center frequency and bandwidth are determined by the circuit elements, highly accurate circuit elements are required, making manufacturing difficult and expensive. Furthermore, since a considerable number of circuit elements and switching means for changing the center frequency and bandwidth are used, the circuit becomes complicated.

It is an object of the invention to provide a tone signal detector with an N-way filter which eliminates the above-mentioned drawbacks.

The tone signal detector of the present invention uses an N-way filter to simplify the circuit, and is particularly characterized by having at least one switch which can be externally controlled when desired and which can speed up the fall time of the bandpass filter. shall be.

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

FIG. 1 shows an embodiment of the tone signal detector of the present invention. In the figure, the tone signal detector is composed of a detector 10 and an N-way filter, which includes a series resistor 34, parallel capacitors 35-37 having mutually equal values, switches 38-40 and a reset switch 41. It consists of.

Switches 38 to 40 are connected in series with parallel capacitors 35 to 37, respectively, to form an N-way filter (N represents the number of parallel capacitors and switch branches, and the figure is written for the case of N = 3). ).

Switches 38-40 are sequentially cycled closed and reopened at the clock pulse frequency.

The fact that a bandpass filter with a small bandwidth can be realized by appropriately selecting the sizes of the resistor 34 and capacitors 35 to 37 is shown in "An Alternative Approach to the Realization" by Frank et al.
of Network Transfer Functions：The N-
"Path Filter" BSTJ, September 1960, pp. 1821-1350 and Harden's "Digital filters with
IC′s boost Q without inductors”
Electronics, July 24, 1967, pages 91-100.

The center frequency fo of this bandpass filter is given by the switch clock pulse frequency fcp and is independent of the filter elements.

That is, the filter center frequency fo becomes fcp/N.

Therefore, once the value of N is determined, the center frequency fo of the filter can be freely changed by changing the value of fcp, and unlike the active filter described above, there is no need to change the configuration of the circuit elements that determine the center frequency. Very stable.

However, since the N-way filter has a predetermined rise and fall time in response to a predetermined tone signal, it is especially continuous when passing a signal in which multiple tones of different frequencies are serially serialized in time (tone signal sequence). unable to successfully pass rapid tone signal sequences.

Therefore, the detector 10, which is composed of, for example, a comparator, generates a detection signal every time it detects each tone signal passing through the N-way filter, and controls the reset switch 41 using this detection signal.
That is, the reset switch 41 is normally in an open state (OFF), but by forcing it into a closed state (ON) by the detection signal of the detector, the band filter is closed regardless of the operation of the switches 38 to 40. Function disappears and capacitor 35-3
By setting capacitors 7 to the same potential, all the charges accumulated in the respective capacitors are added to 0, the filter is placed in its initial state, and as a result, the falling speed of the filter can be increased.

FIG. 2 shows another method of resetting the N-way filter in which switches 46-48 operate at clock frequency fcp and switch 49 is a reset switch.

Normally, the switch 49 is OFF, but when trying to reset the filter, the switches 46 to 4 are turned OFF.
9 is turned on at the same time to hasten the fall of the filter.

FIG. 3 shows another method of resetting the N-way filter, in which the functions of the switches 38-40 and reset switch 41 of the N-way filter in FIG. 1 are performed by switches 56-58. That is, the switches 56 to 58 normally repeat ON/OFF operations at the clock frequency, but when the filter is reset, they are turned ON simultaneously by the reset pulse from the detector 10 to hasten the fall of the filter. be.
A detailed circuit example of the present invention using the method of FIG. 3 is shown in FIG.

A series resistor 61, parallel capacitors 62 to 69 with equal values, switches 70 to 77, and two inputs.
It consists of NAND gates 78-85, a counter 86, and a low-pass filter. As an example of the counter 86, it is composed of four flip-flops 88 to 91 and eight 4-input NAND circuits 92 to 99, and when a signal is applied to the clock pulse signal input terminal 117, the switches 70 to 77 are sequentially activated at the clock pulse frequency for a fixed period of time. Output signal to turn on terminal 10
Output from 0 to 107. The time relationship between this clock pulse signal and the output signal is shown in FIG. It is easy to imagine a switch that is turned on and off by a signal like the one shown in Figure 5, and it can be realized using a transistor or FET. switch 70
-77 are switch control inputs 108-115.
Turns on at HI level and OFF at LO level
This is a switch. Two-input NAND gates (actually operating as OR) 78-85 control the inputs of the switches 108-115. By setting the reset input 116 to HI level, the 2-input NAND gates 78 to 85 output 100 to 1.
A signal inverted from the signal of 07 is output, and switches 70 to 77 are operated at the clock pulse frequency. By setting reset input 116 to LO level, the outputs of 2-input NAND gates 78 to 85 are forced to HI level regardless of the signals at outputs 100 to 107, and all switches 70 to 77 are turned off.
Turn it on. This reset signal 116
Sent from output 0. Therefore, the N-way filter loses its function as a bandpass filter, the capacitors 62 to 69 have the same potential, the stored electrical energy collapses, and the signal instantly falls.

Note that the low-pass filter 87 passes only the desired signal frequency of the N-way filter to the clock component and the harmonic class (nfo; n is an integer) for the fundamental wave.
It is intended to remove.

Although the present invention has been explained with reference to a parallel switching type filter (Shunt-switched filter) in Figs. 1 to 4, this invention also applies to a series-switched filter as shown in Fig. 6. The invention can be applied.

In FIG. 6, 200 is a tone signal input terminal, 201 to 203 are clock signal input terminals, 2
04 is an output terminal, 205 is a reset signal (control signal) input terminal, 210 to 215 are transistors operated by a clock signal, 220 to 222 are resistors,
223 to 225 are capacitors, and 230 to 232 are transistors operated by a reset signal. Since this operation is clear from the above explanation, the explanation will be omitted.

The above-described filter of the present invention is used for detecting continuous and rapid tone signal sequences in individual calling radio equipment, etc., and provides a tone filter that operates extremely stably.

Furthermore, as is clear from FIG. 4, in this filter, everything except the capacitor can be replaced with a semiconductor integrated circuit, which is very advantageous in making the filter smaller and lower in price.

[Brief explanation of the drawing]

1 to 3 are principle diagrams of the tone signal detector of the present invention, FIG. 4 is a circuit diagram of the tone signal detector of the present invention, and FIG. 5 is a clock pulse for operating a switch for explaining FIG. 4. A signal time chart, FIG. 6, shows another embodiment of the invention. 42, 50, 59, 118, 200: Filter input terminal; 43, 51, 60, 119, 204:
Filter output terminal; 34, 42, 52, 61, 2
20-222: Resistance; 35-37, 43-45,
53-55, 62-69, 223-225: Capacitor; 38-41, 46-49, 56-58,
70-77, 210-215, 230-232:
Switch; 86: Counter; 87: Low-pass filter; 116, 205: Reset signal input terminal;
117, 201-203: Clock pulse signal input terminals.

Claims (1)

[Scope of Claims] 1. In a tone signal detector that sequentially receives and passes a plurality of tone signals, the plurality of tone signals are detected by a clock signal having a frequency N times the frequency of the tone signal (N is a positive integer). a resistor that receives the tone signal at one end, N capacitors connected to the other end of the resistor, and a cyclic circuit connected in series to each of the N capacitors; a plurality of first switches that are sequentially opened and closed in response to the clock signal; an N-way filter that is connected to the output of the N-way filter and generates a detection signal every time it detects each of the plurality of selected tone signals; Tone signal detection using an N-way filter, characterized in that it includes: a detector that generates tone signal; and a plurality of second switches that are connected in parallel to the plurality of first switches and are closed all at once by the detection signal. vessel. 2. In a tone signal detector that sequentially receives and passes a plurality of tone signals, each of the plurality of tone signals is selected by a clock signal having a frequency N times the frequency of the tone signal (N is a positive integer); a resistor having one end supplied with the tone signal; N capacitors connected to the other end of the resistor; an N-way filter comprising a plurality of first switches that are opened and closed; a detector connected to the output of the N-way filter and generating a detection signal each time it detects each of the plurality of selected tone signals; A tone signal detector using an N-way filter, comprising a second switch commonly connected in parallel to the plurality of capacitors and the first switch and closed by the detection signal. 3. In a tone signal detector that sequentially receives and passes a plurality of tone signals, each of the plurality of tone signals is selected by a clock signal having a frequency N times the frequency of the tone signal (N is a positive integer). a detector connected to the output of the N-way filter and generating a detection signal each time it detects each of the plurality of selected tone signals, the N-way filter having one end connected to the tone signal; a resistor to which a signal is supplied; N capacitors connected to the other end of the resistor; A tone signal detector using an N-way filter, characterized in that it includes a plurality of switches that are closed all at once.