JPH04319814A - Pulse circuit - Google Patents

Abstract

PURPOSE:To prevent an undesired logical output by providing a DC bias changing means which detects the presence or absence of input of a since wave signal and sets the DC bias of a pulse circuit at an input level 'L' when no input of the sine wave signal is confirmed. CONSTITUTION:When a since wave signal is inputted, the output terminal of a comparison/decision circuit 9 is connected to an input terminal B. Then the bias voltage of the terminal B is supplied by a resistor 5 and set at a level equal to an identification level. Therefore the satisfactory waveform of a 50% duty ratio is outputted to the terminal C of a pulse circuit 4. If no sine wave signal is inputted, this fact is detected by a peak detecting circuit 10. Then the circuit 9 applies the binary logic decision to the detecting result of the circuit 10 and sets the DC bias of the terminal B at a level lower than the level 'L'. Thus, the logical output of the circuit 4 is kept at the level 'L' despite the noises or the voltage fluctuation applied to the circuit 4.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse circuit that outputs a logic level according to the input level of an AC-coupled sine wave signal.

0002

2. Description of the Related Art A conventional pulse circuit of this type will be explained with reference to the drawings.

FIG. 3 is a circuit diagram of a conventional pulse circuit, and FIG. 4 is a waveform diagram for explaining the operation of the pulse circuit shown in FIG.

In FIG. 3, a sine wave signal, which is an input signal, is input from a terminal A to an input terminal B of a pulse circuit 4 via a capacitor 1 that blocks direct current (DC) components of the input signal. The pulse circuit 4 is CMOS in Figure 3.
It is composed of an IC circuit using transistors,
Depending on whether the input level is higher or lower than the discrimination level,
A logic output of "H" (high) level or "L" (low) level is output to terminal C. A resistor 2 connected between terminal D, which supplies positive DC power, and terminal A indicates that the sine wave signal at terminal A contains a DC component. A diode 3 connected between input terminal B and terminal D of the pulse circuit 4 limits the level of the sine wave signal input to the pulse circuit 4. The resistor 5 divides the voltage between the terminal D and the ground and supplies the divided voltage to the input terminal B of the pulse circuit 4, thereby giving the pulse circuit 4 a DC bias. Further, a resistor 6 connected between terminals B and C is a pull-up resistor for the output of the pulse circuit 4.

Next, the operation of the pulse circuit shown in FIG. 3 will be explained with reference to FIG. Now, in the pulse circuit of FIG. 3, when a sine wave signal is input (see FIG. 4(a)), the ratio of the time of the logic output of the pulse circuit 4 at "H" level and "L" level (duty) This is a circuit to make 50%. For this purpose, the bias voltage at the input terminal B of the pulse circuit 4 is given by the resistor 5 and is made equal to the discrimination level of the pulse circuit 4 (see FIG. 4(a1)). As a result,
The waveform output to the terminal C of the pulse circuit 4 is shown in FIG. 4 (a2
), it outputs a good waveform with a duty of 50%. However, even when a sine wave signal is not input (see FIG. 4(b)), the input terminal B of the pulse circuit 4
Since the bias voltage and identification voltage are almost the same (see Figure 4 (b1)), noise and power supply voltage fluctuations may cause
The waveform output to the terminal C of the pulse circuit 4 is as shown in Fig. 4 (b2
), an unnecessary "H" level waveform may be output even though there is no sine wave signal input.

[0006]

SUMMARY OF THE INVENTION The conventional pulse circuit described above has a drawback in that unnecessary logical outputs may be produced even when no sine wave signal is input.

[0007]

[Means for Solving the Problems] The pulse circuit of the present invention has the following features:
In a pulse circuit whose input signals are an AC-coupled sine wave signal and a DC bias, the presence or absence of input of the sine wave signal is detected, and when the sine wave signal is not input, the DC bias is applied to the pulse circuit. It has DC bias changing means to set the input level to "L".

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram of a pulse circuit according to an embodiment of the present invention, and FIG. 2 is a waveform diagram for explaining the operation of the pulse circuit of FIG.

In addition to the conventional pulse circuit shown in FIG. 3, the pulse circuit shown in FIG. The comparison/judgment circuit 9 is connected to the output terminal E of the device 10, the other input terminal inputs a reference voltage, and the output terminal B is connected to the terminal B. The reference voltage is a voltage formed at the midpoint between resistor 7, one end of which is grounded, and resistor 8, one end of which is connected to the D terminal. As the peak detection circuit 10, a voltage doubler detection circuit may be used, for example. When no sine wave signal is input to terminal A, peak detection circuit 1
0 outputs a voltage in a more negative direction than the reference voltage. As the level of the input sine wave signal increases, the output voltage of the peak detection circuit 10 shifts in the positive direction, and when the sine wave signal reaches a predetermined level, the output voltage of the peak detection circuit 10 changes. The potential is more positive than the reference voltage. If the output voltage of the peak detector 10 input to one input terminal is more positive than the reference voltage, the comparison/judgment circuit 9 equivalently disconnects the output terminal from the input terminal B of the pulse circuit 4 . On the other hand, if the output voltage of the peak detector 10 is more negative than the reference voltage, the comparison/judgment circuit 9 sets the potential at the output end closer to ground than the discrimination level of the pulse circuit 4. At this time,
The pulse circuit 4 outputs the "L" level to the terminal C.

Next, the operation of the pulse circuit shown in FIG. 1 will be explained with reference to FIG. Now, like the conventional example, the pulse circuit of FIG. 3 sets the logic output of the pulse circuit 4 to "H" level and "L" level only when a sine wave signal is input (see FIG. 2(a)).
” The proportion of time (duty) for both levels is 50%.
This is a circuit to do this. When a sine wave signal is input, the output terminal of the comparison/judgment circuit 9 is disconnected from the B terminal, so the bias voltage of the input terminal B of the pulse circuit 4 is supplied by the resistor 5 as in the conventional example. It is made equal to the identification level (see FIG. 2(a1)). Therefore, the waveform outputted to the terminal C of the pulse circuit 4 is a good waveform with a duty of 50%, as shown in FIG. 2(a2). On the other hand, when no sine wave signal is input (Fig. 2(b)
), the peak detection circuit 10 detects that no sine wave signal is input. The comparison/judgment circuit 9 makes a binary logical judgment on the detection result, and draws the DC bias of the input terminal B of the pulse circuit 4 to the "L" level, which is lower than the discrimination level (see FIG. 2(b1)). As a result, even if noise or voltage fluctuations are added to the pulse circuit of FIG. 1, the logic output of the pulse circuit 4 remains at the "L" level as shown in FIG. 2 (b2).

0012

As explained above, the present invention detects the presence or absence of input of a sine wave signal, and when there is no input of a sine wave signal, the DC bias of the pulse circuit is changed to the "L" input level. By providing the means, it is possible to prevent unnecessary logic output when there is no input of a sine wave signal.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the pulse circuit in FIG. 1;

FIG. 3 is a circuit diagram of a conventional example.

FIG. 4 is a waveform diagram for explaining the operation of the pulse circuit in FIG. 3;

[Explanation of symbols]

1 Capacitor 2, 5, 6, 7, 8 Resistor 3 Diode 4 Pulse circuit 9 Comparison judgment circuit 10 Peak detection circuit

Claims (1)

[Claims] 1. A pulse circuit that uses an AC-coupled sine wave signal and a DC bias as input signals, and that outputs a binary output depending on the level of the input signal, detects the presence or absence of input of the sine wave signal, and detects whether or not the sine wave signal is input. 1. A pulse circuit comprising: a DC bias changing means for setting the DC bias to an "L" input level of the pulse circuit when no wave signal is input.