JPH05167561A - Pulse signal output circuit - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a measurement error by eliminating the transmission error of an analog signal by suppressing manufacturing cost lower and preventing the occurrence of the level flactuation of the analog signal even if a pulse signal is superimposed on the analog signal. CONSTITUTION:A pulse signal in accordance with digital data is generated by a CPU 1. When the output of the pulse signal is started from the CPU 1, output voltage whose voltage value is gradually increased by an integration circuit 2 is generated. By an analog switch 3, the output voltage to be outputted from the integration circuit 2 in accordance with the pulse signal to be outputted from the CPU 1 is intermittent. Thus, the pulse signal whose amplitude is gradually increased is generated and this is superimposed on a loop 6 of the analog signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse signal output circuit for superimposing a pulse signal on an analog signal for transmission.

[0002]

2. Description of the Related Art In a process instrumentation system used in various processes, a process signal measured by each sensor is output in the form of an analog current signal (4 to 20 mADC) from each sensor.

At present, there has been developed a device capable of setting each sensor from a remote place by superimposing a pulse signal on the analog signal for communication.

[0004]

In the conventional process instrumentation system described above, when a pulse signal is superimposed on an analog signal, the analog signal is generated by the voltage at the rising portion of the pulse signal as shown in FIG. 4 (a). The level fluctuates.

Therefore, when a pulse signal without a DC component such as a biphase signal is continuous, R
Although the influence of the pulse signal can be easily removed by the C-type first-order filter circuit or the like, at the time when the superposition of the pulse signal is started, only the envelope of the pulse signal as shown in FIG. There is a problem that the analog signal level fluctuates and a transmission error occurs in the analog signal, and a measurement error occurs due to the transmission error.

Therefore, in order to prevent the occurrence of such a measurement error, it may be considered that the output stage of the pulse signal has a push-pull structure, but such a method complicates the circuit structure and reduces the manufacturing cost. It will increase.

In view of the above circumstances, the present invention makes it possible to prevent the level fluctuation of the analog signal from occurring even when the pulse signal is superimposed on the analog signal while keeping the manufacturing cost low. It is an object of the present invention to provide a pulse signal output circuit which can eliminate an error and prevent a measurement error from occurring.

[0008]

In order to achieve the above object, a pulse signal output circuit according to the present invention superimposes a pulse signal corresponding to digital data on an analog transmission line for transmitting a process amount by a current signal. In the pulse signal output circuit, a pulse signal generator that generates a pulse signal according to the digital data, and a voltage generator that gradually increases the output voltage when the pulse signal generator starts outputting the pulse signal. A switch unit for intermittently generating an output voltage output from the voltage generation unit according to the pulse signal output from the pulse signal generation unit, generating a pulse signal whose amplitude gradually increases, and superimposing the pulse signal on the analog transmission line. It is characterized by having and.

[0009]

In the above structure, the pulse signal generation unit generates the pulse signal according to the digital data, and when the pulse signal generation unit starts the output of the pulse signal, the voltage generation unit gradually changes the voltage value. And a pulse signal whose amplitude is gradually increased by intermittently increasing the output voltage output from the voltage generation unit according to the pulse signal output from the pulse signal generation unit by the switch unit. Then, this is superimposed on the analog transmission line.

[0010]

1 is a block diagram showing an embodiment of a pulse signal output circuit according to the present invention.

The pulse signal output circuit shown in this figure is a CPU
1, an integrator circuit 2, an analog switch 3, a connection circuit 4, and a connection cable 5, and when the pulse signal is superposed on the analog signal loop 6 to which the pulse signal is superposed, the integration circuit The pulse signal is superposed on the analog signal loop 6 while gradually increasing the amplitude of the pulse signal by 2 to make the envelope curve at the start of superposition of the pulse signal gentle.

When the CPU 1 outputs a pulse signal to a transmitter (not shown) or the like to be controlled, it outputs a pulse signal generated by a modem such as UART provided in the CPU 1 from the output terminal P1. Then, this is supplied to the analog switch 3, and the CTS signal generated immediately before the pulse signal is output as a signal for controlling the modem is output from the output terminal P2 and supplied to the integrating circuit 2.

The integrating circuit 2 has an integrating resistor 7 having one end connected to the output terminal P2 of the CPU 1 and an integrating resistor 7 having one end connected to the other end of the resistor 7 and the other end connected to a ground point. When a CTS signal (+ 5V signal) is output from the output terminal P2 of the CPU 1, the capacitor 8 is integrated to generate an integrated waveform signal shown in FIG. Supply to the analog switch 3.

One of the two input / output terminals of the analog switch 3 is connected to the connection point of the resistor 7 and the capacitor 8 which form the integrating circuit 2, and the control terminal thereof is connected to the output terminal P1 of the CPU 1. , When a pulse signal is output from the output terminal P1 as shown in FIG.
The integrated waveform signal output from the integrator circuit 2 is intermittently generated to generate a pulse signal whose amplitude gradually increases from the start of superimposing the pulse signal, as shown in FIG. And output to the connection circuit 4.

The connection circuit 4 has a primary coil 9a having one end connected to the other input / output terminal of the analog switch 3 and the other end connected to a ground point, and a secondary coil electromagnetically coupled to the primary coil 9a. Transformer 9 having 9b and capacitor 1 having one end connected to one end of the secondary coil 9b
0, and when a pulse signal is output from the analog switch 3, the DC component of the pulse signal is removed and the pulse signal is supplied to the connection cable 5.

One end of the connecting cable 5 is the secondary coil 9
b is connected to one end and the other end is the analog signal loop 6
Cable 5b connected to the
0 is connected to the other end of the analog signal loop 6
And a cable 5a connected to the analog signal loop 6, which takes in the pulse signal output from the connection circuit 4 and superimposes it on the analog signal loop 6.

In this case, the amplitude of the pulse signal superimposed on the analog signal loop 6 via the connection cable 5 is reduced by the integration operation of the integrating circuit 2 at the start of superimposition, and gradually increases with the passage of time. Since the amplitude is finally controlled to be + 5V which is the power supply voltage, even if the pulse signal is superimposed on the analog signal loop 6, it is possible to prevent the analog signal level at the start of superimposing from fluctuating.

As described above, in this embodiment, when the pulse signal is superimposed on the analog signal, the integrating circuit 2
By gradually increasing the amplitude of the pulse signal to smooth the envelope at the start of superimposing the pulse signal, the level fluctuation of the analog signal does not fluctuate even if the pulse signal is superposed on the analog signal while keeping the manufacturing cost low. It is possible to prevent the occurrence of an analog signal transmission error, thereby preventing a measurement error from occurring.

Further, in the above-described embodiment, the integrated waveform signal output from the integrating circuit 2 is converted into the analog switch 3
Although the pulse signal is generated by intermittently generating the pulse signal by using the FET 15, the integrated waveform signal output from the integrating circuit 2 may be intermittently generated by the FET 15 as illustrated in FIG.

Even in this case, it is possible to keep the manufacturing cost low as in the above-mentioned embodiment, and to prevent the level fluctuation of the analog signal even if the pulse signal is superimposed on the analog signal. It is possible to eliminate the transmission error of the analog signal and prevent the measurement error from occurring.

[0021]

As described above, according to the present invention, it is possible to keep the manufacturing cost low and prevent the level fluctuation of the analog signal from occurring even when the pulse signal is superimposed on the analog signal. It is possible to eliminate the transmission error of the analog signal and prevent the measurement error from occurring.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a pulse signal output circuit according to the present invention.

FIG. 2 is a waveform diagram showing an operation example of the pulse signal output circuit shown in FIG.

FIG. 3 is a block diagram showing another embodiment of the pulse signal output circuit according to the present invention.

FIG. 4 is a block diagram showing an example of a conventionally known pulse signal output circuit.

[Explanation of symbols]

 1 CPU (pulse signal generation unit) 2 Integration circuit (voltage generation unit) 3 Analog switch (switch unit) 4 Connection circuit 5 Connection cable 6 Analog signal loop (Analog transmission line)

Claims (1)

[Claims] 1. A pulse signal output circuit that superimposes a pulse signal corresponding to digital data on an analog transmission line that transmits a process amount by a current signal, and a pulse signal generation unit that generates a pulse signal corresponding to the digital data. And a voltage generation section that gradually increases the output voltage when the pulse signal generation section starts outputting the pulse signal, and an output from the voltage generation section according to the pulse signal output from the pulse signal generation section. A pulse signal output circuit, comprising: a switch unit that intermittently generates an output voltage to generate a pulse signal whose amplitude gradually increases and superimposes the pulse signal on the analog transmission line.