JPS5831138B2 - Multi-frequency signal receiving circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multi-frequency signal receiving circuit, and more particularly to a multi-frequency signal receiving circuit that prevents malfunctions.

Linear amplifier method is used for multi-frequency signal reception method.

An AGC method, a variable threshold value (VTR) method, and the like are known.

In the linear amplifier method, after removing noise with a main band filter,
This method performs discrimination using a channel band filter and detects the signal using a fixed threshold.

However, in this method, the channel band filter requires a high attenuation amount in order to prevent malfunction due to adjacent frequencies 200 Hz apart.

Further, the AGC method is a method that can compress the dynamic range of an input signal using an AGC circuit and reduce the amount of attenuation of a channel band filter.

However, this method has problems with the nonlinearity and operating time of the AGC element.

Furthermore, the variable threshold method peak-holds the output of the channel band filter with a variable threshold circuit, and determines the threshold of the signal detection circuit by taking into account the level difference between two frequencies.

In this method, the dynamic range is seemingly completely compressed, so the attenuation amount and order of the channel band filter can be reduced, and it is also possible to integrate the filter into an integrated circuit, so this method has been widely adopted in recent years.

However, even in this method, when an intermediate frequency between two adjacent signal frequencies is input, there is a risk that the two signal detection circuits will be affected at the same time and malfunction.

An object of the present invention is to provide a variable threshold type multi-frequency signal receiving circuit which solves these drawbacks.

In order to achieve this object, the present invention provides a first means for holding the maximum value of the sum of the outputs of bandpass filters whose center frequency is the signal frequency, and a second means for holding a value attenuated by a certain amount from the maximum value of the input. and a third means for comparing the output of the first means and the output of the second means, and controlling the signal detection circuit based on the comparison result.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a block diagram of an embodiment of the present invention.

The signal input to the input terminal 1 is passed through a bandpass filter 2 whose center frequency matches the signal frequency.
~4.

The outputs of the bandpass filters 2 to 4 are summed by an adder 17, and the maximum value of the output is added to the peak hold circuit PH.
18.

This signal is input to one terminal of the comparator COMP 24.Furthermore, the input signal from the input terminal 1 is inputted to the other one of the comparator 24 through a series connection circuit consisting of a peak hold circuit PH19 and an attenuator ATT20. Ru.

The above configuration represents the first to third means of the present invention.

Peak hold circuits PH5 to PH7 are connected to the outputs of the band pass filters 2 to 4, respectively, and the outputs of these peak hold circuits are drawn into the maximum value output circuit 21 (means 4), and the peak values of the peak hold circuits are The maximum one is output and attenuated by a certain amount by an attenuator 22.

The output passes through the gate 23 and comparators COMP8~
This results in 10 variable thresholds.

The attenuator 22 and the gate 23 constitute the means 5.

Signals are input from the bandpass filters to the comparators 8 to 10, and only the channels with amplitudes larger than the variable threshold are impressed, and the signals are converted into direct current by the rectifiers 11 to 13 in the subsequent stage and output from the output terminals 14 to 16 (variable threshold method).

Comparators 8-10 and rectifiers 11-13 constitute means 7.

When a mixed signal is input, each frequency component is output from the bandpass filter corresponding to the input frequency, and is added together in an adder to return to almost the original input mixed waveform, and the peak hold 18 maintains the maximum level. .

This value is approximately equal to the output of the peak hold circuit 19.

Therefore, the comparator 24 is attenuated by the attenuator 20.
The input terminal 26 of is at a lower level than the input terminal 25.

At this time, the gate 23 is opened by the output of the comparator 24, and the signal is received by the circuit operation described above.

A case where an interference wave other than a signal frequency is input will be explained.

Let this frequency be the intermediate frequency of the signal frequency.

At this time, a low-level output is generated as leakage from the band-pass filter, but the peak-hold circuit 19, which peak-holds the input as it is, outputs a higher-level output than the sum of these outputs.

Therefore, even if the signal is attenuated by the attenuator 20, the input terminal 26 of the comparator 24 has a higher level than the input terminal 25, and the output of the comparator 24 is inverted, closing the gate 23 and disabling the receiving circuit.

This protects against single frequency interference.

Further, the means 6 is constituted by a comparator 28 which outputs the output of the maximum value output circuit 21 and the output of the attenuator 20 which is attenuated by a certain amount by the attenuator 27. OR with output by two people
Guard against non-signal inputs is provided in circuit 29.

The attenuation amount of the attenuator 27 is set so that the output level of the attenuator 27 is lower than the output level of the maximum value output circuit 21 with respect to the signal input, and the output of the comparator 28 is gated through an OR circuit 29. 23 is turned on.

For non-signal inputs, the input of the maximum value output circuit 21 is at a low level due to leakage from the bandpass filters 2 to 4, and therefore the output level of the maximum value output circuit 21 is lower than the output level of the attenuator 27. As a result, the output of the comparator 28 is inverted, and the gate 23 is closed through the OR circuit 29 to prevent the receiving circuit from receiving the signal.

The OR circuit 29 receives the comparator 24 for non-signal input.
This is to allow both the outputs of the comparator 28 and the outputs of the comparator 28 to pass through and close the gate 23, so that a double guard is applied.

Next, a more specific circuit example of the present invention is shown in FIG.

When a multi-frequency mixed signal is manually generated, each frequency component passes through one of the band pass filters BPF1 to BPFn, and the maximum amplitude of those frequency components appears at point A, and this is the amplitude attenuated by a certain amount due to the bleeder resistance. This appears at point C.

Since this output becomes the threshold value of the comparator C0 and P1-n, the value of the bleeder resistance is selected so that it is smaller than the maximum value of the output of the bandpass filter centered around the signal frequency.

The maximum value of the input amplitude appears at two points, and the value where the output is attenuated by a certain amount due to the bleeder resistance appears at the point.

The sum of the outputs of all the band-pass filters appears at the point H, and the maximum value thereof appears at the 9 points, and the magnitude of the voltage at the point OUT and the point HO of the comparator COMPy is compared.

As mentioned above, when the input frequency matches the signal frequency, the value of the bleeder resistor is selected so that the voltage at point H is smaller than the voltage at point N, so the voltage at point N is approximately equal to the positive power supply voltage, and the diode D2 cant off and comparator COMP, ~.

The channel corresponding to the input frequency among the comparators COMP1 to COMPn is impressed and a DC output appears without affecting the threshold value.

If the input frequency is different from the signal frequency, the comparator COM
The magnitude relationship of the input of P y is reversed, and the voltage at point N drops to almost the negative power supply voltage. Diode D2 becomes conductive, and the voltage at point C becomes almost equal to the negative voltage, and the voltage at point C becomes almost equal to the negative voltage, and the voltage at point C becomes almost equal to the negative voltage, and the voltage at point C becomes almost equal to the negative voltage, and the voltage at point C becomes almost equal to the negative voltage.
1 to n are not impressed and no DC output appears.

In other words, it was guarded. Further, a voltage obtained by attenuating the voltage at the two points by a certain amount appears at the point B, and this voltage is compared with the voltage at the point A by the comparator COMPx.

When a signal frequency is input, the voltage at point A becomes higher than the voltage at point H, and the voltage at point G rises to almost the positive power supply voltage, diode D1 is cut off, and the voltage at point C increases without affecting the threshold voltage at point C. The voltage becomes equal to the voltage directly at the mouth, allowing signal detection.

When the input frequency is different from the signal frequency, comparator CO
The magnitude relationship of the input to MPx is reversed, and the point T drops to almost the negative power supply voltage, causing diode 1 to conduct.

The voltage at point C drops to almost the negative power supply voltage and the comparator CO
MP1-n are not impressed.

As explained above, the present invention provides a multi-frequency signal receiving circuit that prevents both channels from being affected at intermediate frequencies of adjacent signal frequencies by comparing the sum of outputs and inputs of band-pass filters.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention in the form of a block diagram, and FIG. 2 is a circuit diagram showing one embodiment of the present invention in more detail. 1...Input terminal, 2~4...Band filter, 5~? , 18, 19... Peak hold circuit, 8 to 10.24... Comparator, 11
~13... Rectifier circuit, 14-162...
Output terminal, 17... Adder, 20, 22...
... Attenuator, 21 ... Maximum value output circuit, 23
......Gate, 25, 26...Input terminal of comparator 24, 27...Attenuator, 28.
...Comparator, 29...OR circuit.

Claims (1)

[Claims] 1. In a multi-frequency signal receiving circuit that receives a frequency signal and converts it into a DC output, a first means for holding the maximum value of the sum of the outputs of the band-pass filters having the signal frequency as the center frequency, and a second means for holding a value attenuated by a certain amount; a third means for comparing the output of the first means and the output of the second means; a fourth means for maintaining the maximum value; a fifth means for outputting a value attenuated by a certain amount from the output of the fourth means; and a fifth means for outputting a value attenuated by a certain amount from the output of the second means; a seventh means for comparing the fifth output with the output of the bandpass filter and generating a DC output;
, and the outputs of the third means and the sixth means.
and eighth means for controlling the output of the means.