JPH03293811A - High-precision programmable one shot circuit - Google Patents

Abstract

PURPOSE:To easily vary and set the pulse width of a trigger output pulse with a high precision by inverting a flip flop again at the time when the flip flop is set to the inverted state by the external trigger input and a capacitor is charged to reach a certain voltage. CONSTITUTION:When a flip flop 6 is set to the inverted state by the external trigger input, a capacitor 4 set to the discharging state by a second semiconductor switch 3 till then is set to the charging state. The capacitor 4 is charged like a ramp by the current from a programmable constant current source passing a first semiconductor switch 2; and when it is detected by a comparator 5 that the charging voltage reaches the certain voltage, the flip flop 6 is inverted again by the detection output, and the charged electric charge of the capacitor 4 is discharged through the second semiconductor switch 3 to prepare for the external trigger input. Thus, the trigger output pulse width is easily varied and set with a high precision.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a so-called one-shot circuit, and in particular, a high-precision circuit whose trigger output pulse width can be set arbitrarily and highly precisely. It relates to programmable one-shot circuits.

[Prior Art] Until now, the main parts of a one-shot circuit (monostable multivibrator) have generally been integrated into an IC, and therefore, a capacitor and a resistor that constitute a time constant circuit have been externally attached around the IC. It is now necessary to do so. The trigger output pulse width is uniquely determined by the time constant in this time constant circuit.

[Problems to be Solved by the Invention] However, in conventional one-shot circuits, it is not easy to change the trigger output pulse width. This is because the circuit constants in the time constant circuit are generally fixed. Therefore, in order to be able to change the pulse width, it is necessary to configure the circuit constant of at least one of the externally attached capacitor and resistor to be variable. In order for the trigger output pulse width to reach the desired value, it was necessary to variably adjust the circuit constants.However, setting and adjusting the trigger output pulse width to the desired value is not only troublesome, but also increases the It cannot be set with high precision.

SUMMARY OF THE INVENTION An object of the present invention is to provide a highly accurate programmable one-shot circuit in which the trigger output pulse width can be easily varied and the pulse width can be set with high accuracy.

[Means for Solving the Problem] The above object is to prevent the flip-flop from being discharged by a constant current from a programmable constant current source through the first semiconductor switch when the flip-flop is placed in an inverted state by an external trigger input. This is achieved by charging the capacitor that was left in the state, and when the comparator detects that the charging voltage on the capacitor has reached a certain voltage, the detection output is used to invert the flip-flop again. Ru.

[Operation] When the flip-flop in the initial state is placed in the inverted state by an external trigger input, the capacitor that had been placed in the discharged state by the second semiconductor switch is placed in the charged state for the first time. It is designed to be used. The capacitor is charged in a ramp-like manner by the current from the programmable constant current source via the first semiconductor switch, and when the comparator detects that the charging voltage has reached a constant voltage, The flip-flop is inverted again by the detection output from the comparator, and the charge stored in the capacitor is discharged by the second semiconductor switch, so that it is again ready for external trigger input. be. In this case, the constant current from the programmable constant current source is assumed to be controlled with high precision, and if the constant voltage is appropriately set as the comparison voltage by the comparator, the flip-flop is used as an external trigger input. Since the time from when it is inverted by the switch to when it is inverted again by the comparator is controlled only by the constant current, the trigger output pulse with a pulse width that corresponds to the variably set constant current is generated by the flip-flop. This is something that can be obtained more easily than other types.

[Embodiment] The present invention will be explained below with reference to FIGS. 1 to 4, but before that, the operating principle of the high precision programmable one-shot circuit according to the present invention will be briefly explained as follows.

That is, in general, when a capacitor is charged, there is a relationship between its capacitance C, charging voltage (voltage between terminals), and charge Q as follows: Q = C - V, and the current i (t) It is well known that the relationship f i (Udt=Q holds true between the charge Q and the charge Q. Therefore, 1(t)=
If it is 1 (constant), then the time T from the discharge state of the capacitor
If it is charged with a constant current I, it is clear that the charging voltage V changes with time T as V=IT/C.

Therefore, when the capacitance C is constant, the time T until the charging voltage V reaches a constant voltage (=VTM) is T=C・V
It can be found from T+4/I.

In other words, the time T is uniquely determined according to the constant current I. Therefore, a constant current I
If it is variably set by an external program setting, a trigger output pulse can be obtained from the flip-flop with high accuracy with a pulse width corresponding to the set constant current I.

Now, to specifically explain the high-precision programmable one-shot circuit according to the present invention, FIG. 1 shows the general configuration of one example, and FIG. 2 shows the input/output signal waveforms of the main parts of one example. It is something. As shown in Fig. 1, the high-precision programmable one-shot circuit has a D-type device around the capacitor 4 and the discharge semiconductor switch 3 connected in parallel to the capacitor 4, which is set in the set state by an external trigger input. A trigger flip-flop (hereinafter simply referred to as F/F) 6, a semiconductor switch 2 that is turned on by the F/F 6 in the set state, and a current output whose constant current value can be programmed as variable from the outside. A type D/A converter (programmable constant current source) 1 and a comparator 5 for comparing the charging voltage (2) at the capacitor 4 with a constant voltage vTH are arranged.

Here, the circuit operation will be explained with reference to FIG. 2. In the initial state, the F/F 6 is in the reset state, and therefore the semiconductor switch 2 is in the off state.
Furthermore, the semiconductor switch 3 has been turned on at least once by appropriate means. In this state, the charge in the capacitor 4 has been completely discharged by the semiconductor switch 3. Further, the current output type D/A converter 1 is in a state where it can output a constant current according to the program settings.

Now, in such a state, if an external trigger input appears, F/F6 will be placed in the set state at the time of its rise, and the F/F output (Q output in this example) will start to rise. ing. At the same time, at least the semiconductor switch 3
is set to be in the off state. As a result, F
/F output When the output chamber goes up, the semiconductor switch 2 is turned on, and the constant current I from the current output type D/A converter 1 charges the capacitor 4 via the semiconductor switch 2. be. Due to this charging, the charging voltage V at the capacitor 4 gradually increases, but the charging voltage V is constantly monitored by the comparator 5. Eventually, when the comparator 5 detects that the charging voltage V has reached the constant voltage v7H, it outputs that detection and resets the F/F 6, thereby reducing the F/F output that had been rising until then. When leaving the room, the semiconductor switch 2 is turned off. That is, F
/F output A1 or F/F6 output is obtained as a trigger output pulse. Note that the semiconductor switch 3 needs to be turned on at least once in order to discharge the charge stored in the capacitor 4 before the next external trigger input is input.

FIG. 3 also shows a high-precision programmable one-shot circuit according to the present invention, in which on/off control of the semiconductor switch 3 is specifically taken into consideration. As shown in the figure, the semiconductor switch 3 operates in the opposite manner to the semiconductor switch 2, so the Q output of the F/F 6 is applied to the semiconductor switch 3 via the inverter 7, but the Q output of the F/F 6 is directly applied to the semiconductor switch 3. In this case, the semiconductor switch 3 may be configured to use an external control input (for example, if the pulse width of the external trigger input is considerably larger than the trigger output pulse width, the external trigger input itself (which can be used as an external control input) can be controlled on/off in a predetermined manner by an internally generated signal.

Figure 4 also shows the main input/output signal waveforms at that time.
This is obvious and does not require any special explanation.

[Effects of the Invention] As explained above, according to the present invention, the trigger output pulse width can be easily set variable, and the pulse width can be set with high precision.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a general configuration of an example of a high-precision programmable one-shot circuit according to the present invention, FIG. 2 is a diagram showing main part input/output signal waveforms of an example, and FIG. 3 is a diagram showing a more specific example. FIG. 4 is a diagram showing an example of the configuration of a high-precision programmable one-shot circuit according to the present invention configured as follows.
- is a diagram showing the main part input/output signal waveforms in an example.

Claims (1)

[Claims] 1. A programmable constant current source whose current value can be set variably, a flip-flop that is put into an inverted state by an external trigger input, and a flip-flop that is turned on by an inverted state output by the external trigger input, A first semiconductor switch that controls on and off the current from a constant current source, a second semiconductor switch that is placed in a state opposite to that of the first semiconductor switch, and a second semiconductor switch that is connected in parallel to the second semiconductor switch. , consisting of a capacitor charged by the current from the first semiconductor switch, and a comparator that outputs an output when the charging voltage of the capacitor reaches a certain voltage and inverts the flip-flop by the output. High precision programmable one-shot circuit.