JP2019054345A - Signal detection circuit - Google Patents

Abstract

To accurately demodulate a modulation signal.SOLUTION: A signal detection circuit 10 includes: a comparator 13 that outputs a comparison signal based on difference between voltage based on voltage of a communication line Lc related to communication of fire notification equipment and reference voltage; and a reference voltage generation unit 14 that inputs first reference voltage or second reference voltage in a level lower than the first reference voltage as reference voltage to the comparator 13 after detecting a frequency modulated communication signal flowing through the communication line Lc on the basis of the comparison signal.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a signal detection circuit that detects a communication signal related to communication of a fire alarm facility.

  Conventionally, a method of performing communication by modulating data to be transmitted by FSK (Frequency Shift Keying) is known (see, for example, Patent Document 1).

JP 2000-183782 A

  The FSK modulated signal is detected and then input to the comparator. The comparator outputs a first level signal or a second level signal having a logic opposite to the first level based on the detected voltage of the modulation signal and the reference voltage. A CPU (Central Processing Unit) connected to the subsequent stage of the comparator converts to binary data based on the first level signal and the second level signal, and performs demodulation.

  By the way, in the modulation signal, the voltage of the modulation signal may fluctuate due to ringing at the rise or fall of the signal or noise or the like superimposed on the signal. When the modulation signal fluctuates in the vicinity of the value of the reference voltage input to the comparator, chattering occurs, causing a problem that the modulation signal cannot be correctly demodulated in the CPU.

  Therefore, the present invention has been made in view of these points, and an object thereof is to provide a signal detection circuit that can accurately demodulate a modulation signal.

  The signal detection circuit according to the first aspect of the present invention includes a voltage comparison unit that outputs a comparison signal based on a difference between a voltage based on the voltage of the communication line and a reference voltage, and frequency modulation based on the comparison signal. After detecting that a communication signal is flowing through the communication line, a reference voltage generator that inputs a first reference voltage or a second reference voltage lower than the first reference voltage as the reference voltage to the voltage comparator And having.

  The voltage comparison unit outputs the comparison signal of the first level when the voltage based on the voltage of the communication line is equal to or higher than the reference voltage, and the voltage based on the voltage of the communication line is less than the reference voltage The comparison signal of the second level having the opposite logic to the first level is output, and the reference voltage generation unit inputs the first reference voltage to the voltage comparison unit. The reference voltage input to the voltage comparison unit may be switched from the first reference voltage to the second reference voltage in response to the comparison signal changing from the second level to the first level. .

  The reference voltage generator receives the second reference voltage from the first level to the second level while the second reference voltage is being input to the voltage comparison unit. The input reference voltage may be switched from the second reference voltage to the first reference voltage.

  The reference voltage generation unit is provided between the output unit of the comparison signal in the voltage comparison unit and the input unit of the reference voltage, and is a resistor for switching between the first reference voltage and the second reference voltage And a capacitor.

  The reference voltage generation unit inputs a third reference voltage lower than the second reference voltage as the reference voltage to the voltage comparison unit in a state where the voltage of the comparison signal does not change over a predetermined time, After the comparison signal indicates that the voltage based on the voltage of the communication line has transitioned from a state higher than or equal to the third reference voltage to a state lower than the third reference voltage, the first reference voltage or the second reference voltage May be input to the voltage comparison unit as the reference voltage.

  While the voltage of the comparison signal is changing to a time shorter than the predetermined time, the reference voltage generation unit uses the first reference voltage or the second reference voltage as the reference voltage to the voltage comparison unit. When the voltage is input and the voltage of the comparison signal transitions to a state where the voltage does not change for a predetermined time or longer, the third reference voltage may be input to the voltage comparison unit as the reference voltage.

  The reference voltage generation unit may include a transistor circuit provided between the output unit of the comparison signal in the voltage comparison unit and the input unit of the reference voltage to generate the third reference voltage. Good.

  According to the present invention, there is an effect that a modulated signal can be demodulated with high accuracy.

It is a figure which shows the structure of the fire prevention system which concerns on this embodiment. It is a figure which shows the structure of the signal detection circuit which concerns on this embodiment. It is a figure which shows the circuit structure of the reference voltage generation part which concerns on this embodiment. It is a figure which shows the voltage waveform of the input signal input into the signal detection circuit which concerns on this embodiment, the waveform of the voltage input into the input terminal of a comparator, and the voltage waveform of the comparison signal output from an output terminal. FIG. 5 is a partially enlarged view of a waveform of a voltage input to an input terminal of the comparator shown in FIG. 4 and a waveform of a voltage output from an output terminal of the comparator.

[Outline of fire prevention system 100]
FIG. 1 is a diagram illustrating a configuration of a fire prevention system 100 according to the present embodiment. The fire prevention system 100 includes a plurality of sensors 1 as fire alarm equipment, a section closing device 2, a disaster prevention control panel 3, a control device 4, and a fire sensor 7. In the fire prevention system 100, when any one of the plurality of detectors 1 senses a fire, the fire prevention control panel 3 and the control device 4 work together to close the compartment closing device 2 so that the fire spreads to other compartments. It is a system to prevent. The disaster prevention control panel 3 and the control device 4 are connected by a power line Lp that supplies power from the disaster prevention control panel 3 to the control device 4 and a communication line Lc for transmitting signals. The disaster prevention control panel 3 and the sensor 1 are connected by a communication line Lc. In addition, you may supply electric power to the detector 1 from the disaster prevention control panel 3 via the power wire Lp. Further, the communication line Lc may also serve as the power supply line Lp.

  When detecting the fire, the sensor 1 transmits a fire signal, which is a communication signal indicating that a fire has been detected, to the disaster prevention control panel 3 via the communication line Lc connected to the disaster prevention control panel 3. The section closing device 2 is, for example, a fire shutter or a fire door, and is provided at a boundary position of the section in the building.

  When the fire prevention signal is received from at least one of the plurality of detectors 1, the disaster prevention control panel 3 receives an interlock signal that is a communication signal including an instruction for closing the section closing device 2 via the communication line Lc. It transmits to the control apparatus 4. The fire prevention system 100 is provided with a plurality of compartment closing devices 2, and the disaster prevention control panel 3 transmits an interlock signal to the compartment closing device 2 corresponding to the sensor 1 that has transmitted the fire signal. The compartment closing device 2 corresponding to the sensor 1 that has transmitted the fire signal is, for example, a compartment closure provided between the compartment that includes the sensor 1 that has transmitted the fire signal and the compartment adjacent to the compartment. Device 2.

  The control device 4 closes the section closing device 2 when receiving the interlock signal from the disaster prevention control panel 3. The control device 4 also closes the partition closing device 2 when detecting an abnormality in at least one of the power supply line Lp and the communication line Lc. In this case, the control device 4 switches the power for closing the section closing device 2 from the power supplied from the disaster prevention control panel 3 via the power line Lp to the power supplied by the battery built in the control device 4. Thus, the compartment closing device 2 is closed by the power supplied by the battery.

  The control device 4 includes a repeater 5 and a device control panel 6. The repeater 5 and the device control panel 6 are connected by a communication line Lc, a power supply line Lp, and a control line D. The control line D is a cable for notifying the device control panel 6 of an instruction for closing the section closing device 2 in response to the repeater 5 receiving the interlock signal from the disaster prevention control panel 3.

  The repeater 5 generates a control signal for causing the device control panel 6 to close the section closing device 2 based on the interlocking signal. Specifically, when the relay device 5 receives an interlocking signal including an instruction to close the section closing device 2, the relay device 5 generates a control signal by changing the voltage of the control line D to a predetermined voltage.

  The device control panel 6 is provided with a solenoid for driving the compartment closing device 2 using, for example, power supplied from the repeater 5 through the power line Lp or power supplied by a battery built in the device control panel 6. By operating, the compartment closing device 2 is closed. The device control panel 6 drives the partition closing device 2 based on the control signal input from the repeater 5 in a state where no abnormality has occurred in the power supply line Lp and the communication line Lc, and the power supply line Lp and the communication line Lc. In a state where an abnormality has occurred in at least one of the above, the compartment closing device 2 is driven based on the fire detection signal input from the fire sensor 7.

  In the present embodiment, the fire alarm facility such as the sensor 1, the disaster prevention control panel 3, the repeater 5, and the device control panel 6 includes a signal detection circuit 10 that detects a communication signal related to communication of the fire alarm facility. Here, the communication signal is FSK modulated.

  When the signal detection circuit 10 detects that a communication signal is flowing through the communication line Lc, the signal detection circuit 10 uses the first reference voltage or a second reference voltage lower than the first reference voltage as a reference voltage, and the reference voltage and the communication A comparison signal based on the difference from the voltage corresponding to the line Lc is output as an output signal. The fire alarm facility performs processing corresponding to the output signal output from the signal detection circuit 10.

In this way, the signal detection circuit 10 can perform chattering even when ringing occurs at the rising or falling edge of the communication signal, or ringing occurs due to noise or the like superimposed on the communication signal. And the communication signal can be detected with high accuracy.
Next, the configuration of the signal detection circuit 10 will be described.

[Configuration of Signal Detection Circuit 10]
FIG. 2 is a diagram illustrating a configuration of the signal detection circuit 10 according to the present embodiment. The signal detection circuit 10 includes a filter unit 11, a signal level adjustment unit 12, a comparator 13 as a voltage comparison unit, and a reference voltage generation unit 14.

The filter unit 11 includes, for example, a low-pass filter and a high-pass filter configured by resistors and capacitors. An input signal received via the communication line Lc is input to the filter unit 11. The filter unit 11 removes a low-frequency component included in the input signal by the low-pass filter, passes a signal having a frequency higher than a predetermined frequency by the high-pass filter, and outputs the signal to the signal level adjustment unit 12.
The signal level adjustment unit 12 includes a resistor, a capacitor, and a diode, and is a circuit that adjusts the level of the signal that has passed through the filter unit 11 to be within a predetermined range.

  The comparator 13 outputs a comparison signal based on the difference between the voltage based on the voltage of the communication line Lc related to the communication of the fire alarm facility and the reference voltage. For example, a voltage of a signal whose voltage level is adjusted to be low by the filter unit 11 and the signal level adjustment unit 12 is input to the negative input terminal of the comparator 13 as a voltage based on the voltage of the communication line Lc. A reference voltage is input to the plus input terminal of the comparator 13.

  The comparator 13 outputs a low level (first level) comparison signal when the voltage based on the voltage of the communication line Lc input to the negative input terminal is equal to or higher than the reference voltage input to the positive input terminal. To do. The comparator 13 also has a logic high level opposite to the low level when the voltage based on the voltage of the communication line Lc input to the negative input terminal is lower than the reference voltage input to the positive input terminal. A second level comparison signal is output.

  The comparator 13 outputs a comparison signal as an output signal to the fire alarm facility incorporating the signal detection circuit 10. The comparator 13 outputs a comparison signal to the reference voltage generator 14.

  Note that the fire alarm facility including the signal detection circuit 10 operates in a sleep mode in which the CPU is not operated until a high-level output signal is input. Then, the fire alarm equipment operates the CPU in response to the input of the high level output signal, and performs the demodulation process of the signal output from the comparator 13.

  The reference voltage generator 14 is a circuit that generates a reference voltage to be input to the plus input terminal of the comparator 13. The reference voltage generator 14 is one of a first reference voltage having the highest voltage level, a second reference voltage having a level lower than the first reference voltage, and a third reference voltage having a level lower than the second reference voltage. Is input to the plus input terminal of the comparator 13 as a reference voltage.

  Specifically, the reference voltage generation unit 14 inputs the third reference voltage as a reference voltage to the plus input terminal of the comparator 13 in a state where the voltage of the comparison signal does not change over a predetermined time. The reference voltage generation unit 14 transitions from a state where the voltage based on the voltage of the communication line Lc is equal to or higher than the third reference voltage to a state below the third reference voltage, and the comparison signal output from the comparator 13 is changed. Then, it is detected that a frequency-modulated communication signal is flowing through the communication line Lc. When the reference voltage generator 14 detects that a communication signal is flowing through the communication line Lc, the reference voltage generator 14 inputs the first reference voltage or the second reference voltage as a reference voltage to the plus input terminal of the comparator 13.

  The reference voltage generation unit 14 sets the reference voltage to be input to the comparator 13 in response to the comparison signal changing from the second level to the first level while the first reference voltage is being input to the comparator 13. Switch from the reference voltage to the second reference voltage.

  The reference voltage generation unit 14 sets the reference voltage input to the comparator 13 in response to the change of the comparison signal from the first level to the second level while the second reference voltage is input to the comparator 13. Switch from the reference voltage to the first reference voltage.

  The reference voltage generator 14 inputs the first reference voltage or the second reference voltage to the comparator 13 as the reference voltage while the voltage of the comparison signal output from the comparator 13 is changing to a time shorter than a predetermined time. When the voltage of the comparison signal transitions to a state where it does not change for a predetermined time or longer, the third reference voltage is input to the comparator 13 as the reference voltage. Since the third reference voltage is set lower than the first reference voltage and the second reference voltage, the signal is detected when noise is superimposed on the communication line Lc in a state where the modulation signal is not input to the signal detection circuit 10. It can be prevented that the detection circuit 10 erroneously detects noise as a modulation signal and erroneously activates a CPU in the sleep mode.

[Circuit Configuration of Reference Voltage Generating Unit 14]
Subsequently, the circuit configuration of the reference voltage generator 14 will be described, and then the detailed operation of the reference voltage generator 14 will be described. FIG. 3 is a diagram illustrating a circuit configuration of the reference voltage generation unit 14 according to the present embodiment. The reference voltage generation unit 14 includes a power source P1, resistors R1 to R4, capacitors C1 to C2, and a transistor circuit 141.

One end of the resistor R <b> 1 is connected to the power source P <b> 1 that supplies power to the comparator 13, and the other end is connected to the plus input terminal of the comparator 13.
The resistor R2 has one end connected to the positive input terminal of the comparator 13 and the other end connected to the ground.

The resistor R3 has one end connected to the plus input terminal of the comparator 13 and the other end connected to the transistor circuit 141.
The resistor R4 has one end connected to the positive input terminal of the comparator 13 and the other end connected to the capacitor C2.

  The resistors R <b> 1 to R <b> 4 are used for switching the reference voltage input to the plus input terminal of the comparator 13. Details of the operation for switching the reference voltage will be described later.

  One end of the capacitor C1 is connected to the plus input terminal of the comparator 13, and the other end is connected to the ground. The capacitor C1 allows the high-frequency signal that has passed through the capacitor C2 to flow to the ground so that the high-frequency signal is not input to the positive input terminal of the comparator 13.

  One end of the capacitor C2 is connected to the output terminal of the comparator 13, and the other end is connected to the resistor R4. The capacitor C2 and the resistor R4 are provided between the output terminal of the comparator 13 and the positive input terminal, and are used to switch between the first reference voltage and the second reference voltage.

  The transistor circuit 141 includes a power supply P2, resistors R5 to R9, a capacitor C3, and transistors Tr1 and Tr2. The transistor circuit 141 is provided between the output terminal of the comparator 13 and the positive input terminal of the comparator 13 and is used to generate the third reference voltage.

The resistor R5 has one end connected to the power source P2 and the other end connected to the resistor R6. In FIG. 3, the power source P1 and the power source P2 are separated, but the power source P1 and the power source P2 may be the same power source.
The resistor R6 has one end connected to the resistor R5 and the other end connected to the ground.
The resistors R5 and R6 are used to adjust the voltage applied to the base of the transistor Tr1.

  The resistor R7 has one end connected to a connection point between the resistors R5 and R6, and the other end connected to the emitter of the transistor Tr2. The resistor R7 is used to adjust the voltage applied to the base of the transistor Tr1.

  The capacitor C3 has one end connected to a connection point between the resistor R5 and the resistor R6, and the other end connected to the ground. The capacitor C3 is used to prevent the transistor Tr1 from being turned on for a predetermined time when the transistor Tr2 is changed from the off state to the on state and then to the off state again.

The resistor R8 has one end connected to the output terminal of the comparator 13 and the other end connected to the resistor R9.
The resistor R9 has one end connected to the resistor R8 and the other end connected to the ground.
The resistors R8 and R9 are used to adjust the voltage applied to the base of the transistor Tr2.

The transistor Tr1 has a base connected to a connection point between the resistors R5 and R6, a collector connected to the resistor R3, and an emitter connected to the ground.
The transistor Tr2 has a base connected to a connection point between the resistors R8 and R9, a collector connected to the resistor R7, and an emitter connected to the ground.

  The transistor Tr2 is used to switch the on / off state of the transistor Tr1. The transistor Tr1 is used for controlling the current flowing through the resistor R3 and switching the reference voltage.

[Operation of Reference Voltage Generator 14]
Next, the operation of the reference voltage generator 14 will be described. FIG. 4 is a diagram illustrating a voltage waveform of the input signal input to the signal detection circuit 10, a voltage waveform input to the input terminal of the comparator 13, and a voltage waveform of the comparison signal output from the output terminal. .

  FIG. 4A is a diagram illustrating a voltage waveform of a communication signal input to the signal detection circuit 10 via the communication line Lc. FIG. 4B is a diagram illustrating a waveform of a voltage input to the input terminal of the comparator 13. FIG. 4C is a diagram illustrating a waveform of a voltage output from the output terminal of the comparator 13.

  4B, the voltage waveform Wp indicates the waveform of the reference voltage input to the positive input terminal of the comparator 13, and the voltage waveform Wm is the voltage of the communication signal input to the negative input terminal of the comparator 13. Waveform is shown.

  FIG. 5 is a partial enlarged view of the waveform of the voltage input to the input terminal of the comparator 13 shown in FIG. 4 and the waveform of the voltage output from the output terminal of the comparator 13. FIG. 5A shows a voltage waveform at the start of communication signal input, and FIG. 5B shows a voltage waveform at the end of communication signal input.

  First, before the input of the communication signal shown in FIG. 5A, that is, before the time T1, the input signal input to the negative input terminal of the comparator 13 has not changed over a predetermined time. Therefore, the comparator 13 outputs a low level comparison signal before the time T1.

  Prior to time T1, the transistor Tr2 is in an off state, and no current flows through the resistor R7. Thereby, a voltage for turning on the transistor Tr1 is applied to the base of the transistor Tr1, and the transistor Tr1 is in the on state. Further, since the capacitor C2 has been charged by the low level comparison signal, no current flows through the resistor R4.

  Therefore, the reference voltage input to the positive input terminal of the comparator 13 is the third reference voltage Vb3 determined by the ratio of the resistance value between the parallel resistance of the resistor R2 and the resistor R3 and the resistor R1. For example, if the resistance value of the resistor R1 is 1 MΩ, the resistance value of the resistor R2 is 1.2 MΩ, the resistance value of the resistor R3 is 3.3 MΩ, and the voltage of the power supply P1 is 3.3 V, the third reference voltage Vb3 is It becomes about 1.5V. As a result, the voltage input to the negative terminal can be sufficiently separated from the reference voltage when no communication signal is input, and a high-level comparison signal is output to the comparator 13 even if noise is input. You can avoid it.

  Thereafter, it is assumed that a communication signal having a voltage lower than the third reference voltage Vb3 is input to the negative input terminal of the comparator 13 at time T1 shown in FIG. In this case, the comparator 13 outputs a high level comparison signal.

  When a high-level comparison signal is output at time T1, a voltage for turning on the transistor Tr2 is applied to the base of the transistor Tr2, and the transistor Tr2 is turned on. In this case, the capacitor C3 is instantaneously discharged, and the current supplied from the power source P2 flows through the resistor R7, so that the transistor Tr1 is turned off. Thereby, it changes to the state where an electric current does not flow into resistance R3. Further, since the comparison signal changes from the low level to the high level at time T1, the capacitor C2 starts charging, and a current flows through the resistor R4.

  Therefore, at time T1, the reference voltage input to the positive input terminal of the comparator 13 changes to the first reference voltage Vb1 determined by the ratio between the parallel resistance of the resistor R1 and the resistor R4 and the resistor R2. For example, if the resistance value of the resistor R1 is 1 MΩ, the resistance value of the resistor R2 is 1.2 MΩ, and the resistance value of the resistor R4 is 9.1 MΩ, the first reference voltage Vb1 is about 2.0V. Here, due to the transient response of the RC series circuit of the resistor R4 and the capacitor C2, a slight delay occurs until the third reference voltage Vb3 changes to the first reference voltage Vb1.

  As described above, the reference voltage is switched to the first reference voltage Vb1 higher than the third reference voltage Vb3 in response to a communication signal having a voltage lower than the third reference voltage Vb3 being input to the negative input terminal of the comparator 13. As a result, the voltage of the communication signal is separated from the reference voltage, and chattering does not occur in the comparison signal.

  Subsequently, at time T2, the voltage of the communication signal input to the negative input terminal of the comparator 13 becomes equal to or higher than the first reference voltage Vb1. Thereby, the comparator 13 outputs a low level comparison signal.

  When a low-level comparison signal is output at time T2, the transistor Tr2 is turned off. In this case, since the capacitor C3 starts to be charged, the base voltage of the transistor Tr1 is kept low, and the transistor Tr1 is kept off. As a result, even when the comparison signal changes to the low level, a state in which no current flows through the resistor R3 is maintained for a time determined based on the capacitance of the capacitor C3. This time is longer than the maximum period of the modulation signal. Therefore, even if the level of the comparison signal changes due to the modulation signal entering the signal detection circuit 10, the reference voltage generator 14 generates the first reference voltage Vb1 or the second reference voltage Vb2 near the median value of the modulation signal. Therefore, even if the level of the modulation signal decreases, the CPU can demodulate the modulation signal with high accuracy.

  Further, when the comparison signal changes from the high level to the low level, the capacitor C2 starts discharging, and a current flows through the resistor R4. As a result, the reference voltage input to the positive input terminal of the comparator 13 changes to the second reference voltage Vb2 determined by the ratio of the parallel resistance of the resistor R2 and the resistor R4 and the resistor R1. For example, if the resistance value of the resistor R1 is 1 MΩ, the resistance value of the resistor R2 is 1.2 MΩ, and the resistance value of the resistor R4 is 9.1 MΩ, the second reference voltage Vb2 is about 1.8V. Here, due to the transient response of the RC series circuit of the resistor R4 and the capacitor C2, a slight delay occurs until the first reference voltage Vb1 changes to the second reference voltage Vb2.

  As described above, the reference voltage is switched to the second reference voltage Vb2 lower than the first reference voltage Vb1 in response to the communication signal having a voltage higher than the first reference voltage Vb1 being input to the negative input terminal of the comparator 13. As a result, the voltage of the communication signal is separated from the reference voltage, and chattering does not occur in the comparison signal.

  Subsequently, at time T3, the voltage of the communication signal input to the negative input terminal of the comparator 13 becomes less than the second reference voltage Vb2. In this case, the comparator 13 outputs a high level comparison signal.

  When a high-level comparison signal is output at time T3, the transistor Tr2 is turned on. In this case, the capacitor C3 is instantaneously discharged, and the current supplied from the power source P2 flows through the resistor R7, so that the transistor Tr1 is maintained in the off state. Thereby, the state where no current flows through the resistor R3 is maintained.

  Further, when the comparison signal is changed from the low level to the high level, the capacitor C2 starts charging, and a current flows through the resistor R4. Therefore, the reference voltage input to the positive input terminal of the comparator 13 changes to the first reference voltage Vb1 determined by the ratio of the parallel resistance of the resistor R1 and the resistor R4 and the resistor R2.

  Thereafter, while the communication signal continues to be input, the reference voltage input to the positive input terminal of the comparator 13 is alternately switched between the first reference voltage Vb1 and the second reference voltage Vb2.

  Next, the operation at the end of communication signal input shown in FIG. 5B will be described. When the input of the communication signal is completed at time T27, the voltage of the communication signal input to the negative input terminal of the comparator 13 becomes equal to or higher than the first reference voltage Vb1. In this case, the comparator 13 outputs a low level comparison signal.

  When a low-level comparison signal is output at time T27, the transistor Tr2 is turned off. In this case, since the capacitor C3 starts to be charged, the base voltage of the transistor Tr1 is kept low, and the transistor Tr1 is kept off. Thereby, the state where no current flows through the resistor R3 is maintained.

  Further, when the comparison signal changes from the high level to the low level, the capacitor C2 starts discharging, and a current flows through the resistor R4. Therefore, the reference voltage input to the positive input terminal of the comparator 13 changes to the second reference voltage Vb2 determined by the ratio between the parallel resistance of the resistor R2 and the resistor R4 and the resistor R1.

  Thereafter, the comparator 13 continues to output the low-level comparison signal, so that the charging of the capacitor C3 is completed. Then, since no current flows through the capacitor C3, a voltage that turns on the transistor Tr1 is applied to the base of the transistor Tr1. If charging of the capacitor C3 is completed at time T28, the transistor Tr1 changes to an on state and changes to a state in which a current flows through the resistor R3.

  If the discharge of the capacitor C2 is also completed at time T28, the current does not flow through the resistor R4 at time T28. Therefore, at time T28, the reference voltage input to the positive input terminal of the comparator 13 changes to the third reference voltage Vb3 determined by the ratio of the parallel resistance of the resistor R2 and the resistor R3 and the resistance value of the resistor R1. To do.

[Effect in this embodiment]
As described above, the signal detection circuit 10 according to the present embodiment includes the comparator 13 that outputs a comparison signal based on the difference between the voltage corresponding to the communication line Lc related to communication of the fire alarm facility and the reference voltage. The signal detection circuit 10 detects that the communication signal frequency-modulated based on the comparison signal flows through the communication line Lc, and then detects the first reference voltage Vb1 or the first reference voltage Vb1 lower than the first reference voltage Vb1. 2 has a reference voltage generator 14 for inputting the reference voltage Vb2 to the comparator 13 as a reference voltage. In this way, the signal detection circuit 10 can prevent ringing when the communication signal rises or falls, or even if the voltage fluctuates near the reference voltage due to noise or the like being superimposed on the communication signal. It is possible to prevent chattering from occurring in the output signal. Therefore, the CPU that demodulates the output signal can accurately demodulate the data included in the modulated communication signal.

  Further, although noise may be superimposed on the communication line Lc, since the third reference voltage Vb3 is set lower than the first reference voltage Vb1 and the second reference voltage Vb2, a modulation signal is sent to the signal detection circuit 10. When noise is applied to the communication line Lc when no signal is input, the signal detection circuit 10 erroneously detects the noise as a modulation signal and erroneously starts the CPU in the sleep mode. Can be prevented. As described above, since it is possible to prevent the CPU from being activated at an unnecessary timing, the power consumption of the CPU can be reduced.

  In the signal detection circuit 10, while the modulation signal is received, even if the comparison signal changes to a low level, a state in which no current flows through the resistor R3 is maintained, and the first reference voltage Vb1 or the second reference voltage Vb1 The reference voltage Vb2 can be continuously generated. Therefore, before receiving the modulation signal, the signal detection circuit 10 keeps the reference voltage low to prevent erroneous detection of the modulation signal. After detecting the modulation signal, the signal detection circuit 10 uses the vicinity of the center value of the modulation signal as a threshold value. Therefore, the accuracy of demodulation can be improved.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment, A various deformation | transformation and change are possible within the range of the summary. is there. For example, in the above description, the case where the communication signal is FSK modulated has been illustrated, but the modulation method of the communication signal is not limited to FSK modulation. The communication signal may be modulated by other modulation methods such as PSK (Phase Shift Keying) and QAM (Quadrature Amplitude Modulation). Further, the specific embodiments of the distribution / integration of the devices are not limited to the above-described embodiments, and all or a part of them may be configured to be functionally or physically distributed / integrated in arbitrary units. Can do. In addition, new embodiments generated by any combination of a plurality of embodiments are also included in the embodiments of the present invention. The effect of the new embodiment produced by the combination has the effect of the original embodiment.

DESCRIPTION OF SYMBOLS 1 Sensor 2 Section closure apparatus 3 Disaster prevention control panel 4 Control apparatus 5 Repeater 6 Apparatus control panel 7 Fire sensor 10 Signal detection circuit 11 Filter part 12 Signal level adjustment part 13 Comparator 14 Reference voltage generation part 141 Transistor circuit 100 Fire prevention system

Claims (7)

A voltage comparison unit that outputs a comparison signal based on a difference between a voltage based on the voltage of the communication line and a reference voltage;
After detecting that a communication signal frequency-modulated based on the comparison signal is flowing in the communication line, the first reference voltage or a second reference voltage lower than the first reference voltage is used as the reference voltage. A reference voltage generator to be input to the voltage comparator;
A signal detection circuit. The voltage comparison unit outputs the comparison signal of the first level when the voltage based on the voltage of the communication line is equal to or higher than the reference voltage, and the voltage based on the voltage of the communication line is less than the reference voltage Output the comparison signal of the second level of the logic opposite to the first level,
The reference voltage generator receives the first reference voltage from the second level to the first level while the first reference voltage is being input to the voltage comparator. Switching the input reference voltage from the first reference voltage to the second reference voltage;
The signal detection circuit according to claim 1. The reference voltage generator receives the second reference voltage from the first level to the second level while the second reference voltage is being input to the voltage comparison unit. Switching the input reference voltage from the second reference voltage to the first reference voltage;
The signal detection circuit according to claim 2. The reference voltage generation unit is provided between the output unit of the comparison signal in the voltage comparison unit and the input unit of the reference voltage, and is a resistor for switching between the first reference voltage and the second reference voltage And having a capacitor,
The signal detection circuit according to claim 1. The reference voltage generation unit inputs a third reference voltage lower than the second reference voltage as the reference voltage to the voltage comparison unit in a state where the voltage of the comparison signal does not change over a predetermined time, After the comparison signal indicates that the voltage based on the voltage of the communication line has transitioned from a state higher than or equal to the third reference voltage to a state lower than the third reference voltage, the first reference voltage or the second reference voltage Is input to the voltage comparison unit as the reference voltage,
The signal detection circuit according to claim 1. While the voltage of the comparison signal is changing to a time shorter than the predetermined time, the reference voltage generation unit uses the first reference voltage or the second reference voltage as the reference voltage to the voltage comparison unit. When the input and transition to a state where the voltage of the comparison signal does not change over a predetermined time or more, the third reference voltage is input to the voltage comparison unit as the reference voltage,
The signal detection circuit according to claim 5. The reference voltage generation unit includes a transistor circuit that is provided between an output unit of the comparison signal in the voltage comparison unit and an input unit of the reference voltage, and generates the third reference voltage.
The signal detection circuit according to claim 5 or 6.

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